Friday 5 February 2021

Chapter 21 Neural Control And Coordination







INTRODUCTION:The neural system (previously called nervous system) provides an organised network of point-to-point connections for a quick  coordination.Nervous system provides the fastest means of communication within the body. The neural system of all animals is composed of highly specialised cells called neurons which can detect, receive and transmit different kinds of stimuli.

The human neural system is divided into two parts:

(i) the central neural system (CNS)

(ii) the peripheral neural system (PNS)


(i) Central Nervous System (CNS) includes

(a) Brain

(b) Spinal cord


(ii) Peripheral Nervous System (PNS) includes nerves of body associated

with CNS (brain and spinal cord).

The nerve fibre of PNS are of two types.

(a) Afferent fibres carries impulse from tissue organ to the CNS.

(b) Efferent fibres carries impulse from CNS to the target organ tissue.


(iii) Peripheral nervous system is divided into two parts :

(a) Somatic Nervous System

(b) Autonomic Nervous System


STRUCTURE OF NEURON:The basic structural and functional unit of nervous system is Neuron.It consist of mainly three major parts

1. Cells body

2. Dendrites

3. Axon


1. Cell Body :- It contains cytoplasm, certain in granular bodies called

Nissl’s granules.


2. Dendrites are the short fibre which branch repeatedly and projects out of the cell body. They also contain Nissl' granules. They transmit impulses towards the cell body.


3. Axon is a long fibre its distal end is branched. It terminates as the bulb

like structure called synaptic knob.

Synaptic knob possess synaptic vesicles, which contain certain chemicals called neurotransmitters. Axons transmit the nerve

impulse away from cell body to the neuromuscular junction.Neurons are divided into three types on the basis of number of axon and dendrites.


Axons are mainly of two types :

(1) Myelinated

(II) Non Myelinated





1. The myelinated nerve fibre are enveloped with

(a) Schwann Cells.

(b) Synaptic knob

(c) Dentrites.

(d) Axon


2. The cell body contains

(a) Cytoplasm.

(b) Granular bodies

(c) Both (a) and (b)

(d) None of these


3. The CNS includes the

(a) Brain

(b) Spinal Cord

(c) Both (a) and (b)

(d) None of these


4. The basic structural and functional unit of nervous system is

(a) Neuron

(b) Cell

(c) Dendrites

(d) Axon


5. Synaptic knob possess synaptic vesicles, which contain certain

chemicals called

(a) Neurotransmitter

(b) Synaptic Knob

(c) Dendrites

(d) Neuron



1. The gaps between two adjacent myelin sheaths are called .

2. Each branch terminates as a bulb-like structure called .




1. The afferent fibres transmits impulses from the CNS to the


2. The CNS includes the brain and the spinal cord.

3. Unmyelinated nerve fibres is enclosed by a Schwann cell,which form a myelin sheath around the axon.




1. What is efferent and afferent nerve fibres ?

2. What is the difference between myelinated & non-myelinated?

3. What is nodes of Ranvier?



1. Explain Neuron structure with the help of diagram.






1. (a) Schwann Cells. The myelinated nerve fibres are enveloped with Schwann Cells.

2. (c) Both (a) and (b). The cell body contains cytoplasm and granular bodies.

3. (c) Both (a) and (b). The CNS includes brain and spinal cord.

4. (a) Neuron. The basic structural and functional unit of nervous system is Neuron.

5. (a) Neurotransmitter. Synaptic knob possess synaptic vesicles,which contain certain chemicals called neurotransmitters.



1. Synaptic knob. The gaps between two adjacent myelin sheaths are called Synaptic knob.

2. Nodes of Ranvier. Each branch terminates as a bulb-like structure

called nodes of Ranvier.



1. False. The efferent fibres transmits impulses from the CNS to the tissue/organs.

2. True. The CNS includes the brain and the spinal cord.

3. False. Unmyelinated nerve fibres is enclosed by a Schwann cell,which form a myelin sheath around the axon.




INTRODUCTION:The neural system of all animals is composed of highly specialised cells called neurons which can detect, receive and transmit different kinds of

stimuli. The Neurons exists in a state of excitability called polarised state.

This is a state of rest when the neurons is not conducting an impulse.At this point plasma membrane of nerve impulse is more permeable to potassium ions and impermeable to sodium ions.As aresult, axoplasm has high concentration of K* and negatively

charged proteins and low concentration of Na*.


DEPOLARISATION OF MEMBRANE OF NERVE FIBRES :-Depolarisation occurs as a result of Na+ channels whereas K+ ions channels remain closed.


CONDUCTION OF NERVE IMPULSE ALONG A NERVE FIBRE The polarity of the membrane gets reversed after excitation because Na+

ions move inward and K+ ions move outward.


CONDUCTION OF IMPULSE :- The  electrochemical changes are conducted upto synapses as electric wave of change of potential progresses forward along the fibres.


REPOLARISATION PHASE:- In this phase, axon again restores the concentration by the outside movement of Na+ ions from the inner side of membrane. As the impulses reaches the end knob, a neurotransmitter called acetylcholine is released from the synaptic vesicles present in the end knob.







1. Nodes of Ranvier are present in

(a) Myelinated axon.

(b) Non-myelinated axon

(c) Thalamus

(d) Gene cells


2. Ling fibres that a nerve cell contain is


(b) Axon.

(b) dendrites

(d) Cerebrum


3. Neuron body is called


(b) Soma.

(c) dendrites

(d) myelin



4. Gap between two adjacent myelin sheath is



(c) Node of Ranvier

(d) Dendrites


5. Portion responsible for maintaining posture


(b) Medulla

(c) Cerebellum

(d) Axon



1. Nervous System is made up of specialised cells called Neurons.

2. Hypothalamus is located in Cerebrum.

3. Path travelled by impulse during reflex action is called vision.



1. Forebrain consist of : : .

2. Chemicals released at synaptic function is called .






1. (a) Myelinated axon. Myelinated axon are white in colour and the conduction of impulse is fast and the node of Ranvier are present in them at internals.


