RBSE Class 11 Biology Important Questions Chapter 21 Neural Control and Coordination

Rajasthan Board RBSE Class 11 Biology Important Questions Chapter 21 Neural Control and Coordination Important Questions and Answers.

RBSE Class 11 Biology Chapter 21 Important Questions Neural Control and Coordination

Multiple Choice Questions

Question 1.    
In the nervous system, nerve cells are called:
(a) axon    
(b) dendrite
(c) synapse    
(d) neuron
Answer:
(d) neuron

Question 2.    
The broad classification of human neural system is:
(a) Brain and spinal cord
(b) CNS and Braixl 
(c) CNS and PNS
(d) Nerves and Synapse
Answer:
(c) CNS and PNS

Question 3.    
Dendrites are the portion of:
(a) cyton    
(b) axon
(c) synapse    
(d) schwann cell
Answer:
(a) cyton

Question 4.    
Nissl’s granules are the part of:
(a) axon    
(b) cyton
(c) synapse    
(d) schwann cell
Answer:
(b) cyton

Question 5.    
Neurotransmitters are produced at:
(a) neurolemma    
(b) neuron
(c) synapse    
(d) None of these
Answer:
(c) synapse

Question 6.    
A neuron with a cyton and axon is categorised into:
(a) nerve cell    
(b) unipolar neuron
(c) axon    
(d) bipolar neuron
Answer:
(b) unipolar neuron

Question 7.    
Schwann cells are the characteristic of:
(a) neuron
(b) non - myelinated axon
(c) myelinated axon
(d) All types of axon
Answer:
(c) myelinated axon

Question 8.    
The stage at which neuron is not conducting an impulse is:
(a) action potential    
(b) resting potential
(c) neurolemma    
(d) propagation
Answer:
(b) resting potential

Question 9.
img 1
What does this figure depict?
(a) Action potential    
(b) Resting potential
(c) Neurolemma    
(d) Propagation
Answer:
(b) Resting potential

Question 10.    
When a stimulus is given then there is generation of:
(a) resting potential    
(b) propagation
(c) action potential    
(d) repolarisation
Answer:
(c) action potential

Question 11.    
Conduction/propagation of impulse from neuron - 1 to neuron - 2 and so on is because of:
(a) electrical charger
(b) chemical secretion at synapse 
(c) Both electrical and chemical secretion
(d) In some it is electrical in others it is chemical secretion
Answer:
(d) In some it is electrical in others it is chemical secretion

Question 12.    
Synaptic cleft is the part of:
(a) brain    
(b) spinal cord
(c) synapse    
(d) neuron
Answer:
(c) synapse

Question 12. 
The space found between the cerebrum and brain is called:
(a) ventricle    
(b) second ventricle
(c) third ventricle    
(d) pineal gland
Answer:
(c) third ventricle

Question 13.    
Bowman glands are present in the:
(a) olfactory region    
(b) auditory region
(c) gustatoreceptors    
(d) photoreceptors
Answer:
(a) olfactory region

Question 14.    
‘MIS’ denotes the names of smallest bones in Our body. It is:
(a) Malleus    
(b) Incus
(c) Stapes
(d) Malleus, Incus and Stapes
Answer:
(d) Malleus, Incus and Stapes

Question 15.    
Cochlea is the coiled portion a part of:
(a) bony labyrinth
(b) membranous labyrinth
(c) ear
(d) external ear
Answer:
(b) membranous labyrinth

Question 16.    
Tympanic membrane is also called:
(a) sebum    
(b) drum
(c) cochlea    
(d) ear drum
Answer:
(d) ear drum

Question 17.    
Gustatoreceptors are the:
(a) taste buds    
(b) small receptors
(c) glands    
(d) light receptors
Answer:
(a) taste buds

Question 18.    
Iris is:
(a) pigmented
(b) differential pigmented in different people
(c) having an aperture
(d) All of these
Answer:
(d) All of these

Question 19.    
The pigment that breaks in present of light in eye is:
(a) Retina    
(b) Opsin
(c) Rhodopsin    
(d) Iodopsin
Answer:
(c) Rhodopsin

Question 20.    
Organ of corti is the part of:
(a) external ear    
(b) middle ear
(c) internal ear    
(d) nose
Answer:
(c) internal ear

Very Short Answer Type Questions

Question 1. 
What is ganglion?
Answer:
It is the group of nerve cells found in invertebrates. 

