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(c) Duramater. It is the outermost, thick, double layered and non-vascular. The outer layer of 

duramater is fixed with the cranium inside. The space between arachnoid and duramater is termed

as subdural space.

 

CENTRAL NERVOUS SYSTEM

The Central Nervous System (CNS) is composed of the brain and spinal cord, which are

responsible for the most complicated functions of the human and other organisms. The CNS is composed

of the grey and white matter. The grey matter represents a collection of non-myelinated nerve fibres and

nerve cells (neurons) while the white matter consists of processes of these cells and white medullatednerve fibres. Nerve cells or neurons are absent in the white matter. The neuroglia (glial cells) surrounds

the nerve cells (neurons). The part of CNS, i.e. the brain is lodged in the skull (or cranium) and the spinalcord is protected by the vertebral column. Fluid and tissue also insulate the brain and spinal cord. The

 brain is composed of three main parts: Forebrain, Midbrain and Hindbrain.

FOREBRAIN

The forebrain is the largest and most complex part of the brain. It consists of the cerebrum (thearea with all the folds and grooves), diencephalon and the olfactory lobes.(A) Cerebrum.

It is the largest and most developed part of the brain divided into two parts by a prominent

longitudinal fissure known as Sylvian fissure. These two parts are called as left cerebral hemisphere andright cerebral hemisphere, connected in the middle by a band known as corpus callosum made up of 

large bundle of myelinated fibres. It enables the two hemispheres to communicate with each other. The

left side is considered the logical, analytical and objective side. The right side is thought to be more

intuitive, creative and subjective. Collectively, the cerebrum governs intelligence and reasoning, learning

and memory.

Each cerebral hemisphere is highly folded into gyri (convolutions) and sulci (depressions). These

folding increase the surface area of the brain. The outer layer of cerebrum is the cerebral cortex made up

of grey matter. Information collected by the five senses comes into the brain from the spinal cord to thecortex. This information is then directed to other parts of the nervous system for further processing. The

inner layer of the cerebrum is the cerebral medulla made up of white matter. Each cerebral hemisphere isdivided into four lobes known as frontal, parietal, temporal, and occipital.

LOBES FUNCTIONAL AREAS FUNCTIONS

Frontallobes

(i) Pre central (motor) area(ii) Premotor Area(iii) Motor speech centre (Broca’s

area)(iv) Frontal association area

(i) Controls voluntary muscular movements.(ii) Controls involuntary muscular movements.(iii) Controls delivery of speech.

(iv) Most important part associated with memory,learning and reasoning.

Parietallobes

(i) Post central (sensory) area or somesthetic area.

(ii) Gustatory (taste) area.

(iii) Sensory speech area.(iv) Parietal association area.

(i) Perceives sensation of pain, temperature,pressure and touch.

(ii) Interprets nerve impulses from the tongue.Perceives sense of taste.

(iii) Perceives the spoken words.(iv) Same as frontal association area.

Temporallobes

Olfactory area.

Auditory area.Wernicke’s area.Temporal association area.

(i) Receives impulse from the nose, perceives senseof smell.

(ii) Centre of hearing.(iii) Responsible for understanding speech.(iv) Same as frontal association area.

Occipitallobes

Visual area.Visual association area.

Centre for sight.Same as frontal association area.

Table. 9.1. Four lobes of cerebrum with their functional areas.

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Fig. 9.2. Lateral view of human brain showing important functional areas.

(B) Diencephalon.

It is a part of the forebrain consisting of the thalamus (mid part), hypothalamus (floor) and

epithalamus (roof).(i) Thalamus is the largest paired structure constituting most of 

the part of diencephalons. Messages from all receptors of the

 body (except olfactory) are conveyed through the thalamus to thecerebral cortex; thus the thalamus acts as a relay centre. Inaddition, the thalamus transmits nerve impulses to different

structures of the brain stem. Multiple nuclei are present in thethalamus, functionally divided into two categories: specific

nuclei and the non-specific nuclei.

The specific nuclei receives information from the

receptors and relay it to the specific areas of the cerebral cortex, where it is translated into sensations. Thenon-specific nuclei have no direct connection with the receptors. They receive impulses from the

receptors indirectly through numerous synapses. Thalamus disorders in man may result in loss of emotion

associated facial muscle contraction, sleep disorders, hearing or vision impairment.

(ii) Hypothalamus forms the floor of diencephalon and is partially protected by the sella turcica of the

sphenoid bone. It participates in the control of protein, lipid, carbohydrate, salt and water metabolism,

heat production and loss (thermoregulation), appetite and satiety centre, sleep and waking states. The

anterior hypothalamic areas represent higher centers of the parasympathetic nervous system, while the

 posterior areas represent centers of sympathetic nervous system. Numerous autonomic functions are

controlled by the hypothalamus. Besides the nervous functions, hypothalamus is also connected with the

 pituitary gland for releasing various factors to activate or inhibit functions of other glands, through the

 pituitary gland.

(iii) Epithalamus forms the roof of diencephalon and is not involved in any type of nerve response, i.e. isnon-nervous. It is fused with the piamater to form anterior choroid plexus for the secretion of 

cerebrospinal fluid.

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 Limbic system comprises parts of 

cerebral cortex, corpus callosum,

hippocampus, amygdaloid nucleusand parts of diencephalon. This

 system plays an active role in the

control of autonomic functions,

control of behaviour, emotions

and establishment of memory

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Fig. 9.3. The vital functions of body and its control by the brain.

MIDBRAIN

The midbrain, located underneath the middle of the forebrain, acts as a master coordinator for all

the messages going in and out of the brain to the spinal cord. It is a very small, constricted part of the

 brain. constituting the cerebral peduncles or crura cerebri and four optic lobes or quadrigeminal bodies

collectively called as corpora quadrigemina. In lower vertebrates, optic lobes are two in number, calledas corpora bigemina. The optic lobes are connected with the cerebellum through valves of Vieussens.

The anterior quadrigeminal bodies or superior colliculi receive nerve impulses from the retina.

The response evoked by these signals is the alteration of the pupil lumen and accommodation.

Accommodation is adjustment of the eye to ensure clear vision of objects at different distances bychanging the convexity of the lens. The posterior quadrigeminal bodies or inferior colliculi receive

nerve impulses from the auditory nerve nuclei in the medulla oblongata. This causes reflex control of thetonus of the middle ear muscles helps in sound oriented ear pricking.

Destruction of quadrigeminal nuclei does not affect vision and hearing, but it disrupts orientationresponses to light and sound.

HINDBRAIN

The hindbrain is located at the back end of the cerebrum and consists of the cerebellum, pons and

medulla. The cerebellum is also called the ‘little brain’ because it looks like a small version of the

cerebrum. It is responsible for balance, movement, and coordination. The pons and the medulla, alongwith the midbrain, are often called the brainstem. The brainstem takes in, sends out, and coordinates allof the brain messages. It is also controls many of the body automatic functions like breathing, heart rate,

 blood pressure, swallowing, digestion, and blinking. From an evolutionary viewpoint, the oldest and most primitive part of the brain is the brainstem.

(A) Cerebellum.The cerebellum is the second largest part of the brain

consisting of two cerebellar hemispheres and a central worm-

shaped part, the median vermis. It is situated behind the medulla

oblongata and pons, covered with the occipital lobes of the

cerebrum. The surface of the cerebellum consists of the grey matter,which is defined as the cerebellar cortex and consists of the cell

 bodies of the neurons. The white matter is composed of processes of these neurons and forms a branched

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The first part of the brain to beaffected by alcohol is thecerebellum. Therefore a drunk 

  person first loses his balance

and is unable to walk properly.

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Fig. 9.4. Schematic representation of ventricles of the brain.

tree like structure called as arbor vitae or  tree of life. The main functions of the cerebellum are

coordination of movement, equilibrium of the body, maintenance of body posture, normal distribution of 

muscle tone and regulation of autonomic functions.

Disorders associated with the cerebellum are atonia (lack of impairment of muscle tone),

asthenia (loss of rapid onset of muscle fatigue), and astacia  (loss of the capacity for sustained titanic

contractions). Motor disturbances associated with cerebellar injury are collectively defined ascerebellar ataxia.

(B) Medulla Oblongata.The medulla oblongata is closest to the spinal cord, and is the most important part of the brain.

The anterior region of medulla has intermixed grey and white matter while the posterior region has grey

matter to the interior and white matter towards the exterior side, as is spinal cord. The roof of medulla isattached to the piamater constituting the posterior choroid plexus for the secretion of cerebrospinal fluid

(CSF). The roof has three openings below the plexus providing the passage for CSF. These openings arecalled as foramina of Luschka (laterally placed on either side) and foramen of Magendie (single,

median). Medulla oblongata is involved with the regulation of heartbeat, breathing, vasoconstriction

(blood pressure), and reflex centers for vomiting, coughing, sneezing, swallowing, hiccupping, etc.

(C) Pons Varolli.It is located in front of the cerebellum below the midbrain and above the medulla oblongata. It

consists mainly of nerve fibres which forms a bridge (pons = bridge) between the two cerebellar 

hemispheres and of fibres which pass between the higher levels of the brain and the spinal cord. Pons also

contains the pneumotaxic and aponeustic area which helps in the control of respiration.