2. (c) Axon. It is a long fibre that terminates as a bulb like structure.


3. (c) Soma. Neuron body is basic unit of neural system which is not divisible

and is called Soma.


4. (b) Node of Ranvier. The gaps between two adjacent myelin sheaths are

called nodes of Ranvier.


5. (b) Cerebellum. It is developed part of hindbrain responsible for posture and

equilibrium of the body.



1. True.

2. False.

3. False.



1. Forebrain consist of Cerebrum, thalamus, hypothalamus.

2. Chemicals released at synaptic function is called Neurotransmitter.



1. Difference between myelinated and non-myelinated.

2. Difference between dendrites and axon.

3. Explain role of Na+ generation of action potential.




1. Write brief note on generation and conduction of nerve impulse.






INTRODUCTION:Central nervous system consist of brain and spinal cord. Brain control

voluntary moments, balance of the body, functioning of vital in voluntary

organs (e.g. lungs heart kidneys etc.),thermoregulation hunger and thirst ,

circadian(24-Hour) rhythms of our body, activities of several endocrine

glands and human behaviour. It is also the site for processing of vision,hearing, speech, memory, intelligence, emotions and thoughts.


MENINGES :The menings are connective tissue membranes which surround the brain and spinal cord.In human CNS is covered by 3 Meninges

1. © +s —It is inner thin vascular membrane which is in contact

with the brain tissue .


2. 2 eco se sein = lt is middle and formed of reticular connective tissue and form spider web like structure.


3. 20) +. set is outer and lies along inner side of cranial cavity.The spaces between these three menings is filled with fluid

called cerebrospinal fluid ' CSF protect the brain from mechanical shocks and maintaines a constant pressure inside the cranium.


BRAIN:Brain can be divided into three major parts

(i) forebrain


(iii) hindbrain


Forebrain It forms anterior two-third part of the brain. It is formed of three parts.

1.Cerebrum 2.Thalamus 3.Hypothalamus



1. It forms the major part of human brain and cover almost all other parts of brain.

2. It forms 80% of the weight of the brain.

3. A deep cleft divides the cerebrum longitudinally into two equal halves called left and right cerebral hemispheres.

4. The hemispheres are connected by a tract of nerve fibres called corpus callosum.

5. The roof of cerebrum is called pallium which is highly folded to form ridges and depressions.

6. The gyri and sulci increase the surface area of cerebral cortex.

7. Few sulci are deep and well developed called fissures, which divide the cerebral hemispheres into 4 lobes.

Anterior-Middle- os Posterior- Occipital lobe Lateral- Temporal lobe


8. The peripheral portion of each cerebral hemisphere is formed of grey matter is called cerebral cortex and the deeper part is made up of white matter and is called cerebral medulla.

9. Cerebral cortex is the highest centre for many sensory areas:

a) =. » + -Inthe frontal lobe, controls the voluntary movements of the muscles.


b) Premotor area- In frontal lobe, controls involuntary movements of —

muscles and ANS.


c) Association area-In frontal lobe controls association between sensation

and movements and learning.


d) Somaesthetic area-In parietal lobe, controls general sensation like pain,

touch etc.


e) Visual area-In occipital lobe, controls visual sensation.


f) Auditory or acoustic area-In temporal lobe, controls hearing.


g) Motor speech area (Broca’s area) — In frontal lobe.


h) Sensory speech area- In lower part of parietal lobe.


i) Olfactory area-In temporal lobe, controls smell.


j)Taste area-In parietal lobe, controls gustation.


k)Wernicke’s area-In temporal area, helps in understanding speech.


THALAMUS:The cerebrum wraps around a structure called thalamus.These are masses of grey matter present in cerebral medulla of cerebral hemispheres.They act as relay centres.They receive sensory nerve impulses like pain, touch etc. and conduct

them to cerebral hemisphere.


HYPOTHALAMUS: It is, formed by masses of neurons in cerebral medulla below

thalamus.It controls involuntary functions like hunger, thirst, sweating, sleep, _

anger, BP, fear etc.It regulates body temperature so also called the Thermostat of the body.It also secretes neurohormones needed to stimulate Pituitary.Hypothalamus is an important link between nervous system and endocrine system.

NOTE: The inner part of cerebral hemisphere and a group of associated deep structure called the limbic lobe or limbic system.

Along with the hypothalamus, It is involved in the regulation of sexual behaviour, expression of emotional reactions (e.g.

excitement, pleasure, rage and fear), and motivation.


MIDBRAIN: It is located between the thalamus/Hy pothalamus of forebrain

and pons of hindbrain.It is completely covered by cerebral hemispheres.

It is made up of two parts.


1. Optic lobes- Each lobe is divided transversely into upper large superior

coliculus and lower smaller inferior coliculus. There are 4 lobes called optic

quadrigemina (only in mammals).It controls vision (superior coliculus) and

auditory stimuli (inferior coliculus).


2. Cerebral peduncles- It is a pair of thick bands of longitudinal nerve fibres

present at the floor of midbrain. It coordinate between fore and hind brains.

HINDBRAIN- It is formed of three Parts


CEREBELLUM :Cerebellum has very convoluted surface in order to provide the

additional space for many more neurons.

Functions: It controls voluntary movements and maintains equilibrium and posture.

Pons verolii It is made up of thick band of nerve fibres present at the floor of upper

part of medulla oblongata.It helps in coordination of 2 sides of the body.

