NCERT Solutions for Class 11 Biology Chapter 21: Neural Control and Coordination

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1. Briefly describe the structure of the following:

(a) Brain

(b) Eye

(c) Ear

Ans. (a) Brain: The brain is a highly specialised organ, present in the cranium. It acts as a control and command system of the body. It
is covered by three meninges. It is divisible into three main regions:

(i) Forebrain,

(ii) Midbrain,

(iii) Hindbrain.

(i) Forebrain: It consists of three regions:

Cerebrum: It is the largest and most complex of all the parts of the human brain.
It consists of two cerebral hemispheres (Right and left) joined together by nerve fibres called the corpus callosum. Each cerebral hemisphere is divided into four lobes namely frontal, parietal, temporal and occipital. The cerebral hemisphere's outer region has highly packed nerve cells called the cerebral cortex which forms grey matter.
Beneath the cerebral cortex is the white matter of the cerebrum.
Role: The cerebrum is the centre of memory, intelligence, consciousness, voluntary actions and willpower.
Thalamus: It is the region present at the centre of the forebrain. All sensory information that reaches the cerebral hemispheres first passes through the
thalamus.
Role: Its main function is to interpret sensory and motor signals and then channel them to the appropriate cerebral cortex region.
Hypothalamus: It is present beneath the thalamus and consists of masses of grey
matter scattered in the white matter.
Role: It is the control centre for many internal control mechanisms and is associated with the thermovascular system, water balance, hunger drinking etc. It is also a reflex control centre. Along with the limbic system, the hypothalamus also plays a part in regulating sexual behaviour.

(ii) Midbrain: It is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. It consists of a group of nerve cells—grey matter is scattered in the white matter.

Role: It connects the forebrain and hindbrain. Its four corpora quadrigemina control eye movement and auditory responses. The lower part of the midbrain is associated with muscular reflexes.

(iii) Hindbrain: It consists of three parts:

Cerebellum: The second largest part of the human brain is the cerebellum. It consists of two lateral cerebellar hemispheres and
a central worm-shaped part, the vermis. It has grey matter on the surface called the
cerebellar cortex and white matter in the centre called the cerebellar medulla.
Role: It is a reflex centre for the coordination of muscular body movements and maintenance of posture or equilibrium.
Pons: An oval mass, called the pons Varolii, lies above the medulla oblongata. It consists mainly of nerve fibres which interconnect different regions of the brain.
Role: It sends impulses to the cerebral cortex and cerebellum.
Medulla oblongata: It extends from the pons Varolii above and is continuous with the spinal cord below. The midbrain, pons Varolii and medulla oblongata are
collectively called the brain stem.
Role: It serves as a passage to conduct nerve impulses from the spinal cord to the brain. It controls all the activities of the internal organs, breathing and heartbeat.

(b) Eye: The eye is a hollow spherical structure composed of three coats as follows:

(i) Fibrous coat: It is thick and protects the eyeball. It has two distinct regions called
the sclera and cornea. Sclera which is white, covers most of the eyeball and contains
many collagen fibres. The cornea is an avascular, transparent portion that forms the anterior of the eyeball.

(ii) Vascular coat: It comprises 3 regions as follows:

Choroid: It lies adjacent to the sclera and contains numerous blood vessels and pigmented cells.
Iris: The iris is a circular muscular diaphragm containing the pigment giving the eye its colour. It extends from the ciliary body across the eyeball in front of the lens. It has an opening in the centre called the pupil which has two types of smooth muscles called circular muscles and radial muscles.
Ciliary body: Behind the peripheral margin of the iris, the vascular coat is thickened to form the ciliary body. It is composed of the ciliary muscles and the ciliary processes.

(iii) Nervous coat: It consists of the retina which is a neural and sensory layer of an eyeball. It also consists of three layers called ganglion cells, bipolar cells and photoreceptor cells (rods and cones).

Lens: It is a biconvex, transparent, avascular elastic structure that bends light waves as they pass through its surface. It is composed of epithelial cells that have large amounts of clear cytoplasm in the form of fibres.

Chambers of eyeball: The lens is held in position by suspensory ligaments attached to the ciliary body. The lens divides the eyeball into two chambers — an anterior aqueous and posterior vitreous.