VENTRICLES OF THE BRAIN

The ventricles consist of four 

hollow spaces inside the brain filled

with the cerebrospinal fluid. The

first two ventricles are present

inside the two cerebralhemispheres, collectively known as

lateral ventricles or  paracoel. Theventricle in the right cerebral

hemisphere is the first ventricle,whereas left cerebral hemisphere

contains the second ventricle. Eachlateral ventricle is connected to the

third ventricle by an

interventricular foramen (foramenof Monro). The third ventricle or diocoel is present in the

diencephalons. The fourth

ventricle or metacoel is present in

the pons and medulla oblongata and continues with the central canal of the spinal cord. Three openings in

the roof of medulla oblongata known as foramina of Luschka (laterally placed on either side) and

foramen of Magendie (single, median) allows the CSF to move upward to the subarachnoid space that

surrounds the brain and the spinal cord. The third and fourth ventricles are connected together by the

aqueduct of Sylvius or Iter in the midbrain portion of the brain stem.

CEREBROSPINAL FLUID (CSF)

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Fig. 9.5. C.S. of spinal cord illustrating a typical reflex arc.Arrows indicate the direction of impulse transmission.

Spaces under the brain meninges, ventricles and central canal of the spinal cord are filled with the

cerebrospinal fluid. An average amount of CSF in an adult is 100-150ml. It is a clear, colourless, slightly

alkaline fluid (7.33 pH). It contains small number of lymphocytes, 0.02% protein, 0.06% glucose, and

inorganic compounds in the amounts similar to those in the blood.

The CSF is continuously produced from the blood plasma by the anterior and posterior choroid

 plexus. It serves the internal environment of the brain, which maintains its stable mineral composition,osmotic pressures and protects it against mechanical injury.

WHITE AND GREY MATTER 

The CNS is composed of the grey and white matter. The grey matter represents a collection of nerve cells while the white matter consists of processes of these cells. In the brain (except medulla), the

white matter is internal and grey matter is external. In the anterior part of medulla the grey and whitematter are intermixed, and the posterior part of medulla has grey matter towards the inner side and white

matter towards the outer side. In the spinal cord the white matter is external and grey matter is external, asthat of posterior part of medulla.

SPINAL CORD

The spinal cord acts as a communication link between the brain and the peripheral nervous

system. It is continuous with the brain and emerges from an opening at the base of the skull called as

foramen magnum. The spinal cord stretches downward for approx. 42 - 45 cm throughout the vertebral

column. At the first lumbar vertebra (13th vertebra) the spinal cord constricts to form conus medullaris,

and then continues as loose

filaments of connective tissue

called as filum terminale, up to

the coccyx.

There are 31 pairs of 

spinal nerves, called as cauda

equina, part of the peripheral

nervous system, that emerge from

the spinal cord for carryingmessages to and from the spinal

cord. The nerves are namedaccording to their respective

vertebrae. Each spinal nerveconsists of a dorsal root and a

ventral root. The dorsal roots

contain neurons that carry signals

to the CNS from various types of sensory neurons. The ventral

roots contain the axons of motor 

neurons, which are neurons that

contact and carry information to

the muscles and glands. Within the

spinal cord and else where in the

 body are interneurons, which are

neurons that connect neurons to each other.

In addition to carrying impulses to and from the brain, the spinal cord regulates reflexes. A reflex

is the simplest response to a stimulus, e.g. sneezing, blinking, etc. A reflex produces a rapid motor 

response to a stimulus because the sensory neuron synapses directly with a motor neuron in the spinalcord. Reflexes are very fast and most reflexes never reach the brain.

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PERIPHERAL NERVOUS SYSTEM

The Peripheral Nervous System (PNS) contains only nerves and connects the brain and spinal

cord (CNS) to the rest of the body. The axons and dendrites are surrounded by a white myelin sheath.

Cell bodies are in the central nervous system (CNS) or ganglia. Ganglia are collections of nerve cell

 bodies. Cranial nerves in the PNS take impulses to and from the brain (CNS). Spinal nerves takeimpulses to and away from the spinal cord. There are two major subdivisions of the PNS motor pathways:

the somatic (voluntary) and the autonomic.

(A) Voluntary Nervous System.It constitutes the nerves arising from the brain (cranial nerves) and the spinal cord (spinal nerves).

(i) Cranial Nerves. There are twelve pairs of cranial nerves in man (amniotes) and ten pairs in frog(anamniotes), mainly innervating the head region. In frog, the spinal accessory and hypoglossal are absent

thereby reducing the number to ten. In man, there are three pairs of sensory (1, 2, 8), five pairs of motor (3, 4, 6, 11, 12) and four pairs of mixed (5, 7, 9, 10) cranial nerves. Of these, the trochlear is the smallest

cranial nerve, while vagus is the longest cranial nerve, having maximum branches, therefore also referredto as wandering nerve. Trigeminal is the largest cranial nerve, divided into three parts namely,

opthalamic, maxillary and mandibular.

No. NAME ORIGIN LOCATION NATURE FUNCTION

1. Olfactory Olfactorylobe

Nasal cavity Sensory Sense of smell

2. Optic Optic lobe Retina Sensory Sense of sight

3. Oculomotor Midbrain Muscles of the eyeball Motor Movement of eye ball andconstriction of pupil

4. Trochlear  (Pathetic)

Midbrain Muscles of the eyeball Motor Rotation of eyeball

5. Trigeminal(Mandibular)

Opthalamic

Maxillary

Mandibular 

Pons varolli

• Eyelids, lacrimalglands, conjuctiva

• Teeth and gums of upper jaw

• Teeth and gums of lower jaw

Mixed Movement of tongue and jaw muscles

6. Abducens Medullaoblongata

Muscles of the eyeball Motor Rotation of eyeball

7. Facial Medullaoblongata

Taste buds, salivaryglands and facial

muscles

Mixed Sense of taste, facialexpressions

8. Auditory Medullaoblongata

Internal ear (Organ of Corti and semicircular canals)

Sensory Sense of hearing andmaintenance of equilibrium

9. Glossopharyngeal

Medullaoblongata

Tongue and musclesof pharynx

Mixed Sense of taste and touch,swallowing

10. Vagus(Pneumogastric)

Medullaoblongata

Pharyngeal muscles,lungs, heart,alimentary canal

Mixed Respiratory reflex,peristalsis, heart beat,secretion of gastric glands

11. Spinalaccessory

Medullaoblongata

Palate, larynx, vocalcords, neck andshoulder 

Motor Pharyngeal muscles, Neckand shoulder movements

12. Hypoglossal Medullaoblongata

Muscles of tongue Motor Movement of tongue

Table. 9.2. Cranial nerves of human brain showing their nature and function.

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Fig. 9.6. Diagrammatic representation of human cranial nerves with their site of action.

(ii) Spinal Nerves. These are 31 pairs in man divided into five groups, having the formula C8T12L5S5C1.

• Cervical nerves- 8 pairs.

• Thoracic nerves- 12 pairs.

•  Lumbar nerves- 5 pairs.

• Sacral nerves- 5 pairs.

• Coccygeal nerves- 1 pair.These arise from the spinal cord and formed by the union of dorsal and ventral roots. All the spinal nerves

are of mixed type, containing both sensory and mixed neurons. These leave the vertebral column through

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Fig. 9.7. Spinal nerves and their functions.

the intervertebral foramina. Each spinal nerve is divided into four branches, collectively known asrami, having separate functions.

•  Dorsal rami- Innervates the dorsal side of the body.

• Ventral rami- Innervates the ventral side of the body.

• Meningeal rami- Innervates the spinal cord by re-entering into it to supply nerves to vertebra,

 blood vessels and meninges.• Communicans rami- Part of autonomic nervous system.

(B) Autonomic Nervous System.

The autonomic nervous system is

an entire little brain and it regulates the

functions of our body without our 

awareness or control. This system is

entirely motor having efferent fibres. It

innervates the internal organs, exocrine and

endocrine glands, blood and lymph vesselsand cardiac muscles. It is divided into two

systems which, when act together, often

oppose each other- the sympathetic and

  parasympathetic systems. The sympathetic

system evokes responses characteristic of the ‘fight-or-flight’ response such as pupils

dilate, muscle vasculature dilates, the heartrate increases, and the digestive system is

  put on hold. The parasympathetic systemhas many specific functions, including

slowing the heart, constricting the pupils,stimulating the gut and salivary glands, and

other responses that are not a priority. The

state of the body at any given time is

represented by a balance between these two

systems.

The best way to learn the functions and

structures of each system is by comparison.

PARASYMPATHETIC NERVOUS SYSTEM SYMPATHETIC NERVOUS SYSTEM

• The cells of parasympathetic nervous systemare located in different nuclei throughout thebrainstem, as well as a few in the sacral spinalcord.

• The cells of the sympathetic nervous system

are located in the inter -medio-lateral column inthe thoracic spinal cord.

• The pre ganglionic fibres (axons) originate fromthe brain and spinal cord and travel to thetarget organ, and so are longer.

• The pre ganglionic fibres (axons) originate fromthe thoracic spinal cord , and so are shorter.

• The pre ganglionic fibres branch beforeentering the ganglia, therefore many organs areaffected by one fibre (multiple effect).

• The pre ganglionic fibres do not branch andenters singly in a ganglion, therefore only oneorgan is affected by one fibre (single effect).

• The ganglia are near the target organs, so thepost ganglionic fibres are short.

• The sympathetic ganglia are often far from thetarget organs, so the post ganglionic fibres arelong.

•

The post ganglionic fibres release theneurotransmitter acetylcholine, therefore calledas cholinergic.

•The post ganglionic fibres release theneurotransmitter noradrenaline, thereforecalled as adrenergic.

