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Chapter 5

Nervous System in Humans

Class 7 - Living Science Biology Ratna Sagar


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Question 1

The reaction of an organism to a stimulus is called a ............... .

Answer

The reaction of an organism to a stimulus is called a response.

Question 2

The basic structural unit of the nervous system is called a ............... .

Answer

The basic structural unit of the nervous system is called a neuron.

Question 3

............... nourishes the brain and absorbs shocks.

Answer

Cerebrospinal fluid nourishes the brain and absorbs shocks.

Question 4

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

Answer

Cerebrum is the largest part of the brain.

Question 5

............... maintains the balance of the body.

Answer

Cerebellum maintains the balance of the body.

Tick the most appropriate answer

Question 1

Short fibres extending from the cell body of a nerve cell are called

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

Answer

dendrons

Reason — Short fibres extending from the cell body of a nerve cell are called dendrons which further divide to form dendrites.

Question 2

The message that travels along a nerve is called

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

Answer

impulse

Reason — Messages along the neuron travel in the form of a wave of chemical disturbance. This chemical disturbance is called an impulse.

Question 3

Breathing and heartbeat are controlled by the

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

Answer

medulla oblongata

Reason — Medulla oblongata controls involuntary movements like breathing and heartbeat.

Question 4

This is the centre for intelligence and memory

  1. cerebellum
  2. cerebrum
  3. medulla oblongata
  4. spinal cord

Answer

cerebrum

Reason — Centre for intelligence and memory is cerebrum.

Question 5

This part of the brain maintains the balance of the body.

  1. cerebellum
  2. cerebrum
  3. medulla oblongata
  4. spinal cord

Answer

cerebellum

Reason — Cerebellum maintains the balance of the body.

Fill in the blanks

Question 1

............... is the basic structural unit of the nervous system.

Answer

Neuron is the basic structural 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 comprises ............... and ............... .

Answer

The central nervous system comprises brain and spinal cord.

Question 4

The ............... nervous system comprises the nerves arising from the brain and spinal cord.

Answer

The peripheral nervous system comprises the nerves arising from the brain and spinal cord.

Question 5

The brain is enveloped by three membranes called ............... .

Answer

The brain is enveloped by three membranes called meninges.

Match the following

Question 1

Sl.
No.
Column AColumn B
1.Spinal cordbody balance
2.Cerebrumreflex action
3.Cerebellumintelligence and memory
4.Medulla oblongatajunction of two neurons
5.Synapsecarries messages to the brain
6.Sensory nerveheartbeat

Answer

Sl.
No.
Column AColumn B
1.Spinal cordreflex action
2.Cerebrumintelligence and memory
3.Cerebellumbody balance
4.Medulla oblongataheartbeat
5.Synapsejunction of two neurons
6.Sensory nervecarries messages to the brain

Write true of False. Correct the false statements.

Question 1

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

Answer

False

Corrected statement — Each nerve cell consists of a cell body, many short fibres which further divide into dendrites and a long fibre.

Question 2

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

Answer

False

Corrected statement — Mixed nerves contain both sensory and motor fibres hence they perform the function of both sensory nerves and motor nerves.

Question 3

The cerebellum is the largest part of the brain.

Answer

False

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

Question 4

Thinking, reasoning and memory are controlled by the medulla oblongata.

Answer

False

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

Question 5

The cerebrum controls the balance of the body.

Answer

False

Corrected statement — The cerebellum controls the balance of the body.

Differentiate between

Question 1

neuron and nerve

Answer

Sl.
No.
NeuronNerve
1.A neuron is a specialized cell for receiving messages from one part of the body and conducting them to the other parts.Nerve cells when joined end to end form a nerve.
2.Each nerve cell consists of a cell body (cyton), many short fibres (dendrons) which further divide into dendrites and a long fibre (axon).A nerve consists of a cord-like structure with a number of nerve fibres bundled together.

Question 2

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 3

central nervous system and peripheral nervous system

Answer

Sl.
No.
Central Nervous SystemPeripheral Nervous System
1.It consists of the brain and the spinal cord.It comprises of the nerves arising from brain and the spinal cord.
2.It is the main part of nervous system which stores information and processes it.It participates in receiving information and stimulus response

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.

Find the odd one out. Give reasons for your choice.

Question 1

dendron, cyton, cerebrum, dendrite, axon

Answer

cerebrum

Reason — Cerebrum is the part of brain while others are part of nerve cell or neuron.

Question 2

thinking, reasoning, memory, body balance

Answer

body balance

Reason — Body balance is the function of cerebellum while thinking, reasoning and memory are functions of cerebrum

Answer the following in short

Question 1

What is a stimulus?

Answer

Any sudden change in the environment of an organism that causes a reaction in that organism is called a stimulus.

Question 2

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 3

Write the function of the cerebrospinal fluid.

Answer

The functions of the cerebrospinal fluid are:

  1. Nourishes the brain.
  2. Protects it by absorbing shocks.

Question 4

What is a reflex action?

Answer

Reflex action is a quick, automatic response to a stimulus, without the involvement of the brain.

Answer the following in detail

Question 1

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

Answer

A nerve cell or neuron is the basic structural unit of the nervous system. 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 2

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 3

Describe the 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

Explain how messages reach the brain.

Answer

The peripheral nervous system transmits messages to and from the sense organs and is responsible for voluntary actions such as cycling, swimming and so on. Messages enter the spinal cord from all parts of the body and reach the brain, which sends back the messages to various body parts through the spinal cord.

Label the parts

Question 1

What does this picture show? Label the parts.

What does this picture show? Label the parts. Nervous System in Humans, Living Science Biology Ratna Sagar Solutions ICSE Class 7.

Answer

This picture shows 'Synapse between neurons'. The labelled parts are shown below:

What does this picture show? Label the parts. Nervous System in Humans, Living Science Biology Ratna Sagar Solutions ICSE Class 7.

Think and answer

Question 1

When you step on a needle, you immediately withdraw your foot. Which part of the nervous system makes this happen?

Answer

Spinal cord is responsible for this action. Immediately withdrawing our foot after stepping on a needle is a reflex action which happens without thinking i.e., the brain is not involved. Reflex actions are controlled by spinal cord.

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