(c) Ear: An ear has three parts:

(i) External ear: It has the pinna and the external auditory canal (meatus). The pinna gathers the vibrations in the air that generate sound. The external auditory canal extends up to the eardrum (tympanic membrane). It has very fine hair and wax-secreting glands in the skin of the meatus and the pinna. The tympanic membrane consists of connective tissues covered with the mucous membrane inside and with skin on the outside.

(ii) Middle ear: It consists of three ossicles known as the malleus, incus and stapes that are linked to one another in a chain pattern. The malleus is linked to the tympanic membrane and the stapes are linked to the oval window of the cochlea. The ear ossicles increase the efficiency of transmission of sound waves to the inner ear. The middle ear cavity is connected to the pharynx through the Eustachian tube which aids in equalizing the pressure on both sides of the eardrum.

(iii) Inner ear: It is also known as the labyrinth which is split into a membranous labyrinth and the bony labyrinth. The membranous labyrinth is filled with endolymph while the bony labyrinth is filled with perilymph. The Membranous labyrinth is segregated into two portions – the vestibular apparatus and the cochlea. The vestibular apparatus consists of three semi-circular canals and an otolith. Each semi-circular canal lies in a different plane at right angles to each other. The membranous canals are suspended in the bony canals (perilymph). The base of the canals is swollen and is known as ampulla containing crista ampullars – a projecting ridge which has hair cells. The utricle and the saccule have a projecting ridge known as the macula. The macula and the crista are the particular receptors of the vestibular apparatus that have a role to play in maintaining posture and body balance. Sacculus has a coiled and long outgrowth – cochlea which is the chief hearing structure consisting of three membranes. A hearing organ, the organ of Corti, is situated on the basilar membrane possessing hair cells.

2. Compare the following:

(a) Central neural system (CNS) and Peripheral neural system (PNS).

(b) Resting potential and action potential.

(c) Choroid and retina.

Ans. (a) Difference between Central Neural System (CNS) and Peripheral Neural System (PNS):

Central Neural System (CNS)	Peripheral Neural System (PNS)
This system consists of the brain and the spinal cord.	This consists of spinal nerves and cranial nerves.
It has no subdivisions.	It is divided into the autonomic and somatic nervous systems.
It processes information and regulates the responses to impulses.	Nerves pass impulses to the CNS and responses from the CNS send to the various structure of the body.
Group of neurons are called nuclei.	Group of neurons are called ganglia.

(b) Difference between Resting potential and Action potential.

Resting Potential	Action Potential
It is the potential difference across the membrane when the neuron is at the resting phase.	It is the potential difference across the membrane when the neuron is triggered.
The Interior side is negatively charged and the exterior side is positively charged.	The Interior side is positively charged and the exterior side is negatively charged.
Permeability of potassium ions (K⁺) to be more by the plasma membrane of neurons.	Permeability of potassium ions (Na⁺) to be more by the plasma membrane of neurons.
To maintain the resting position, the sodium-potassium ATPase pump is activated, sending Na⁺ ions outside the neurons.	To maintain the resting position, the sodium-potassium ATPase pump is activated, sending Na⁺ ions into the neurons.

Choroid	Retina
It is the middle layer of the eye.	It is the inner layer of the eye.
Does not contain photosensitive cells.	Contains photosensitive cells.
A vascular layer.	A layer containing neurons.
No image is formed on choroids.	An inverted image is formed on the retina.

3. Explain the following processes:

(a) Polarisation of the membrane of a nerve fibre.

(b) Depolarisation of the membrane of a nerve fibre.

(c) Conduction of a nerve impulse along a nerve fibre.

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

Ans. (a) Polarisation of the membrane of a nerve fibre:

When the nerve fibre is at the resting state it is called the polarized state of the nerve. At this stage the membrane of the nerve fibre experiences resting potential. Following are the steps that take place during the process of polarisation of the membrane of a nerve fibre.