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Fig. 9.8. Sympathetic and parasympathetic nervous system showing their site of action in human bod .

• They have calming effect on the body andoperate during normal conditions of the body.

• They have excitatory effect on the body andoperate during stress activity or danger, i.e.during emergency situations.

Notable Structures Notable Structures

• Edinger- Westphal nucleus - Axons from this

nucleus travel with cranial nerve III and helps inpupil constriction and lens accommodation.

• Superior cervical ganglion - supplies

sympathetic nerves to the head for dilating thepupils, stimulating sweat glands and lifting of the eyelids.

• Salivatory nuclei - These nuclei in the medullasend axons to the salivary glands via the VIIthand IXth nerves.

• Celiac and mesenteric ganglia - Theseganglia distribute sympathetic nerves to thegut. Functions include vasoconstriction andinhibition of secretions.

• Dorsal nucleus of the vagus - This nucleusgives rise to the secretomotor fibers of thevagus nerve (X). Its functions includestimulating gastric secretion, gut motility andrespiratory secretion.

• Chain ganglia - running along the spinal corddistribute sympathetic nerve to the thorax andperiphery to increase heart rate, dilate bronchi,selectively, vasoconstriction and vasodilation inactive muscles.

• Nucleus ambigus - Axons from these cellsproject via the vagus to the heart, lungs, andpharynx. It helps in decreasing the heart rateand bronchial constriction.

Table 9.3. Comparison between the two components of the Autonomic Nervous System. 

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Fig. 9.9. Basic structure of a neuron.

Fig. 9.10. Schematic representation of transfer of nerve impulses.

NOTE: The sympathetic afferents mainly carry information about visceral pain. Since this information

converges with pain from the body surface, the pain is often perceived as originating at the body surface

instead of deep in the viscera. This phenomenon is called referred pain. For example, afferents from the

heart enter the spinal cord at the same level as those from the shoulder region. This is why pain in the

heart (heart attack ) is often referred to the shoulder.

STRUCTURE OF NEURON 

The basic functional units that carry messages throughout the nervous system are calledneurons.

Messages take the form of electrical signals, and are known as impulses. Neurons may have dozens or 

even hundreds of dendrites but usually only one axon. The axons of most neurons are covered with a lipid

layer known as the myelin sheath. The myelin sheath both Insulates and speeds up transmission of action

 potentials through the axon. In the peripheral nervous system, myelin is produced by Schwann cells,which surround the axon. Gaps (nodes) in the myelin sheath along the length of the axon are known as the

nodes of Ranvier. Irrespective of their specific function, all neurons have the same physical parts: thecell body, dendrites and axon.

• Cell body – It is the largest part, contains the nucleus and much of the cytoplasm (area between the

nucleus and the cell membrane). It is responsible for most of the metabolic activity of the cell,

including the generation of ATP and synthesis of protein.

• Dendrites  – These are short branch extensions spreading out from the cell body. Dendrites receive

stimulus (action potentials) and carry impulses from the environment or from other neurons and carry

them towards the cell body.

• Axon – It is a long fiber that carries impulses away from the cell body. Each neuron has only one

axon. The axon ends in a series of small swellings called axon terminals.

 Neurons can be classified into three types:

• Sensory neuron (afferent) - Carry impulses from the sense organs (receptors) to the brain and spinal

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Fig. 9.11. Potential versus time graph showing action potential in a neuron.

cord. Receptors detect external or internal changes and send the information to the central nervous

system in the form of impulses by way of the afferent neurons.

• Motor neurons (efferent) - Carry impulses from the brain and spinal cord to muscles or glands.Muscles and glands are two types of effectors. In response to impulses, muscles contract and glands

secrete enzymes or hormones, as the need of the body.

• Interneurons - Connect sensory and motor neurons and carry impulses between them. They arefound entirely within the central nervous system.

CONDUCTION OF NERVE IMPULSES

The Italian scientist Luigi Galvani found that nervous tissue (groups of cells that conduct

impulses) displays electrical activity in the form of a nerve impulse, which is a flow of electrical charges

along the cell membranes of a neuron. This electrical activity is due to movement of ions (charge

  particles) across the cell membrane, namely sodium and potassium. The movement of these ions is

affected by their ability to pass through the cell membrane, their concentration inside and out of the cell,

and their charge. Neurons have an electrical charge different from the extracellular fluid that surrounds

them. A difference in electrical charge between two locations is called apotential.

(a) Resting Potential.A nerve cell has electric potential across its cell membrane because of a difference in the number 

of positively and negatively charged ions on each side of the cell membrane, which carries a sodium

pump. During resting stage, the electrical potential is due to the poor permeability of the membrane

towards sodium and higher permeability towards potassium, which move sodium ions (Na+) out of the

cell and actively pump potassium ions (K +) into the cell. The result of this active transport of ions is the

cytoplasm of the neuron contains more K + ions and fewer Na+ ions than the surrounding medium. The

concentration of sodium ions becomes about 14 times more in extracellular fluid and constitutionof 

 potassium ions will be 28-30 times more in axoplasm. This charge difference is known as the restingpotential (about 70mV) of the neuron's cell membrane. As a result of its resting potential, the neuron issaid to be polarized which means negatively charged on the inside of the cell membrane and positively

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Fig. 9.12. Conduction of nerve impulse in (A)Myelinated; and (B) Non-myelinated nerve fibre.

charged on the outside. A neuron maintains this polarization until it is stimulated. A stimulus is a change

in the environment that may be of sufficient strength to initiate an impulse. The ability of a neuron to

respond to a stimulus and convert it into a nerve impulse is known as excitability.

(b) Action Potential.

A Nerve Impulse causes a movement of ions across the cell membrane of a neuron. The cellmembrane of a neuron contains thousands of tiny molecules known as gates. These gates allow either 

sodium or potassium ions to pass through. Generally the gates on a neuron are closed. A nerve impulse

starts when pressure or other sensory inputs, disturbs a neuron's plasma membrane, causing sodium gates

to open thereby changing the membrane permeability. At the beginning of an impulse, the sodium gatesopen, allowing positively charged Na+ ions to flow inside the cell membrane. The inside of the membrane

temporarily becomes more positive than the outside. This is called depolarized, i.e. the charge inside theaxon changes from negative to positive as sodium ions enter the interior.

As the impulse passes, the potassium gates open, allowing positively charged K + ions to flowout. The membrane is now said to be repolarized. Once again negatively charged on the inside and

 positively charged on the outside. The depolarization and repolarization of a neuron membrane is called

an action potential (20-30mV). Action potential is another name for a nerve impulse or simply animpulse. After a nerve impulse is period when the neuron is unable to conduct a nerve impulse called therefractory period. The refractory period is a very short period during which the sodium-potassium pump

continues to return sodium ions to the outside and potassium ions to the inside of the axon. Thus returning

the neuron to the resting potential. An impulse is not an electric current; it is a wave of depolarization and

repolarization. Or a nerve impulse is actually the movement of an action potential along a neuron as a

series of voltage-gated ions channels open and close. An impulse is much slower than an electric current.

Unlike an electric current, the strength of an impulse is always the same. There is either an impulse to a

stimulus or there in not (all or none law).

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Saltatory Conduction.Myelin sheaths greatly increase the speed of impulse along an axon. These are composed of 80%

lipid and 20% protein. Myelin is made of special cells called Schwann Cells that forms an insulated

sheath, or wrapping around the axon. There are small nodes or gaps called the nodes of Ranvier between

adjacent myelin sheath cells along the axon. As an impulse moves down a myelinated (covered with

myelin) axon, the impulse jumps form node to node instead of moving along the membrane, known assaltatory conduction. This jumping from node to node greatly increase the speed of the impulse. Some

myelinated axons conduct impulses as rapid as 200 meters per second. The formation of myelin around

axons can be thought of as a crucial event in evolution of vertebrates. Destruction of large patches of 

myelin characterize a disease called multiple sclerosis. In multiple sclerosis, small, hard plaques appear throughout the myelin. Normal nerve function is impaired, causing symptoms such as double vision,

muscular weakness, loss of memory, and paralysis.

Threshold Stimulus.The strength of an impulse is always the same. Either there is an impulse in response to a

stimulus or not. A stimulus must be of adequate strength to cause a neuron to conduct an impulse. The

minimum level of a stimulus that is required to activate a neuron is called the threshold. Any stimulusweaker than the threshold will produce no impulse. Any stimulus stronger than the threshold will produce

an impulse. A nerve impulse follows the all-or-none principle.

TRANSMISSION OF NERVE IMPULSES

The axon ends with many small swellings called axon terminals. At these terminals the neuron

may make contact with the dendrites of another neuron, with a receptor or with an effector. Receptors are

special sensory neurons that receive stimuli from the external environment. Effectors are muscles or 

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glands that bring about a coordinate response. The point of contact at which impulses are passed from one

cell to another are known as the synaptic cleft or  synapse. Neurons that transmit impulses to other 

neurons do not actually touch one another. The small gap or space between the axon of one neuron and

the dendrites or cell body on the next neuron is called the synapse. One importance of the presence of 

synapses is that they ensure one-way transmission of impulses in a living person.  A nerve impulse cannot 

 go backward across a synapse. The axon terminals at a synapse contain tiny synaptic vesicles, or sacs.These tiny vesicles are filled with chemicals known as neurotransmitters, usually acetylcholine.

 Neurotransmitter is a chemical substance that is used by one neuron to signal another. The impulse is

changed from and electrical Impulse to a chemical impulse (electrochemical impulses).

