Chapter 14 Neural Control and Coordination by TEACHING CARE online tuition and coaching classes

Chapter 14 Neural Control and Coordination by TEACHING CARE online tuition and coaching classes

File name : Chapter-14-Neural-Control-and-Coordination.pdf

 

  Introduction                                                                                                                                                            

In all the multicellular animals above the level of sponges, the system meant to perceive stimuli detected by the receptors, to transmit these to various body parts, and to effect responses through effectors, is called nervous

system. In vertebrates, it is highly specialized and plays at least three vital roles

  • Response to stimuli : By responding to all sorts of stimuli, it acquaints the organism with them so that the organism may react and orient itself favourably in the surrounding
  • Coordination : Along with endocrine system, the nervous system also serves to coordinate and integrate the activities of various parts of the body so that they act harmoniously as a unit. This makes possible the integrated control of the internal body environment (homeostasis). However, the nervous system brings about rapid coordination by means of nerves, whereas the endocrine system does so gradually and slowly by secreting hormones into
  • Learning : By accumulating memories from past experiences, in higher vertebrates at least, the nervous system serves as a centre for The branch of medical science dealing with the structure (anatomy), functions (physiology) and diseases (pathology) of nervous system is called neurology.

 Nervous system in various animals

  • Coelenterata : True nerve cell or ganglion cells occur for the first time in coelenterates. They are derived from interstitial cells of epidermis, forming nerve net or nerve plexus below whole
  • Platyhelminthes : Nervous system of planarians marks the beginning of a centralized nervous system encountered in higher That is made up of brain or cerebral ganglia, two lateral longitudinal nerve chords, numerous peripheral nerves and transverse commissures or connectives. This is sometimes called the ladder type of nervous system. In addition to the centralized nervous system planaria also possesses a sub-epidermal nerve net like that of coelenterates. Brain receives stimuli from the sense organs and conveys them to different parts of body. Special receptors, as found in turbellarians, are lacking in tapeworm. However numerous free sensory nerve- endings are present throughout the body specially in the scolex.

In Nematoda (e.g. ascaris) these system made up of central nervous system, peripheral nervous system and rectal nervous system. Rectal nervous system more developed in male.

  • Annelida : Nervous system well developed and It consists of three parts : central nervous system, peripheral nervous system and sympathetic nervous system, central N.S. made up of Nerve ring and ventral nerve cord. Nerves are of mixed type, consisting of both afferent (sensory) and efferent (motor) fibres.
  • Arthopoda : The nervous system of prawn or arthopods is of the annelidan type. However it is somewhat larger and has more fusion of ganglia. It consists of (i) The central nervous system including brain connected with a ventral ganglionated nerve cord through a pair of circum-oesophageal commissures, (ii) The peripheral nervous system including nerves and (iii) The sympathetic nervous
  • Mollusca : In gastropodes (g. pila) consists of paired ganglia, commissures and connective uniting them and nerves running from these central organs to all parts of the body. It has various type of ganglia as cerebral, buccal, pleuro-pedal, supraintestinal and visceral etc. In palecypoda nervous system is greatly reduced due to sluggish and sedentary mode of life and there is little evidence of the brain. But in cephalopoda shows a high grade of organization attained only by some insects and arachnids among the other invertebrates.’

 

 

 

 

  • Echinodermata : Echinodermates has simple and primitive type nervous system. It has the form of a nerve net, consisting of nerve fibres and a few ganglion cells, all confined to the body wall except the visceral nerve plexus situated in the gut wall. At certain places the nervous tissue is concentrated to form distinct nerve cords. It is made up of (i) Superficial or ectoneural nervous system (ii) Hyponeural or deep nervous system (iii) Aboral or coelomic nervous system and (iv) Visceral nervous ’
  • Hemichordata : Nervous system is of primitive type resembling that of coelenterates and

Chordates : Nervous system well developed and formed by ectoderm. It is formed by CNS, peripheral nervous system and autonomous N.S.

 Development of central nervous system in human

The central nervous system of vertebrates includes the brain and the spinal cord. These are derived from a longitudinal mid-dorsal ectodermal thickening of the embryo, called the meduallary or neural plate. This neural plate or neural groove is converted by fusion into a closed mid-dorsal longitudinal neural tube lying above the notochord. Histologically, the embryonic neural tube exhibits three zones of cells.

 

 

ENCEPHALON

FOREBRAIN (PROSENCEPHALON)

 

 

 

SPINAL CORD

HINDBRAIN (RHOMBENCEPHALON)

 

SPINAL CORD

 

 

 

ECTODERM NEURAL PLATE                    NEURAL GROOVE        NEURAL FOLD

 

A                                                MID BRAIN                B

 

PINEAL BODY PARIETAL BODY

CEREBRUM (TELENCEPHALON)

 

PALLIUM

(MESENCEPHALON) OPTIC LOBES

CEREBELLUM

(METENCEPHALON)

MEDULLA OBLONGATA (MYELENCEPHALON)

 

SPINAL CORD

 

 

 

ECTODERM

 

NOTOCHORD

 

NEURAL CREST NEUROCOEL

 

 

 

 

GANGLION

 

 

OLFACTORY LOBE (RHINENCEPHALON)

CORPUS STRIATUM OPTIC CHIASMA

CRUS CEREBRUM

DIENCEPHALON              C                                 C THALAMUS

NEURAL TUBE

 

NOTOCHORD                                    D

 

HYPOPHYSIS PITUITARY BODY

INFUNDIBULUM

Fig. – Stages in the embryonic development of central

nervous system inT.S.

 

Fig. – Stages in development of brain. A – Anterior end of neural tube in lateral view. B – M.L.S. of embryonic brain to show three primary cerebral vesicles. C – Differentiation of brain from three vesicles.

 

  • Germinal layer : These are actively dividing cells lining the neural They form the connective tissue lining of neural canal, called ependyma, and also proliferate into mantle layer cells.
  • Mantle layer : It consists of embryonic neurons or nematoblasts, forming the gray
  • Marginal layer : It consists of nerve fibres, mostly surrounded by fatty myelin sheaths, and forms the white matter. Neurons and fibres are supported by a special connective tissue of ectodermal origin, the neuroglia, cells of which become increasingly abundant and diversified in higher

 

 

 

 

 

 

 

 

 

 

Development of brain : The anterior end of embryonic neural tube is already enlarged forming the embryonic

 

brain, called encephalon. By differential growth and two constrictions, it is divided into a linear series of three primary cerebral vesicles, termed the forebrain, midbrain and hindbrain. These give rise to the three major divisions of the adult brain – (1) prosencephalon (forebrain), (2) mesencephalon (midbrain), and (3) rhombencephalon (hindbrain).

These further become subdivided into 5 subdivisions.

The various parts of the adult brain in different vertebrates are formed by modifications. That is, by

OLFACTORY LOBES

 

CEREBRAL HEMISPHERES

 

 

PINEAL BODY

INFUNDIBULUM OPTIC LOBES

CEREBELLUM MEDULLA OBLONGATA

SPINAL CORD

A                                                                      B

RHINENCEPHALON TELENCEPHALON

 

PROSENCEPHALON DIENCEPHALON

MESENCEPHALON

 

METENCEPHALON MYELENCEPHALON

 

C

 

thickenings and foldings of these 5 subdivisions. The adult brain has a series of cavities, called ventricles, which are in continuation with the central canal of the spinal cord and filled with a cerebro-spinal fluid.

Fig. – Pattern of generalized vertebrate brain. A – Lateral view.

B – Dorsal surface. C – H.L.S. showing ventricles

 

 Parts of nervous system

Nervous system is divided into three parts

  • Central nervous system (CNS) : In all the vertebrates including man, CNS is dorsal, hollow and non- ganglionated while in invertebrates when present, it is ventral, solid and ganglionated. CNS is formed of two parts : Brain – Upper and broader part lying in the head; and Spinal cord – Lower, long and narrow part running from beginning of neck to
  • Peripheral nervous system (PNS) : It is formed of long, thin, whitish threads called nerves which extend between CNS and body parts (muscles, glands and sense organs). It controls the voluntary functions of the It has cranial and spinal nerves.
  • Autonomic nervous system (ANS) : It is formed of nerve fibres extending upto visceral organs and controls the involuntary functions of visceral organs of body like heart beat, peristalsis etc. It is again formed of two systems: sympathetic and para-sympathetic nervous system which have opposing

 

 

 

Central Nervous System (CNS)              Peripheral Nervous System (PNS)                  Autonomic Nervous System (ANS)

 

 

Brain        Spinal cord                    Cranial Nerves         Spinal Nerves

(All Mixed)

Sympathetic Nervous System

Parasympathetic Nervous System

 

 

 

Sensory Nerves (I, II, VIII)

Motor Nerves (III, IV, VI, XI, XII)

Mixed Nerves (V, VII, IX, X)

 

(i) Central nervous system : Central nervous system is made up of brain and spinal cord. CNS is covered by 3 meninges and its wall has two type of matter.

Types of matter : CNS of vertebrates is formed of two types of matter –

  • Grey matter : It is formed of cell-bodies and non-medullated nerve

 

 

 

 

  • White matter : It is formed of only medullated nerve fibres which appear white due to presence of medullary

Meninges : The meninges are connective tissue membranes which surround the brain and spinal cord of CNS. In the fishes, there is only one meninx called meninx primitiva. In amphibians, reptiles and birds, the brain is covered by two meninges or membranes : inner pia-arachnoid and outer dura mater. In mammals, CNS is covered by three meninges or membranes

  • Duramater (Dura = tough; mater = mother): Outermost, thick, fibrous, 2-layered meninge. The outer layer adheres to skull at many places while the inner layer follows the major convolutions (sulci and gyri) of the brain and spinal Meningeal artery traverses via duramater. The two layers of duramater are widely separated at some places to form the large sinuses called

 

venous sinus. This drains deoxygenated (= venous) blood from the brain to the large veins that return it to the heard. The space between duramater and the next meninge in succession is called sub-dural space is filled with cerebrospinal fluid and has arachnoid villi in the region of dural space. Similarly the space between the skull and

 

 

 

SEROUS MEMBRANE (RECTICULAR CONNECTIVE TISSUE

 

FIBROUS          

ARACHNOID
DURAMATER

CONNECTIVE TISSUE

 

OUTER

       DURAMATER

 

MIDDLE

ARACHNOID

 

 

INNER

PIAMATER

 

durameter is called epidural space. Duramater extends in the form of straight sulcus between cerebrum and cerebellum posteriorly. Here it is called tentorium.