Medulla oblongata It is the posterior most part of the brain, located beneath the



Functions: It controls involuntary functions through a number of

centres like heart beat (cardiac centre), rate of respiration (respiratory centre), contraction of blood vessels (vasomotor

centre), salivation (salivary centre). It also controls coughing,sneezing, urination, vomiting, BP, peristalsis, swallowing, defecation etc.

NOTE — Micdbrain and Hindbrain constitute the brain stem.


SPINAL CORD It is long (45 cms), soft, whitish, cylindrical rod which runs through

neural canal of vertebral column.

It weights about 35 gms.

It extends from the lower end of the medulla to the first lumber vertebra where it tapers to a point called conus medularis, and then it becomes

non- nervous. This non- nervous part is called filum terminale which goes up to coccyx.Spinal cord is not of uniform diameter. It has two swellings- upper and

lower lumbar.Spinal cord has a narrow central canal (neurocoel) which is connected anteriorly to forth ventrical but closed posteriorly.It is filled with cerebrospinal fluid.



It controls reflex action.

It conduct sensory and motor impulses to and from brain.





1. The correct sequence of meninges from inner to outer side is

a) Duramater- arachnoid membrane-piamater

b) Duramater-piamater-arachnoid membrane

c) Piamater-arachnoid membrane-duramater

d) Arachnoid membrane- duramater- piamater


2. Pons connects the

a) Two lobes cerebellum

b) Two cerebral hemispheres

c) Cerebrum and cerebellum

d) Spinal cord and brain


3. Human body temperature is maintained by

a) Hypothalamus

b) Medulla oblongata

c) Pituitary

d) Cerebral cortex


4.Which of the following parts of brain constitute the brain stem?

a) Midbrain and Hindbrain

b) Hindbrain and forebrain

c) Forebrain and midbrain

d) Forebrain only


5. The respiratory and cardiac centres are located in

a. Cerebrum

b. Medulla oblongata

c. Cerebellum

d. Pons varolii



1. Cerebellum is the largest part of forebrain

2. Sense of smell is perceived by olfactory lobe

3. Forebrain control the urge for eating and drinking



1. The part of human hindbrain that is responsible for hand-eye

coordination is -------

2. The optic lobes in human are represented by corpora-----------





Answer 1: (C) .Pia mater — It is inner thin vascular membrane which is in contact with the brain tissue .Arachnoid mater- It is middle and formed of reticular connective tissue Dura mater- It is outer and lies along inner side of cranial cavity.


Answer 2: (A) Pons is made up of thick band of nerve fibres present at the floor of upper part of medulla oblongata.It helps in coordination of 2 sides of the body.


Answer 3: (A) Hypothalamus regulates body temperature so also called the Thermostat of the body.


Answer 4:(A) Midbrain and Hindbrain constitute the brain stem.


Answer 5: (B) Medulla controls involuntary functions through a number of centres like heart beat (cardiac centre), rate of respiration (respiratory centre),

contraction of blood vessels (vasomotor centre), salivation (salivary centre).

It also controls coughing,







1. Cerebellum

2. Quadrigemina



1. Explain about the parts of forebrain

2. Write about the functions of medulla oblongata



1. Draw a well labelled diagram of human brain and Explain about different

parts of human brain



It is the rapid, involuntary and unconscious action of body in response to a stimulus.An involuntary or instantaneous action by the human body parts in response to a stimulus is called reflex action. It is because of numerous neural pathways that are known as reflex arcs that act on an impulse before it reaches the brain. Reflex

action doesn't need any conscious thought or awareness about the automatic


Reflex Action Examples in Humans Include:

-Closing of eyes when a bright light hits

our eyes.

-Blinking eyes when insects come in contact.

-Sucking reflex in infant Grasp reflex in infant

-Sudden withdrawing hands or legs when

they touch something hot or pricking.


REFLEX ARC:The reflex arc is the neural pathway controlling the reflexes and acts on an impulse even before it reaches the brain. Some stimuli require an automatic, quick response that does not involve conscious thought.The two types of reflex arcs are:

Autonomic Reflex Arc: It affects the functioning of inner organs.

Somatic Reflex Arc: It affects the functioning of muscles.


The Various Parts of the Reflex Arc are described as follows-The reflex arc consists of a receptor, sensory neuron, interneuron, motor neuron, and effector


Receptor - It receives the information and assists in generating impulses.


Sensory Nerve - It carries information from the receptor to the interneurons in the spinal cord.


Interneuron - It processes the information and generates effective responses.


Motor Nerve - It carries the information from the spinal cord to the effector organ.


Effector Organ - It receives information from effector neurons and results in the appropriate action.

Information regarding changes in the environment is received by the CNS through the sensory organs which are processed and analysed. Signals are then sent for necessary adjustments.

Eyes are highly developed photosensitive organs for analyzing the form, intensity, and color of light reflected from

objects and providing the sense of sight. Protected within the orbits of the skull which also contain adipose cushions,

each eyeball consists externally of a tough, fibrous globe that maintains its overall shape.Internally the eye contains transparent tissues that refract light to focus the image. a layer of photosensitive celis and a system of neurons that collect. process. and transmit visuai information to the brain A tough external fibrous layer consisting of the sclera and the transparent cornea.A middle vascular layer that includes the choroid, ciliary body. and iris: and An inner sensory layer, the retina, which communicates with the cerebrum through the posterior optic



SCLERA:The external layer formed of dense connective tissue Anterior transparent portion of sclera is called cornea.


CHOROID:Bluish middle laye.Contains many biood vessels.It is thin over posterior two third of the eyeball,but it is thick in the anterior part to form ciliary body.

ciliary body continues forward to form a visible pigmented ans opaque portion called iris.Iris has a central opening called pupil.The diameter of pupil is regulated by muscles of fibres of iris.Eyeball contains a transparent crystalline is held by ligaments attached to ciliary body.