1. When an impulse reaches the axon terminal, increasing the permeability of presynaptic cell membrane

towards calcium ions, which causes dozen of synaptic vesicles to fuse with the membrane anddischarge the neurotransmitter into the synaptic cleft.

2. The molecules of the neurotransmitter diffuse across the gap and attach themselves to specialreceptors on the postsynaptic membrane of the neuron receiving the impulse.

3. When the neurotransmitter becomes attached to the cell membrane of the adjacent nerve cell, it

changes the permeability of that membrane.

4. As a result, Na+ ions diffuse through the membrane into the cell. If enough neurotransmitter is

released by the axon terminal, so many Na+ ions diffuse into the neuron that the neuron becomes

depolarized. This causes a threshold to be reached and an impulse (action potential) begins in the

second cell.

5. After the neurotransmitter relays it message it is rapidly removed or destroyed, thus halting its effect.

The molecules of the neurotransmitter may be broken down by enzymes, particularly by

cholinesterase. This enzyme hydrolyses acetylcholine to choline, which is taken up again by the axon

terminal and recycled by using energy from ATP present in mitochondria.

Synapses are the slowest part of the nervous system. The advantage to having many neurons,

with gaps between them, is that we can control and receive information from different parts of the body atdifferent times. They also ensure one-way transmission of impulses in a living person. Nerve gas

  prevents enzymes from breaking down neurotransmitters, as a result muscles in the respiratory andnervous system becomes paralyzed.

ELECTROENCEPHALOGRAM (EEG)

The function of the brain can be evaluated by the pattern of its electric activity by recording biopotentials from the exposed brain, called as electrocorticography (ECoG). In humans, cerebral

 biopotentials are recorded using electrodes applied to the skin of the head. Since the potential difference

in the brain is negligible, biopotential amplifiers and oscillographs are required for recording the

 biopotentials. This method of recording of electric potential fluctuations of the brain is named aselectroencephalography, and the tracing is called as electroencephalogram.

Electroencephalography has found wide applications in clinical practice. Neurosurgeons,

neuropathologists, psychiatrists and other specialists use it. It allows for an objective evaluation of 

lability, distribution and inter-relationships of excitatory and inhibitory processes in the brain.

EEG Rhythms. Electric waves registered on the EEG have different frequency, duration, amplitude and

shape, depending upon the mental activity of the organism. Four major rhythms are distinguished as

follows.

The alpha rhythm is a regular sinusoid-shaped rhythm with a frequency of 8-13 waves/sec and

amplitude of 20-80 μV. These rhythms are registered in a resting man with his eyes closed and external

stimuli absent.The beta rhythm has the frequency of 14-35 waves/sec and amplitude of 10-30 μV. After 

applying stimuli, when the eyes are opened or mental activity is performed, the alpha rhythm rapidly

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vanishes and the beta rhythm appears. The replacement of the slow rhythm with a more rapid one is

termed burst response or desynchronization.

The delta rhythm is characterized by slow potential fluctuation having frequency of 0.5-3

waves/sec and a high amplitude of 250-300 μV or even 1000 μV. It is detected during profound sleep and

general anaesthesia. In children under the age of 7 years, the delta rhythms can be registered in the

waking state.The theta rhythm has the frequency of 4-7 waves/sec and amplitude of 100-150 μV. It is

observed during light sleep, oxygen deficiency and moderate anaesthesia.

BRAIN AND DRUGS

Some neurotransmitters are excitatory, such as acetylcholine, norepinephrine, serotonin, and

dopamine. Some are associated with relaxation, such as dopamine and serotonin. Dopamine release

 seems related to sensations of pleasure. Endorphins are natural opioids that produce elation and reduction

of pain, as do artificial chemicals such as opium and heroin. Neurological diseases, for exampleParkinson's disease and Huntington's disease, are due to imbalances of neurotransmitters. Parkinson's

is due to a dopamine deficiency. Huntington's disease is thought to be cause by malfunctioning of an

inhibitory neurotransmitter. Alzheimer's disease is associated with protein plaques in the brain. Drugsare stimulants or depressants that block or enhance certain neurotransmitters. Dopamine is thought

involved with all forms of pleasure. Cocaine interferes with uptake of dopamine from the synaptic cleft.

Alcohol causes a euphoric "high" followed by a depression.

• Marijuana, material from the Indian hemp plant, Cannabis sativa has a potent chemical THC

(tetrahydracannibinol) that in low concentrations causes a euphoric high (if inhaled, the most commonform of action is smoke inhalation). High dosages may cause severe effects such as hallucinations,

anxiety, depression and psychotic symptoms.

• Cocaine is derives from the plant   Erthoxylon coca. It can be inhaled, smoked or injected. Cocaine

users report a "rush" of euphoria following use. Following the rush is a short (5-30 minute) period of arousal followed by a depression. Repeated cycle of use terminate in a "crash" when the cocaine is

gone. Prolonged used causes production of less dopamine, causing the user to need more of the drug.

• Heroin is a derivative of morphine, which in turn is obtained from opium poppy, Papaver somniferum.

Heroin is usually injected intravenously, although snorting and smoking serve as alternative delivery

methods. Heroin binds to ophioid receptors in the brain, where the natural chemical endorphins are

involved in the cessation pain. Heroin is physically addictive, and prolonged use causes less endorphin

 production. Once this happens, the euphoria is no longer felt, only dependence and delay of withdrawal

symptoms.

DISORDERS OF NERVOUS SYSTEM

Brain tumors. A tumor is a swelling caused by overgrown tissue. A tumor in the brain may grow

slowly and produce few symptoms until it becomes large, or it can grow and spread rapidly, causing

severe and quickly worsening symptoms. Brain tumors in children can be benign or malignant.Benign tumors usually grow in one place and may be curable through surgery. A malignant tumor is

cancerous and more likely to grow rapidly and spread.

Cerebral palsy. Cerebral palsy is the result of a developmental defect or damage to the brain before

or during birth. It affects the motor areas of the brain. A person with cerebral palsy may have averageintelligence or can have severe developmental delays or mental retardation. Cerebral palsy can affect

 body movement in many different ways. In mild cases of cerebral palsy, there may be minor muscle

weakness of the arms and legs. In other cases, there may be more severe motor impairment, a child

may have trouble talking and performing basic movements like walking.

Coma. It is a state of unconsciousness in which the person is unable to respond to a stimuli. It mayoccur due to injury in the brain, chemical imbalance or intake of poison. Its recovery may be followed

 by loss of memory (amnesia).

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Epilepsy. This condition is made up of a wide variety of seizure disorders. Partial seizures involve

specific areas of the brain, and symptoms vary depending on the location of the seizure activity.

Generalized seizures involve a larger portion of the brain and usually cause uncontrolled movements

of the entire body and loss of consciousness when they occur. Although the specific cause is unknown

in many cases, epilepsy can be related to brain injury, tumors, or infections. The tendency to developepilepsy may be inherited in families.

Headaches. Of the many different types of headaches, the most frequently occurring include tension

headache, caused by muscle tension in the head, neck, and shoulders; migraine, an intense, recurring

headache with an unclear cause; and cluster headache, considered by some to be a form of migraine.

Migraines occur with or without warning and may last for several hours or days. There seems to be an

inherited predisposition to migraines as well as certain triggers that can lead to them. People with

migraines may experience dizziness, numbness, sensitivity to light, and nausea, and may see flashing

zigzag lines before their eyes.

Meningitis and encephalitis. These are infections of the brain and spinal cord that are usuallycaused by bacteria viz. Streptococcus pnueumonie,   Neisseria meningitides and  Haemophilus

influenza. Meningitis is an inflammation of the coverings of the brain and spinal cord, and

encephalitis is an inflammation of the brain tissue. Both conditions may result in permanent injury to

the brain.

Mental illness. Mental illnesses are psychological and behavioral in nature and involve a wide range

of problems in thought and function. Certain mental illnesses are now known to be linked to structural

abnormalities or chemical dysfunction of the brain. Some mental illnesses are inherited, but often the

cause is unknown. Injuries to the brain and chronic drug or alcohol abuse also can trigger some

mental illnesses. Mental illnesses that can be seen in younger people include depression, eating

disorders such as bulimia or anorexia nervosa and phobias.

Head Injuries. Head injuries fall into two categories: external (usually scalp) injuries and internal

head injuries. Internal injuries may involve the skull, the blood vessels within the skull, or the brain.

An internal head injury could have more serious implications because the skull serves as the

 protective helmet for the delicate brain. Concussions are also a type of internal head injury. It is thetemporary loss of normal brain function as a result of an injury. Repeated concussions can result in

 permanent injury to the brain.

Stroke. It is a reversible or irreversible damage to the brain due to lack of oxygen, caused by

interrupted blood flow, clotting of blood, etc.

REFLEX ACTION

The cerebral cortex and sub-cortical centers represents higher divisions of the central nervous

system (CNS) in warm-blooded animals and man. They subserve the reflex responses underlying the

most complicated interactions of the animal and human organisms with the external environment. The

two mechanisms of the higher nervous activity are instincts and conditioned reflexes.