(AREOLAR HIGHLY VASCULARISED TISSUE)

SKULL

 

 

Fig. – Meninges of brain

 

  • Arachnoid (= spider-like web) : It is closely related to duramater on its outside and with piameter on the The space between the arachnoid and piameter is called sub-arachnoid space and is filled with cerebro-spinal fluid.
  • Piameter (Pia = soft = tender) : This is the innermost meninge and follows the convolutions of the outer surface of brain and spinal cord. It is highly vascular and penetrates deeply in certain places bringing it with its vasculature and placing it in contact with the ventricles of the brain and neurocoel of spinal

Cerebrospinal fluid : All the ventricles of the brain are continuous and lined by a columnar, ciliated epithelium, the ependyma. They contain lymph-like extracellular fluid called the cerebrospinal fluid (C.S.F.). This fluid is secreted by the choroid plexuses by filtration of blood. The choroid plexuses consist of loose connective tissue of pia mater covered internally by a simple cuboidal epithelim of secretory (glandular) nature. The cerebrospinal fluid slowly flows toward the fourth ventricle by secretion pressure and passes into the spinal cord. Some fluid escapes into the subarachnoid spaces through three pores in the roof of the fourth ventricle in the medulla. From the subarachnoid spaces, the cerebrospinal fluid is transferred to the blood of the venous sinuses. Nervous tissue is without lymphatic vessels.

The cerebro-spinal fluid (CSF) provides

  • Protection to brain from mechanical
  • Optimum physiological fluid environment for neural functions g. conduction of nerve impulses, transport of aminoacids, sugars, O2 etc.

 

 

 

 

  • ‘Relief’ mechanism for the increase in intracranial pressure that occurs with each arterial pulse of blood to
  • ‘Sink’ like facility for metabolites of
  • The blood CSF barrier for selective transport process between blood and CSF.

Major site of CSF formation is choroid plexus, and mid ventricular wall and sub-arachnoid wall also contribute. CSF is cell free, slightly alkaline, and is isotonic to plasma. Rate of formation of C.S.F is 80 ml/hour approx, 1/2 litre per day. Total amount present in and around CNS is 150 ml it means there is atleast 3 times renewal of C.S.F. every day.

Blood brain barrier facilitate maintenance of stable internal environment. Its acts as physiological and pathological barrier as well. Hydrocephalus : The enlargement of head, a pathological condition characterized by an abnormal accumulation of cerebrospinal fluid resulting headache, vomiting, pain and stiffness of the neck.

  • Increased cerebrospinal fluid may result
  • Meningites may appear due to infection and inflamation of meninges or injury of
  • Infection may be viral, bacterial or The most common cause of meningitis in the infection of streptococcus and neumoniae, neisseria meningitidis and haemophilus influenzae.
  • Lumber puncture is done for drainage of excess of cerebrospinal fluid during
  • Cerebro-spinal fluid is formed by choroid plexus (ACP and PCP).

There are three choroid plexus in humans

  • Lateral choroid plexus : It is in the roof of I and II
  • Anterior choroid plexus : It is in the roof of III ventricle (diacoel).
  • Posterior choroid plexus or pelochoroida : It is in the roof of IV

Oxygen and glucose requirements : Brain controls the functions of our body organs and also provides the qualities of mind – learning, reasoning, and memory. For these activities, brain needs a large and constant energy supply. At any given time, the activities of the brain account

 

for 20% of the body’s consumption of oxygen and 15% of its consumption of blood glucose. Brain deprived of oxygen for just 5 minutes is permanently damaged. Mental confusion results if brain is deprived of glucose.

(a) Brain (Encephalon) : It is soft, whitish, large sized and slightly flattened structure present inside cranial cavity of cranium of the skull. In man, it is about 1200-1400 gm in weight and has about 10,000 million neurons. Brain is made up of 3 parts

CEREBRUM

 

 

 

 

 

 

 

 

 

 

 

SULCI

GYRI          PONS MEDULLA

 

 

 

 

 

 

 

 

 

 

CEREBELLUM SPINAL

CORD

 

  • Fore brain (Prosencephalon) Main parts of human brain visible from lateral view

 

 

 

 

 

  • Olfactory lobe – Rhinencephalon
  • Cerebrum – Telencephalon
  • Diencephalon – Diencephalon

(2)  Mid brain (Mesencephalon)

  • Optic lobes – Mesencephalon

(3)  Hind brain (Rhambencephalon)

  • Cerebellum – Metencephalon
  • Medulla oblongata – Myelencephalon
    • Fore brain or Prosencephalon : It forms anterior two-third of brain and is formed of three
      • Olfactory lobes : These are one pair, small sized, club-shaped, solid, completely covered by cerebral hemisphere Each is differentiated into two parts –
    • Olfactory bulb : Anterior, swollen part, and
    • Olfactory tract : Posterior and narrow part which ends in olfactory area of temporal lobe of cerebral

Function : These control the smell.

  • It is normal in frog, rabbit and
  • It is well developed in So power of smell is more in dog.
  • These are also well developed in dog fish and name dog fish is on the basis of well developed olfactory
    • Cerebrum : (a) Structure is divided into 5 lobes (i) frontal (ii) parietal, (iii) occipital, (iv) temporal and (v) A lobe called insula is hidden as it lies

 

deep in the sylvian fissure. The cerebral hemisphere are separated from olfactory lobes by rhinal fissure. The median fissure divides the cerebrum into a right and a left cerebral hemisphere.

A few sulci are well developed and form three deep and wide fissures which divide each cerebral hemisphere into four lobes : anterior frontal lobe, middle parietal lobe,

 

FRONTAL LOBE

 

 

 

TEMPORAL LOBE HYPOTHALAMUS

PITUITARY GLAND CEREBRAL PEDUNCLE

 

 

 

 

 

 

 

 

 

 

 

 

PONS.

HUMAN BRAIN

PARIETAL LOBE

GYRUS

SULCI CORPUS

CALLOSUM PINEAL GLAND

OCCIPITAL LOBE

 

CEREBELLUM

 

posterior occipital lobe and lateral temporal lobe e.g. Fissure lying between the frontal and parietal lobes is central fissure, that lying

MEDULLA OBLONGATA

 

 

Fig. – Sagittal section of human brain

 

between the parietal and occipital lobes is parieto-occipital fissure and that demarcating frontal and parietal lobes from the temporal lobe is lateral or Sylvian fissure. Each cerebral hemisphere is with a fluid-filled cavity called lateral ventricle or paracoel.

 

 

 

 

 

 

 

FRONTAL LOBE

 

CENTRAL SULCUS PARIETAL LOBE

LIMBIC LOBE

 

PARIETO- OCCIPITAL- SULCUS

 

OCCIPITAL LOBE

 

CEREBRAL (=MEDIAN) FISSURE

 

 

CORPUS CALLOSUM

LATERAL VENTRICLE

INTERNAL CAPSULE

INSULA

 

 

LATERAL FISSURE

TEMPORAL LOBE

CORPUS STRIATUM

+ GLOBUS PALLIDUS

= BASAL GANGLION

TEMPORAL LOBE

 

Fig. – Medial surface of cereberal hemisphere

Fig. – Cross section of cerebrum

 

Two cerebral hemispheres are interconnected by thick band of transverse nerve fibres called corpus callosum. The peripheral portion of each cerebral hemisphere is formed of grey matter and is called cerebral cortex, while deeper part is formed of white matter and is called cerebral medulla. Cerebral cortex is the highest centre for many sensations and activities and is with a number of sensory areas.

Important areas in the human brain

 

AreaLocationFunction
Premotor areaFrontal lobeThe highest centre for involuntary movements of muscles and ANS.
Motor areaFrontal lobeControls voluntary movements of the muscle
Broca’s areaFrontal lobeMotor speech area
Somesthetic areaParietal lobePerception of general sensation like pain, touch and temperature
Auditory areaTemporal lobeHearing
Olfactory areaTemporal lobeSense of smell
Wernicke’s areaTemporal lobeUnderstanding speech written and spoken
Gustatory areaParietal lobeSense of taste
Visual areaOccipital lobeSensation of light

 

 

  • Histology of cerebrum : The whole brain possess grey matter outside and white matter inside around
    • Grey matter : In cerebrum grey matter is very much developed, it is on an average 5 mm. thick but at poles its thickness is 1.3 mm. It is thickest at pre central gyrus (4.5 mm thick). Grey matter of cerebrum is called cortex or pallium. Phyllogenetically or evolutionarily cortex is divided into 3 parts –
      • Allocortex or paleocortex : It is the

 

 

 

 

 

 

 

SPEECH AREA

 

OLFACTORY AREA

 

GENERAL MOTOR AREA

 

 

 

 

 

 

 

 

 

PONS VAROLI

 

 

 

MEDULLA

SOMAESTHETIC AREA

GUSTATORY AREA VISUAL AREA

SPEECH AREA

(READING/LANGUAGE)

 

CEREBLLUM

 

 

 

 

 

SPINAL CORD

 

cortex of olfactory area of frontal lobe and olfactory

Fig. – Sensory areas of human brain

 

bulbs. In lower vertebrates (cartilagenous fish) olfact lobes occupy most of the part of cerebrum. So in these animals sense of olfection is very-very much developed. Sense of olfaction is oldest sense.

  • Mesocortex : It is relatively not much older in

 

 

 

 

  • Neocortex or neopallium or isocortex or neencephalon : It is most recent cortex and is developed maximum only in It is in prefrontal cortex or prefrontal region (organ of mind), precentral and precentral gyrus etc. The neocortex is having 6 (six) layer of neurons while remaining cortex possess only 5 layers.

The cerebral cortex is having area of about 2200 cm2 while the cranial cavity is only 1450 cm3, so to accomodate cerebrum there appears foldings in the cortex. The ridges are called gyrus (or gyri) or convolution while the depression are called sulcus (sulci in plural).

 

  • White matter : It is inner part of brain. Its fibres are divide into 3 categories –
  • Commissural fibers : These neurons connect gyri of 2 hemispheres, such as corpus habenular commissure, anterior commissure, posterior commissure.
  • Associate fibres : They connect gyri of same
  • Projection neuron : They are infact assending and descending nerve

GYRUS SULCUS CORTEX

SUB CORTEX WHITE MATTER

 

tract, they connect one part of brain to another part of brain or to spinal cord. (In spinal cord they were called as columo).

  • Associated structures    of    cerebrum : Cerebrum has following specific

 

  • Sub cortex : Nuclei on white matter. It is cluster of grey neurons in depth of white matter, they are formed in whole brain and are named
  • Basal granules or central nucleus : Basal ganglia is the name given to many sub cortical structure

of walls of paracoel, hypothalamus and mid brain –

 

V1         V2

 

 

 

 

V3

CAUDATE NUCLEUS

THALAMUS CLAUSTRUM

                   INSULA

PUTAMEN

LENTICULAR

 

  • Corpus striatum : Corpus striatum is the

                                      GLOBUS

PALLIDUS

NUCLEUS

 

name given to caudate nucleus and lenticular nucleus.                                           PITUITARY

 

Caudate is tail shaped while the lenticular nucleus is

BODY

 

lenti shaped. The lenticular nucleus is sub-divided in putamen (outer shell) and globus pallidus (ball).