Question 2. 
Categorised the types of synapses.
Answer:
There are two types of synapses:

• Electrical synapse.
• Chemical synapse.

Question 3. 
Define neurotransmitters.
Answer:
The chemicals released at the synaptic cleft of synapsis by a neuron during the propagation of impulse are called neurotransmitters.
 
Question 4.
Where are meninges located? What is their function?
Answer:
Meninges are located as the protective covering of CNS. Their function is to protect the CNS.

Question 5. 
Give the suitable reason for the appearance of certain portion of CNS white and grey.
Answer:
Certain portion of CNS appears white because of presence of Myelinated nerves that have fat layer and appearence of some gives grey colour.

Question 6. 
Mention any two function of cerebrum.
Answer:

• Sensory function: Control of creative ideas.
• Motor function: Control of voluntary actions.

Question 7. 
Mention the role of efferent neuron.
Answer:
The efferent neuron takes the signal/message/ action to be taken information from CNS to the effector organ.

Question 8. 
Where are the following located?
(a) Iris 
(b) Pupil 
(c) Iodopsin 
(d) Tympanic membrane
Answer:
(a) Iris: In eye
(b) Pupil: In the eye.
(c) Cone cells
(d) Internal ear.

Question 9. 
Mention the location of macula lutea.
Answer:
It is a yellow coloured spot located slightly above the blind spot in the retina of eye.

Question 10. 
Mention the name and shapes of ear ossicles. 
Answer:
M - Malleus: Hammer shaped.
I - Incus: Anvil shaped.
S - Stapes: Stirrup shaped.

Question 11. 
Mention the role of schwann cell.
Answer:
It produces myelin sheath on the axon fibre.

Question 12. 
Mention the charges and the ions present on neurolemma during action potential.
Answer:
On the outerside of neurolemma: + charge, Na⁺
On the innerside or neurolemma: - charge, K⁺.

Question 13. 
Where is the fourth ventricle present in the body?
Answer:
Fourth verticle is present in medulla oblongata. 

Question 14. 
Name the components/parts of brain stem. 
Answer:

• Mid brain 
• Pons and 
• Medulla oblongata. 

Question 15. 
Which cranial nerves are responsible for sensing taste.
Answer:
VIIth and IXth cranial nerves.

Short Answer Type Questions

Question 1. 
What is the function of neural system?
Answer:
The function of the neural system is to:

1. Input of the information: The neural system collects the information from outside the body, (i.e., from environment) and sends into the CNS.
2. Processing and controlling the actions.
3. Out put sending the message to the concerned organs for the desired actions.

Question 2. 
Classify the human neural system.
Answer:
The human neural (nervous) system originates from the ectoderm. The human neural system can be divided into:
img 2
Two main parts of human neural/nervous system are:

• Central Nervous System (CNS).
• Peripheral Nervous System (PNS).

1. Central Nervous System (CNS) indicates the (i) brain which is located in skull/cranium and protected by meninges (membranes) and cerebro spinal fluid to avoid jerks and shocks. Spinal cord is the extension of brain into the vertebral column. Both are the sites of information processing and control. The Peripheral Nervous System (PNS) is made up of all the nerves of the body and are associated with the CNS. The PNS has two types of nerve fibres.
(a) Afferent Fibres: Those nerve fibres that transmit impulses from body tissues/organs to CNS are called afferent fibres.
img 3
(b) Efferent Fibres: Those nerve fibres that transmit regulatory impulses from CNS to concerned peripheral tissues/organs are called efferent fibres.
img 4

2. Peripheral Nervous System (PNS) is divided into (a) somatic nervous system and (b) autonomic nervous system.
(a) Somatic Nervous System sends impulses from the CNS to skeleted muscles (voluntary) of the body.
(b) Autonomic neural system sends impulses from the CNS to involuntary muscles and organs of the body.
It is further classified into: (i) Sympathetic nervous system, (ii) Parasymphathetic nervous system. Visceral nervous system is the part of peripheral nervous system that comprises of: Whole complex nerves, fibres, ganglia and plexuses. By which the impulses travels from
CNS → Visceral → PNS