•  Instincts or unconditioned reflexes are a complicate cascade of inborn, unconditioned reflexes

resulting primarily from the activities of the subcortical and diencephalic nuclei. They remain after the

removal of the cerebral cortex. Instincts are identical in all individuals of the same species; they are

inherited and related to the vital activities of the body- nutrition, defense, reproduction, etc. The

responses are relatively stable, stereotyped and unchangeable; due to this, unconditioned reflexes alone

cannot ensure proper adaptations to changing environmental conditions.• Conditioned reflexes are individual acquired reflexes based on the unconditioned ones. They are

  produced primarily due to the activity of the cerebral cortex. These reflexes vary in different

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individuals of a species. They are changeable and easily induced or lost depending upon the

environmental conditions. Conditioned reflexes were categorized by Pavlov into natural and artificial.

1. Natural conditioned reflex  arc induced by the natural properties of unconditioned stimuli, e.g.

nutritional conditioned reflex is evoked by the odour or sight of the food.

2. Artificial conditioned reflex arises from a variety of artificial stimuli of a given unconditioned reflex

(light, sound, odour, temperature, etc.). Any change in the external or internal environment of the bodymay become a conditioned stimulus.

Mechanism of Reflex Action. The nerve impulse

travels through a path in a reflex action known as

reflex arc. It the reflex action is controlled by thespinal cord, it is called as spinal reflex action and if 

it is controlled by the brain, it is called as cerebral

reflex action. The components of a reflex arc,

mediating a reflex are:(i) Receptor, which may be an organ, tissue or a

cell receiving a stimulus.

(ii) Sensory (or afferent) nerve fibres, which passes

the sensory impulses generated by the receptor 

to the CNS.

(iii) CNS (or integrating center), which may be

spinal cord or brain, analyses the condition and decides specific action to be performed.

(iv) Motor (or efferent) nerve fibres, which carry the motor impulses generated in the CNS to the

effector.

(v) Effector, which may be an organ, muscle or gland receives an order from the CNS via the motor 

neurons and works as ordered by the brain or spinal cord.

CONSCIOUSNESS

Consciousness is the subjective experience of man varying from simple sensation to abstract

thinking. It emerged only at the highest developmental stages, in the humans. It is an active reflection of 

objective reality. Although the spinal cord and other divisions of the central nervous system performs thereflective function, this reflection is not psychic. Only the cerebral cortex is capable of perceiving psychic

qualities. Consciousness is the product of evolution. Labour and verbal communications led to thedevelopment of consciousness in humans. It enables man to explore the properties and qualities of objects

and phenomena, to understand their laws, and to discriminate between the relevant and irrelevant.

PHYSIOLOGY OF SLEEP

Sleep is a universal feature of the living nature; it is a physiological requirement of an organism.Man spends one third of his lifetime in the stage of physiologically recurring sleep. During sleep,

multiple changes occur in the physiological systems of man; consciousness and responses to many

environmental stimuli are not operative, motor reflex responses are subdued, and conditioned activities

are completely inhibited. There are numerous changes in the autonomic functions: the heart and arterial

 pressure are decreased, respiration is slower and shallow, metabolic rate and body temperature are

slightly reduced, and digestion and renal functions are attenuated. Profound sleep is associated with a

decrease in muscle tone and complete relaxation of most of the muscles.

The sleeping-waking cycle in humans follows the diurnal day and night sequence. An adult

sleeps once a day, or has monophasic sleep. Children, especially infants, have multiphasic sleep. Sleep

requirements are age related. Daily sleep of newborns is 20-23 hours, 2-4 years old children sleep 16

hours, 4-8 years old sleep 12 hours, 8-12 years old 10 hours, 12-16 years old 9 hours, and adults 7-8hours.

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Fig. 9.14. Reflex action and reflex arc.

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Mechanism of Sleep.Several concepts have been proposed to explain the physiology of sleep. These may be divided

into humoral and nervous. The most popular of the humoral concepts is the ‘sleep poisons’

(‘autointoxication’) hypothesis. It suggests that sleep is the product of brain autointoxication with

metabolites accumulated during the waking state (lactic acid, carbon dioxide, ammonium, etc.). During

the recent years, there has been an increasing focus on the chemical theories of sleep. This is related tothe identification and manufacturing of a hypogenic factor, a sleep inducing low-molecular weight

 polypeptide. The naturally occurring hypogenic factors include serotonin.

  Natural onset of normal physiological sleep is related to the activity of cortical neurons.

Functioning neurons gradually develop fatigue, which provides conditions for inhibition allowing for restoration and rest of neurons. Inhibition initially occurs in a limited group of cortical cells. If it is not

counteracted by a strong excitation focus, inhibition irradiates over the entire cortex and reaches thesubcortical centers. Pavlov considered that sleep is ‘internal inhibition’ that had irradiated throughout the

hemispheres and to the lower-lying brain parts.Pavlov classified sleep into active and passive. Active sleep is induced by prolonged

monotonous stimuli like a lullaby or train-wheel rattle. Passive sleep is induced by a restriction of the

impulse flow to the cerebral cortex.The presence of a sleeping and waking center in the brain (thalamus and hypothalamus) has been

hypothesized on the basis of clinical and experimental findings. The current explanations of this

hypothesis relate it to the function of the reticular formation and its connections with the cerebral cortex.

Afferent impulses going through the reticular formation to the cerebral cortex activate the reticular 

formation. Destruction or pharmacological suppression (aminazine) of the reticular formation induces

sleep. Therefore, the sleeping and waking center may be interpreted as structures, which modulate

cortical-subcortical communications, which act to induce sleep under some circumstances and maintain

wakefulness under the other. Therefore, the concept of sleeping and waking center may be accepted as

arbitrary. In brief, sleep should not be considered as the inactivity of the cortical neurons but as a change

in the activity of the cerebral cortex.

COMPETITION DESK # 09

1. Ninth pair of cranial nerve in frog is

(AFMC 2005)

(a) Hypoglossal (b) Glossopharyngeal

(c) Vagus (d) Trigeminal

2. Which cranial nerves show the maximum

 branching? (AFMC 2003)

(a) Trigeminal (b) Vagus(c) Optic (d) Facial

3. Which part of the brain is associated withsmell? (AFMC 2003)

(a) Olfactory lobes(b) Cerebral hemispheres

(c) Medulla oblongata

(d) Cerebrum

4. The impulses from the one neuron to

another are send in the form of ( AFMC 2003)

(a) Mechanical impulses

(b) Chemical impulses

(c) Electrical impulses

(d) Magnetic impulses

5. In homeotherm, the brain centre, which

regulates body temperature, is situated in

(AFMC 2003)

(a) cerebellum (b) cerebral lobe(c) hypothalamus (d) medulla oblongata

6. Venom of cobra affects (AFMC 2001)

(a) circulatory system

(b) digestive system(c) nervous system

(d) respiratory system

7. Which cranial nerve controls the heart

muscles? (AFMC 1998)

(a) Facial (b) Vagus(c) Auditory (d) Trochlear  

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8. Mammalian brain differs from an amphibian

 brain in possessing (AFMC 1998)

(a) olfactory lobe (b) cerebellum

(c) hypothalamus (d) corpus callosum

9. Resting potential of a nerve is (AFMC 1998)

(a) +70 millivolt (b) +30 millivolt

(c) -30 millivolt (d) -70 millivolt

10. The number of spinal nerves in frog is(AFMC 1995)

(a) 9 pair (b) 10 pairs(c) 11 pairs (d) 31 pairs

11. Which of the following pair of ions play a

great role in nervous transmission and

marinating potential difference? (AFMC 

1995)

(a) Na+ and K+ (b) Na+ and Ca++

(c) Na+ and Cl־ (d) K+ and Ca++

12. The transmission of nerve impulse, from one

neuron to other, is facilitated by (AFMC 

1995)

(a) kinetin (b) cholesterol

(c) adrenaline (d) acetylcholine

13. Respiration is controlled by (AFMC 1995)(a) cerebellum

(b) medulla oblongata(c) olfactory lobes

(d) hypothalamus

14. True nervous system first of all originated in(AFMC 1995)

(a) Taenia (b) Ascaria(c) Hydra (d) Hirudinaria

15. Earthworm and cockroach have which of thefollowing thing common? (AFMC 1995)

(a) Ventral nerve chord

(b) Closed blood vascular system

(c) Nephridia

(d) Cocoon

16. Nissl granules are rich in (AIIMS 2002)

(a) protein and lipids

(b) ribonucleoproteins

(c) fatty acids

(d) nucleic acids

17. Secretion of which of the following is under neurosecretory nerve axons? (AIIMS 1998)

(a) Pineal gland

(b) Adrenal cortex

(c) Anterior pituitary

(d) Posterior pituitary

18. Sympathetic nerves in mammals arise from(AIIMS 1998)

(a) sacral region

(b) cervical region

(c) thoraco-lumbar region

(d) 3rd, 7th and 9th and 10th cranial nerves

19. Arbor vitae is mainly composed by (AIIMS 

1998)

(a) grey mater (b) neuroglial cells(c) white mater (d) all of these

20. Preganglionic sympatheic fibers are (AIIMS 

1995)

(a) adrenergic (b) cholinergic

(c) synergic (d) hypergonic

21. Which of the following cranial nerve of man

is both sensory and motor? (AIIMS 1994)

(a) Optic (b) Auditory

(c) Olfactory (d) Trigeminal

22. Node of Ranvier is a place where (CBSE 

2002)(a) medulla sheath is discontinuous

(b) medullary sheath and neurilemma isdiscontinuous

(c) axolemma is absent(d) axolemma is discontinuous

23. During activation of nerve the impulse is

conducted in a fibre by (CBSE 2000) (a) more movement of sodium ions inside

and potassium ions outside

(b) less sodium coming out and more potassium coming in

(c) equal movement of both ions

(d) more movement of potassium ions

towards inside and sodium ions outside

24. The vagus nerve is the cranial nerve

numbering (CBSE 1997)

(a) 10 (b) 9

(c) 7 (d) 5

25. By which nervous system and of what type,

the blood is supplied into visceral organ?