RETINA:inner layer It contains 3 layers of cells-from inner to outer-ganglion cells, bipolar cells and photoreceptor ceils

Photoreceptor cells are of two types-rods and cones.They contain photosensitive proteins (photopigments)Photopigments are formed of opsin (a protein) and retinal (an aldehyde of vitamin A)


CONE CELLS:Function-Daylight (phototopic) vision and colour vision.There are three types of cones containing photopigments that respond to red ,green and

biue lights.The sensations of different colours are produced by combination of these cones and their photo pigments.


ROD CELLS:Function Twilight (scotopic) vision.They contain a purplish —red protein called rhodopsin (visual purple).it contains a derivative of vitamin A.

At the region, slightly above the posterior pole of eyeball,optic nerves leave the eye and retinal blood vessels enter

it. here,photoreceptor cells are absent. it is called blind spot .Lateral to blind spot ,there is a yellowish pigmented spot called mucula lutea(yellow spot)with a central pit ( fovea).


The fovea is thinned —out portion of retina

where only the cones are densely is the point of greatest visual activity (resolution).


AQUEOUS AND VITREOUS HUMORS:The space between cornea and lens is called

aqueous contains aqueous humor

(thin watery fluid).The space between the lens and retina is called vitreous contains vitreous humor(a transparent gel).












Let us know what we have learnt!




1. Light rays entering the eye is controlled by

(a) pupil

(b) iris

(c) cornea

(d) lens.




2. Retina is most sensitive at

(a) optic disc

(b) periphery

(c) macula lutea

(d) fovea centralis.


3.Function of iris is to

(a) move lens forward and backward

(b) refract light rays

(c) bring about movements of eye lids

(d) alter the size of pupil.


4. Iris is part of

(a) sclerotic

(b) choroid

(c) choroid and retina

(d) sclerotic and choroid


5. Sensitive pigmented layer of eye is

a) comea

(b) retina

(c) sclerotic

(d) iris


2. Fill ups

1. Rods containthe pigment_____——S.

2 Pupil is the opening which controls :



1. The fovea has cone cells only.

2. The point on the retina from where the optic nerve starts is called the blind spot.



1.Write a short note on retina?

2.Differentiate between rods and cones.

3.Describe briefly how does the eye regulate the amount of light that falls on




1.Draw a labelled diagram of human eye.

2.Give a brief mechanism of vision.

3.Explain reflex action in human beings with the help of examples.





1.(a) : Pupil is the opening which controls the amount of light entering in eye.


2.(d) Fovea Centralis has only cone cells,is place of most distict.


3.(d) The iris contains two sets of smooth muscles: sphincters and dilators.These muscles regulate the amount of light entering the eye.


4.(d) At the junction of the sclera and the cornea, the vascular coat sharply bends into the cavity of the eyeball to form a thin, coloured partition. This partition is called iris



1.Rods contain the pigment rhodopsin and are essential for vision in dim light.

2. Pupil is the opening which controls the amount of light entering in eye.



1 .TRUE The fovea has cone cells only, and is the place of most distinct vision.

2. TRUE The point on the retina from where the optic nerve starts is called the blind

spot, or optic disc, as it lacks the receptor cells and is insensitive to light.




INTRODUCTION:Anatomically ear can be divided into three parts:Outer Ear Middle Ear Inner Ear Outer Ear : It consists of the pinna and external auditory meatus. Pinna collects the vibrations in the air and the external auditory meatus extends to

tympanic membrane (ear drum)


Middle ear: It consists of three ear ossicles called MALLEUS, INCUS and

STAPES attached to one another in a chain like fashion. Ear ossicles increase the efficiency of transmission of sound waves to the inner ear. An Eustachian tube connects the middle ear cavity with the pharynx, thus equalising the pressure on both sides of the ear drum.


Inner Ear: Fluid filled part called LABYRINTH consists of two parts, the bony

and membranous labyrinth.The bony labyrinth is a series of channels and inside these channels lies the membranous labyrinth which is surrounded by a fluid called perilymph.The membranous labyrinth is also filled from inside with a fluid called

Endolymph. The coiled portion of labyrinth is called COCHLEA. The membranes

constituting COCHLEA. THE REISSNER’S MEMBRANE and THE BASILAR MEMBRANE divide the bony labyrinth into two parts, upper Scala Vestibuli and lower Scala Tympani.

The ORGAN OF CORT is located on the basilar membrane which contains hair cells as auditory receptors. The basal end of the hair cells is in close contact with the afferent nerve fibres. Above the rows of hair cells is a thin elastic membrane called Tectorial Membrane.

Mechanism of hearing:The external ear receives sound waves and directs them to the ear drum which vibrates and transmits these waves to the ear ossicles and then to the oval window, part of ear where scala vestibuli ends on to the outer side.

Now these vibrations generate waves in the lymphs, both Endolymph and Peri Lymph. These waves induce ripples in basilar membrane and this rippling of the basilar membrane bends the hair cells, pressing them against tectorial membrane. As a result of this nerve impulse are generated in the afferent neurons.These impulses are transmitted via auditory nerves to the auditory cortex of brain where these impulses are analysed and sound is recognised.


ANOTHER FUNCTION OF EAR:Apart from hearing ear also performs the function of MAINTENANCE OF BODY BALANCE and for this function internal ear has a special complex

system called vestibular apparatus located above the cochlea.The vestibular apparatus is composed of three semi-circular canals and the Otolith. These canals are at right angles to each other.There is membranous labyrinth suspended in the perilymph of the bony canals.The swollen base of these canals is called AMPULLA which contains

projecting ridge called Crista Ampullaris. Crista Ampullaris has hair cells.

The SACCULE and UTRICLE are the bed of sensory ceils for change in vertical and horizontal direction of head.The Sacula and Utricle contain a projecting ridge called MACULA.