Question 3. 
Draw the neuron system of earthworm.
Answer:
img 5

Question 4. 
Give the diagrammatic representation of propagation of action potential in an axon.
Answer:
img 6

Question 5. 
Repeat fig 21.5. Label the diagram.
Answer:
Axon, Axon terminal, synaptic vesicle, presynaptic membrane, synaptic cleft, post synaptic membrane, receptors.
img 7

Question 6. 
Mention the functions of hypothalamus.
Answer:
Functions of hypothalamus:

1. Because it is connected to pituitary endocrine gland the neural system is connected to endocrine system.
2. The neurosecrectory cells release releasing and inhibitory hormones that regulates/controls the secretion of pitutiary glands.
3. The neurosecretory cells produce/synthesis ADH and oxytocin which is circulated in pituitary gland by blood.
4. It has autonomic nervous system (ANS) that have centre for control hunger, thirst, affection, hate, sleep, happiness, satisfaction, emotions, anger and sexual intercourse.
5. It controls the body temperature (thermo regulation). 
6. It maintains homeostasis. It along with limbic lobe it is involved in sexual behaviour, expression of emotional reactions and motivation.

Question 7. 
Briefly mention about pons varolli.
Answer:
Pons varolli: It is small but most important portion that consists of fibre tracts that interconnects the different regions of the brain. It is located below the cerebellum peduncles and above the medulla oblongata. It interconnects the posterior/distal cerebral colliculi and other portion of the brain with each other. It is made up of white matter.
Functions of Pons:

1. It is the path between the brain and medulla oblongata.
2. It acts an intermediator for chewing, saliva secretion, speed of eyes and tear secretion.
3. It has the respiratory centre.

Question 8. 
Draw the labelled diagram of section of spinal cord and label its parts.
Answer:
img 8

Question 9. 
Mention the steps/path taken for the relfex or knee jerk.
Answer:
Knee Jerk:

1. A stimulus is given to the leg just below the knee cap with a hammer on a rubber pad.
2. The stimulus travels/received by afferent nerve moves from the muscle spindle (receptor - sensory) to spinal cord (CNS) through dorsal root ganglion.
3. The stimulus is further sent to spinal cord.
4. The motor neuron receives the action to be taken message from CNS (spinal cord) and gives it to efferent nerve.
5. The efferent nerve takes it and leaves the spinal cord to give it to effector the motor end plate present on muscle fibre.
6. Effector on receiving the message - contracts rapidly resulting.
7. In shift movement upwards called jerk.

This all happens without any conscious effort/thought and in the fraction of second.

Question 10. 
Give the classification of sense organs or receptors.
Answer:
Our body has sensory organs. These organs collect the all types of changes that takes place in environment and sense appropriate signals to the CNS. Where all these are processed and analysed.
img 9
The processed and analysis takes place by CNS and then the signals are sent to different parts of the brain. Then our body can sense these changes in the environment. Sense Organs: Those organs or the body parts that are capable to receive the changes (stimuli) in the environment and effect the changes in body are called sense organs. They are also called receptors.
img 10
We will study in detail about eye and ear in this chapter.

Question 11. 
Classify the peripheral nervous system.
Answer:
Peripheral Nervous System (PNS) is divided into (a) somatic nervous system and (b) autonomic nervous system.
(a) Somatic Nervous System sends impulses from the CNS to skeleted muscles (voluntary) of the body.
(b) Autonomic neural system sends impulses from the CNS to involuntary muscles and organs of the body.
It is further classified into: (i) Sympathetic nervous system, (ii) Parasymphathetic nervous system. Visceral nervous system is the part of peripheral nervous system that comprises of: Whole complex nerves, fibres, ganglia and plexuses. By which the impulses travels from
CNS → Visceral → PNS

Question 12. 
Classify the neurons on the basis of its functions.
Answer:
Neurons are excitable cells because their membranes (neurolemma) are in a polarised state. It is because of the different types of the ion channels that are present on the neural membrane (neurilemma). These ion channels are selectively permeable to different ions e.g., Na⁺ , K⁺ and proteins.
1. When the neuron is not conducting any impulse it is in resting state: It is known as resting potential.