(CBSE 1996)

(a) Sympathetic nervous system, involuntary

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(b) Sympathetic nervous system, voluntary

(c) Both SNS and PNS, involuntary

(d) Para-sympathetic nervous system,

involuntary

26. The parasympathetic nerves in mammalsarise from (CBSE 1995)

(a) thoraco-lumbar nerves

(b) cervical nerves

(c) sacral nerves

(d) 3rd, 7th, 9th, 10th cranial nerves and 2nd, 3rd,4th sacral nerves

27. According to the accepted concept of 

hormone action, if receptor molecules areremoved from target organs, then (CBSE 

1995)

(a) the target organ will continue to respond

to the hormone but will require higher 

concentration

(b) the target organ will continue to respond

to the hormone but in the opposite way

(c) the target organ will continue to respond

to the hormone without any difference

(d) the target organs will not respond to the

hormone

28. The gilal cells that from the blood-brain

  barrier by lining brain capillaries are the(CPMT 2000)

(a) Schwann cells(b) astrocytes

(c) oligodendrioglial cslls(d) Raniver cells

29. The neurotransmitter between a motor 

neuron and a muscle cell is (CPMT 2000)

(a) endorphin (b) serotonin

(c) dopamine (d) acetylcholine

30. Which of the following is a structure in the

mesencephalon? (CPMT 2000)

(a) Inferior colliculi (b) Thalamus

(c) Cerebellum (d) Mammillare body

31. In earthworm neurons are (CPMT 2000)

(a) motor (b) sensory

(c) both above (d) absent

32. Breathing is controlled by which part of the

 brain? (CPMT 1998)

(a) lungs (b) trachea

(c) medulla oblongata(d) hypothalamus

33. Which of the following is not essentially a

 part of nervous system? (CPMT 1998)

(a) Cyton (b) Axon

(c) Myelinated (d) Intermedin

34. Which one of the following can act as spinalnerve? (CPMT 1998)

(a) Hypolgossal (b) Trigeminal

(c) Olfactory (d) None of these

35. Conditioned reflexes are different thanunconditioned reflexes in that (CPMT 1998)

(a) conditioned reflexes are limited to brain(b) unconditioned reflexes are limited to

 brain(c) both

(d) none of the above

36. Saltatory conduction occurs in (CPMT 

1998)

(a) myelinated nerve fibres

(b) non-mylenated nerve fibres

(c) both

(d) none of these

37. Which one of the following acts as slow

neurotransmiitter? (CPMT 1998)

(a) GABA (b) Adrenaline

(c) Epinephrine (d) Acetylcholine

38. Which of the following pairs of  elements/ions required for nerve

conduction? (CPMT 1998)

(a) Ca, Na and K (b) Ca and Mg

(c) Mg and K (d) Na and Mg

39. Structures typically represented in everysegment of earthworm are (CPMT 1996)

(a) ganglia (b) lateral hearts

(c) genital ducts (d) septal nephridia

40. The autonomic nervous system has control

over (KPMT 2003)

(a) Reflex action (b) Skeletal muscle

(c) Sense organs (d) Internal organs

41. The most appropriate definition for 

neuroglial cells are that they are (KPMT 

2003)

(a) Nonsensory supporting cells

(b) Nonsensory supporting or secretory cells

(c) Sensory cells

(d) Central nervous system

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42. The energy transformation in the nervous

system is (KPMT 2002)

(a) chemical to radiant

(b) chemical to mechanical

(c) chemical to electrical

(d) chemical to osmotic

43. In the nerve cells, the reversal of the resting

  potential is known as depolarization. This

occurs due to (KPMT 2001)

(a) influx of Sodium ions(b) infux of Calcium and chloride ions

(c) influx of Potassium ions(d) influx of Sodium ions

44. Nissl granules could be seen in (KPMT 

2001)

(a) bone cells (b) gland cells

(c) myofibrils (d) neurons

45. The first cranial nerve is (KPMT 2000)

(a) occulomotor (b) auditory

(c) trigeminal (d) olfactory

46. The parasympathetic nerve ending release

(KPMT 2000)

(a) acetylcholine (b) serotonin

(c) adrenaline (d) dopamine

47. Pons connects the (KCET 2003)

(a) two lobes of cerebellum(b) two cerebral hemisphere

(c) spinal cord with the brain(d) cerebrum and cerebellum

48. The correct sequence of meninges from

inner to out side is (KCET 2003)

(a) duramater—piamater—arachnoid

(b) duramater—archanoid—piamater 

(c) arachnoid—duramater—piamater (d) piamater—arachnoid—duramater 

49. Which of the following is a part of human

 brain? (KCET 2002)

(a) Corpora bigemina

(b) Corpora quadrigemina

(c) Corpora allata

(d) Corpora adiposa

50. A bipolar neuron has (KCET 2002)

(a) 2 dendrites and 1 axon

(b) 2 axons and 1 dendrite

(c) 1 dendrite and 1 axon(d) 2 axons and 2 dendrites

51. Corpus callosum is seen in the (KCET 

2001)

(a) pituitary (b) ovary

(c) brain (d) corpus luteum

52. The transmission of impulse in the axon is

(KCET 2000)

(a) both away and towards cyton

(b) not found

(c) away from cyton(d) towards cyton

53. Cavities of brain are called (KCET 1998)

(a) auricles (b) coelom(c) ventricles (d) lumen

54. Acetylcholine is a (KCET 1994)

(a) enzyme (b) chemical transmitter  

(c) toxin (d) vitamin

55. Each spinal nerve in a mammal arises from

the spinal cord by two roots, a dorsal and a

ventral. Of these the ventral root is

composed of (KCET 1994)

(a) somatic motor and visceral motor fibres

(b) somatic sensory and visceral motor 

fibres

(c) somatic sensory and visceral sensoryfibres

(d) somatic motor and visceral sensoryfibres

56. In motor nerve fibers the impulse in the

axon travels (CET 2003)

(a) towards the cell body

(b) away from the cell body(c) both a and b

(d) cell body is not involved

57. Synapse is proximity of (CET 2002)

(a) two neurons (b) two veins

(c) two arteries (d) venules

58. One of these is wrong statement

I. Neurotransmitter jumps from one junction

to another 

II. After signal transmittance post synaptic

membrane is destroyed

III. Neurotransmitter is permanently

destroyed after the transmission of nerve

impulse has taken place (CET 2001)

(a) I and II (b) II and III(c) I andII (d) none of these

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59. Schwann cell is part of (CET 2000)

(a) excretory system (b)nervous system

(c) respiratory system (d)muscular system

60. ANS is not involved in (CET 2000)(a) heart beat

(b) control of viscera

(c) mictuiration

(d) learning and memory

61. In a human being, the numbers of cranial

nerve are (CET 2000)

(a) 6 pairs (b) 20 pairs

(c) 10 pairs (d) 12 pairs

62. Axon is characterized by (CET 2000)

(a) conduction of impulse

(b) transformation of energy

(c) receiving the impulse

(d) providing energy for impulse

63. Neurocyton is located (CET 2000)

(a) cortex of the brain

(b) outside the brain

(c) outside the spinal cord

(d) white matter 

64. The impulse for voluntary forced breathingstarts in (CET 1997)

(a) medulla oblongata(a) cerebral hemispheres

(c) vagus(d) spinal cord

65. Brain component regulating temperature of 

  body, the ectoderm is responsible for theformation of (CET 1997)

(a) hypothalamus (b) pituitary

(c) medulla (d) cerebellum

66. The impulse for voluntary forced breathing

starts in (CET 1997)

(a) medulla (b) vagus

(c) spinal cord (d) cerebral hemisphere

67. Cerebrum controls (Manipal 2003)

(a) vision (b) speech

(c) hearing (d) all above

68. Myelin sheath has which of the following?

(Manipal 2003)

(a) Carbohydrate (b) Starch(c) Protein (d) Phospholipid

69. The fluid which circulates in cerebrospinal

cavities is secreted by (Manipal 2002)

(a) Pons Varoili

(b) Corpus callosum

(c) Choriod plexi(d) Foramen of magendie

70. Arbor vitae is (Manipal 2002)

(a) tree like structure in body

(b) tree of life in cerebellum(c) tree of life in cerebrum

(d) ends part of spinal cord

71. Preganglionic sympathetic fibres are

(Manipal 2001)

(a) adrenergic (b) cholinergic

(c) synergic (d) hypergonic

72. Which nerve is exclusively motor?

(Manipal 2000)

(a) Vagus (b) Facial

(c) Spinal accessory(d) Maxillary

73. A disease occurring generally above 40s in

which person starts forgetting and hand

starts trembling, having poor CNS

coordination is (Manipal 2000)

(a) Alzhiemer’s disease(b) epilepsy

(c) Parkinson’s disease(d) migration

74. One of these nerve is completely motor 

(Wardha 2002)

(a) I (b) VII

(c) X (d) VI

75. Route of reflex arc is (Wardha 2002)

(a) receptors, effectors, grey mater andmotor fibers

(b) receptors, sensory fibers, grey mater,

motor fibers ad effectors

(c) sensory fibers, grey mater, motor,

sensory fibres, receptors and effectors

(d) effectors, grey mater, motor, sensory

fibers and receptors

76. Conduction of nerve impulse is connected

with (Wardha 2002)

