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Chapter 6

Nervous System in Humans

Class 8 - Living Science Biology Ratna Sagar


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Question 1

The basic structural and functional unit of the nervous system is a ............... .

Answer

The basic structural and functional unit of the nervous system is a nerve cell or neuron.

Question 2

............... is covered by a sheath called myelin sheath.

Answer

Axon is covered by a sheath called myelin sheath.

Question 3

............... is the largest part of the brain.

Answer

Cerebrum is the largest part of the brain.

Question 4

The ............... fluid nourishes the brain and absorbs shocks.

Answer

The Cerebrospinal fluid nourishes the brain and absorbs shocks.

Question 5

The ............... coordinates the movement of the voluntary muscles.

Answer

The Cerebellum coordinates the movement of the voluntary muscles.

Think and answer

Question 1

People who have had too much alcoholic drinks have problems in walking straight and driving. Which part of their brain has been affected?

Answer

Cerebellum is the part of brain which is affected by alcohol as it is the part which maintains the balance of the body and controls the coordination of voluntary muscles.

Tick the most appropriate answer

Question 1

Many short fibres extending from the cell body of a nerve cell are called

  1. dendrons
  2. axon
  3. dendrites
  4. ganglia

Answer

dendrons

Reason — Many short fibres called dendrons arise from the cell body. They further divide to form dendrites.

Question 2

Motor nerve carries messages to the

  1. heart
  2. spinal cord
  3. muscles and glands
  4. brain

Answer

muscles and glands

Reason — Motor nerves carry messages from brain or spinal cord to the muscles and glands of the body.

Question 3

These nerves emerge from the brain and reach organs in the head region.

  1. spinal
  2. cranial
  3. vagus
  4. pelvic

Answer

cranial

Reason — Cranial nerves emerge from the brain and reach organs in the head region.

Question 4

The message that travels along a nerve in the form of a wave of chemical disturbance is called

  1. stimulus
  2. response
  3. sensation
  4. impulse

Answer

impulse

Reason — Messages travel along the nerve cells in the form of a wave of chemical disturbance called an impulse. An impulse is like an electrical signal.

Question 5

Junction of the two neurons is called

  1. joint
  2. synapse
  3. association neuron
  4. synaptic button

Answer

synapse

Reason — A synapse is a junction where communication between two neurons occurs.

Question 6

The human brain is enveloped by three membranes called

  1. impulses
  2. meninges
  3. synapses
  4. none of these

Answer

meninges

Reason — The human brain is enveloped by three membranes called meninges.

Question 7

Breathing and heartbeat are controlled by the

  1. cerebellum
  2. cerebrum
  3. medulla
  4. nerve cells

Answer

medulla

Reason — The medulla oblongata controls involuntary actions of the body like breathing, heartbeat, coughing, sneezing, etc.

Question 8

The central canal of the spinal cord is surrounded by an H-shaped area called

  1. grey matter
  2. white matter
  3. black matter
  4. silver matter

Answer

grey matter

Reason — The central canal of the spinal cord is surrounded by an H-shaped area called grey matter.

Question 9

Reflex actions are the actions controlled by

  1. brain
  2. spinal cord
  3. both brain and spinal cord
  4. neither brain nor spinal cord

Answer

spinal cord

Reason — Reflex actions are the actions controlled by spinal cord.

Question 10

The peripheral nervous system transmits messages to and from the sense organs and is responsible for

  1. involuntary actions
  2. reflex actions
  3. autonomic actions
  4. voluntary actions

Answer

voluntary actions

Reason — Peripheral nervous system is responsible for voluntary actions such as cycling, swimming, etc.

Fill in the blanks

Question 1

A neuron is the basic structural and functional unit of the ............... system.

Answer

A neuron is the basic structural and functional unit of the nervous system.

Question 2

A single long fibre extending from the cell body of a neuron is called ............... .

Answer

A single long fibre extending from the cell body of a neuron is called axon.

Question 3

The central nervous system consists of ............... and ............... .