  • Claustrum : It is the name given to grey matter present between insula and patamen.
  • Epistriatum or Amygdaloid body : It is structure present at the end of caudate
  • Red nucleus and substantia nigra of mid

The basal ganglia controls automatic movements of skeletal muscles like swinging, walking etc.

  • Corpus callosum : It is the band of white neurons present between both cerebral hemisphere and connect them on medial It is present only mammal. It

 

has anterior part genu, middle part trunchus and last part splenium.

Below corpus callosum there are two fused band of

TRUNCUS

GENU                                                               SPLENIUM

 

white neurons called fornix. There anterior part is called column and posterior part is called crura. Between column and genu a membrane is called septum lucidum or septum pellicidum. Septum lucidum encloses a space called V5 or

SEPTUM PELLICIDUM

 

 

 

ROSTRUM

CRURA COLUMN

FORNIX

 

Pseudocoel, because it is not possessing C.S.F. i.e. why it is called pseudocoel.

 

 

 

 

  • Limbic system : It is also called emotional brain or animal Limbic system controlling emotion, animal behaviour like chewing, licking, sniffing,

 

rage, pain, plessure, anger, sexual feelings, grooming. It has following structure

  • Singulate gyrus : It is a region of pre central
  • Hippocampal gyrus : It is a region of temporal lobe near colossomarginal These two structure are combinely called limbic lobe.
  • Amygdaloid body : It is the end of caudate

 

 

 

 

OCCIPITAL

 

 

 

 

HIPPOCAMPAL GYRUS

 

 

 

 

 

 

 

 

 

 

 

 

DENTATE GYRUM

STRAE MEDULARIS

 

MAMILLARY BODY CAUDATE NUCLEUS

                          SIGNATURE GYRUS

 

 

OLFACTORY BULB

             FRONTAL AMYGDALOID BODY

 

  • Olfactory bulb : They are on the inferior anterior surface of brain. Olfactory nerve ends in these
  • Mammillary body : They are found in Olfactory bulb and mammillary body both are centre of olfaction.

From a evolutionary point of view, the cerebral hemisphere are the highly evolved structure and this is manifested by

  • Great increase in the number of feed back circuits between cerebral cortex and sub cortical
  • The ability of man and other primates to perform variety of complex function.
  • The lobe of cerebrum are delineated by fissure and
  • A corpus callosum connects the left and right cerebral hemisphere. This is a unique property of mammals as it facilitates flow of information between the 2
  • The cortical layer of cerebrum is thrown into folds (= gyri) separate by sulci. All the larger mammalian brains exhibit well developed gyri. The degree of convolutions of the cortex is a fairly reliable indicator of the evolutionary stages of development of brain. The roof of cerebrum is called pallium while the ventrolateral walls are thick and are called corpora
  • Diencephalon cavity is called, III vertricle or diacoel : The thin roof of this cavity is known as the epithalamus, the thick right and left sides as the thalami, and floor as the
  • Epithalamus : The epithalamus is not formed of nervous

 

tissue. It consists of piamater only. Hence, it is of relatively little significance as a nerve centre. Its anterior part is vascular and folded. It is called anterior choroid plexus. Behind this plexus, the epithalamus gives out a short stalk, the pineal stalk which hears a small, rounded body, the pineal body, at its tip.

  • Thalami : A pair of mass of grey matter formes the major part of the wall and floor of diancephalon. Its nuclei have complex connection with the sensory area of the cerebral cortex. It receives and integrates sensory impulses from the eye, ear and It has

nerve connection with motorcortex and act as relay centre. Habenular

 

 

 

 

 

 

 

 

 

 

 

 

 

LAMINA TERMINALS

 

 

 

 

 

 

 

 

DIOCOEL

OPTIC CHIASMA PINEAL BODY

PINEAL STALK

 

ANTERIOR CHOROID PLEUXES

 

OPTIC THALAMI HYPOTHALAMUS

INFUNDIBUIUM

PITUITARY (HYPOPHYSIS)

 

commissure is a band of nerve fivers connecting two thalami. On the

inferior surface of each thalamus there are two rounded bodies of grey matter.’

Fig. – Diencephalon

 

  • Median geniculate body (M.G.B) : It receives hearing impulse and relay into cerebral

 

 

 

 

 

  • Lateral geniculate body (L.G.B) : They are concern with vision (optic nerve) and relay visual impulse towards cerebral
  • Hypothalamus : The hypothalamus is visible in the ventral view of the brain and forms the floor of diencephalon. Hypothalamus also gives a nervous process called infundibulum (forms pars nervosa) which meets a rounded non-nervous pharyngeal outgrowth called hypophysis. Both collectively form master gland called pituitary body. A stalked outgrowth

 

EPITHALAMUS

 

 

THALAMUS

 

 

      M.G.B.

L.G.B.

 

PINEAL BODY

 

of infundibulum combines with a pouch-like epithelial outgrowth (Rathke’s                           pouch) of the roof of embryonic mouth (= stomodaeum), forming a

pituitary gland or hypophysis. Which secretes a number of hormones. In front of hypothalamus, there is cross of two optic nerves called optic chiasma. Behind the hypothalamus, there is one pair of small, rounded,

nipple-like bodies called mammilary bodies or corpora mammillares. The

CEREBELLER PEDUNCLE

 

hypothalamus consists of many masses of grey matter, called hypothalamic nuclei, scattered in the white matter.

In man and some other mammals, most fibres of optic nerves cross, but some fibres do not cross and

 

 

OLFACTORY BULB OLFACTORY

TRACT

Fig. – Posterior aspect of brain

LONGITUDINAL FISSURE

 

 

FRONTAL

 

innervate the eyes of their own respective sides. This arrangement enables man and these mammals to have a binocular vision. Rabbits simply have a monocular vision.

Pineal gland is a pine cone-shaped gland. It is located in the center of brain with which it loses all nerves connection after birth. It is innervated by sympathetic nerves. It has a photosensory role in amphibian and primitive reptiles and is called ‘Third eye’. Pinealocytes secretes melatonin. Mammalian pineal does not act as photoreceptor but it produces the hormone called melatonin which is anti FSH, and anti LH. It inhibits

LATERAL FISSURE

 

OPTIC CHAISMA

 

 

 

 

MAMMILLARY BODIES

 

 

SPINAL CORD

 

 

 

 

 

 

 

 

PONS

LOBE

 

 

 

 

 

 

 

TEMPORAL

LOBE

HYPOPHYSIS

 

 

INFUNDIBULUM

 

 

CEREBRAL PEDUNCLE

 

 

MEDULLA

 

 

MEDULLA OCCIPITAL LOBE

 

reproductive function. Melatonin secretions decrease after puberty.

Function of fore brain

 

 

 

ARM

 

THINKING

Fig. – Ventral view of brain

 

PRIMARY MOTOR AREA

 

 

 

PARETAL LOBE

 

  • Olfactory lobe : It is centre of
  • Cerebrum : Cerebral cortex is made up of grey matter and differentiated into –
    • Sensory area
    • Motor area
    • Associated area

Sensory and associated area confirm, recognise and evaluate for shape, colour, sound, taste and smell for sensory

FRONTAL LOBE MEMORY FACE

INTELLIGENCE

 

BROCA’S AREA RIGHT HAND NESS

SMELL

 

 

 

 

 

 

 

 

 

 

 

 

TASTE

WERNIKE’S AREA SPEECH

 

OCCIPITAL LOBE

 

 

 

VISUAL CORTEX

 

 

 

AUDITORY                                   BALANCE

 

cells in relation with object.                                                         Fig. – Man-different areas in brain(functional and structural)

 

 

 

 

 

Broca’s area : Known as sensory speech area or motor speech area. Translate thought into speech. Located into frontal lobe towards left side. It is associated with language area and also interpriate translation of written words into speech. Damage or injury in Broca’s area (sensory or motor speech area) may result

(i) Aphasia(Inability to speak) (ii) Word deafness, (iii) Word blindness

Cerebrum is a centre for

 

(i) Intelligence(ii) Emotion(iii) Will power
(iv) Memory(v) Consciousness(vi) Imagination
(vii) Experience(viii) Knowledge(ix) Reasoning
(x) Voluntary controls(xi) Weeping and laughing(xii) Micturition
(xiii) Defecation  

If cerebrum is removed animal becomes simple reflax animal.

  • Diencephalon : It is centre for
    • Carbohydrate metabolism (ii) Fat metabolism
  • It relays impulses from posterior region of brain and also to posterior region of brain.
  • Its secretes neurohormone (v) From part of pituitary gland

(vi) Secrete cerebrospinal fluid

Hypothalamus : It is floor of diencephalon and centre for

 

(i) Hunger(ii) Thirst(iii) Sweating
(iv) Sleep(v) Fatigue(vi) Temperature
(vii) Anger(viii) Pleasure, love and hate(ix) Satisfaction
  • It is also centre to release factors for endocrine glands.
  • It also control N.S (autonomic nervous system)
  • Centers for regulation of parasympathetic (cranio-sacral) activity. When stimulated, it causes slowing down of heart beat, contraction of the visceral
  • Mid brain or mesencephalon : It is also completely covered by cerebral It is formed of two parts –
    • Optic lobes : These are one pair, large sized lobes present on dorsal Each is divided transversely into

upper and larger superior coliculus and lower and smaller inferior coliculus. So there are four optic lobes, so called optic quadrigemina (only in mammals). In frog these are known as

 

bigemina. Valve   of   vieussens     It joins the optic lobe with cerebellum.

(a)   Superior optic lobe or superior celliculus : They are

TEGMENTUM OR CEREBRAL PEDUNCLE             TECTUM

 

 

 

CRUS OF                                CEREBRUM

 

concerned with reflex action of eye, head and neck in response to                            

                     ITER

 

visual stimulus.

  • Inferior calliculus : They are concerned with movement of head and trunk in response to hearing

PIGMENTUM                    

 

 

Fig. –Lateral view

 

 

 

 

 

  • Cerebral peduncle (crura cerebri) : They are the pair of thick bands of longitudinal nerve fiber present on the floor or ventral side of mid The dorsal part of cerebral peduncle (white matter) is called Tagmentum while most ventral part (gray matter) is called crura cerebrae or crus of cerebrum. Dorsal thick wall of mid brain is known as optic tectum. Iter is between tegmentum and tectum. Cerebral peduncle are infect possessing assinding and

 

desending tracts, connecting upper and lower region of brain.