(a) Ca and Mg (b) Ca and K only

(c) Na and K (d) K and Mg

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77. Which one of the following is not the reflex

action? (Wardha 2002)

(a) Blinking of eye

(b) Swallowing of food

(c) Removal of hand on pricking

(d) While hand is put on hot substance

78. Iter is (Wardha 2001)

(a) part of alimentary canal

(b) connection between third and fourth

ventricle(c) lateral ventricle in cerebrum

(d) ear canal

79. CNS controls various body activities exceptone of the following (AMU 2003)

(a) heart beat

(b) reflex action

(c) function of kidney

(d) digestion of food

80. At the beginning of the start of nerve

impulse, the concentration of Na+ and K+

are in the ratio (AMU 2003)

(a) 30 : 1 (b) 1 : 10

(c) 10 : 30 (d) 1 : 20

81. Which cells cannot divide following birth in

humans? (AMU 1997)(a) Muscle cells (b) Erythroblasts

(c) Osteoblasts (d) Neuron

82. Salivation is mammal is under the control of (AMU 1997)

(a) medulla oblongata(b) mesencephalon

(c) hypothalamus(d) cerebellum

83. Refractory period is during (BHU 2002)(a) polarization (b) depolarization

(c) repolarization (d) both b and c

84. Nerve impulse conduction is unidirectional

as (BHU 2002)

(a) axons combine with axon

(b) neurotransmitters are site specific

(c) neurotransmitters can nerve be relapsed

from dendrites

(d) Ca++ cannot be liberated at post synaptic

 junction

85. Foramen of Monro connects (BHU 2002)

(a) third ventricle with the fourth

(b) two lateral ventricles

(c) two cerebral hemispheres

(d) cerebellum and cerebrum

86. Which cranial nerve controls the movement

of eyeball? (BHU 2002)(a) Occulomotor (b) Optic

(c) Opthalimic (d) Trochlear 

87. The Broca’s area and Wernicke’s center are

the association area situated in cerebrum.These are associated with (BHU 2000)

(a) voluntary actions(b) blind spot(c) memory (d) none of these

88. Nissl’s granuales are absent in (BHU 1997)

(a) dendrite (b) cyton

(c) axon (d) both a and b

89. In the development of the human body, the

ectoderm is responsible for the formation of 

(BHU 1997)

(a) sweat glands (b) cutaneous glands

(c) lens of the eye (d) all of these

90. Which of the following is the part of mid

 brain of rabbit? (BHU 1996)

(a) Diencephalon

(b) Cerebrum(c) Corpora quadrigemina

(d) None of these

91. The 3rd, 6th and 11th cranial nerves are(BHU 1995)

(a) optic, facial and spinal nerves(b) occulomotor, trigeminal and spinal

accessory(c) occulomotor, abducens and spinal

accessory

(d) trochlear, abducens and vagus

92. Lateral ventricle and diocoel of brain (third

ventricle) are connected by (BHU 1995)

(a) occipital foramen

(b) foramen of Monro

(c) foramen Magnum

(d) aqueduct of Sylvius

93. Which brain structure in rabbit is directly

related to vision? (BHU 1994)

(a) Corpus callosum

(b) Corpus albicans

(c) Corpus quadrigemina(d) None of these

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94. Nervous secreting hormone like substances

are (HPMT 2003)

(a) sensory (b) neurosecretory

(c) motor (d) a and b

95. The nature of nerve impulse conduction is

(HPMT 2002)

(a) mechanical (b) thermal

(c) electrochemical (d) chemical

96. The number of spinal nerve in man are …..

 pairs (HPMT 2002)

(a) 42 (b) 31

(c) 15 (d) 12

97. Which part of our brain controls balance and

co-ordination? (HPMT 2000)

(a) Cerebrum

(b) Cerebellum

(c) Medulla oblongata

(d) Hypothalamus

98. Centre of thirst and hunger is (HPMT 2000)

(a) medulla oblongata(b) cerebellum

(c) cerebrum (d) hypothalamus

99. When the direction of nerve impulse is

reversed the condition is (HPMT 2000)(a) axo-axentic

(b) axo-dedrite(c) axo-axendendrite

(d) none of the above

100.Commissure uniting two cerebralhemispheres of mammalian brain is (HPMT 

2000)

(a) Corpus spongiousm

(b) Corpus callosum

(c) Corpus quadrigemina(d) Corpus cavernosum

101.The medulla oblongata enclose the (HPMT 

2000)

(a) optic capsule (b) optic lobe

(c) third ventricle (d) fourth ventricle

102.What is common between acetylcholine,

nor-adrenalin and serotonin (HPMT 2000)

(a) All are anticoagulants

(b) All lower the blood pressure

(c) All are neurotransmitters

(d) None of these

103.Anterior to enlargement of spinal cord is

known as (HPMT 1998)

(a) filum terminale

(b) conus terminale

(c) cervical swelling

(d) cauda equine

104.The flow of tears in women is stimulated by

(HPMT 1998)

(a) CNS

(b) Peripheral nervous system(c) Parasympathetic system

(d) Sympathetic system

105.Apolar nerve cells are found in (HPMT 

1997)

(a) brain (b) retina

(c) vertebrate’s embryo(d) cochlea

106.Which of the following animal has a false

nervous system but not brain? (HPMT 

1997)

(a) Hydra (b) Amoeba

(c) Cockroach (d) Earthworm

107.Heart is innervated by (HPMT 1996)

(a) trigeminal (b) vagus nerve

(c) glossopharyngeal(d) facial

108.Acetylcholine is a hormone secreted by

nerve which aids in (HPMT 1994)

(a) diastole of the heart

(b) blood clotting(c) systole of the heart

(d) both a and c

109.Glands of Swammerdam are (HPMT 1994)

(a) ganglia of sympathetic nervous system

(b) glands which are secreting hormone

(c) calcareous bodies protecting the gangliain frog

(d) none of these

110.Corpus callosum is a bridge of nerve fibers

which connects (HPMT 1995)

(a) two cerebral hemispheres

(b) two cerebellar hemisphere

(c) cerebrum to cerebellum

(d) none of the above.

111.Corpus callosum is absent in the brain of 

(DYPATIL 2003)

(a) Echidna (b) Monkey(c) Rat (d)Rabbit

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112.Parasympathetic and sympathetic are

(DYPATIL 2003)

(a) Antagonistic

(b) Similar 

(c) Parallel inactive(d) Always working together at the same

time

113.Towards the periphery of the spinal cord is

(DYPATIL 2003)

(a) grey matter (b) white matter 

(c) cytons (d) both a and b

114.Diencephalon has no command over 

(DYPATIL 2003)

(a) heat (b) heart beat

(c) love (d) anger  

115.Anterior choroids plexus is formed in

(DYPATIL 2003)

(a) cerebral hemispheres

(b) olfactory lobes

(c) medulla oblongata

(d) diencephalon

116.Which is activated in stress condition?

(DPMT 2003)

(a) parasympathetic (b) sympathetic(c) somatic (d) whole ANS

117.Acetylcholine helps in (DPMT 2003)

(a) synaptic transmission(b) membrane permeability

(c) synaptic delay(d) none of these

118.Cranial nerves numbering IV, V and VII are

respectively (DPMT 2001)

(a) Trochlear, trigeminal, auditory(b) Trochlear, trigeminal, facial

(c) Auditory, facial, trochlear 

(d) Auditory, trochlear, facial

119.Brain and spinal cord are (PPMT 2003)

(a) Intermediary neurons

(b) Effectors

(c) Receptors

(d) Sensory organs

120.Extension of sympathetic nervous system is

(PPMT 2003)

(a) pineal (b) neurohypophysis(c) adrenal cortex (d) adrenal medulla

121.At a resting state a nerve cell has (PPMT 

2000)

(a) high K+ outside and low of Na+ inside

(b) low K+ outside and high Na+ inside

(c) high K+ inside and low Na+ outside(d) high K+ inside and high Na+ outside

122.The bridge of nerve fibres connecting two

cerebellar lobes is (PPMT1998)

(a) corpus callosum (b) conus medularis(c) medulla oblongata(d) pons

123.Pneumogastric branch of vagus nerve

supplies (PPMT 1997)

(a) muscles of larynx

(b) supplies diaphragm

(c) muscles

(d) oesophagus, lungs, stomach

124.Which chemical is released by vagus nerve

to slow down the heart beat? (RPMT 1998) 

(a) Adrenalin (b) Acetylcholine

(c) Nor epinephrine (d) Epinephrine

125.The sound reception can be interpreted by

(RPMT 1998)

(a) olfactory lobe (b) cerebral hemisphere

(c) cerebellum (d) medulla oblongata

126.Which two extra cranial nerves are presentin amniotes? (RPMT 1998)

(a) Laryngeal and hypoglossal(b) Spinal accessory and hypoglossal

(c) Hypoglossal and facial(d) Trigeminal and glossopharyngeal

127.Arbor vitae controls (RPMT 1996)

(a) voluntary actions

(b) involuntary actions as group movementof muscles

(c) involuntary actions like secretion of 

gland

(d) none above

128.VIII cranial nerve connects which part of 

the body? (BVP 2003)

(a) Eye (b) Ear  

(c) Nose (d) Tongue

129.Decrease in heart beat is caused by (BVP 

2003)

(a) parasympathetic system(b) sympathetic system

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(c) central nervous system

(d) reflex action

130.Which of the following is not reflex action?