When a depolarized region of a nerve fibre starts becoming polarized initially, there are more K⁺ ions outside the nerve fibre and the axon membrane contains a large amount of Na⁺ ions.
As
the region of the membrane starts attending the polarized state, the axon membrane is about 20 times more permeable to the K⁺ ion than to Na⁺ ion.
3
Na⁺ ions are sent outside the axon and
2 K⁺ ions are sent into the axon by a sodium-potassium transmembrane pump by an active transport system.
This results in greater total concentration of cations outside the membrane resulting in a negative charge within the axon.
A t this stage, the membrane is said to be polarized and has a resting potential of –70 mV.

(b) Depolarisation of the membrane of a nerve fibre:

When the nerve fibre is stimulated it is called the depolarized state of the nerve. When a stimulus is applied to the nerve a disturbance occurs at the point of stimulation and brings about changes in the potential in that area. Following are the steps that take place during the process of depolarisation of the membrane of a nerve fibre.

The permeability of the membrane changes. It becomes more permeable to Na⁺.
The gates of Na⁺ ion channel open and it results Na⁺ ions diffuse in from ECF and so the number of positive ions inside the axon increase.
The membrane potential becomes progressively less. From – 70mV, it changes to + 60 mV.
The change in potential is called an action potential and the membrane is called to be at depolarized state.

(c) Conduction of a nerve impulse along with a nerve fibre:

A nerve impulse is conducted across the length of a nerve fibre in an organised manner. During the conduction of an impulse, a region on the nerve is always depolarised and another region next to it will be polarised. To send the impulse forward, the depolarised region repolarises and the polarised region depolarises repeatedly and this is repeated across the length of the nerve fibre which helps in the conduction of the impulse.

Neural Control and Coordinationans3(c(ii))

At a depolarised region, consider site A, there will be a positive charge on the inner surface of the membrane and a negative charge on the outer surface of the membrane.
In the region next to it which is polarised, consider site B, there will be a positive charge on the outer surface of the membrane and a negative charge on the inner surface of the membrane.
Because of the different poles, at site A, the current will flow on the inner surface of the membrane from A to B, and at site B, the current will flow on the outer surface from B to A. This will complete the circuit of the current flow.
This will help site B to depolarise so that the impulse is conducted to site B.
As soon as the impulse is conducted to site B, site A will get repolarised.
When site B will be in the depolarised state, the region next to it, consider site C, will be polarised.

(d) Transmission of a nerve impulse along a nerve fibre: Transmission of a nerve impulse across a chemical synapse step is as follows:

Step-1: An action potential arrives at the synaptic knob.

Step-2: It stimulates the opening of voltage-gated Ca++ channels in the presynaptic membrane.

Step-3: Ca++ ions rapidly diffuse into the synaptic knob.

Step-4: It stimulates the movement of synaptic vesicles towards the presynaptic membrane and they fuse with it.

Step-5: As synaptic vesicles fuse with the membrane, they rupture and release the neurotransmitter chemicals by exocytosis.

Step-6: Neurotransmitter molecules quickly pass through synapse and reach the other membrane. Now they bind with the receptor molecules of the post-synaptic membrane.

Step-7: Cause a second electric current or action potential in the target cell.

4. Draw labelled diagrams of the following:

(a) Neuron

(b) Brain

(c) Eye

(d) Ear

(b) BRAIN:

(c) EYE:

(d) EAR:

5. Write short notes on the following:

(a) Neural coordination

(b) Forebrain

(c) Midbrain

(d) Hindbrain

(e) Retina

(f) Ear ossicles

(g) Cochlea

(h) Organ of Corti

(i) Synapse

Ans. (a) Neural coordination: Coordination is the process through which two or more organs interact and complement the functions of one another. In humans and animals, there are two ways to achieve this neural and chemical coordination. Former is carried out by highly specialized cells called neurons and the neural system is a network of point-to-point connections between the neurons and the organs and it operates through nerve impulses. Neural coordination is always between the stimulus and the response—receptors and effectors. All body functions are carried out and controlled by neural coordination. It is a phenomenon through which two or more organs interact and complement functionalities of each other through the neural system of the body. The various physiological processes that take place in the body are interlinked with each other. The stimulus is received from organs such as the skin and a response is generated which is sent to the muscles or glands. The previous stimulus is always stored in memory by the neural system. Neural coordination helps in controlling and harmonizing voluntary actions such as running, walking, writing and talking. It helps us to remember, analyse, think and reason because the brain, a part of the neural system, is the site of intelligence. All vital functions such as breathing, working of the heart and digestion are controlled by neural coordination. It helps maintain homeostasis by coordinating various metabolic activities of the body.

