Nervous System Class 8 Biology Selina Concise ICSE Solutions for Chapter 7

Selina Concise ICSE Solutions for Class 8 Biology Chapter 7 Nervous System

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) Medulla oblongata controls

1. Smelling
2. Beating of heart and respiratory movement
3. Intelligence and will power
4. Balancing the body

(b) Balance of body is controlled by:

1. Spinal cord
2. Cerebellum
3. Cerebrum
4. Medulla

(c) The smell of good food causes watering of your mouth. It is a

1. Natural reflex
2. Acquired relfex
3. Inborn reflex
4. Ordinary reflex

(d) The structural and functional unit of nervous system is a

1. Axon
2. Nephron
3. Neuron
4. Texon

Short Answer Questions:

Question 1.
Name the two types of coordination which take place in our body.
Answer:
(a) Nervous coordination: By nerves and brain
(b) Chemical coordination: By hormones

Question 2.
You are driving your bicycle at a fast speed. Suddenly, a small boy comes in front of your cycle and, without wasting any time in thinking, you immediately apply the brakes, and accident is avoided. What name is given to such an action?
Answer:
Reflex action (acquired).

Question 3.
Given below is the diagram of a neuron. Name the parts numbered 1-5.

Answer:

1. Dendrite
2. Nucleus
3. Cell Body (Nyton)
4. Axon (Nerve fibre)
5. Node of Ranvier

Question 4.
Write one word in the space provided to complete the second pair of the related words pertaining to the nervous system.
Memory : cerebrum : : breathing :
Balance : cerebellum : : reasoning :
Answer:
Memory : cerebrum : : breathing: medulla oblongata
Balance : cerebellum : : reasoning : cerebrum

Question 5.
Differentiate between the following pair of terms:
(a) Stimulus and impulse
(b) Receptor and effector
(c) Motor nerve and sensory nerve
Answer:
(a) Stimulus: Any change in the environment that usually results in a change in the activity of the body.
Impulse: A wave of electrical disturbance that runs through the nerves.

(b) Receptor: The nerve cell on receiving the stimulus sets up the waves of impulses towards the central nervous system.
Effector: Any muscle or gland receiving the impulse from the brain (or the spinal cord), contracts or secretes.

(c) Motor nerve: It contains only motor neurons,
Example: Nerves going to the muscles of the eyeball.
Sensory nerve: It contains only sensory neurons.
Example: optic nerve of the eye.

Question 6.
(a) Name the three major divisions of the human nervous system.
(b) Name the three main parts of the human brain.
Answer:
(a)

1. The central nervous system (brain and spinal cord)
2. The peripheral nervous system
3. The autonomic nervous system

(b)

1. Cerebrum
2. Cerebellum
3. Medulla oblongata

Question 7.
Give the function of each of the following:
(a) Olfactory nerve:
(b) Optic nerve:
(c) Facial nerve:
Answer:
(a) Olfactory nerve: The sense of smell is present in the epithelial layers of the nasal chambers. The sense of smell is carried to the brain by the olfactory nerve. They arise from the anterior ends of the olfactory lobes and are distributed to lining of nasal chambers.
(b) Optic nerve: It carries the reflection of the object from the retina to the brain. The image formed on the retina is in a reverted position and the correct picture is formed in the brain as the object is. The optic nerves arise from the side of diencephalon. They innervate the retina of the eye and are sensory in nature.
(c) Facial nerve: It carries message and all expressions of the face, mastication work alone by the teeth, movement of the neck and the activities of the salivary glands to the brain. It arises from the side of medulla. On the whole facial nerves are mixed in nature.

Long answer questions

Question 1.
With the help of a suitable diagram describe the structures of a neuron.
Answer:
Nervous system consists of special cells called nerve cells or neurons. It has a main cell body called cyton. It gives out many processes called dendrites. From it a very long process is given out. It is called axon or nerve fibre.

The cell body has a nucleus. The dendrites get the message from the organs and send this message to the axon through the cell body. Then the axon sends the message to muscles to contrast or to the gland for secretion.
The neurons make contact with one another through their processes. The axon at its end branches and meets the dendrites of another neuron. The meeting point is called synapse. The message is passed on from one axon to the dendrites of another neuron. How the message goes ? It is like this:
Organ → Message goes to dnedrites → Cell body → Axon → Muscles or glands

Question 2.
Briefly describe the structure of the cerebrum in human brain and mention its functions.
Answer:
Brain consists of main three parts and lies in the cranial cavity of skull.

1. The cerebrum
2. The cerebellum
3. The medulla oblongata

Cerebrum: It is very large and form two-third of the whole brain. The two hemispheres are separated from each other by a deep longitudinal groove, the median fissure. The outer surface is folded with ridges and grooves. The hemispheres are hollow from inside and their walls have outer and inner portions. The outer portion has cell bodies of the neurons and it is called grey matter.
The wavery edges of the folded layer has large number of neurons to the extent of nine billion. The inner portion of the cerebrum has axons and it is called white matter.

Functions:

1. It controls all voluntary activities.
2. It is the seat of intelligence, consciousness, and willpower.

Question 3.
Mention the three functions of the spinal cord.
Answer:
Spinal cord has the following functions.

1. It is the centre of reflex actions below the neck.
2. It carries messages from the skin and muscles to the brain.
3. All the stimuli and responses are passed from and to the brain through the spinal cord.

Question 4.
With the help of suitable example, describe reflex action.
Answer:
Reflex action: Reflex actions are automatic responses to stimuli. These actions are not under the control of the animal. They are of definite and mechanical type. Peripheral nervous system and spinal cord both control certain action and the brain is not in action.
Some examples of reflex actions are:

1. Pupil becomes narrow when strong light falls on it.
2. The aroma of the food makes the mouth watering.
3. The hand is withdrawn as we touch the hot plate.
4. Flow of bile from the gall bladder into the duodenum.
5. A loud thud may lead to opening of the mouth.

In a reflex action brain is not involved, removing the hand on touching a hot plate is a reflex action. The impulse of heat goes from the hand to the spinal cord and the order is sent back to the muscles of the hand to remove the hand from the hot plate.

Question 5.
Describe three kinds of nerves, giving the example of each.
Answer:
A nerve is formed by a group of nerve fibres (axons) encased by tubular medullary sheath. The medullary sheath acts as insulation and do not allow mixing up of impulses of the neighbouring axons (nerve fibres) We have three kinds of nerves:

1. Sensory nerve: It brings impulses from sense organs as these have sensory fibres. These nerve carry the impulses from the sense organs to the brain or to the spinal cord as optic nerve of the eye.
2. Motor nerves: These carry impulses to muscles or glands from the brain or spinal cord. These nerves have only motor fibres as nerves to the muscles of the eyeball.
3. Mixed nerve: It has both sensory and motors fibres as nerve going to the tongue.

Question 6.
Differentiate between natural reflex and conditioned reflex. Give examples to illustrate your answer.
Answer:
Natural reflex: It is one in which no previous experience or learning is required. These reflexes are inborn i.e. inherited from the parents.
Examples are

1. Blinking, coughing, sneezing these are protective reflexes
2. Salivation, swallowing, peristalsis provide functional efficiency.
3. Dilation of the eyes pupil to look in the dark and vice versa. It is muscular movement.
4. Pushing along of swallowed food through the food canal. It is muscular movement.

Conditioned Reflex: It is one which develops during a lifetime due to experience or learning.
Examples are:

1. Watering of mouth (Salvination) at the sight of a tasty food.
2. Surfing the channels while watching the television.
3. Typing of a keyboard of a computer.
4. Playing a musical instrument.