General Science 8th Class Chapter 2 Human Nervous System Solved Exercise

General Science

8th Class

Chapter 2

Human Nervous System

Questions

1. Encircle the correct option.

(i) The neurons which decide about the action for a certain stimulus:

a. sensory neuron        b. motor neuron        c. inter-neuron        d. all of above

(ii) The parts of a neuron which receive messages are:

a. cell bodies        b. dendrites        c. axons        d. nuclei

(iii) Heartbeat is controlled by:

a. cerebrum        b. cerebellum        c. medulla oblongata        d. hypothalamus

(iv) Many axons present side by side and enclosed in a common sheath from:

a. nerve cell        b. nerve        c. dendrite        d. spinal cord

(v) Sensory neurons carry messages towards:

a. muscles        b. glands        c. sense organs        d. brain and spinal cord

(vi) Which part of brain is involved in precise and accurate body movements?

a. Cerebellum        b. Cerebrum        c. Thalamus        d. Midbrain

(vii) When you have a toothache, you feel pain because:

a. there is a cavity in your tooth

b. tiny bits of food are left between your teeth

c. bacteria digest the food left between your teeth and produce an acid

d. the cavity reaches the nerves and the nerves send a message to the brain

2 Write short answers.

(i) Write the functions of midbrain, hypothalamus and spinal cord.

Ans.

Midbrain:

Midbrain is a small part of the brain which is present below the cerebrum. It receives information from sense organs which is then passed to the appropriate part of the forebrain.

Hypothalamus:

Hypothalamus lies at the base of thalamus. It controls body temperature, hunger and thirst.

Spinal cord:

Spinal cord creates a link between brain and different body parts. It also controls some reflex actions (immediate and involuntary actions) and some other involuntary actions.

(ii) Differentiate between:

    (a) Receptors and effectors

    (b) Neuron and nerve

    (c) Sensory neuron and motor neuron

    (d) Cerebrum and cerebellum

Ans.

(a) Receptors and effectors

Receptors:

• Detect stimuli from the environment.
• Convert stimuli into electrical impulses.
• Send impulses to the brain and spinal cord.
• Examples include the eyes, ears, nose, tongue, and skin.

Effectors:

• Respond to stimuli by carrying out instructions from the brain and spinal cord.
• Examples include muscles and glands.

 (b) Neuron and nerve

Neuron:

Neuron or nerve cell is the basic structural and functional unit of the nervous system. All parts of the neuron system, i.e., brain, spinal cord and nerves are made up of neurons. Neurons transmit messages in the form of electrochemical waves.

Nerve:

A nerve is cable-like bundle of axons enclosed in a common sheath. Nerve transmits messages from one part of body to another.

 (c) Sensory neuron and motor neuron

Sensory neuron:

Sensory neurons carry nerve impulses from sense organs (ears, eyes, skin, tongue, nose, etc.) to the central nervous system.

Motor neuron:

Motor neurons carry nerve impulses from central nervous system to effectors (muscles and glands),i.e., the parts which respond.

 (d) Cerebrum and cerebellum

Cerebrum:

Cerebrum is the topmost and the largest part of the brain. It is divided into right and left cerebral hemisphere. Each hemisphere controls the opposite side of the body. In general, the left hemisphere controls speech, comprehension, arithmetic, and writing. The right hemisphere controls creativity, spatial ability, artistic, and musical skills. Inside cerebrum there is a small structure called thalamus. It controls many sensory functions.

Cerebellum:

Cerebellum lies under the back part of the cerebrum. It acts as a controller for maintaining the body balance and making precise and accurate movements.

(iii) Write a note on the central nervous system.

Ans.

Central nervous system acts as a control centre of the whole nervous system. It comprises brain and spinal cord.

Brain:

Human brain is enclosed in a body skull called cranium, and consists of billions of inter-neurons. It is divided into the following parts.

1. Forebrain:

Forebrain is the largest part of the brain. It consists of three main parts, i.e., cerebrum, thalamus and hypothalamus. Cerebrum is the topmost and the largest part of the brain. It is divided into right and left cerebral hemisphere. Each hemisphere controls the opposite side of the body. In general, the left hemisphere controls speech, comprehension, arithmetic, and writing. The right hemisphere controls creativity, spatial ability, artistic, and musical skills. Inside cerebrum there is a small structure called thalamus. It controls many sensory functions. Hypothalamus lies at the base of thalamus. It controls body temperature, hunger and thirst.

2. Midbrain:

Midbrain is a small part of the brain which is present below the cerebrum. It receives information from sense organs which is then passed to the appropriate part of the forebrain.

3. Hindbrain:

Hindbrain consists of three parts, i.e., cerebellum, pons and medulla oblongata.

Cerebellum lies under the back part of the cerebrum. It acts as a controller for maintaining the body balance and making precise and accurate movements. Pons is an oval structure present beneath midbrain. It controls many functions like sleep, swallowing, equilibrium and taste, etc. Medulla oblongata forms the posterior part of the brain where it is connected with the spinal cord. Medulla oblongata controls heartbeat, breathing and digestion, etc. Medulla oblongata keeps on working when rest of the brain goes to sleep.

Spinal Cord:

Spinal cord is an extension of medulla oblongata. It runs backwards inside the backbone up to its lower end. It is also made up of inter neurons.

Spinal cord creates a link between brain and different body parts. It also controls some reflex actions (immediate and involuntary actions) and some other involuntary actions.

(iv) Identify and label the following diagram.

Ans.