Let us know what we have learnt!


A. MCQs:

1. Which part of the ear has no role to play in hearing but is very important?

(a) Ear ossicles

(b) Organ of Corti

(c) Eustachian tube

(d) Vestibular apparatus


2. It receives sound vibration and passes to the eardrum

(a) outer ear

(b) middle ear

(c) inner ear

(d) eustachian tube


3. The border between the middle and inner ear is formed by

(a) incus

(b) oval window

(c) pinnae

(d) tympanic membrane


4. The Organ of Corti is present in

(a) scalavestibuli

(b) scala tympani

(c) scala media

(d) none of the above


5. The membranous labyrinth contains

(a) Cystolymph 7

(b) Otolymph

(c) Perilymph

(d Endolymph



1. The middle ear contain three ossicles . and.

2. The fluid filledinner earis called.

3. The coiled portion oflabyrinthis called.



1 The human ear performs only one function i.e. hearing.

2. The external auditory meatus extends up to tympanic membrane.

3. Organ of corti is located on the Reissner’s membrane.



A. Multiple choice Questions:









B. Fill in the blanks:

1 Malleus, incus and stapes

2. Labyrinth

3. Cochlea


C. True /False:

1 False: The human ear performs two functions i.e. hearing and balancing.

2. True

3. False: Organ of corti is located on the Basilar membrane.



1. Discuss structure of inner ear.

2. What is function of cochlea?



1. Discuss mechanism of hearing.





Coordination is the process through which two or more organs interact and complement the function of each other.Neural system provides an organized network of point to point connection for quick coordination. The endocrine system provides chemical integration through hormones.Neural system of animals is composed of specialized cells called neuron, which candetect, receive and transmit different kinds of stimuli.

In hydra neural system is composed of network of neuron. In insects it

consists of brain and a number of ganglia. Vertebrates have highly developed neural system.Central nervous system (CNS) includes brain and spinal cord. It is the

site forinformation processing and control.

Peripheral nervous system includes all nerves associated with CNS. There

are two types of nerve fibers:


Afferent fibers- transmit impulses from tissue/organ to CNS.


Efferent fibers- transmit regulatory impulses from CNS to concerned peripheralorgans.Somatic neural systems relay impulses from CNS to skeletal muscles.Autonomicneural system transmits impulses from CNS to involuntary

system and smooth muscles.




The brain is the central information processing organ of the body acting as the

command and control system’. It is protected in the skull.


1. It is covered by three membranes known as cranial meninges — the outer layer is the dura mater which is a fibrous and a tough membrane, the middle layer is the arachnoid, which is delicate and thin, the innermost layer is the pia mater which is an extension of the brain tissue. This layer is extremely vascular and supplied richly with blood.


2. The three main regions of the brain are:

(i) Forebrain

(ii) Hindbrain 

(iii) Midbrain


(1). Forebrain —has three main parts: Cerebrum, Thalamus, Hypothalamus.

1. Cerebrum forms the most important and major part of the entire brain. It is

longitudinally segregated into halves by a deep cleft, each half is known as the

cerebral hemisphere. Both these hemispheres are linked by the corpus callosum

which is a tract of nerve fibres. The cerebral hemispheres are internally hollow and the walls of the cerebrum have an inner medulla and the outer cortex.1 The cerebral cortex consists of cell bodies of neurons which imparts the grey appearance; hence it is referred to as grey matter. The grey matter has many grooves (sulci) and folds (gyri). Higher the number of convolutions, greater the intelligence. The cerebral cortex consists of senso ry areas, motor areas and association areas (neither motor nor sensory). These specific areas are responsible for the complex functions namely communication, memory and inter sensory associations.The cerebral medulla is made of axons of nerve fibres, imparts a white appearance, hence it is referred to as white matter. There a group of interrelated deep structures inside the cerebral hemispheres, namely the AMYGDALA and HIPPOCAMPUS, which results in the formation of a complicated structure known

as the limbic system or the limbic lobe.

Role — The cerebrum is the centre of memory, intelligence, consciousness,

voluntary actions and will power.


2. Thalamus:It is made up of grey matter and located superior to the midbrain.

Role — it relays motor and sensory impulses to the cerebrum and also controlsthe manifestation of emotions, comprehends heat, pain and cold.


3.Hy pothalamus:Located at the base of the thalamus, it consists of the optic chiasma. It is a point wherein the optic nerve fibers cross opposite sides. Behind this structure is the infundibulum, which is a greyish protuberance of the hypothalamus. It contains the pituitary gland.

Role — The hypothalamus has centers, responsible in regulating temperature of

the body, homeostasis, blood pressure, center to control appetite, hunger, sleep,

fatigue, thirst, pleasure, anger and penance. Along with the limbic system, the

hypothalamus also plays a part in regulating the sexual behavior.

(ii)Midbrain-It consists of the Cerebral Peduncles and the Corpora



1. Cerebral Peduncles:They are fibrous thick tracts which connect the cerebrum and the cerebellum.

Role — Relay the sensory and the motor impulses between the hindbrain and the



2. Corpora quadrigemina:The dorsal part of the brain has two pairs of solid lobes which are referred to as the corpora quadrigemina, where one pair is referred to as the Superior Colliculi and the other pair is referred to as the Inferior Colliculi.

Role — Corpora Quadrigemina controls the visual reflexes and the movement ofthe

eye and head. They also regulate auditory reflexes and movement of the head to

identify and detect the source of sound.


(iii).Hindbrain-it consists of the Cerebellum, Pons Varolii and Medulla

oblongata. There are many neurons in the cerebellum so its surface is very

convoluted in order to accommodate those extra neurons. The hindbrain

coordinates functions that are fundamental to survival, including respiratory

rhythm, motor activity, sleep and wakefulness. The medulla controls autonomic

functions such as heartbeat and respiration. The pons is partly made up of tracts that connects the spinal cord with higher brain levels and it also contains cell groups that transfer info. from cerebrum to cerebellum.