In white matter of cerebral peduncle these are following sub cortical structure

  • Red nucleus or rustrum nucleus : They are red because rich blood supply and iron containing pigment or
  • Substantia nigra : It is black because of much deposition of

 

 

 

 

 

OCULOMOTOR NUCLEUS

 

 

 

 

 

RED NUCLEUS

 

 

 

 

 

 

 

 

 

 

 

 

 

RUBROSPINAL DECUSSATION

CORPORA QUADRIGEMINA

LATERAL LEMNISCUS CEREBRAL AQUEDUCT

MESIAL LEMNISCUS SUBSTANTIA NIGRA

TEMPOROPONTINE TRACT

CORTICOSPINAL (PYRAMIDAL) TRACT

FRONTOPONTINE TRACT

 

OCULOMOTOR NERVE

 

  • Occulomotor nucleus : It is origin point of 3rd cranial nerve (occulomotor) from this region 4th (Trochlear) nerve also

Reticular activating system : A diffuse network of nerve cell bodies and nerve tracts extends through the brain stem. It is called reticular activating system (RAS). It screens sensory information so that only certain impulses reach the cerebrum. For example, when you are alternatively listening to a lecture in the classroom, you are unaware of rustle of papers from those around you and from the touch of your clothes to the skin. The RAS is also important in overall activation and arousal. When certain neurons in RAS are active, we are awake, when they are inhibited by other neurons, we sleep. The pons and medulla have sleep centres that cause sleep when stimulated. Midbrain has an arousal centre which causes arousal.

Function of Mid brain

  • Pair of anterior optic lobes (which are also known as superior collici) is related with vision.
  • Pair of posterior optic lobe (known as inferior collici) related with
  • These act as coordination centres between hind and fore
  • Hind brain : Consists of (i) cerebellum and (ii) medulla oblongata (iii) Pons
    • Cerebellum (Sandwitched brain) : Cerebellum is highly convoluted and well developed in mammals. It controls the most intricate movements of the body. It coordinates sensory information received from muscles/joints, visual, auditory and equilibrium receptors as well as flow of impulses from cerebral

Cerebellum is made up of –

(a) Vermis, (b) Cerebellar lobes (= floccular lobes), (c) Lateral lobes, (d) Pons.

The pons is a thick band of transverse nerve fibers. Cerebellum is joined to parts of brain by afferent and efferent fibres. Mid brain, pons and medulla have several similar functions and they constitute the brain stem. Peripheral part is formed of grey matter and is called cerebellar cortex while the central part is formed of white matter and is called cerebellar medulla. The white matter forms a tree-like branching pattern called arbor vitae, so the cerebellum is solid internally.

 

 

 

 

 

 

 

 

 

 

CEREBRUM

CORPUS CALLOSUM

 

 

FORNIX

 

 

ANTERIOR CHOROID PLEXUS

 

THALAMUS

 

 

 

 

HYPOTHALAMUS

 

MID BRAIN MAMMILARY

BODY

 

OPTIC CHIASMA

 

HYPOPHYSIS CEREBRI (PITUITARY)

THIRD VENTRICLE PINEAL BODY

COLLICUS

 

 

 

 

CEREBRAL AQUEDUCT OF SYLVIUS

 

FOURTH VENTRICLE

 

 

 

CEREBELLUM

 

 

 

PONS

 

MEDULLA

ARBOR VITAE SPINAL CORD

 

Fig. – Sagittal section of human brain showing the structures around third ventricle and parts of midbrain and hindbrain

(ii) Medulla oblongata

Medulla oblongata is the hindest and posterior most part of brain. Cavity is known as IVth ventricle (metacoel). Which is continuous with central canal of spinal cord. It has

a pair of lateral Foramina of Luschka and a median foramen magendic. Cerebrospinal             v4

fluid come in contact by these apertures from internal cavity of the brain to outer fluid of meninges. A arrangement on its ventral surface there are buldgings of ascending and

descending tract which are called pyramids. On the ventral surface these pyramids cross each other which is called deccusatn of pyramids. On the dorsal side of medulla there are two nuclei which are called nucleus gracitis (long) and nucleus cunaeus. On floor of V4 there is groove called calamus scroptosious.

In the medulla oblongata, most of the sensory and motor fibres cross from one side to the other. Thus, the left cerebral hemisphere controls the right side of the body and vice versa. The reason for this is not known. The lower end of medulla passes into the spinal cord. There is no demarcation between the two. However, the medulla is considered to start at the level of the foramen magnum of the cranium.

  • Ponus Varolii : An oval mass, called the pons varolii, lies above the medulla oblongata. It consists mainly of nerve fibres which interconnect the two cerebellar hemispheres and also join the medulla with highrt brain centres, hence its name pons means bridge. Pons possess pneumotoxic and apneustic areas or centre. From pons 5, 6, 7 and 8th cranial nerve

Function of hind brain

  • Cerebellum –
    • Poorly developed in frog but well developed in
    • It is centre for co-ordination of muscular movement.
    • It is primary centre for balancing, equilibrium, orientation.

 

 

 

 

(2)  Medulla oblongata contain centre for

  • Heart beats (ii) Respiration                                                (iii) Digestion

(iv) Blood pressure                            (v) Gut peristalsis                                          (vi) Swallowing of food

  • Secretion of gland
  • Involuntory function – g. vomiting, coughing vasoconstrictor, vasodilater, sneezing, hiccouping.
  • It control urination,

Differences between Cerebrum and Cerebellum

 

CerebrumCerebellum
(1) It is the largest part of the brain, forming four-fifths of its weight.(1) It is the second largest part of the brain, forming one-eighth of its mass.
(2) It covers the rest of the brain.(2) It covers the medulla oblongata only.
(3) It is a part of the forebrain.(3) It is a part of the hindbrain.
(4) It consists of 2 cerebral hemispheres each comprising 4 lobes : frontal, occipital, parietal, temporal.(4) It consists of two cerebellar hemispheres and a median vermis.
(5) It encloses 2 lateral ventricles.(5) It is solid.
(6) White matter does not form arbor vitae.(6) White matter form arbor vitae.
(7) It initiates voluntary movements, and is  a seat of will, intelligence, memory etc.(7) It maintains posture and equilibrium.

 

 

 

Cavities or ventricles the brain : The ventricles consist of four hollow fluid filled space inside the brain and same duct for connection between these ventricte.

  • Olfactory lobe – Rhinocoel
  • Cerebrum – I and II ventricle or lateral ventricle or
  • Foramen of monero : I and II ventricle communicating with IIIrd ventricle by foramen of They are two in human and single in rabbit and frog.
  • Diencephalon : Third ventricle or
  • Iter or cerebral aquiduct or aquiduct of sylvius : It is very

OLFACTORY CEREBRUM

FORAMEN

OF MONRO

THIRD VENTRICLE

LATERAL VENTRICLE

 

OPTIC LOBES

ITER

CEREBELLUM FOURTH

VENTRICLE MEDULLA

 

Fig. Ventricles of brain of rabbit

 

narrow cavity between III and IV ventricle.

  • Optic lobe :
  • Cerebellum :
  • Medulla oblongata : 4th ventricle or

Cavities of brain and spinal cord are modified neurocoel. They are lined by low columnar ciliated epithelium called ependyma.

METACOEL

 

 

 

 

 

 

 

 

FORAMEN OF MONRO

THIRD VENTRICLE

 

 

 

 

 

 

 

 

 

 

 

CEREBRAL AQUEDUCT

 

 

 

 

 

 

 

 

 

 

FOURTH VENTRICLE

 

Fig. Diagram showing ventricles of human brain

 

 

 

 

Subdivisions, parts and associated strcutures of a vertebrate brain

 

DivisionsSubdivisionsPartsCavityAssociated strcutures
 (1) TelencephalonRhinencephalonI Ventricle (Rhinocoel)Olfactory bulbs Olfactory tracts Olfactory lobes

Palaeocortex on pallium

 Cerebral hemispheresII or Lateral Ventricles

(Paracoels)

¯

Formen of Monro

Corpora striata or basal ganglia

Corpus callosum Neocortex on pallium

Paraphysis

(I) Prosencephalon (Forebrain)(2) DiencephalonEpithalamus (roof)¯

III Ventricle (Diacoel)

Habenulae Pineal apparatus

Parapineal or parietal

 Thalamus (sides)  
Hypothalamus (floor) Hypothalamic nuclei Optic chiasma Median eminence Infundibular stalk Pituitary

Saccus vasculosus Mamillary bodies

Anterior choroid plexus

(II) Mesencephalon (Midbrain)Crura cerebri (floor)Iter or cerebral aqueductOptic lobes       ù Tectum Auditory lobesúû

Cerebral peduncles

(III) Rhombencephalon (Hind brain)(1) MetencephalonCerebellum Trapezoid body

Pons

(2) MyelencephalonMedulla oblongataIV Ventricle (Metacoel)Restiform bodies

Pyramids

Salient or mammalian features of human brain

The salient or mammalian features in the human brain are

  • Relatively small, solid olfactory
  • Very large cerebral hemispheres divided into lobes and with highly folded surface, fully cover the rest of the
  • Corpus callosum interconnecting the cerebral
  • Very small pineal
  • A pair of mammillary bodies joined to
  • Relatively small, solid optic lobes divided into 4 corpora
  • Large, solid cerebellum, with highly folded surface and divided into

 

 

 

  • Pons varolii present anterior to the

Important Tips

  • Tela choroidea is the term used for epithalamus and piamater
  • Tela choroidea is made up of epithelium and blood
  • Ataxia mean lacks of muscle Damage to cerebellum is characterized by ataxia.
  • Dyslexia involves an inability of an individual to comprehend written
  • Multiple sclerosis is the destruction of myelin sheath of neurons of
  • An American scientist Roger Sperry got Nobel Prize in 1981 for his outstanding work on split brain theory.
  • Parkinson’s disease or Paralysis agitans is a defect of
  • Parkinsonism is characterised by tremors and progressive rigidity of limbs caused by a degeneration of brain neurons and a neurotransmitter called dopamine.
  • Avian brain has large sized optic lobes to see the objects on the earth while flying so is called eye brain, while fish brain has large sized olfactory lobes to smell the prey from a distance so is called nose brain.
  • In fishes : Cerebrum is not differentiated in two cerebral
  • Hypothalamus has additional lobes to note pressure
  • In reptilian brain, pineal eye (parietal body) present in front of pineal
  • In birds, instictive behaviour is well developed so corpora striata are well
  • Grey matter of spinal cord of frog is rectangular white it is butterfly-shaped in
  • Central canal : Cavity of spinal
  • Optic bigemina : Two optic lobes in brain and are found from fishes to
  • Optic lobes of man are solid and have no optocoel but those of frog have
  • Optic tectum : Dorsal thick wall of optic
  • Cerebellum is also called little brain.
  • Thalami of diencephalon act as relay centres as well as gate keepers of
  • Optic chiasma is meant for binocular
  • Olfactory lobes of human brain have no rhinocoel while those of frog have
  • Man and birds are less dependent upon smell so olfactory lobes are small sized but are large sized in cartilage fishes (dog fish), dogs and reptiles as are more dependent upon
  • Cerebellum is large sized in fishes, birds and rabbit due to their multidirectional movements and increased dependency on
  • Stimulus for hunger : In February 1998, an American scientist Masashi Yanagisawa reported that a drop of sugar level in blood stimulates the apettite centres of lateral hypothalamus to release oraxin hormone (Gr. Oraxis = hunger) which stimulates hunger.
  • Nervous disorders

Agnosia : Failure to recognize; Alexia : Failure to read; Agraphia : Failure to write;

Aphasia : Failure to speak (due to injury to Broca’s area) Analgesia : Loss of sensation of pain;

Anaesthesia : Loss of feeling; Insomnia : Inability to sleep;

Amnesia : Partial or complete loss of memory; Coma : Complete loss of consciousness.