Answer

The central nervous system consists of brain and spinal cord.

Question 4

The ............... is the continuation of the medulla oblongata of the brain.

Answer

The spinal cord is the continuation of the medulla oblongata of the brain.

Question 5

The nerve pathway of a reflex action is called a ............... .

Answer

The nerve pathway of a reflex action is called a reflex arc.

Question 6

The peripheral nervous system consists of ............... and ............... nerves.

Answer

The peripheral nervous system consists of cranial and spinal nerves.

Write true or false. Correct the false statements.

Question 1

Each nerve cell consists of a cell body, many short fibres and a long fibre.

Answer

True

Question 2

Motor nerves carry impulses from the sense organs to the spinal cord.

Answer

False

Corrected statement — Motor nerves carry impulses from the spinal cord to the sense organs.

Question 3

The largest portion of the brain is the cerebellum.

Answer

False

Corrected statement — The largest portion of the brain is the cerebrum.

Question 4

Thinking, reasoning and memory are controlled by the medulla.

Answer

False

Corrected statement — Thinking, reasoning and memory are controlled by the cerebrum.

Question 5

A reflex action is a spontaneous response to a stimulus.

Answer

True

Question 6

The central nervous system consists of nerves only.

Answer

False

Corrected statement — The central nervous system consists of brain and spinal cord.

Differentiate between

Question 1

sensory nerves and mixed nerves.

Answer

Sl.
No.
Sensory NervesMixed Nerves
1.Sensory nerves are the nerves that carry messages from the sense organs to either the spinal cord or the brain.Mixed nerves perform the function of both sensory nerves and motor nerves. They transmit messages from the central nervous system to the muscles of the body.
2.They contain only sensory fibres.They contain sensory fibres as well as motor fibres.
3.For example, the optic nerve that sends messages from the eye to the brain is a sensory nerve.For example, the nerve that transmits messages to the tongue is a mixed nerve.

Question 2

cranial nerves and spinal nerves

Answer

Sl.
No.
Cranial NervesSpinal Nerves
1.These nerves arise from the brain and reach organs in the head region.These nerves arise from the spinal cord and reach various parts of the body.
2.There are 12 pairs of cranial nerves in the body.There are 31 pairs of spinal nerves in the body.

Question 3

sensory nerves and motor nerves.

Answer

Sl.
No.
Sensory NervesMotor Nerves
1.Sensory nerves are the nerves that carry messages from the sense organs to either the spinal cord or the brain.Motor nerves carry messages in the form of responses from the brain or spinal cord to other parts of the body such as muscles and glands.
2.They contain only sensory fibres.They contain only motor fibres.
3.For example, the optic nerve that sends messages from the eye to the brain is a sensory nerve.For example, nerves arising from the brain leading to muscles of the eye balls are motor nerves.

Question 4

cerebrum and cerebellum

Answer

Sl.
No.
CerebrumCerebellum
1.It is the uppermost, largest and the most prominent part of the brain.It is a small, egg-shaped lobe located at the base under the cerebrum.
2.It is highly convoluted in appearance with ridges and grooves.It does not have convolutions, but has many furrows.
3.It controls mental activities such as thinking and reasoning, memory, intelligence and perception of taste, pain and touch etc.It coordinates the movement of voluntary muscles and maintains the balance of the body.

Question 5

brain and spinal cord

Answer

Sl.
No.
BrainSpinal Cord
1.The brain is the main control centre of the nervous system.The spinal cord is the continuation of the medulla oblongata of the brain.
2.It is situated in the cranium of the skull.It runs through the vertebral column.
3.It controls your thinking, feeling, movement and senses.It conducts reflexes below the neck.

Find the odd one out. Give reasons for your choice

Question 1

dendron, cyton, cerebrum, dendrite, axon

Answer

cerebrum

Reason — cerebrum is part of brain while dendron, cyton, dendrite and axon are parts of neuron cell.