(b). Structure of the Eye —

Ans: Lens- The human eyeball is almost cylindrical in shape. There are three layers to the eyeball. X-rays can reveal the existence of a dense connective tissue layer that surrounds the eyeball called the Sclera. This layer includes the Cornea on its anterior portion. A blue-colored layer at the middle of the choroid is composed of blood vessels. As the eyeball approaches the middle, the choroid layer becomes thin, but becomes thicker underneath. Iris, the coloured portion of the eye, is formed from the pigmented ciliary body. An eyeball is supported by a clear crystalline lens

whose position is maintained by ligaments attached to the ciliary body. Iris

muscle fibers control the diameter of the pupil; the pupil's opening surrounding the lens. The Retina is the inner layer of the eye, which is composed of three layers of neural cells beginning on the outside and

continuing inwards - ganglion cells, bipolar cells, and photoreceptor cells.

Both RODS and CONES can serve as photoreceptor cells.A cone is responsible for vision in daylight (photo pic) and color vision, and arodis responsible for vision in twilight (scotopic).

Ganglion cells form the optic nerve fibers that are connected to the brain by

the optic nerve in each eye


(c) Ear:Ans: It is a sensory organ that protects the body from danger, and it helps

keep it balanced.

Outer ear: is made up of the pinna and external auditory meatus(canal).As sounds arecreated in the air, the pinna collects its vibrations. An external auditory meatus runs from the tympanic membrane (eardrum)

inward. In the pinna and meatus skin, hairs are very fine and waxglands are present.


Middle ear: The middle ear is divided into three ossicles—the malleus,the incus and the stapes. The incus and the stapes are linked together in a chain-like arrangement. This complex of bones is attached to the tympanic membrane

and the oval window of the cochlea by the malleus and stapes. It increases the

efficiency of sound waves being transmitted to the inner ear through ear ossicles. Middle ear cavities connect to pharynx through a Eustachian tube. As the pressure is equalized on both sides of the eardrum, the Eustachian tube works.


Inner ear: Also referred to as a LABYRINTH. Bony labyrinths and membranous labyrinths exist within the labyrinth. The bony labyrinth is filled with perilymph, whereas the membrane labyrinth is filled with endolymph. Vestibular apparatus and cochlea are the two parts of the labyrinthine membrane. There are three semicircular canals and an otolith in the vestibular apparatus (the macular nerve forms the sensory pathway between the utricle and saccule). Several semicircular canals lie at right angles to one another in a different plane. A perilymph surrounds the bony canals, permitting the membranous canals to travel. Canaisare swollen at the bottom and have thick ridges called ampullae,which attach to a projection called crista ampullaris. Maculas are ridges that project from the saccule and utricle.In addition, the vestibular apparatus maintains posture and balance when the crista and macula are activated. An extension of Sacculus is the Cochlea.

Besides being the main organ for hearing, it also controls balance. Three

membranes make up the cochlea. A hearing organ called the organ of corti is

found on the basilar membrane, which is covered in hair cells.


Q3. Explain the following processes:

(a) Polarization of the membrane of a nerve fiber:

Ans: The membrane becomes polarized when its resting potential changes. The

K* and negatively charged proteins in the axoplasm are higher than the Na*

concentration inside the axon when in resting condition. Thus, K* movefaster

from the inside to the exterior than Na*. A positively charged membrane becomes negatively charged inside and a positively charged membrane becomes negative. An example of this would be polarized nerves or polarized membranes.


(b) Depolarization of the membrane of a nerve fiber:

Ans: An action potential occurs when a nerve fiber receives an electrical

stimulus.As sodium ions pass through the membrane, potassium ions are less


POTTED Consequently, the nerve fiber becomes positively charged inside, and negatively charged outside. This depolarization of the membrane is referred to as depolarization.


(c) Conduction of a nerve impulse along a nerve fiber:

Ans: Nerve fibers are divided into two types - myelinated and unmyelinated. Since

Schwann cells surround the axon of a myelinated nerve fiber and form the myelin

sheath, the impulse travels back and forth rapidly in myelinated nerve fiber. lons

cannot pass through the myelin sheath. The nerve fibres do not exchange ions

and depolarize efficiently along their entire length as a result. Ranvier's nodes

occur only at some points. A normal unmyelinated nerve fibre experiences ionic

exchange along its full length, which then causes repolarization of depolarized

areas and depolarization of other areas.


(d)Transmission of a nerve impulse across a chemical synapse:

Ans: In a chemical synapse, there is a fluid-filled space between pre- and post-

synaptic neurons, called a synaptic cleft. After receiving an impulse, the synaptic

vesicles move toward the plasma membrane and fuse with the plasma membrane

in the synaptic cleft. Here they release their neurotransmitters. A number of

receptors are present on the postsynaptic membrane, which bind to release the

neurotransmitters. Postsynaptic neurons form new potentials in response to ion

channels opened by this binding. An excitatory or inhibitory potential can be



Q. 5.Write short notes on the following:

(a) Neural coordination

Ans: A neural system facilitates the interaction and complementing of the activities of two or more organs. Coordinating and integrating all the organ's functions, the brain and endocrine system work together. Brain systems provide fast coordination by organizing a network of interconnected points. Hormones enable chemical integration by the endocrine system.


(b) Forebrain

Ans: Among the three parts of the cortex are Cerebrum, Thalamus, and

Hypothalamus.The brain's main structure is the CEREBRUM. Left and right cerebral

hemispheres are separated by a fissure in the cerebrum. Connecting the hemispheres is the corpus callosum. Cells that cover the cerebral hemisphere make up the cerebral cortex. It is referred to as grey matter because of its greyish coloration. Several portions of the cerebral cortex have no obvious sensory or motor function. A variety of complex activities are performed by association areas, including intercessory associations, memory, and communication. In the cerebral hemisphere-

interior section, the fibers of the tract are protected by the myelin sheath.