Aproxia : Inability to carry out purposeful movements.

Multiple sclerosis : Progressive degenerative disease of CNS and is characterized by many hard scar tissues.

  • Caudal equamma : Bundle of roots in last segment of spinal
  • Brain stem : Diancephalon + mid brain + pons
  • Cerebro vascular accident (C.V.A) or stroke : Blocking of blood supply of a part of
  • Alzeimer : It is the disease appearing usually after 65 It is characterized by dementia usually. Usually in this disease is ACH producing neurons of cerebral cortex and hippocampal lobe are degenerated. It is also seen that a amyloid protein is accumulated in the brain. It is the matter of research.
  • Comissure : The band of neurons connecting similar structure of brain or spinal
  • Connective : The band of neurons connecting two different structure of brain and spinal cord.

 

 

 

 

 

 

Spinal cord : Present in spinal canal or vertebral canal of

vertebral column. It is extended from foramen magnum to between I and II lumber vertebra. Spinal cord is swollen in cervical and lumber region which are called cervical and lumber enlargement.

Structure of spinal cord

Conus medullaris : It is last tapering ends of spinal cord, its ciliated central canal is called Vth ventricle.

Cauda equine : Nearly upto birth the length of spinal cord corresponds the length of V.C. but after birth there is vertically no growth of spinal cord but vertebral column grow upto I lumber vertebra in adult. Spinal nerve come out through their respective intervertebral foramen, form horse tail hair like

DORSAL FISSURE

 

DORSAL SEPTUM

 

 

 

 

 

 

 

 

 

 

 

CENTRAL CANAL VENTRAL FISSURE

BLOOD VESSELS

DORSAL FUNICULUS OF WHITE MATTER

DORSAL ROOT

DORSAL HORN OF GREY MATTER

LATERAL FUNICULUS DURA MATER PIA MATER

MOTOR NEURONS

SUBARACHNOID SPACE

VENTRAL ROOT VENTRAL HORN OF

VENTRAL GREY MATTER

FUNICULUS

 

cluster below conus medullaris it is called cauda equine.

Filum terminales : It is extension of piamater below

Fig – T.S. of the spinal cord of mammal

 

conus up to coccyx. In frog spinal cord also extends upto end of vertebral column.

Cisterna terminalis : It is last dilation of subarachnoid space below 1st lumbar vertebra. It is a proper site for lumber puncture or spinal tap, which is done to drain C.S.F out (5 to 10 ml). This C.S.F is used in diagnosing many diseases of CNS like meningitis, cyphalis, inter cranial pressure, menningococcal inferaction etc.

Meninges : Like brain, spinal cord is also enclosed with in three membranes. In this case duramater does not remain attached with the vertebra, instead there is a space between duramater and vertebra called epidural space. The epidural space is filled with a fluid. The distribution of duramater and piamater in spinal cord is the same as that of brain.

The cross section of spinal cord reveals the following structures

  • Central canal : In the centre of spinal cord, there is a canal called central c It is filled with cerebrospinal fluid.
  • Dorsal fissure : In the mid dorsal line, there is a groove extending throughout its
  • Ventral fissure : It is also a groove situated in the mid ventral line throughout the length of spinal
  • Dorsal septum : It is a partition extending from dorsal fissure to central
  • Grey matter : It lies around the central canal in the form of a
  • Dorsal horns : It is like horn of grey matter on the dorsal
  • Ventral horns : On the ventral side of the grey matter are horn like structures the ventral
  • Lateral horns : These are horns on the lateral side of grey
  • White matter : White matter is present around grey Spinal cord provides pathway for the impulses from the brain and to the brain.

Reflex action

First of all Marshal Hall (1833) studied the reflex action. Best and Taylor defined reflex action “simplest form of irritability associated with the nervous system is reflex actions or a reflex reaction is an immediate involuntary response to a stimulus.” The reflex actions are involuntary actions because these are not under the conscious control of the brain. The spinal cord and brain stem are responsible for most of the reflex movements. A few examples of the reflex actions are withdrawal of hand or leg if pricked by a pin, secretion of saliva as soon as one thinks of delicious food or mere its sight causes salivation, if the body part is touched with acid or hot object it is

 

 

 

 

automatically, without thinking and planning is withdrawn, cycling, motor driving etc. Central nervous system is responsible for the control of reflex action.

Reflex arc is formed by the neurons forming the pathway taken by the nerve impulses in reflex action. The simplest reflexes are found in animals involving a single neuron and the following pathway —

 

Stimulus

®  Receptor ¾¾Neu¾ro¾n ®

Effector

® Response

 

The reflex areas in all the higher animals than coelenterates, include at least two neurons, an afferent or sensory neuron carrying impulses from a receptor towards aggregation of nervous tissue which may be a ganglion, nerve cord or central nervous system and an efferent or motor neuron carrying impulses away from the aggregation to an effector.

  • Component of reflex action : The whole of the reflex are includes six parts –

NERVE IMPULSE FROM PAIN RECEPTOR

 

 

PAIN RECEPTOR

 

SPINAL

CELL BODY

RELAY NEURONE

 

 

 

RECEPTOR, e.g., FREE NERVE ENDING

NEEDLE PRICK

NERVE

DORSAL ROOT

 

 

 

 

MOTOR NEURON

 

 

WHITE MATTER

 

 

 

SYNAPSE

 

 

 

GRAY MATTER

 

SPINAL CORD IN TRANSVERSE SECTION

 

 

 

EFFECTOR, e.g., MUSCLE FIBRES

Fig. Reflex arc

 

  • Receptor organs : Receptors are windows of the body or guards of the These are situated on all, important organs, for example – eyes, nose, ear, tongue, integument etc. These perceive the stimuli from out side the body.
  • Sensory neurons : These are also termed afferent neurons. These carry the stimuli from receptors to spinal These neurons are situated in the ganglion on the dorsal side of spinal cord.
  • Nerve centre : Spinal cord is termed as nerve Synaptic connections are formed in it.
  • Association neurons : These are also called intermediate neurons or interstitial These are found in spinal cord. They transfer the impulses from sensory neurons to motor neurons.
  • Motor neurons : These are situated in the ventral horn of spinal These carry the impulses to effector organs.
  • Effector organs : These are the organs, which react and behave in response to various stimuli, for example – muscles and
    • Mechanism of reflex action : The time taken by a reflex action is too short, for example – in frog it is
    • meter per second and in man 5-120 meter per second. Whenever, a part of the body is stimulated by any stimulus, for example – pin pricking, then the stimulus is converted into This impulse is perceived by the dendrites of sensory neurons. From here, the stimulus reaches the spinal cord through axonic fibres. In the spinal cord, this stimulus passes through synaptic junctions and reaches the intermediate neurons, from where this stimulus reaches the effector organs through visceral motor nerve fibres. As soon as the stimulus reaches the effector organs,

 

 

 

it is stimulated and that part of the body is immediately withdrawn. The whole reflex action takes place so rapidly and quickly that we know it when it is completed.

  • Type of reflexs : The reflexes are of following types –
    • Monosynaptic reflex (2) Polysynaptic Spinal Reflex

(3) Polysynaptic Spinal/Brain Reflexes                 (4) Unconditioned or Simple reflex

(5) Conditioned or Acquired reflexe

  • Monosynaptic reflex : This is the simplest reflex found in vertebrates. The simplest reflex found in The sensory neuron synapses directly on to the motor neuron cell body. In this case the reflex action takes place without the involvement of brain.
  • Polysynaptic spinal reflex : This has at least two synapses situated within the spinal It involves a third type of neuron also – the internuncial or inter-mediate relay neuron. The synapses take place between the sensory neuron and intermediate neuron, and between intermediate neuron and the motor neuron. These two reflex arcs allow the body to make automatic, involuntary, homeostatic adjustments, to changes in the external environment, such as the iris pupil reflex and balance during locomotion, and also in the internal environment such as breathing rate and blood pressure.
  • Polysynaptic spinal/brain  reflexes  :  In this case the sensory neuron synapses in the spinal cord with a second sensory neuron, which passes to the brain. The latter sensory neurons are part of the ascending nerve fibre tract and have their origin in preintermediate neuron synapse. The brain is capable of identifying this sensory information and stores it for further use. The motor activity may be initiated by the brain anytime and the impulses are transmitted down the motor neurons in descending nerve fibre tract, to synapse directly with spinal motor neurons in the postintermdiate synaptic
  • Simple reflex : Simple reflex is also known as unconditioned reflex. It is inborn, unlearned, reflex to a Simple reflex is mostly protective in function. Example of simple reflex are
    • Knee jerk – Tendon of patella
    • Corneal reflex (blinking reflex) – closing of
    • Rapid withdrawal of hand while burned or pricked.
    • Quick recovery of balance while
    • Scratch reflex of frog – in pitched frog with acetic
    • Coughing, sneezing and yawning.
  • Acquired reflex : Acquired reflex is also known as conditioned It is not inborn, but acquired and dependent on past experience, training and learning. Demonstration of conditioned reflex was first made by Russian physiologist Ivan Petrovitch Pavlov (1846-1936) in hungry dog. Pavlov rang the bell while feeding dog, thus associated the unconditioned response with additional stimulus. Examples of conditioned reflex are learning of dancing, cycling, swimming, singing,, driving, etc. These actions are under cerebral control during learning.