(b) Forebrain: It consists of three regions:

(i) Cerebrum: It is the largest and most complex of all the parts of the human brain.

It consists of two cerebral hemispheres (Right and left) joined together by nerve fibres called the corpus callosum. Each cerebral hemisphere is divided into four lobes namely frontal, parietal, temporal and occipital. The cerebral hemisphere's outer region has highly packed nerve cells called the cerebral cortex which forms grey matter. Beneath the cerebral cortex is the white matter of the cerebrum.

Role: The cerebrum is the centre of memory, intelligence, consciousness, voluntary actions and willpower.

(ii) Thalamus: It is the region present at the centre of the forebrain. All sensory information that reaches the cerebral hemi-spheres first passes through the thalamus.

Role: Its main function is to interpret sensory and motor signals and then channel them to the appropriate cerebral cortex region.

(iii) Hypothalamus: It is present beneath the thalamus and consists of masses of grey matter scattered in the white matter.

Role: It is the control centre for many internal control mechanisms and is associated with thermovascular system, water balance, hunger, drinking etc. It is also a reflex control center. Along with the limbic system, the hypothalamus also plays a part in regulating sexual behaviour.

(c) Midbrain: It is located between thalamus/hypothalamus of forebrain and pons of the hind brain. It consists of a group of nerve cells—grey matter is scattered in the white matter.

Role: It connects the forebrain and hindbrain. Its four corpora quadrigemina control eye movement and auditory responses. The lower part of the midbrain is associated with muscular reflexes.

(d) Hindbrain: It consists of three parts:

(i) Cerebellum: The second largest part of the human brain is the cerebellum. It consists of two lateral cerebellar hemispheres and a central worm-shaped part, the vermis. It has grey matter on the surface called the cerebellar cortex and white matter in the center called the cerebellar medulla.

Role: It is a reflex centre for the coordination of muscular body movements and maintenance of posture or equilibrium.

(ii) Pons: An oval mass, called the pons Varolii, lies above the medulla oblongata. It consists mainly of nerve fibres which interconnect different regions of the brain.

Role: It sends impulses to the cerebral cortex and cerebellum.

(iii) Medulla oblongata: It extends from the pons Varolii above and is continuous with the spinal cord below. The midbrain, pons Varolii and medulla oblongata are collectively called the brain stem.

Role: It serves as a passage to conduct nerve impulses from the spinal cord to the brain. It controls all the activities of the internal organs, breathing and heartbeat.

(e) Retina: It is the inner layer of an eye which is made up of three layers of cells. The three layers are ganglion cells, bipolar cells and photoreceptor cells. Photoreceptor cells are of two types: rod cells and cone cells. These cells contain light-sensitive photo pigments. Daylight vision and colour vision are functions of cones whereas twilight vision is the function of rod cells. Rods contain rhodopsin pigment which contains a derivative of vitamin A. In the human eye, there are three types of cones found with photo pigments red, green and blue. The sensation of different colours is produced by various combinations of these cones and their photo pigments. When these cones are equally stimulated a white colour light is sensed. There are two spots found in the retina called blind spots and yellow spots. Blind spot is the point where the optic nerve leaves the brain and the retinal vessels enter the brain and photoreceptor cells are absent. Yellow spot also known as macula lutea is the spot which has yellowish pigmented and lies exactly opposite the centre of the cornea. Its central pit is called the fovea. Fovea has only one cone cell and it’s the region of most distinct vision.

(f) Ear ossicles: In the tympanic cavity of the middle ear, three bones are present—they are malleus, incus and stapes. Handle of the malleus is attached to the central part of the tympanic membrane which is called umbo. Other end of the malleus is attached to the incus by ligaments. The incus on its other end is attached to the stapes by ligaments. Another end of the stapes covers an opening called fenestra ovalis or oval window of the cochlea. Ear ossicles transfer the vibration from the external ear to the inner ear.