Question 2

cerebrum, cerebellum, medulla oblongata, dendrite

Answer

dendrite

Reason — cerebrum, cerebellum and medulla oblongata are parts of brain but dendrite is part of neuron.

Answer the following in short

Question 1

Define nervous system.

Answer

The organ system in our body that brings about coordination and integration of different body activities is called the nervous system.

Question 2

Name the parts of a nerve cell.

Answer

The parts of a nerve cell are cell body, axon and dendrites.

Question 3

What are motor nerves?

Answer

The nerves that carry messages in the form of responses from the brain or spinal cord to other parts of the body such as muscles and glands are called motor nerves. They contain only motor fibres. For example, nerves arising from the brain leading to muscles of the eye balls are motor nerves.

Question 4

How many cranial nerves are there in brain?

Answer

There are 12 pairs of cranial nerves.

Question 5

What is a synapse?

Answer

A synapse is a junction where communication between two neurons occurs.

Question 6

Write the function of the cerebrospinal fluid.

Answer

The functions of the cerebrospinal fluid are:

  1. It nourishes the brain.
  2. It protects the brain from shocks by absorbing them.

Question 7

Name the three important parts of the brain.

Answer

The three important parts of the brain are:

  1. Cerebrum
  2. Cerebellum
  3. Medulla oblongata

Question 8

Give two examples of reflex actions.

Answer

Two examples of reflex actions are:

  1. Blinking of eyes when a foreign particle enters the eye.
  2. Immediate withdrawal of hand if you unknowingly touch a hot object.

Answer the following in detail

Question 1

Distinguish between motor, sensory and mixed nerves with respect to their functions.

Answer

Motor nervesSensory nervesMixed nerves
It carries messages in the form of responses from the brain or spinal cord to other parts of the body such as muscles and glands.It carries messages (impulses) from the sense organs to either the spinal cord or the brain.It performs the function of both motor and sensory nerves. They transmit electrical impulses from the central nervous system to the muscles of the body.

Question 2

Explain the structure of a motor nerve cell with the help of a diagram.

Answer

A neuron is the longest cell of our body. It has three parts — cell body, axon and dendrites.

  1. The cell body called cyton contains the nucleus.
  2. Many short fibres called dendrons arise from the cell. They further divide to form dendrites. Dendrites receive messages from other neurons.
  3. A single, long fibre called axon extends from the other side of the cell body. It is covered by a sheath called myelin sheath.

Below diagram shows the structure of a neuron:

Explain the structure of a motor nerve cell with the help of a diagram. Nervous System in Humans, Living Science Biology Ratna Sagar Solutions ICSE Class 8.

Question 3

Describe the human central nervous system along with its parts and functions.

Answer

The central nervous system consists of the brain and the spinal cord. It is the control centre for all body functions. It is the site for all information processing in the body. It is responsible for processing every sensation and thought a human being experiences. It has two parts — Brain and Spinal Cord.

  1. Brain — The Brain is the main control centre of the nervous system situated in the cranium of the skull. It controls our thinking, feelings, movement and senses. It has three parts — Cerebrum, Cerebellum and Medulla oblongata.
    1. Cerebrum — The cerebrum is the uppermost, largest and the most prominent part of the brain. It is responsible for the sensation of pain, temperature, touch, sight, sound, taste and smell. It also controls mental activities such as memory, intelligence, thinking and reasoning.
    2. Cerebellum — The cerebellum is a small, egg-shaped lobe located at the base under the cerebrum. It helps in the muscle coordination and balance of the body.
    3. Medulla oblongata — The Medulla oblongata is the lowermost part of the brain located at the base of the skull. It controls breathing, heartbeat, coughing, sneezing and other involuntary functions.
  2. Spinal cord — The spinal cord is the continuation of the medulla oblongata of the brain. It is like a cord that emerges from a hole at the base of the skull and runs through the vertebral column. The spinal cord conducts reflexes below the neck. It conducts sensory impulses from the skin and muscles to the brain. It conducts motor responses from the brain to the muscles of the trunk and limbs.