1. During this shape the axonal membrane is comparatively more permeable to potassium ions (K⁺) and it is nearly impermeable to sodium ion (Na⁺ ). Similarly, it is also impermeable to negatively charged protein (-) present in the axoplasm of the axon.
2. And consequently or as a result of it, the axoplasm of axon has high concentration of K⁺ and negatively charged proteins and low concentration of Na⁺.
3. In contrast to it there is high concentration of Na⁺ and low concentration of K⁺ in the fluid outside the axon.

Thus, it forms a concentration gradient. These ionic gradients across the resting membrane are maintained by the active transport of ions by the Na - K pump (sodium potassium pump). It transports 3Na⁺ outwards for 2K⁺ into the cell.
img 11
As a result of it the outer surface of the axonal membrane becomes (+) charged and therefore the membrane is polarised. This electrical potential difference that occurs across the resting plasma membrane is called as resting potential.

2. When a stimulus is applied/given to neuron at a point then action potential is created. The generation of nerve impulse and its propagation/condition along an axon is due to conversion of resting potential to action potential.
(i) When the stimulus is applied at a site - A on the polarised membrane then the side - A becomes freely permeable to Na+ ions.
(ii) This lead to rapid influx of Na+ inside the axon and reversal of polarity takes place at site - A. i.e., the outer surface of membrane becomes (+) and inner surface becomes ( - ). This is depolarisation. This difference across the plasma membrane at site - A is called action potential. This is actually the nerve impulses generated.

(iii) Now the impulses (action potential) generated at site - A propagates towards site B. Where the membrane is (+) charged outside and ( - ) charged inside. On the outer surface current flows from site B to site A to complete, the circuit of current flow. The polarity is reversed at the site. At point site B the action potential is generated. Resulting in the shift of action potential from site A to site B. This takes place repeatedly along the axon and then the impulse is propagated.

(iv) The time for rise in the structures induced permeability to K⁺ is very short. It is quickly followed by a rise in the permeability to K⁺ into the neurilemma. The time taken is fraction of a second K⁺ diffusion outside the membrane. Due to this the resting potential of the membrane at the site of excitation is restored. The fibre again
becomes more responsive to further stimulation.
img 12

 
Question 13. 
Mention about the different folds/lobes of cerebral cortex.
Answer:
According to the cerebral lobes:

1. Frontal lobe controls creative ideas.
2. Temporal lobe receives hearing sensation.
3. Parietal lobe senses - feelings, touch, hot, cold, pain, prick, knowledge, intellegence etc.
4. Occipital lobe senses - vision.

Question 14. 
Draw the diagram of mucus of olfactory region label it.
Answer:
img 13

Long Answer Type Questions

Question 1. 
Draw a labelled diagram of a multipolar neuron. Write in brief about each labelled pair (At least 5).
Answer:
Neurons are excitable cells because their membranes (neurolemma) are in a polarised state. It is because of the different types of the ion channels that are present on the neural membrane (neurilemma). These ion channels are selectively permeable to different ions e.g., Na⁺ , K⁺ and proteins.
1. When the neuron is not conducting any impulse it is in resting state: It is known as resting potential.

1. During this shape the axonal membrane is comparatively more permeable to potassium ions (K⁺) and it is nearly impermeable to sodium ion (Na⁺ ). Similarly, it is also impermeable to negatively charged protein (-) present in the axoplasm of the axon.
2. And consequently or as a result of it, the axoplasm of axon has high concentration of K⁺ and negatively charged proteins and low concentration of Na⁺.
3. In contrast to it there is high concentration of Na⁺ and low concentration of K⁺ in the fluid outside the axon.