(ii) Peripheral nervous system : It is formed of a number of long, thin, whitish threads called nerves extending between central nervous system and body tissues. Each nerve is formed of bundles of nerve fibres, fasciculi, held together by connective tissue and surrounded by a white fibrous connective tissue sheath called epineurium.

The nerve fibres are classified into two categories on the basis of presence or absence of myelin (white fatty) sheath.

  • Medullated or Myelinated nerve

 

 

 

  • Non-medullated nerve

On the basis of function, the nerves are of three types

 

(a) Sensory nerve(b) Motor nerve(c) Mixed nerve
(1) It contains only sensory nerve fibres.(1) It contains only motor nerve fibres.(1) It contains both sensory and motor nerve fibres.
(2) It conducts nerve impulses from sense organs to CNS to produce sensation.

e.g. Optic nerve, auditory nerve.

(2) It conducts nerve impulses from CNS to some muscles or glands to control their activities.

e.g. Occulomotor nerve, hypoglossal nerve.

(2) It conducts both sensory and motor impulses.

e.g. All spinal nerves, trigeminal nerve.

On the basis of their origin, nerves are of two types

  • Cranial or cerebral nerves which either arise from or end into
  • Spinal nerves which arise from spinal

(a)  Cranial nerves

  • 10 pairs of cranial nerves are present in an anamniote (fishes and amphibians).
  • Number of cranial nerves found in frog is ten pairs (20).
  • 12 pairs of cranial nervers are present in an amniote (reptiles, birds and mammals).
  • Number of cranial nerves found in rabbit and man is 12 pairs (24).
  • The first 10 pairs are common for frog and The additional pairs found in rabbit are spinal accessory and hypoglossal.
  • The smallest cranial nerbe is trochlear in human beings, but all animals smallest cranial nerve is abducens.
  • The largest cranial nerve is trigeminal in human beings but vagus is largest cranial nerve in all
  • Vagus supplies the regions other than
  • The sensory cranial nerves are

I Olfactory       –        Smell

II Optic           –        Vision

VIII Auditory    –        Hearing and equilibrium

  • The motor cranial nerves are : III, IV, VI, XI and XII.
  • Extraocular muscle nerves are : III, IV and
  • The mixed cranial nerves are : V, VII, IX and X (4 pairs).

Cranial nerves of mammal at a glance

 

 NameNatureOriginDistributionFunction
(1)Olfactory NervesSensoryOlfactory lobeSensory epithelium of olfactory sacsReceive stimuli from the sensory epithelium of olfactory sac and carry them to olfactory lobes
(2)Optic nervesSensoryOptic lobesRetina in EyesStimulus of light is carried to optic lobes
(3)Occulomotor nervesMotorCrura cerebriEye ball muscles, except superior oblique muscleCarry the impulses from crura cerebri to the eye muscles
(4)Trochlear nervesMotorFrom in between the optic lobes and cerebellumSuperior oblique muscle of eye ballCarry the impulses from the brain to superior oblique muscles of the eye

 

 

 

 

(5)Trigeminal nervesMixedFrom the gassarion galglia situated on the lateral side of medulla oblongata
(i)Ophthalmic nerveSensory,,Skin of lips 
(ii)MaxillarySensory,,Upper lip, skin of nose, lower eye lid.Carry the stimuli from these organs to brain
(iii)Mandibular nerveMixed,,Lower lip and skin of jawCarry the stimuli from these organs to brain
(6)Abducens nervesMotorMedullaEye musclesCarry the impulses from the brain (medulla) to eye muscles
(7)Facial nervesMixedBehind trigeminal nerve, from geniculate ganglion
(i)PalatinusSensoryIn the roof of mouth cavityCarry the impulses from roof of mouth cavity
(ii)Hyoman dibularMotorMuscles of low jaw, muscles of neck and pinna (external ear)Carry the impulses from brain muslces of lower jaws, neck and pinna.
(iii)ChordotympaniMixedIn salivary glands and taste budsReceives the stimuli from the taste buds and carry the stimulus to salivary gland.
(8)Auditory nervesSensoryMedulla
(i)Vestibular nerve,,,,Utriculus, sacculus, semicircular canals and Cochlea.Receives impulses from the internal ear and carry to brain.
(ii)Cochlear nerve,,,,Cochlea
(9)Glossopharyngeal nerveMixed,,Taste buds present in tongue and muslces of oesphagusCarry sound impulses to brain, to muscles of oesophagus and carry the taste impulse of tongue to the brain
(10)Vagus nerveMixedAfter arising from medulla, 9th and 10th cranial nerves unite to form vagus nerve but become separate and divide into branches
(i)Superior laryngeal nerveMotorGlottisCarry the impulse to muscle of glottis
(ii)Recurrent laryngeal nerveMotorGlottis,,
(iii)Cardiac nerveMotorHeart MusclesFrom brain to heart muscles
(iv)PneumogastricMotorIn the abdominal cavity, in stomach and lungs.Carry impulse from these organs to brain and from brain to muscles of these organs.
(v)Depresser nerveMotorDiaphragmCarry the impulse to diaphragm

 

 

 

 

 

(11)Spinal accessoryMotorMedullaMuscles of neck and shouldersFrom brain to muscles of neck and shoulder
(12)Hypoglossal nerveMotor,,Muscles of tongue and neckFrom brain to their muscles

 

SUPERIOR RECTUS MUSCLE

 

 

I – OLFACTORY (S) II – OPTIC (S)

III – OCULOMOTER (M) IV – TROCHLEAR (M)

V – TRIGEMINAL (MIXED) VI – ABDUCENS (M)

VII – FACIAL (MIXED) VIII – AUDITORY (S)

IX – GLOSSOPHARYNGEAL (MIXED)

 

VAGUS (X) (MIXED)

XI – ACCESSORY (M)

 

XII–HYPOGLOSSAL (M)

Fig. Diagrammatic presentation of 12 (paired) cranial nerves in

CORNEA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LATERAL RECTUS MUSCLE

INFERIOR OBLIQUE MUSCLE

RING CARTILAGE SUPERIOR

OBLIQUE MUSCLE

 

INFERIOR RECTUS MUSCLE

MEDIAL RECTUS MUSCLE

 

 

 

OPTIC NERVE

 

human. (3 sensory, 5 motor, 4 mixed), 30% of nerves supply to eye indicating the importance of vision.

Fig. The extraocular muscles

 

 

Eyeball muscleNerve supply
Superior rectusOculomotor
Inferior rectusOculomotor
Internal rectusOculomotor
External rectusAbducens
Superior obliqueTrochlear
Inferior obliqueOculomotor
  • Spinal nerves : Spinal nerves arise from gray matter of spinal There are 31 pairs of spinal nerves in man (37 pairs in rabbit). All spinal nerves are mixed. The spinal nerves in man are divided into 5 groups.

 

(1) Cervical (C)®8 pairs––in Neck region
(2) Thoracic (T)®12 pairs––in thoracic region
(3) Lumbar (L)®05 pairs––upper part of abdomen
(4) Sacral (S)®05 pairs––lower part of abdomen
(5) Coccygeal (CO)®01 pairs

31 pairs

––represent the tail nerves

 

 

 

 

Number of spinal nerves in frog is 10 pairs. In some frog like Rana tigrina, 10th pair may reduced or absent. The first pair of spinal nerves in frog is hypoglossal. The last pair of cranial nerves of mammals has the same name. Brachial plexus is formed by 2nd and 3rd spinal nerves in frog. Sciatic plexus is formed by 7, 8 and 9 spinal nerves in frog. Glands of Swammerdam are calcareous glands found at the places of emerging of spinal nerves in frog.

Spinal nerve formula can be written as : C8, T12, L5, S5, CO1,

 

Spinal nerves exit via intervertebral foramen. Each spinal nerve arises from spinal cord by 2 roots

  • Dorsal (= Afferent = Sensory = Posterior) root is a continuation of dorsal horn and is formed of gray It presents a ganglionic swelling in middle, called dorsal root ganglion. These transmit sensory nerve impulses from the sense organs to spinal cord (touch, pain, temperature). They activate involuntary reflexes.
  • Ventral (= Efferent = Motor) root are continuation of ventral root and is also formed of gray matter. No ganglion are present. It is formed of only efferent nerve filers. They transmit motor nerve impulses to effector organs g., glands and muscles. Each spinal nerve has 3 branches –
  • Ramus dorsalis : Supplies to skin and muscles of dorsal
  • Ramus ventralis : Supplies to skin and muscles of ventral and

CERVICAL NERVES (1-8)

 

 

 

 

THORACIC NERVES (1-12)

 

 

 

 

 

 

 

 

LUMBAR NERVES (1-5)

 

 

 

SACRAL NERVES (1-5)

 

 

 

 

 

 

SPINAL CORD

 

 

 

 

 

END OF SPINAL CORD (CONUS MEDULLARIS)

 

CAUDA EQUINA

 

 

 

 

FILUM TERMINALE

 

lateral sides and also to upper and lower limbs. Ventral root of certain

spinal nerve form 5 nerve plexi on either side, i.e., cervical, thoracic,

lumber, sacral, caudd.

  • Ramus communicans : It joins sympathetic ganglion of autonomic nervous
  • Autonomic nervous system : As mentioned

COCCYGEAL NERVE

 

Fig. – Spinal cord and spinal nerves

DORSAL ROOT

 

 

RAMUS DORSALIS DORSAL ROOT

GANGLION

 

before, the visceral part of peripheral nervous system regulates and co-ordinates the activities of internal or visceral organs. Autonomic nervous system was discovered by Langley. Autonomic nervous system (ANS) automatically

SPINAL CORD

VENTRAL ROOT

 

 

 

SYMPATHETIC GANGLION

RAMUS VENTRIALS

 

RAMUS COMMUNICANS

 

regulates the activities of smooth muscles, cardiac muscles and glands. This co-ordination is involuntary. Autonomic

Fig. – Origin and distribution of spinal nerve

 

nervous system usually operates without conscious control. Autonomic nervous system is entirely motor. All autonomic axons are efferent fibres. Efferent neurons are preganglionic with myelinated fibres and postganglionic with unmyelinated fibres. Autonomic nervous system is regulated by centres in brain like cerebral cortex, hypothalamus and medulla oblongata. Autonomic fibres release chemical transmitters at synapse. On the basis of the transmitter produced, these fibres may be classified as cholinergic or adrenergic. Cholinergic fibres release acetylcholine. Adrenergic fibres produce norepinephrine (noradrenaline), also called sympathetin.