White matter is named as a result of their impenetrable appearance. Intercessory

associations, memory, and communication are all tasks that the association areas

are accountable for. The myelin sheath, which makes up the interior section of the

cerebral hemisphere, protects the tract fibres. They give the layer an impenetrable

white appearance, thus the name "white matter.


Thalamus: There is a region within the cerebrum wrapped around the middle ofthe

forebrain named the Thalamus. Sensory and motor signalling are coordinated at this



Hypothalamus: In the hypothalamus there are numerous centres that regulate

body temperature, urges for eating, and thirst.


(c) Midbrain

Ans: The midbrain: From the forebrain to the hindbrain, the midbrain lies between

the thalamus and the hypothalamus. This section of the brain passes through a

canal known as the cerebral aqueduct.


(d) Hindbrain

Ans: In the hindbrain, you will find pons varolli, cerebellum, and medulla.There are many neurons in the cerebellum, so its surface is very convoluted.Medulla is home to centers that regulate respiratory functions, cardiovascular reflexes, and gastric secretions.


(e) Retina

Ans: Retina, also known as the photoreceptor, is a layer of neural cells located at the back of the eye. It includes ganglion cells, bipolar cells and astrocytes. They act as photoreceptors. A cone is a sensory organ that is responsible for the perception of daylight and colour whereas the rods are responsible for twilight vision. Images of objects are formed on the retina by the light entering through cornea and the lens.


(f) Ear ossicles

Ans: Malleus, incus, and stapes are three ossicles located in the middle ear, which

are connected to each other. Among the three components of the ear, malleus is

connected to the tympanic membrane, incus is attached to the stapes, and stapes

is attached to the cochiea's oval window. By transmitting sound waves effectively

into the inner ear, ear ossicles increase hearing efficiency.


(g) Cochlea

Ans: The cochlea is the coiled section of the labyrinth. There is an upper and a

lower scala tympani in the cochlea, composed of reissner's and basilar

membranes. Scala media, which fills the cochlea, contains endolymph. A

rectangular window open to the middle ear accompanies the oval window at the

base of the cochlea, and a round window opens to it at the base of the cochlea.


(h) Organ of Corti

Ans: In the organ of corti, hair cells function as auditory receptors located on

the basilar membrane. On the inside surface of the Corti organ, hair cells are

arrangedin rows.


(i) Synapse

Ans: The synaptic cleft is a gap between postsynaptic cells and presynaptic cells

that divides the synaptic membranes. Synapses are of two different types:

chemicaland electrical.


Q.6 Give a brief account of:

(a} Mechanism of synaptic transmission:


Ans: A synapse is a point where two neurons meet. It exists between one

neuron's axon terminal and the dendrite of the next neuron, divided by a cleft.

Synaptic transmission occurs in two ways.


(1) Chemical Transmission- A neurotransmitter (acetylcholine) is released across the synaptic cleft when a nerve impulse reaches the end plate of an

axon. This substance is produced in the neuron's cell body and delivered to

the axon terminal.Acetylcholine diffuses over the cleft and attaches to receptors on the surface ofthe next neuron's membrane. This results in membrane depolarization and

the initiation of an action potential.


(2) Electrical transmission- An electric current is created in the neuron in this

sort of transmission. This electric current causes an action potential, which

resultsin nerve impulse transmission across the nerve fibre. This technique of

nerve conduction is quicker than the chemical method of transmission.

(b) Mechanism of vision:

Ans: The retina is the eye's innermost layer. Inner ganglion cells, middle

bipolarcells, and outermost photoreceptor cells make up the three layers. A

photo- receptor cell is made up of a protein called opsin and a vitamin A

aldehyde known as retinal. The separation of the retinal from opsin protein

occurs when light rays are focused on the retina through the cornea. Opsin's

structure is altered as a result of this. The permeability of the membrane changes

as the structure of opsin changes, resulting in a potential differential in the cells.This causes an action potential in the ganglionic cells, which is then communicated to the brain's visual cortex via optic nerves. The impulses are analysed in the cortex portion of the brain, and an image is generated on the retina.


(c) Mechanism of hearing:

Ans: Sound waves are collected by the pinna of the external area and sent to the

external auditory canal. Vibrations are formed when these waves hit the tympanic

membrane. The vibrations are then conveyed to the oval window, fenestra ovalis,

via the malleus, incus, and stapes, three ear ossicles. These ossicles in the ear

operate as a lever, transmitting sound waves to the inner ear. The vibrations of

the fenestra ovalis are conveyed to the cochlea. The lymph produces sound

waves as a result of this. A ripple in the basilar membrane is caused by the

creation of waves. The sensory hair cells on the organ of corti bend against the

tectorial membrane as a result of this action. Sound waves are turned into nerve

impulses as a consequence of this. Auditory nerves then carry these signals to

the auditory cortex of the brain. The impulses are analysed and sound is

identified in the cerebral cortex of the brain.


Q.7.Answer briefly:

(a} Howdo you perceive the colour of an object?

Ans: Color vision is mediated by cones. Cones respond to different types of light

depending on their characteristics, such as green, blue and red. Light from

different sources stimulates these ceils in different ways.


(b) Which part of our body helps us in maintaining the body balance?

Ans: Cochlear canals are formed by three semicircles in the inner ear. Keepingthe

body in balance is the job of the Cochlea.


(c) How does the eye regulate the amount of light that falls on the retina?

Ans: The pupil is a small opening between the iris and the lens of the eye that

regulates light entering the eye. In dim light, they expand to let more light fall on the retina, whereas in the presence of intense light they contract.