Thus, it forms a concentration gradient. These ionic gradients across the resting membrane are maintained by the active transport of ions by the Na - K pump (sodium potassium pump). It transports 3Na⁺ outwards for 2K⁺ into the cell.
img 11
As a result of it the outer surface of the axonal membrane becomes (+) charged and therefore the membrane is polarised. This electrical potential difference that occurs across the resting plasma membrane is called as resting potential.

2. When a stimulus is applied/given to neuron at a point then action potential is created. The generation of nerve impulse and its propagation/condition along an axon is due to conversion of resting potential to action potential.
(i) When the stimulus is applied at a site - A on the polarised membrane then the side - A becomes freely permeable to Na⁺ ions.

(ii) This lead to rapid influx of Na⁺ inside the axon and reversal of polarity takes place at site - A. i.e., the outer surface of membrane becomes (+) and inner surface becomes ( - ). This is depolarisation. This difference across the plasma membrane at site - A is called action potential. This is actually the nerve impulses generated.

(iii) Now the impulses (action potential) generated at site - A propagates towards site B. Where the membrane is (+) charged outside and ( - ) charged inside. On the outer surface current flows from site B to site A to complete, the circuit of current flow. The polarity is reversed at the site. At point site B the action potential is generated. Resulting in the shift of action potential from site A to site B. This takes place repeatedly along the axon and then the impulse is propagated.

(iv) The time for rise in the structures induced permeability to K⁺ is very short. It is quickly followed by a rise in the permeability to K⁺ into the neurilemma. The time taken is fraction of a second K⁺ diffusion outside the membrane. Due to this the resting potential of the membrane at the site of excitation is restored. The fibre again
becomes more responsive to further stimulation.
img 12

Question 2. 
Classify the nerves on the basis of:
(a) Structure 
(b) Function 
(c) Myelin sheaths and write in brief about it. (Only one types).
Answer:
Neurons are excitable cells because their membranes (neurolemma) are in a polarised state. It is because of the different types of the ion channels that are present on the neural membrane (neurilemma). These ion channels are selectively permeable to different ions e.g., Na⁺ , K⁺ and proteins.
1. When the neuron is not conducting any impulse it is in resting state: It is known as resting potential.

1. During this shape the axonal membrane is comparatively more permeable to potassium ions (K⁺) and it is nearly impermeable to sodium ion (Na⁺ ). Similarly, it is also impermeable to negatively charged protein (-) present in the axoplasm of the axon.
2. And consequently or as a result of it, the axoplasm of axon has high concentration of K⁺ and negatively charged proteins and low concentration of Na⁺.
3. In contrast to it there is high concentration of Na⁺ and low concentration of K⁺ in the fluid outside the axon.

Thus, it forms a concentration gradient. These ionic gradients across the resting membrane are maintained by the active transport of ions by the Na - K pump (sodium potassium pump). It transports 3Na⁺ outwards for 2K⁺ into the cell.
img 11
As a result of it the outer surface of the axonal membrane becomes (+) charged and therefore the membrane is polarised. This electrical potential difference that occurs across the resting plasma membrane is called as resting potential.

2. When a stimulus is applied/given to neuron at a point then action potential is created. The generation of nerve impulse and its propagation/condition along an axon is due to conversion of resting potential to action potential.
(i) When the stimulus is applied at a site - A on the polarised membrane then the side - A becomes freely permeable to Na⁺ ions.

(ii) This lead to rapid influx of Na⁺ inside the axon and reversal of polarity takes place at site - A. i.e., the outer surface of membrane becomes (+) and inner surface becomes ( - ). This is depolarisation. This difference across the plasma membrane at site - A is called action potential. This is actually the nerve impulses generated.

(iii) Now the impulses (action potential) generated at site - A propagates towards site B. Where the membrane is (+) charged outside and ( - ) charged inside. On the outer surface current flows from site B to site A to complete, the circuit of current flow. The polarity is reversed at the site. At point site B the action potential is generated. Resulting in the shift of action potential from site A to site B. This takes place repeatedly along the axon and then the impulse is propagated.