Nature of autonomic control : The autonomic nervous system regulates and co-ordinates such vital involuntary activities like heart beat, breathing, maintenance of the composition of body fluids (= homeostasis) and body temperature, gut peristalsis, secretion of glands, etc. For this control, a visceral organ is normally innervated by

 

 

 

 

two, instead of only one, postganglionic fibres having antagonistic excitatory effects; while one fibre promotes the activity of an organ, the other fibre retards it. Autonomic nervous system consists of two divisions

(a) Sympathetic (= Thoracolumbar out flow)          (b) Parasympathetic (= Cranio-sacral out flow)

(a)  Sympathetic ANS

  • Thoraco Lumber out flow (all thorocic + 3 lumber)
  • Preganglionic nerve smal
  • Post ganglionic nerve long.
  • Preganglionic nerve secrete acetyl choline.
  • Postganglionic nerve secrete sympathatin. (nor-epinephrine)
  • It shows sympathy (generally increase the function).
  • Expenditure of energy takes
  • It increase defence system of body against adverse

 

  • It is active in stress condition, pain, fear and

 

 

 

EYE

 

(++)           STIMULATION

BLOOD VESSEL OF LACRIMAL, MUCOUS

AND

 

 

 

 

CONTRACTION OF ARRECTOR
INCREASES SECRETION =

SWEAT HAIR

 

 

 

 

VASOMOTO R

 

 

 

 

 

 

COELIAC GANGLIO

2.

LUNGS AND

  1. ARTERIAL BLOOD PRESSURE INCREASE
  2. RBC COUNT INCREASES
  3. BLOOD CLOTTING PERIOD DECREASES
  4. BLOOD SUPPLY TO SKIN DECREASES

RATE     OF     HEART      BEAT

 

 

 

VENTRA L

SUPERIOR MESENTRIC

3.

BILE SECRETION

INFERIOR MESENTRI PROMOTES

ADRENAL

 

KIDNEY

 

LIVER

 

 

VASOMOTOR FIBRES

 

INTESTINAL GLAND SECRETION INHIBITED
PANCREATI

C SECRETION

GANGLIONIC CHAIN (INTERCONNECTED)

 

 

(21

STOMAC

COLO

 

 

URINARY

RELAXE

RECTU

 

ANUS

 

Fig. – Sympathetic nervous system and its function

 

 

 

 

 

(b)  Parasympathatic

  • ANS Cranio sacral outflow (cranial-III, VII, IX, X Nerves)-(sacral-II, III, IV Nerves)
  • Preganglionic nerve long.
  • Postganglionic nerve smal
  • Secrete acetyl choline only.
  • It provide relaxation, comfort, pleasure, at the time of
  • Restoration and conservation of energy takes
  • Collateral ganglia present in sympathetic nervous
  • Horner’s syndrome results from the damage of sympathetic trunk of one
  • A patient of Horner’s syndrome exhibits lack of sweating (on affected side), sunken eyes and constricted

 

 

HYPOTHALAMUS CILIARY GANGLION

++

DECREASE IN TEAR SECRETION

LACRIMAL GLAND

 

 

SUB. MAXILLARY GLAND

 

 

SALIVARY NUCLEI DORSAL VAGAL NUCLEUS

 

 

 

SUB. MANDIBULAR GANGLION

BLOOD VESSEL AND GLANDS OF HEAD PAROTID GLAND

 

 

 

1.  RELAXATION OF ARRECTOR PILLI MUSCLES

2.  SWEATING DECREASES

BRONCHUS LUNGS

HEART

ADRENAL                                                     LIVER

 

GLYCOGENESIS INCREASES

KIDNEY

STOMACH

GASTRIC SECRETION IS STIMULATED

PANCREATIC SECRETION STIMULATED

SMALL INTESTINE

 

 

 

 

 

 

URETER

++ URINARY

¯ BLADDER

INTESTINAL SECRETION STIMULATED

RELAXES ANAL SPINCTER TO OPEN ANUS

COLON RECTUM

 

Fig. Parasympathetic nervous system and its functions

 

 

 

 

 

S.No.NameSympatheticPara sympathetic
(1)SecretionAcetyl choline and + sympathiatinAcetyl choline only
(2)Blood pressureIncreaseDedrease
(3)Blood vessel to skinConstrictDilate
(4)Blood vessel to heartDilateConstrict
(5)Blood vessel to lung and muscleDilateDilate
(6)PupilDilateConstrict
(7)Lacrymal glanStimulateInhibits
(8)Heart beatIncreaseDecrease
(9)Adrenal secretionStimulateInhibit
(10)Breathing and BMRIncreaseDecrease
(11)NostrilsDilateConstrict
(12)Urinary bladderRelaxConstrict
(13)IrisConstrictDilate
(14)Salivary glandDecreaseIncrease
(15)Digestive glandDecreaseIncrease
(16)Gut peristalsisDecreaseIncrease

Cutting of sympathetic or parasympathetic nerve to heart will not stop functioning of heart. Heart will beat but without any nervous control. Autonomic nervous system functions rapidaly to alter visceral functions (3-5 seconds). It is activated mainly by centers located in spinal cord, brain stem and hypothalamus. Limbic cortex also influences its function often this system function via visceral reflexes i.e. sensory signal ® enter autonomic ganglia ® spinal cord ® brain stem ® or hypothalamus can elicit reflex responses back to visceral organs to control their activities.

 Biochemical Aspect of Nervous Physiology

Nerve cells (= neurons) : Irritability is a basic characteristic of the “living substance”, i.e., the protoplasm.

 

Consequently, every living cell becomes excited when stimulated. However, the nerve cells and muscle fibres are specialized excitable cells of body, capable of transmitting or conducting excitations along their membranes. Of these, muscle cells are further specialized for contraction while nerve cells are further specialized for receiving stimuli (as sensory or receptor cells) and transferring excitations from one to the other.

A typical neuron consists of a nucleated cell body (= cyton, soma or perikaryon), five to seven short, slender and branched (= arborized) dendrites, and a single, relatively thicker and longer fibrous axon. The latter is terminally branched into short telodendria. Each

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ca+ Mg

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ORGANIC ACIDS(6)

CELL CYTOPLASM

 

telodendron bears a terminal knob or bouton. Boutons of one neuron lie upon dendrites or cytons of adjacent neurons

Fig. – Electrolyte composition of ECF and cell cytoplasm figures indicate mEq/litre H2O for different electrolytes

 

 

 

 

 

(figure), or upon muscle fibres or glands.

Nerve fibres : Although, all parts of a neuron transmit excitations (= impulses), but the transmission is always unidirectional. The dendrites and cytons usually constitute the impulse receiving parts which receive impulses directly from receptors, or from other adjacent neurons. The axons are specialized as fibres conducting impulses away from the receiving parts. Thus, the reaction or response impulses are always carried to the effectors by axons. That is why, the term ‘nerve fibres’ is usually applied to the axons. The latter are 0.1 mm to one or more (upto 10) metres long and about 0.025 m thick on an average.

Main properties of nervous tissue : The nervous tissue has two outstanding properties excitability and conductivity.

  • Excitability : It is the ability of the nerve cells and fibres to enter into an active state called the state of excitation in response to a Excitation arises at the receptors on account of various stimuli such as light, temperature, chemical, electrical or pressure which constantly act on the organisms.
  • Conductivity : The excitation does not remain at the site of its origin. It is transmitted along nerve fibres. The transmission of excitation in a particular direction is called conductivity.

Definition of nerve impulse : A wave of reversed polarity or depolarization (action potential) moving down an axon is called a nerve impulse.

Mechanism of conduction of nerve impulse : Most accepted mechanism of nerve impulse conduction is ionic theory proposed by Hodgkin and Huxley. This theory states that nerve impulse is an electro-chemical even governed by differential permeability of neurilemma to Na+ and K+ which in turn is regulated by the electric field.

 

(i) Transmission of nerve impulse along the nerve fibre

(a) Polarization (Resting membrane potential-RMP) : In a resting nerve fibre (a nerve fibre that is not conducting an impulse), sodium ions (Na+) predominate in the extracellular fluid, whereas

STIMULUS

 

+++++++++++++++++++++++++++++++

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

 

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

+++++++++++++++++++++++++++++++

 

potassium ions

(K + )

predominate in the intracellular fluid (within the

POLARIZED MEMBRANE

 

fibre). Intracellular fluid also contains large number of negatively charged (anions) protein molecules. Na+ are 10 times more outside the neuron and K+ ions are 25 times more inside the cell. Thus it makes a

– – – – – – – – – – +++++++++++++++++++++

+++++++++ – – – – – – – – – – – – – – – – – – – – – –

 

+++++++++ – – – – – – – – – – – – – – – – – – – – – –

– – – – – – – – – – +++++++++++++++++++++

 

considerable difference between the ion concentration outside and inside

the plasma membrane. It also causes a difference in electrical charges on

DEPOLARIZED REGION

POLARIZED REGION

 

either side of the membrane. The plasma membrane is electrically

++++++++++ – – – – – – – – – – – ++++++++++

– – – – – – – – – – +++++++++ – – – – – – – – – –

 

positive outside and negative inside. This difference is called potential

– – – – – – – – – – +++++++++   – – – – – – – – – –

 

difference. The potential difference across the plasma membrane is known as resting potential. This potential averages – 70 mv (– 60 to – 90 mv) in inner side of membrane in respect to outer side.

Due to different concentrations of ions on the two sides of the membrane, sodium ions tend to diffuse into the nerve fibre and potassium ions tend to diffues out of the nerve fibre. The membrane of a resting nerve fibre is more permeable to potassium than to sodium. So

++++++++++ – – – – – – – – – – – ++++++++++

 

REPOLARIZED DEPOLARIZED        POLARIZED

 

+++++++++++++++++++++ – – – – – – – – – –

– – – – – – – – – – – – – – – – – – – – – – +++++++++

 

– – – – – – – – – – – – – – – – – – – – – – +++++++++

+++++++++++++++++++++ – – – – – – – – – –

 

REPOLARIZED REGION            DEPOLARIZED

  • Transmission of nerve impulse

 

potassium leaves the nerve fibre faster than sodium enters it. This results in a higher concentration of cations outside the membrane compared to the concentration of cations inside it. This state of the resting membrane is called polarised state and makes its inner side electronegative to its outerside.

 

 

 

 

  • Depolarization (Action membrane potential or AMP) : When the nerve fibre is stimulated mechanically, electrically, thermally or chemically a disturbance is felt at the point of stimulation which gives rise to a local excitatory The membrane becomes permeable to sodium ions. Suddenly sodium ions rush inside the nerve fibre and potassium ions diffuse out of the axon membrane. Due to the diffusion of ions, more sodium ions enter the axon than potassium ions leave it, so that the positive and negative charges on the outside and inside of the axon membrane are reversed. The membrane is negatively charged on the outside and positively charged on the inside. The membrane with reversed polarity is said to be depolarized. The depolarization of the membrane suddenly passes as a wave along the nerve fibre. Thus the impulse is propagated as a wave of depolarization (reversed polarity). This wave of depolarization travelling down a nerve fibre is called action potential. Infact, the action potential “moves” in the manner of a spark moving along a fuse. This “moving” action potential constitutes the nerve impulse. The action potential (impulse) is the basic means of communication within the nervous system. The action potential of + 45 mv on inner side of axolemma in respect to its outer side is also called spike potential.