(g) Cochlea: The cochlea is a bony coiled structure of the inner ear. It arises from the saccule. The cochlear cavity is divided into three chambers by the two membranes—Reisnner's membrane and Basilar membrane. The upper chamber is called the scala vestibule, the middle chamber is scala media and the lower chamber is scala tympani. Scala tympani and scala vestibule are filled with the perilymph, while scala media is filled with the endolymph. The basilar membrane bears the organ of Corti. The organ of Corti is connected with the nerve fibres of the auditory nerve which connects to the brain. The organ of Corti is the organ of hearing.

(h) Organ of Corti: It is the organ of hearing which is located on the basilar membrane of the inner ear. It contains hair cells which are auditory receptor cells. These cells are present in rows on the internal side of the organ. The apical ends of the hair cells have processes called stereo cilia. The basal parts of the hair cells have synaptic contacts with the afferent nerve fibres. Above the rows of hair cells, there is a smooth gelatinous layer called the tectorial membrane.

(i) Synapse: A synapse is a small gap between two neurons, where nerve impulses are relayed by a neurotransmitter from the axon of a presynaptic neuron to the dendrite of a postsynaptic neuron. It is referred to as the synaptic cleft or synaptic gap. During synaptic transmission, the action potential triggers the synaptic vesicles of the pre-synaptic neuron to release neurotransmitters. These neurotransmitters diffuse across the synaptic cleft and bind to specialized receptor sites on the post-synaptic neuron. If the neurotransmitter is excitatory then the post-synaptic neuron is more likely to fire an impulse. If the neurotransmitter is inhibitory then the post-synaptic neuron is less likely to fire an impulse. The excitatory and inhibitory influences are summed to determine whether/how frequently the neuron will fire. At the dendrites, the chemical message is converted back into an electrical impulse and the process of transmission occurs again.

6. Give a brief account of:

(a) Mechanism of synaptic transmission

(b) Mechanism of vision

(c) Mechanism of hearing

Ans. (a) Mechanism of synaptic transmission: During synaptic transmission, the action potential triggers the synaptic vesicles of the pre-synaptic neuron to release neurotransmitters. These neurotransmitters diffuse across the synaptic cleft and bind to specialized receptor sites on the post-synaptic neuron. If the neurotransmitter is excitatory then the post-synaptic neuron is more likely to fire an impulse. If the neurotransmitter is inhibitory then the post-synaptic neuron is less likely to fire an impulse. The excitatory and inhibitory influences are summed to determine whether/how frequently the neuron will fire. At the dendrites, the chemical message is converted back into an electrical impulse and the process of transmission occurs again.

(b) Mechanism of vision: Light rays from the object pass through the cornea and the lens. These are focused on the retina of the eye. The rods and cones contain photo pigments which are mainly conjugate proteins. They are composed of opsin and retinol. The light induces dissociation of retinol from the opsin resulting in changes in the structure of opsin. This causes a change in the permeability of retinal cells. It generates an action potential which is carried via bipolar neurons and ganglion cells and further conducted by the optic nerves to the visual cortex of the brain. The neural impulses are analysed and the image formed on the retinal is recognised.

(c) Mechanism of hearing: The sound waves are received by the external ear pinna. These sound waves then move in the inner ear and vibrate the tympanic membrane (also called ear drum). The eardrum vibrates in response to the sound waves and these vibrations are transmitted through the ear ossicles (malleus, incus and stapes) to the oval window. The vibrations are passed through the oval window onto the fluid of the cochlea, where they generate waves in the lymph. The waves in the lymph induce a ripple in the basilar membrane. These movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane. As a result, nerve impulses are generated in the associated afferent neurons. These impulses are transmitted by the afferent fibres via auditory nerves to the auditory cortex of the brain, where the impulses are analysed and the sound is recognised.

Ans. (a) Retina contains cone cells and this is responsible for colour vision. Cone cells are of three types which respond to red, green and blue light respectively. When light rays are reflected back from the object (colour) the wavelength according to the colour of the object trigger different cone cells. Simultaneous stimulation of more than one kind of cone cell, causes the other colours to be detected. A sensation of white light is observed when all the three types of cone cells are triggered at the same time. This is how colour is perceived by the brain.