(BVP 2003)

(a) weeping (b) sneezing(c) coughing (d) yawning

131.Which part of the brain affects the

endocrine system the most? (BVP 2003)

(a) Cerebellum (b) Medulla(c) Hypothalamus (d) Cerebrum

132.The difference between cranial and spinal

nerves is (BVP 2003)

(a) spinal nerves comprise sensory and

motor fibers and cranial nerve has only one

kind

(b) spinal sensory nerve from dorsal root

ganglia at their origin from spinal cord and

cranial nerves originate from brain

(c) both above

(d) none above

133.Duct of Sylvius is another name of  (BVP 

2002)

(a) Iter (b) sulci

(c) foramen of Monro(d) gyrus

134.Fourth cranial nerve is (BVP 2002)

(a) trochlear (b) abducens(c) trigeminal (d) vagus

135.Longest nerve which ends in cephalic

region is (BVP 2001)

(a) sciatic (b) vagus

(c) trigeminal (d) pathetic

136.Corpus callosum in mammals joins (CMC 

2003)(a) two cerebellar lobe

(b) two pelvic girdles

(c) two pectoral girdles

(d) two cerebral hemisphere

137.During the period before excitation the

condition of nerve is (CMC 2002)

(a) resting period (b) action potential

(c) reflex action (d) spike potential

138.The aqueduct of Sylvius is a duct (CMC 

2002)

(a) connecting of the two lateral ventriclesof brain

(b) connecting utricle and saccule of inner 

ear 

(c) passing through spinal cord

(d) connecting the third and fourth ventricles

of brain

139.During conduction of nerve impulse

(MPPMT 2002)

(a) Na+ moves into axoplasm

(b) Na+ moves out of axoplasm

(c) K+ moves into axoplasm(d) Ca++ moves into axoplasm

140.Which one of the following is a purely

motor nerve? (MPPMT 2002)

(a) Vagus (b) Facial

(c) Abducens (d) Trigeminal

141.The ventricles of cerebral hemispheres

communicate through (BPMT 1997)

(a) foramen magnum

(b) foramen opali

(c) foramen of Monro

(d) optic foramen

142.Which one of the ventricles helps in

communication of medulla oblongata of 

 brain with spinal cord? (JIPMER 2002)

(a) II (b) III(c) IV (d) V

143.Chemical substance released in synapse

during transmission of an impulse is(JIPMER 1997)

(a) aceto-acetic acid (b) adrenine(c) acetic acid (d) acetylcholine

144.Which one of the following is an excitatory

neurotransmitter? (EAMCET 2001)

(a) Acetylcholine (b) Dopamine(c) Glycine (d) Oxytocin

145.The cranial nerves which control the

movement of eyeball are (EAMCET 1998)

(a) 4, 6and 7 (b) 3, 4 and 6

(c) 2, 3 and 5 (d) 5, 8and 9

146.Which one of the following is sensory

nerve? (EAMCET 1998)

(a) Trigeminal nerve (b) Vagus nerve

(c) Pathetic nerve (d) Auditory nerve

147.Synaptic fatigue is due to (EAMCET 1998)

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(a) exhaustion of neurotransmitter 

(b) release of more acetylcholine

(c) release of more adrenaline

(d) none of these

148.Sympathetic nervous system is also called

(EAMCET 1998)

(a) visceral (b) thoracico-lumbar  

(c) cranio-sacral (d) mesentric

ANSWERS # 09

EXPLANATION # 09

1. (b) Ninth pair of cranial nerve in frog is glossopharyngeal, originating from the lateral sides of medulla oblongata. It is a mixed cranial nerve. It functions in the sense of taste and touch and

movement of pharynx during swallowing.

2. (b) Vagus is the longest cranial nerve having maximum branching and so it is called as wondering

nerve.

3. (a) Olfactory lobes are paired short club shaped structures present at the anterior part of the brain.

They are responsible for the sense of smell and are not well developed in humans.

7. (b) Vagus, the longest cranial nerve controls the heart muscles, inhibiting the heart beat.

8. (d) Corpus callosum, a bundle of nerve fibres connecting the two cerebral hemispheres is absent inamphibians and present in mammals.

9. (d) In resting condition, there is high concentration of sodium ions on the outside of nerve fibre and

less concentration of potassium ions on the inner side. This creates a negative potential of about 70

mV relative to the outside called as resting membrane potential.

12. (d) Transmission is accomplished by a neurotransmitter, acetylcholine present in the synaptic vesicles

of the presynaptic knob. This neurotransmitter diffuses in the synaptic cleft and activates the post

synaptic membrane, so that the conduction starts again.

18. (c) sympathetic nervous system is represented by a chain of 21 sympathetic ganglia on either side of spinal cord. It receives preganglionic fibres from the spinal cord which make their exit along with

thoracic and lumbar nerves and constitute thoraco-lumbar outflow.

1. b 2. b 3. a 4. b 5. c 6. c 7. b 8. d 9. d 10.b11. a 12. d 13. b 14. a 15. a 16. b 17. d 18. c 19. c 20. b21. d 22. a 23. a 24. a 25. c 26. d 27. d 28. b 29. d 30. a31. c 32. c 33. a 34. a 35. d 36. a 37. a 38. a 39. a 40. a41. b 42. c 43. b 44. d 45. d 46. a 47. a 48. d 49. b 50. c51. c 52. a 53. c 54. b 55. a 56. b 57. a 58. b 59. b 60. d61. d 62. a 63. a 64. b 65. a 66. d 67. d 68. d 69. c 70. b71. b 72. c 73. c 74. d 75. b 76. c 77. b 78. b 79. a 80. c

81. d 82. a 83. d 84. b 85. b 86. a 87. a 88. c 89. d 90. c91. c 92. b 93. c 94. b 95. c 96. b 97. b 98. d 99. a 100.b101.d 102.c 103.c 104.c 105.c 106.a 107.b 108.d 109.c 110.a111.a 112.a 113.b 114.b 115.d 116.b 117.a 118.b 119.d 120.d121.d 122.d 123.d 124.b 125.b 126.b 127.b 128.b 129.a 130.a131.c 132.b 133.a 134.a 135.b 136.d 137.a 138.d 139.a 140.c141.c 142.c 143.d 144.a 145.b 146.d 147. b 148. b

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19. (c) The grey matter of cerebellum is called cerebellar cortex, while the white matter inside formed a

 branched tree like structure called arbor vitae or tree of life.

22. (a) In the peripheral nervous system, myelin is produced by Schwann cells, which surround the axon.

Gaps (nodes) in the myelin sheath along the length of the axon are known as the nodes of Ranvier.

26. (d) Preganglionic parasympathetic fibres make their exit along with the 3rd, 7th, 9th, 10th cranial nerves

and 2nd, 3rd, 4th sacral nerves. They together form the cranio-sacral outflow.

36. (a) Myelin is made of special cells called Schwann Cells that forms an insulated sheath, or wrappingaround the axon. There are small nodes or gaps called the nodes of Ranvier between adjacent myelin

sheath cells along the axon. As an impulse moves down a myelinated (covered with myelin) axon, theimpulse jumps form node to node instead of moving along the membrane, known as saltatory

conduction.

47. (a) Pons consists mainly of nerve fibres which form bridges between the two cerebellar hemispheres

and of fibres which pass between the higher levels of the brain and the spinal cord.

48. (d) Piamater is the innermost covering lying in close contact with the brain, arachnoid is the middle

layer and also vascular and duramater is the outermost, thick, double layered and non-vascular.

53. (c) Cavities of the brain are called as ventricles which consist of four hollow fluid filled spaces

inside the brain. (See ventricles of brain).

69. (c) Cerebrospinal fluid, present in the ventricles of brain is secreted by the anterior choroids plexus

(formed by epithalamus and piamater) and posterior choroids plexus (formed by the roof of medulla

oblongata and piamater).

78. (b) Iter or aqueduct of Sylvius is a narrow canal, which connects the third ventricle to the fourth

ventricle.

83. (d) After a nerve impulse is period when the neuron is unable to conduct a nerve impulse called therefractory period. The refractory period is a very short period during which the sodium-potassium

 pump continues to return sodium ions to the outside and potassium ions to the inside of the axon.Thus returning the neuron to the resting potential.

87. (a) Broca’s area is present in the parietal lobe of cerebral hemisphere and is concerned with the motor 

speech area. Wernicke’s area is present in the temporal lobe of cerebral hemisphere and is concerned

with the sense of understanding speech.

97. (b) Cerebellum helps in control of body posture, co-ordinates voluntary muscle activities and

equilibrium of body.

98. (d) Hypothalamus contains reflex centres linked to the autonomic system. It includes appetite and

satiety centre to control the desire for food.

112. (a) Sympathetic and parasympathetic nervous system work against one another which enables the

 body to make rapid and precise adjustment of involuntary activities in order to maintain a steady

state.

115. (d) Anterior choroids plexus is formed by the association of epithalamus (roof of diencephalon) and

 piamater.

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126. (b) In amniotes the last two pairs of cranial nerves are extra, i.e. spinal accessory (eleventh) and

hypoglossal (twelfth).

128. (b) Eight cranial nerve is auditory, distributed along the organ of Corti and semicuircular canals,

functioning in hearing and equilibrium.

145. (b) Oculomotor (III), trochlear (IV) and abducens (VI) function in the rotation of the eyeball, iris,

lens, eyelids and constriction of pupil.

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