 

  • Repolarization : With the increase of sodium ions inside the nerve cell, the mebrane becomes less permeable to sodium ions whereas the permeability membrane to potassium ions increases. The sodium ions are pumped out of the cell and potassium ions are pumped into the cell until the original resting state of ionic concentration is achieved. Thus this makes the membrane negative on inside and positive on This process is called repolarization.

The last movement of ions is thought to take place by an active

+30

 

0

 

 

 

–70

1        2        3        4        5

TIME IN MILLISECONDS (MESC)

  • Record of potential

ACTION POTENTIAL

 

 

 

RESTING MEMBRANE POTENTIAL

 

transport mechanism called sodium potassium pump (also called sodium potassium exchange pump or sodium pump). The sodium-potassium pump is a process of expelling out sodium ions and drawing in potassium ions against concentration and electrocemical gradient. The entire process of repolarization requires some time during which the nerve cannot be stimulated again. This period is called refractory period. During repolarization, as the cell returns to its resting potential, the neuron is ready to receive another stimulus.

 

  • The synapse : The synapse is an area of

PRESYNAPTIC KNOB

 

SYNAPTIC

 

functional contact between one neuron and another for the

purpose of transferring information. Synapses are usually

SYNAPTIC TELODENDRIUM OF VESICLE

PRESYNAPTIC

TRANSMITTER SUBSTANCE

CLEFT      DENDRITE OF

POSTSYNAPTIC

NEURON

 

found between the fine terminal branches of the axon of one neuron and the dendrites or cell body of another. This

NEURON

+ + + + + + + + + + –

 

+ + + + + + + + + +

– – –

+ + +

– – –

+ – + + + + + + + +

++ – – – –    – – – –

+       – – – – – – – –

 

type of neuron is called axo-dendrite synapse. Sir Charles

–  +                        +  – + + + + + + + +

+

–     +                 + –

 

Sherrington (1861-1954) was the first person who used the term ‘synapse’ to the junctional points between two

REPOLARIZED REGION

– –              – –

DEPOLARIZED REGION

POLARIZED REGION

 

neurons.

Fig. Impulse conduction at synapse

 

Structure of synapse : A typical (generalized synapse) consists of a bulbous expansion of a nerve terminal called a pre-synaptic knob lying close to the membrane of a dendrite. The cytoplasm of the synaptic knob contains mitochondria, smooth endoplasmic reticulum, microfilaments and numerous synaptic vesciles. Each vescile contains neurotransmitter (chemical substance) responsible for the transmission of the nerve impulse across the synapse. The membrane of the synaptic knob nearest the synapse is thickened and forms the presynaptic membrane. The membrane of the dendrite is also thickened and is called the post synaptic membrane. These membranes are separated by a gap, the synaptic cleft. It is about 200 Å across The post synaptic membrane contains large protein molecules which act as receptor sites for neurotransmitter and numerous channels and pores.

 

 

 

The two main neurotransmitters in vertebrate nervous system are acetylcholine (ACh) and noradrelaine although other neurotransmitters also exist. Acetylcholine (ACh) was the first neurotransmitter to be isolated and obtained by Otto Loewi in 1920 from the endings of parasympathetic neurons of the vagus nerve in frog heart. Neurons releasing acetylcholine are described as cholinergic neurons and those releasing noradrenaline are described as adrenergic neurons.

Mechanism of transmission of nerve impulse at a synapse : The process of chemical transmission across synapses was discovered by Henry Dale (1936). The physiological importance of synapse for the transmission of nerve impulses was established by McLennan in 1963. A brief description of the mechanism of synaptic transmission is given below

  • When an impulse arrives at a presynaptic knob, calcium ions from the synaptic cleft enter the cytoplasm of the presynaptic
  • The calcium ions cause the movement of the synaptic vesicles to the surface of the The synaptic vesciles are fused with the presynaptic membrane and get ruptured (exocytosis) to discharge their contents (neurotransmitter) into the synaptic cleft.
  • The synaptic vesicles then return to the cytoplasm of the synaptic knob where they are refilled with
  • The neurotransmitter of the synaptic cleft binds with protein receptor molecules on the post synaptic This binding action changes the membrane potential of the postsynaptic membrane, opening channels in the membrane and allowing sodium ions to enter the cell. This causes the depolarization and generation of action potential in the post-synaptic membrane. Thus the impulse is transferred to the next neuron.
  • Having produced a change in the permeability of the postsynaptic membrane the neurotransmitter is immediately lost from the synaptic cleft. In the case of cholinergic synapses, acetylcholine (ACh) is hydrolysed by an enzyme acetylcholinesterase (AChE) which is present in high concentration at the
  • The products of the hydrolysis are acetate and choline which are reabsorbed into the synaptic knob where they are resynthesized into acetylcholine, using energy from

Neuromuscular junction : Impulses are conducted from a neuron to a muscle cell across an area of contact called neuromuscular junction. When a nerve fibre ends on a muscle fibre, it forms motor end plate. The motor end plates have vesicles and mitochondria. The vesicles secrete neurotransmitter. When the motor impulse from the nerve is reveived on the motor end plates, a local depolarization occurs there resulting in the excitation of the muscle fibre.

Neuroglandular junction : It is an area of contact between a neuron and glandular cells. There is also a gap which is bridged at the time of the transmission of the impulse by a neurontransmitter.

Neurotransmitters : As explained in the discussion of synapses, neurotransmitters are chemicals released from a presynaptic neuron that interact with specific receptor sites of a postsynaptic neuron. At least thirty chemicals thought to have the capacity to act as neurotransmitters have been discovered.

 

 

 

 

ExcitoryInhibitory
(1) Acetylcholine(1) Gamma amino butyric acid (GABA)
(2) Norepinephrine (NE)(2) Glycine
(3) Serotonin 
(4) 5-hydroxy tryptamine (5-HT) 
(5) Dopamine 
(6) Histamine 
(7) Glutamate 

Synapse, A one-way valve : The synapse cannot transmit an impulse in the reverse direction as the dendrites cannot secrete a neurotransmitter. Thus, the synapse acts as a one-way valve, allowing the conduct of impulse from axon to dendron only.

Synaptic delay : Transmission of an impulse across a synapse is slower than its conduction along a neuron. This is because of the time needed for the release of a neurontransmitter, its diffusion through the synaptic cleft, and its action on the postsynaptic membrane. The difference in the rate is called synaptic delay. It amounts to about half a millisecond at body temperature (37oC).

Synaptic fatigue : Repeated stimulation of the presynaptic knob may deplete the neurotransmitter, and this may fail to stimulate the postsynaptic membrane. This condition of the synapse is termed synaptic fatigue. It lasts for several seconds during which the neurotransmitter is resynthesized. Synaptic fatigue is the only fatigue that affects the nervous tissue. Conduction of the nerve impulse along the neurons is not subject to fatigue.

“All or None law” (Keith Lucas, 1905) : When stimulated, the axon membrane (= axolemma) does not respond for a moment due to its resistance or threshold to stimulation. However, when its threshold is broken, the stimulation is conducted through its whole length as a strong impulse. If the stimulationm is too weak to break the axon’s threshold, impulse is not established, but if the intensity of stimulation is much more than the threshold value, impulse conduction remains normal. Thus, the action potential obeys “all or none law”. In other words, impulse conduction is such a triggered phenomenon which, though occurs in a twinkling, like an explosion, but only when it reaches “ignition point” or firing level”.

Important tips

 

 

 

 

  • Bipolar nerve cell and ganglia cell are found in the
  • Lateral funiculi have motor type of
  • Six separate layers of neurons present in cerebral
  • Arbor vitae are composed of white
  • IIIrd, IVth and VIth cranial nerves control eye-ball movemen
  • A cavity in the ventricle of a brain is known as cerebral aqua.
  • VII, IX, X, XI and XIIth cranial nerve originating from medulla
  • Cycling is an example of conditioned reflex.
  • The ganglia of sympathetic and central nervous system in frog develops from the neural crest
  • Cerebellum of post brain involved in loss of control when a person drinks
  • The maximum current required to stimulate a nerve is called rheophase or threshold current or firing level of It is about 15 mv.
  • A fibres is the largest mammalian
  • Hyperpolarization of a dendrite is due to presynaptic inhibition.
  • Amygaloid nucleus, hippocampus and fornix is the part of limbic
  • Posterioplegia is the paralysis of both lower limb due to damage of spinal
  • Earthworm has both sensory and motor
  • The glial cells that form the blood brain barrier by lining brain capillaries are the astrocytes.
  • Axo-axentic is the condition when direction of nerve impulse is
  • Neurocyton is located in cortex of the
  • Cervical swelling is the anterior enlargement of spinal
  • Hydra has false nervous system but not
  • A polar nerve cells are found in vertebrates
  • Saltatory conduction is found in all
  • In frog, the nerve impulses for hearing start from lagena
  • Corpus callosum is absent in the brain of prototherians.
  • Degeneration or imperfect development of corpus callosum in human brain results in a neurological disorder called schizophrenia.
  • g-amino butyric acid is a
  • Acetylcholine is the cardian inhibitor.
  • 5’-hydroxytryph amine is a chemical
  • Spike phase of action potential is 2 sec.
  • Sylvian fissure divides the brain of rabbit into frontal lobe and temporal
  • Dorsal root has the ganglion made of unipolar
  • All cell bodies of afferent fibres lie in the dorsal root
  • EEG – Electro-Encephalo gram : Electrical tracing of the cerebral cortex is call ECG Berger in 1929 was first to record Instrument for the recording is Electroencephalograph or cathode ray oscillosco.
  • It is record of brain Brain waves are of following type
    • a–wave : These are rhythmic waves (10-12 cycles per These are produced normal awaking condition. These disappear in sleep.
    • b–wave ; 15-16 cycle per These are produced when nervous system is active e.g. Mental work
    • q–wave : 5-8 cycle per Produced in children.
    • d–wave : 1-5 cycle per In normal condition these are produced in awake infants. These are produced in deep sleep. In damage condition of the brain waves may produce in awaking condition in adults.
  • The sensation of sight in human brain is perceived by oceipital
  • The sensation from skin one perceived in the cerebrum in parietal
  • Fundamental character of chaordates is the presence of dorsal hollow nerve
  • Somesthatic & test area present in parietal lobe of cerebrum

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