Q.8. Explain the following:

(a) Role of Na in the generation of action potential:

Ans: lonization of Na* is responsible for the action potential. By diffusion into

the inside of the axoplasm, the Na* channels, which are normally closed, become

opened and allow the inflow of Na* ions. After the membrane has depolarized,

its electrical potential moves from 70 mV toward zero.


(b) Mechanism of generation of light-induced impulse in the retina:

Ans: Photo pigments composed of both retinal and opsin in the eye are

photosensitive and pigmented substances. Retinal dissociates from opsin when

exposed to light, altering the structure of opsin. The bipolar neurons generate

action potentials. In order to recognize the correct image, the brain analyzes the

neural signals and action potentials presented by the optic nerves.


(c) Mechanism through which a sound produces a nerve impulse in the innerear.

Ans: Acoustic energy is transmitted to the inner ear when it falls on the ear drums.

Vibrations are transferred to the lymphatic fluid from the oval window in

the cochlea.When the waves are accompanied by ripples in the basilar membrane,

the cells of the hair are bent, forcing them against the techtonial membrane. The

result of this is the generation of nerve impulses in the associated afferent neurons

and their transmission to the auditory cortex of the brain, where they are analyzed and recognized as sound.


Q.10.Answer the following:

(a) Which part of the ear determines the pitch of a sound?

Ans: Cochlea


(b) Which part of the human brain is the most developed?

Ans: Cerebrum


(c) Which part of our central neural system acts as a master clock?

Ans: Hypothalamus


Q11. The region of the vertebrate eye, where the optic nerve passes out of

theretina, is called the:

(a) fovea

(b) iris

(c) blind spot

(d) opticcharisma

Ans:(c) blindspot




INTRODUCTION:Dear students, we have learnt all about neural neural control and coordination in previous assignments, now we are going to revise important questions and diagrams of this chapter.




1. What is the basic unit of neural system?

Ans. Neuron.


2. Name the band of nerve fibers that joins the two cerebral hemisphere in mammals.

Ans. Corpus callosum.


3. What is threshold stimulus for nerve cell?

Ans. The minimum intensity / strength of a stimulus required to initiate depolarization of neuron is called threshold stimulus.


4. What types of neurons are found in dorsal root of spinal nerve?

Ans. Sensory neurons.



5. Name the inner most meanings of the brain.

Ans. Piamater is the inner most meanings of the brain.


6. To which part of the brain communication and memory arc associated?

Ans: Cerebrum.


7. Why can impulses fiow only in one direction?

Ans. Because each synoapse allows impulse to cross it in a single direction.


8. How does an impulse travel across a synapse?

Ans. The impulse travel across a synapse from the axons to the cell body and

dendrites to the next neuron.


9. Where is hypothalamus located in the brain?

Ans. Hpothalamus is located at the base of thalamus in the brain.


10. Name the fluid present in membranous labyrinth.

Ans. Endolymph fluid is present in membranous labyrinth.



1. Where does cerebrospinal fluid occur in our body? Mention two if its function.

Ans. Cerebrospinal fluid is found in the subarachnoid space between arachnoids and parameter of the menings around the brain and spinal cord and also in the cavities of the brain.Functions —

1) It protects brain and spinal card by acting as a cushion to absorb shocks

2) It helps in removing harmful metabolites drugs etc. away from the brain.



2. What is a reflex?

Ans. Reflex is an involuntary action performed by muscle under the direction

of spinal cord in response to the stimulus. It is an automatic response to a

stimulus which is not under conscious control. A large number of activities of

animals are conducted by reflexes e. g. Respiration, peristalsis, watering of

the mouth, secretion of saliva in the mouth, etc.


3. What is a synapse?

Ans. It is the junction between axon terminals of a neuron and dendrites or

the cell body of another neuron. There is a narrow fluid-filled space, called

Synaptic Cleft separating axon terminals and dendrites at the synaptic

junction. So, the two-neurons forming synapse does not form actual continuity

between the neurons.



1. Give parts of neuron.

Ans. Neuron is a microscopic structure made up of 3 parts

a) Cell body — In contains cytoplasm with typical cell organelles and some

granular bodies called Nissl's granules.


b) Dendrites — The short fibers that branch repeatedly and project out of the

cell body. They transmit impulse towards the cell body or cyton.


c) Axon — It is a long fibre. Its distal end is branched. Each branch terminates into bulblike structure called as synoptic knob.


2. Describe human neural system.

Ans. It is divided into two parts

1) Central Neural system (CNS) — CNS includes brain and spinal cord. This

is the site of information processing and control.


2) Peripheral neural system (PNS) — PNS consists of all nerves of the body

associated with the CNS. Nerve fibers of PNS are of two types i.e. afferent

fibers and efferent fiber.


(a) Afferent nerve fibers transmit impulses from tissues / organs to CNS.

(b) Efferent nerve fibers transmit impulses from CNS to concerned peripherel tissues / organs.PNS is further divided into —

(1) Somatic neural system — It relays impulse from CNS to skeletal muscles.

(2) Autonomic neural system — ANS transmits impulses from CNS to involuntary organs as well as the smooth muscles of body It is again divided into two parts -

a) sympathetic neural system

b) Para sympathetic neural system.


3. Why are nerve impulses conducted more rapidly in myelinated nerve fiber than in a non — myelinated one? Explain.

Ans. In a myelinated nerve fiber, the lipid rich myelin acts as an insulator

and depolarization occurs in the nodes of Ranvier where myelin sheath is absent. Since the action potential jumps from one node of Ravines to another, the conduction becomes faster and such a type of conduction is called saltatory conduction.

In a non-myelinated fiber, the depolarization occurs all along its length and hence conduction becomes slower.

Chapter 21 Neural Control And Coordination