(iv) The time for rise in the structures induced permeability to K⁺ is very short. It is quickly followed by a rise in the permeability to K⁺ into the neurilemma. The time taken is fraction of a second K⁺ diffusion outside the membrane. Due to this the resting potential of the membrane at the site of excitation is restored. The fibre again
becomes more responsive to further stimulation.
img 12

Question 3. 
Write in short about each:
(a) Resting potential
(b) Action potential
(c) Types of synapses.
Answer:
(a) When the neuron is not conducting any impulse it is in resting state: It is known as resting potential.

1. During this shape the axonal membrane is comparatively more permeable to potassium ions (K⁺) and it is nearly impermeable to sodium ion (Na⁺ ). Similarly, it is also impermeable to negatively charged protein (-) present in the axoplasm of the axon.
2. And consequently or as a result of it, the axoplasm of axon has high concentration of K⁺ and negatively charged proteins and low concentration of Na⁺.
3. In contrast to it there is high concentration of Na⁺ and low concentration of K⁺ in the fluid outside the axon.

Thus, it forms a concentration gradient. These ionic gradients across the resting membrane are maintained by the active transport of ions by the Na - K pump (sodium potassium pump). It transports 3Na⁺ outwards for 2K⁺ into the cell.
img 11
As a result of it the outer surface of the axonal membrane becomes (+) charged and therefore the membrane is polarised. This electrical potential difference that occurs across the resting plasma membrane is called as resting potential.

(b) When a stimulus is applied/given to neuron at a point then action potential is created. The generation of nerve impulse and its propagation/condition along an axon is due to conversion of resting potential to action potential.

(i) When the stimulus is applied at a site - A on the polarised membrane then the side - A becomes freely permeable to Na⁺ ions.

(ii) This lead to rapid influx of Na⁺ inside the axon and reversal of polarity takes place at site - A. i.e., the outer surface of membrane becomes (+) and inner surface becomes ( - ). This is depolarisation. This difference across the plasma membrane at site - A is called action potential. This is actually the nerve impulses generated.

(iii) Now the impulses (action potential) generated at site - A propagates towards site B. Where the membrane is (+) charged outside and ( - ) charged inside. On the outer surface current flows from site B to site A to complete, the circuit of current flow. The polarity is reversed at the site. At point site B the action potential is generated. Resulting in the shift of action potential from site A to site B. This takes place repeatedly along the axon and then the impulse is propagated.

(iv) The time for rise in the structures induced permeability to K⁺ is very short. It is quickly followed by a rise in the permeability to K⁺ into the neurilemma. The time taken is fraction of a second K⁺ diffusion outside the membrane. Due to this the resting potential of the membrane at the site of excitation is restored. The fibre again becomes more responsive to further stimulation.
img 12

(c) Types of synapses:
1. Electrical Synapse: The synapse that transmits the impulses via the synapse directly from one neuron to another by electrical charges is called electrical synapse. The membranes of pre and post neurons are very close to each other, (i.e., there is no gap). The electric current can flow like axon. It is always faster than the chemical synapse in transmission. This type of synapsis are rare in our body system.

2. Chemical Synapse: The synapse that transmits the impulses via the synapse by release of chemicals (neurotransmitter) at synaptic cleft are called chemical synapses. In such as synapse there is a space called synaptic cleft that is filled with a fluid between the pre and post synaptic neurons. The axon terminals have vesicles filled with these neurotransmitters. When an impulse (action potential) reaches the axon terminal then the synaptic vesicles gets stimulated and moves towards the plasma membrane. It fuses with it and release their neurotransmitters in the synaptic cleft.

On the release of neurotransmitters bind to their specific receptors which are present on the post - synaptic membrane. Due to it the binding opens ion channels allowing the entry of ions. It generates a new potential in the post - synaptic neuron. The new potential developed may be either excitatory or inhibitory in nature.
img 14
Transmission of implse follows the following path: 
Axon → Terminals    Synaptic cleft → Synapse → Dendrite → Next neuron

Question 4. 
Draw a labelled diagram of human brain and show its major portions by labelling it.
For example: Cerebrum, corpus callosum, pons, medulla, thalamus.
Write their one function each also.
Answer:
img 15
The brain appears like the walnut. For the sake of convenience it can be divided into three parts/regions:

1. Forebrain or prosencephalon.
2. Mid brain or mesencephalon
3. Hind brain or rhombencephalon

The fore brain is made up of (A) Cerebrum, (B) thalamus and (C) hypothalams. (It is also divided as : cerebrum and rhinocephalon and diencephalon).
A. Cerebrum: The major portion of the brain is formed of cerebrum. A deep cleft divides it into two longitudinal halves called as left and right cerebral hemispheres. Corpus callosum is a tract of nerve fibres likes in between and connects it. The layer of cells that covers the cerebral hemisphere is called cerebral cortex and it is having prominent folds.
Four folds are:

1. Frontal lobe: It is in the front and larger in size. It is separated from temporal lobe by sylvian cleft/fissure. It controls communication/ articulation or speech.
2. Parietal lobe: It is behind the frontal lobe and separated by fissure kolendo.
3. Temporal lobe: It is under the parietal lobe and towards the front. It is separated by sylvian cleft/ fissure from frontal lobe.
4. Occipital lobe: It is comparatively smaller and it is located at the posterior portion. It is found around the foramen of magnum. It is separated by parieto - occipital cleft/fissure from parietal lobe.

The cerebral cortex is about 2 - 4 cm thick. The cerebral hemisphere has ridges called gyri and furrows called sulci. This increases the surface area of this region/brain.

Grey Matter : The cerebral cortex has collection of cell bodies of nervous and it appears greyish hence, it is called grey matter. This portion has motor areas, sensory areas and large region that are neither sensory or motor in function. These regions are called association areas. They are responsible for complex function like: memory, communication and intersensory association.

White Matter: Inner part of the cerebral hemisphere are formed by fibres of the tracts which are covered with interior sheath. Hence, it appears opaque whitish in colour and is called white matter.

Function of Cerebrum:
(a) Sensory function: These are controlled by the sensory areas located behind central fissure. It sensar/receives sensory stimuli from different parts of the body. Such as heat, touch, pressure, prick, pain etc. According to the cerebral lobes:

• Frontal lobe controls creative ideas.
• Temporal lobe receives hearing sensation.
• Parietal lobe senses - feelings, touch, hot, cold, pain, prick, knowledge, intellegence etc.
• Occipital lobe senses - vision.

(b) Motor functions: It is controlled by the simulator centre located in the front of frontal lobe near to the central cleft. The cells found in this area control all the voluntary actions of voluntary muscles.

(B) Thalamus: It is the structure wrapped by the cerebrum. It is regarded on the major co - ordinating centre for sensory and motor signaling. The third ventricle is the space found between the cerebrum and mid brain. 

The epithalamus forms the roof of third ventricle and in the midline is present a gland called pineal gland. Thalamus forms the upper part of the posterior walls of diencephalon.

Functions are: Relay centre for sensations of vision, touch, temperature, pain, hearing, taste etc. Some portions of it regulate/control functions related to affection/love, hate, emotion, intellegence and knowledge etc.

(C) Hypothalamus: Hypo means below. Hypothalamus is located below/base of the thalamus. It has many centres that control body temperature, urge for eating (food) and drinking water. It also has many groups of neurosecretory cells. These are responsible for secretion of hypothalamic hormones. It has at about a dozen large nuclei. It also has optic chiasma formed of four parts.

Functions of hypothalamus:

1. Because it is connected to pituitary endocrine gland the neural system is connected to endocrine system.
2. The neurosecrectory cells release releasing and inhibitory hormones that regulates/controls the secretion of pitutiary glands.
3. The neurosecretory cells produce/synthesis ADH and oxytocin which is circulated in pituitary gland by blood.
4. It has autonomic nervous system (ANS) that have centre for control hunger, thirst, affection, hate, sleep, happiness, satisfaction, emotions, anger and sexual intercourse.
5. It controls the body temperature (thermo regulation). 
6. It maintains homeostasis. It along with limbic lobe it is involved in sexual behaviour, expression of emotional reactions and motivation.

Limbic lobe/Limbic system: A complex structure is formed by the inner parts of cerbral hemispheres and a group of associated deep structures like amygdala, hippocampus etc. This is called Limbic lobe.

