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Chapter 7

Nervous System

Class 8 - Concise Biology Selina


Multiple Choice Questions

Question 1

Medulla oblongata controls

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

Answer

Beating of heart and respiratory movement

Reason — Medulla oblongata controls breathing, heart function, blood vessel function, digestion, sneezing, and peristalsis of the alimentary canal, etc.

Question 2

Balance of body is controlled by

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

Answer

Cerebellum

Reason — Body balance and muscular coordination is controlled by the cerebellum of the brain.

Question 3

The smell of good food causes watering of your mouth. It is

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

Answer

Acquired reflex

Reason — Salivation on smelling good food is an acquired reflex that occurs because our brain remembers the taste of the food due to a previous experience.

Question 4

The structural and functional unit of nervous system is

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

Answer

Neuron

Reason — Neurons are the structural and functional unit of the nervous system.

Short Answer Questions

Question 1

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 the accident is avoided. What name is given to such an action ?

Answer

This is a Conditioned or Acquired Reflex action. This reflex is one which is developed during the lifetime due to experience or learning.

Question 2

Name the following :

(a) The long, extended process of a neuron

(b) The point of contact between two neurons

(c) The kind of nerve which carries both sensory and motor neurons

(d) The nerve which connects the eyes to the brain

(e) The nerve which connects the nose to the brain

(f) The nerve which connects the ears to the brain

(g) Two sub-divisions of the peripheral nervous system

(h) Two parts of the autonomic nervous system

Answer

(a) Axon

(b) Synapse

(c) Mixed nerve

(d) The Optic nerve

(e) Olfactory nerve

(f) Auditory nerve

(g) Somatic nervous system and Autonomic nervous system.

(h) Sympathetic and Parasympathetic systems

Question 3

Define the terms :

(a) Coordination

(b) Synapse

(c) Impulse

(d) Reflex action

(e) Reflex arc

Answer

(a) Coordination — The interlinking of various activities and organs of a living being as per the needs of the body internally or externally is called coordination.

(b) Synapse — A synapse is a small junction used for communication between two neurons.

(c) Impulse — A wave of electrical disturbance that runs through the nerves.

(d) Reflex action — Reflex action is the quick, immediate and automatic response to a stimulus without the involvement of the brain.

(e) Reflex arc — The shortest pathway of the nerve impulse from a receptor to the effector which makes a reflex action possible is called a reflex arc.

Long Answer Questions

Question 1

Differentiate between the following pairs of terms on the basis of what is indicated within the brackets :

(a) Stimulus and response (definition)

(b) Receptor and effector (examples)

(c) Motor nerve and sensory nerve (function)

(d) Cranial and spinal nerves (number in pairs)

(e) Cerebrum and medulla oblongata (function)

(f) Cerebrum and spinal cord (arrangement of white and grey matter)

Answer

(a) Difference between Stimulus and Response (definition)

StimulusResponse
Any change in the environment that usually results in change in the activity of the body.The activity of the body due to the stimulus.

(b) Difference between Receptor and Effector (examples)

ReceptorEffector
The nerve cells in the skin that receives the stimulus is the receptor.The muscle of the hand receiving the command from the brain is an effector.

(c) Difference between Motor nerve and Sensory nerve (function)

Motor NerveSensory Nerve
Motor nerve carries impulses from the brain and spinal cord to the muscles and glands.Sensory nerve carries impulses from the sense organs to the spinal cord or brain.

(d) Difference between Cranial and Spinal nerves (number in pairs)

Cranial NervesSpinal Nerves
There are 12 pairs of cranial nerves.There are 31 pairs of spinal nerves.

(e) Difference between Cerebrum and Medulla oblongata (function)

CerebrumMedulla oblongata
The cerebrum is the seat of intelligence, consciousness and will power. It controls all the voluntary activities.Medulla oblongata controls the activities of the internal organs.

(f) Difference between Cerebrum and Spinal cord (arrangement of white and grey matter)

CerebrumSpinal cord
In Cerebrum, the outer portion contains grey matter and inner portion contains white matter.In Spinal cord, the inner part contains grey matter and the outer part contains white matter.

Question 2

With the help of a suitable diagram, describe the structure and function of a neuron.

Answer

A neuron is made up of two main parts —

  1. A main cell body called Cyton
  2. A long process called Axon

The cell body contains a nucleus. The dendrites are cytoplasmic extensions of the cell body. From the cell body arises one long process called the axon. Its length may vary from a few millimetres to 1 metre. The end of the axon terminates in a number of branched filaments called terminal branches.

With the help of a suitable diagram, describe the structure and function of a neuron. Nervous System, Concise Biology Solutions ICSE Class 8.

The function of a neuron is to receive messages (impulses) from the organs and transmit them through the cell body into the axon which transmits the message. Message is relayed from one neuron to the other through the synapse which is a small junction used for communication between two neurons.

Question 3

Briefly describe the structure of the cerebellum in human brain and mention its functions .

Answer

Cerebellum is much smaller compared to Cerebrum and is located under the cerebrum. Its function is to balance the body and coordinate muscular activities. The cerebrum decides an action, whereas the cerebellum implements the action. For example, if we get an idea to stand up and walk, it arises in the cerebrum, but the muscles involved in this process contract or relax under the control of the cerebellum.

Question 4

Mention the three functions of spinal cord.

Answer

Spinal cord has the following functions —

  1. To control reflexes below the neck.
  2. To conduct messages from the skin and muscles to the brain.
  3. To conduct commands from the brain to muscles of the trunk (or torso) and limbs.

Question 5

With the help of a suitable example, describe reflex action.

Answer

The peripheral nervous system and spinal cord together control certain actions where the brain is not involved, e.g. when we touch a hot object or get pricked by a pointed object, we instantly remove our hand, without thinking about it. Such an action is called a reflex action.

With the help of a suitable example, describe reflex action. Nervous System, Concise Biology Solutions ICSE Class 8.

Question 6

Briefly differentiate between the following by giving examples:

(a) Voluntary and involuntary action.

(b) Inborn and acquired reflexes.

Answer

(a) Difference between Voluntary and involuntary action

Voluntary ActionInvoluntary Action
Voluntary actions occur knowingly.Involuntary actions occur unknowingly.
Cerebrum controls voluntary actions.Medulla oblongata and Spinal cord controls involuntary actions.
Eating apple, watching TV are examples of voluntary actions.Breathing, beating of heart are examples of involuntary actions.

(b) Difference between Inborn and acquired reflexes.

Inborn ReflexesAcquired Reflexes
No previous experience or learning is required for inborn reflexes.Acquired reflexes develop with experience and learning during the lifetime.
Blinking, coughing, sneezing, vomiting are examples of inborn reflexes.Typing on the keyboard, playing a musical instrument are examples of acquired reflexes.
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