(b) The part of the body that helps in maintaining the body balance are:

Crista ampullaris: It is located in the three semicircular canals and senses the angular acceleration and deceleration.
Macula sacculi: It is located in the saccule of the inner ear and senses vertical linear acceleration.
Macular utriculi: It is found in the utricle. This bends hair cells in the direction of gravity. It responds to the gravitational pull.

(c) The iris has two types of muscles, namely the radial smooth muscles and circular smooth muscles that check the amount of light falling on the retina. The pupil diminishes in size when the smooth circular muscles contract in bright light. Therefore, less amount of light falls on the retina. The pupil widens, when the light is dim, due to the contraction of the radial smooth muscles such that enough light is incident on the retina.

7. Answer briefly:

(a) How do you perceive the colour of an object?

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

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

(b) The part of the body that helps in maintaining the body balance are:

Crista ampullaris: It is located in the three semicircular canals and senses the angular acceleration and deceleration.
Macula sacculi: It is located in the saccule of the inner ear and senses vertical linear acceleration.
Macular utriculi: It is found in the utricle. This bends hair cells in the direction of gravity. It responds to the gravitational pull.

8. Explain the following:

(a) Role of Na⁺ in the generation of action potential.

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

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

Ans. (a) Sodium ions play an important role in the generation of an action potential. When a nerve fibre is stimulated, the disturbance caused to the membrane of a nerve fibre by a stimulus results in leakage of Na⁺ into the nerve fibre, the membrane potential decreases. The membrane becomes more permeable to Na⁺ ions than to K⁺ ions. As a result, Na⁺ diffuses from the outside to the inside of the membrane. This causes the inside of the membrane to become positively charged, while the outer membrane gains a negative charge. This reversal of polarity across the membrane is known as depolarisation. The rapid inflow of Na⁺ ions causes the membrane potential to increase, thereby generating an action potential.

(b) Eye contains photosensitive compounds which are composed of opsin and retinal. Light induces dissociation of retinal and opsin which changes the structure of opsin. This results in the generation of an action potential in the bipolar neurons. These action potentials are transmitted by the optic nerves to the visual cortex of the brain where the neural impulses are analysed and the erect image is recognised.

(c) The sound waves are received by the external ear pinna. These sound waves then move in the inner ear and vibrate the tympanic membrane (also called eardrum). The eardrum vibrates in response to the sound waves and these vibrations are transmitted through the ear ossicles (malleus, incus and stapes) to the oval window. The vibrations are passed through the oval window onto the fluid of the cochlea, where they generate waves in the lymph. The waves in the lymph induce a ripple in the basilar membrane. These movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane. As a result, nerve impulses are generated in the associated afferent neurons.

9. Differentiate between:

(a) Myelinated and non-myelinated axons

(b) Dendrites and axons

(c) Rods and cones

(d) Thalamus and Hypothalamus

(e) Cerebrum and Cerebellum

Ans. (a) Difference between Myelinated and Non-myelinated axons:

Myelinated Axons	Non-myelinated Axons
Myelin sheath is present.	Myelin sheath is absent.
Nodes of Ranvier observed.	Nodes of Ranvier not present.
Conduction of nerve impulse is through node to node point.	Conduction of nerve impulse is smooth.
Ion exchange can occur only at the nodes.	Ion exchange can occur all over the surface.
Mainly found in grey matter in brain, autonomous nervous system and spinal cord.	Mainly found in white matter in brain, autonomous nervous system and spinal cord.
Speed of impulse conduction is 50 times higher than non-myelinated axon.	Speed of impulse conduction is slower.

(b) Difference between Dendrites and Axons:

Dendrites	Axons
Usually more than one found per neuron.	Only one found per neuron.
They are short processes.	They are long processes.
It carries impulses towards the cell body of the neuron.	It carries impulses away from the cell body of the neuron.
Always branched.	May or may not make branch.
Nissl’s granules are present in neuroplasm.	Nissl's granules are absent in the neuroplasm.
No knobs at the tip of the branch.	Terminal branches enlarge to form knob.

Rods	Cones
Number of rod cells present in eye is more.	Number of cone cells present in eye is less.
Insufficient Rhodopsin results night— blindness.	Insufficient iodopsin results colour—blindness.
Rod cells are alike.	Cone cells are three types: Blue, green and red.
Very sensitive to lower intensive lights.	Very sensitive to bright lights.
Rods are mainly for night vision.	Cones are mainly for colour vision.