Question 5. 
Write in brief about mid brain.
Answer:
The portion of brain which is located between the thalams/hypothalamus of the forebrain and pons of hind brain is called the mid brain. Its cavity is very narrow like a canal and it is called cerebral aqueduct/ aqueduct of sylvius or iter which passes through it. The mid brain is divisible into:
1. Cerebral peduncles or crura cerebri: These structures are made up of myelinated neurons that appears like a stalk. They connect the cerebrum with the spinal cord. 

2. Corpora quadrigemina: These structures are made up of grey matter forming four lobes globular (round) structures behind aqueduct/at the dorsal portion of the midbrain. Each swelling/lobe is terms as colliculus and collectively called corpora quadrigemina. The upper - superior colliculi are associated with vision and lower - inferior colliculi are with hearing reflex sentres.

Question 6. 
Write about mechanism of vision.
Answer:
Mechanism of Vision/Process of Vision:
Our eye behaves like a camera, when the light rays in the visible wavelength of 380 to 760 nm get focused on the retina through cornea and lens then it generates potentials - impulses in rods and cone cells.
1. The light induces the dissociation of the retinal form opsin and changes the structure of opsin. (The rods and cones have photo sensitive compounds) photopigments composed of retinal- (an aldehyde of vitamin) A and opsin (a protein).

2. This causes permeability changes of the membrane. Resulting in generation of potential differences in the photoreceptor cells.

3. Due to this a signal of action potential (impulses) is generated in ganglion cells through the bipolar cells. Which is transmitted by the optic nerves (axons) to the visual cortex area of the brain. Here, the neural impulses are analysed and the image formation on the retina is recognised based on the earlier memory and experience.
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Question 7. 
How do we hear? Describe in short. Draw the section of cochlea showing different compartments.
Answer:
How do we Hear:

1. The external ear (pinna) receives the sound waves and directs/conducts it to ear drum. This causes vibrations in the ear drum due to sound waves. Vibrations are further conducted/passed to the ear ossicles to oval window.
2. The vibrations are passed through the oval window to the fluid of cochlea. This causes waves in the lymphs and it induces a ripple in the basal membrane.
3. These ripple/movements bend the hair cells of the basilar membrane pressing them against the tectorial membrane.

As a result of it, the nerve impulse is generated in the associated afferent neurons. It is carried/propagated to the auditory cortex of the brain through auditory nerve. In brain the impulses are analysed and the sound is recognised.

Structure of the cochlea:
The cochlea contains the sensory organ of hearing. It bears a striking resemblance to the shell of a snail and in fact takes its name from the Greek word for this object. The cochlea is a spiral tube that is coiled two and one-half turns around a hollow central pillar, the modiolus. It forms a cone approximately 9 mm (0.35 inch) in diameter at its base and 5 mm in height. When stretched out, the spiral tube is approximately 30 mm in length. It is widest - 2 mm - at the point where the basal coil opens into the vestibule, and it tapers until it ends blindly at the apex. The otherwise hollow centre of the modiolus contains the cochlear artery and vein, as well as the twisted trunk of fibres of the cochlear nerve. This nerve, a division of the very short vestibulocochlear nerve, enters the base of the modiolus from the brainstem through an opening in the petrous portion of the temporal bone called the internal meatus. The spiral ganglion cells of the cochlear nerve are found in a bony spiral canal winding around the central core.

A thin bony shelf, the osseous spiral lamina, winds around the modiolus like the thread of a screw. It projects about halfway across the cochlear canal, partly dividing it into two compartments, an upper chamber called the scala vestibuli (vestibular ramp) and a lower chamber called the scala tympani (tympanic ramp). The scala vestibuli and scala tympani, which are filled with perilymph, communicate with each other through an opening at the apex of the cochlea, called the helicotrema, which can be seen if the cochlea is sliced longitudinally down the middle. At its basal end, near the middle ear, the scala vestibuli opens into the vestibule. The basal end of the scala tympani ends blindly just below the round window. Nearby is the opening of the narrow cochlear aqueduct, through which passes the perilymphatic duct. This duct connects the interior of the cochlea with the subdural space in the posterior cranial fossa (the rear portion of the floor of the cranial cavity).
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