Question 4

What is reflex action? Explain the reflex arc with the help of an example.

Answer

An automatic, spontaneous and mechanical response to a stimulus controlled by the spinal cord without the involvement of the brain is called a reflex action.

The path that an impulse takes in a reflex action is called a reflex arc. The reflex arc involves three neurons — sensory neurons, association neurons and motor neurons.

  • If we touch a hot object, a stimulus triggers an impulse in a receptor on the skin.
  • The impulse then travels from the receptor through a sensory neuron to the spinal cord.
  • In the spinal cord, it passes through an association neuron to a motor neuron and finally reaches the muscles.
  • The muscles of the effector organ contract moving it away from the hot object.

Below flow chart shows a simple reflex action of immediate withdrawal of hand on touching a hot object:

What is reflex action? Explain the reflex arc with the help of an example. Nervous System in Humans, Living Science Biology Ratna Sagar Solutions ICSE Class 8.

The diagram

Question 1

The diagram represents the external view of the human brain. Study it and then answer the questions that follow.

  1. Name the parts numbered a to d.
  2. What is the main function of the parts numbered c and d?
The diagram represents the external view of the human brain. Study it and then answer the questions that follow. 1. Name the parts numbered a to d. 2. What is the main function of the parts numbered c and d? Nervous System in Humans, Living Science Biology Ratna Sagar Solutions ICSE Class 8.

Answer

  1. The parts numbered a to d are:
    a → Cerebrum
    b → Cerebellum
    c → Meninges
    d → Medulla oblongata

  2. The main function of the parts numbered c and d are:

    1. Function of Meninges (Part C) — They act as protective covering of brain with cerebrospinal fluid between them. They protect the brain from shock.
    2. Function of Medulla oblongata (Part D) — It controls the heartbeat, breathing and other involuntary movements.

Question 2

The diagram shows a reflex arc. Study it and answer the following questions.

  1. Name the parts numbered a to d.
  2. Using the letters of alphabet shown in the diagram, indicate the direction in which the impulse enters and leaves part c. X to Y or Y to X?
  3. What is reflex action?
  4. With the help of a flow chart, show a simple reflex action.
The diagram shows a reflex arc. Study it and answer the following questions. 1. Name the parts numbered a to d. 2. Using the letters of alphabet shown in the diagram, indicate the direction in which the impulse enters and leaves part c. X to Y or Y to X? 3. What is reflex action? 4. With the help of a flow chart, show a simple reflex action. Nervous System in Humans, Living Science Biology Ratna Sagar Solutions ICSE Class 8.

Answer

  1. The parts numbered a to d are:
    a → sensory neurons
    b → motor neurons
    c → association neurons
    d → cell body of motor neurons
  2. The impulse enters through X and leaves through Y.
  3. An automatic, spontaneous and mechanical response to a stimulus; controlled by the spinal cord without the involvement of the brain is called a reflex action.
  4. Below flow chart shows a simple reflex action of immediate withdrawal of hand on touching a hot object:
The diagram shows a reflex arc. With the help of a flow chart, show a simple reflex action. Nervous System in Humans, Living Science Biology Ratna Sagar Solutions ICSE Class 8.

Think and answer

Question 1

When you smell tasty food, your mouth waters. Which part of the nervous system makes this happen?

Answer

The watering of mouth with smell of tasty food is a conditioned reflex. Thus, Spinal cord is involved in it.

Question 2

Rakesh was walking barefoot in a park. Suddenly, he stepped on a nail and withdrew his foot spontaneously. Name the pathway involved in this action. Which organ in our body controls such actions?

Answer

Below flowchart shows the reflex arc pathway involved in the action. The organ that controls such action is spinal cord.

Rakesh was walking barefoot in a park. Suddenly, he stepped on a nail and withdrew his foot spontaneously. Name the pathway involved in this action. Which organ in our body controls such actions? Nervous System in Humans, Living Science Biology Ratna Sagar Solutions ICSE Class 8.
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