(d) Difference between Thalamus and Hypothalamus:

Rods	Cones
Thalamus	Hypothalamus
It is present below the cerebrum.	It is present below the thalamus.
It does not secrete any hormone.	It secretes several hormones.
It is the major coordination center for sensory and motor signaling.	It regulates thermo vascular system, thirst, hunger and such other feelings.

(e) Difference between Cerebrum and Cerebellum:

Cerebrum	Cerebellum
It is a part of forebrain.	It is a part of hind brain.
It is largest part of the brain.	It is smaller than cerebrum.
It consists of two cerebral hemispheres, each comprising 4 lobes: frontal, occipital, parietal and temporal.	It consists of two cerebellar hemispheres and a median vermis.
It’s associated with the memory, intelligence, sensation like pain, touch etc., and voluntary and involuntary activities of muscles.	Associated with involuntary muscles movement and maintenance of equilibrium.

10. Answer the following:

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

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

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

Ans. (a) Pitch of a sound is determined by the receptor cells in the organ of Corti in internal ear.

(b) Forebrain is the part of brain which is most developed.

11. The region of the vertebrate eye, where the optic nerve passes out of the retina, is called the:

(a) fovea

(b) iris

(c) blind spot

(d) optic chaisma.

Ans. (d) Blind spot

12. Distinguish between:

(a) Afferent neurons and efferent neurons

(b) Impulse conduction in a myelinated nerve fibre and non myelinated nerve fibre

(c) Aqueous humor and vitreous humor

(d) Blind spot and yellow spot

(e) Cranial nerves and spinal nerves.

Ans. (a) Difference between Afferent neurons and Efferent neurons:

Afferent neurons	Efferent neurons
These are sensory neurons.	These are motor neurons.
Conduction of sensory impulses from the receptors towards the central nervous system.	Conduction of motor impulses from the central nervous system to the responsive or effector organs.
hese are located in sense organs.	These are located in brain and spinal cord.

(b) Difference between Impulse conduction in a myelinated nerve fibre and non-myelinated nerve fibre:

Impulse conduction in a myelinated nerve fibre	Impulse conduction in a non-myelinated nerve fibre
Impulse travels from node to node.	Impulse travels along the length of the entire nerve fibre.
Its speed of conduction is about 50 times faster than non-myelinated nerve fibre.	The speed of conduction is slower.
Energy required to send impulse is less.	Energy expenditure to send impulse is more.

Aqueous Humor	Vitreous Humor
It is a clear, watery, salt solution that fills up the anterior compartment of the eye.	It is clear, transparent, jelly like substance that fills up the posterior compartment of the eye.
It is located between cornea and the lens.	It is located between lens and retina.
Its secreted by ciliary processes.	It is apparently secreted by retina during development of eye.
It is continuously absorbed into blood and replaced.	It is not absorbed or replaced.
It supplies nutrition to lens and cornea.	It helps in maintaining the shape of the eyeball and supports both lens and retina.

(d) Difference between Blind spot and Yellow spot:

Blind Spot	Yellow Spot
It is the region at the back of the eye where optic nerve leaves.	It is the region at the back of eye where light rays get focused in the normal eye.
It contains no pigment.	It contains yellow pigment.
Rods and cones both are absent.	Has high concentration of cones but rods are absent.
The eye coats are absent at blind spot.	Eye coats are present at yellow spot.
It lacks a depression.	It has a shallow depression which is known as fovea centralis.
No image is formed.	Greatest visual acuity is observed.
Rods and cones both are absent.	Has high concentration of cones but rods are absent.

(e) Difference between Cranial nerves and Spinal nerves:

Cranial Nerves	Spinal Nerves
These arise from different parts of the brain.	These arise from each segment of spinal cord.
Total number is 12 pairs.	Total number is 31 pairs.
It is either sensory or motor or mixed type nerve.	Each nerve is mixed nerve and carries both the sensory and the motor nerve fibres.
These are numbered in roman number.	These are classified in five groups: cervical (16), thoracic (24), lumbar (10), sacral (10) and coccygeal (2).