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CNMS ICSE - 7 Std
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Answers to textbook exercises

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Chapter: 07. Nervous System

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Check Point

Write True or False.
The receptors detect changes in the environment.
True
The nerves are structural and functional units of nervous system.
False (Neurons are the structural and functional units of the nervous system, while nerves are bundles of axons).
Gyri and sulci are found in cerebellum.
False (Gyri and sulci are folds and grooves found in the cerebrum).
Motor neuron conducts sensory impulses to the central nervous system.
False (Sensory neurons conduct sensory impulses to the CNS, while motor neurons carry impulses from the CNS to the effector organs).
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Test Yourself

A. Multiple Choice Questions
The message travels along a nerve fibre in the form of
(a) Stimulus
(b) Response
© Impulse
(d) Reflex
© Impulse
Reflex actions are under the control of
(a) Brain
(b) Spinal cord
© Medulla
(d) Autonomic nervous system
(b) Spinal cord
Functioning of visceral organs is controlled by
(a) Cerebellum
(b) Medulla oblongata
© Spinal cord
(d) Hypothalamus
(b) Medulla oblongata
The number of cranial nerves and spinal nerves in man is
(a) Ten pairs and twenty-four pairs
(b) Twelve pairs and thirty-one pairs
© Thirty-one pairs and twelve pairs
(d) Twenty-four pairs and ten pairs
(b) Twelve pairs and thirty-one pairs
The junction between the two nerve cells is known as
(a) Synapse
(b) Synaptic node
© Isthmus
(d) Synaptic buttons
(a) Synapse
Body posture is maintained by
(a) Cerebrum
(b) Medulla oblongata
© Cerebellum
(d) Spinal cord
© Cerebellum
Fine projections from the neuron are called
(a) axons and receive sensory impulses
(b) dendrites and receive sensory impulses
© dendrites and transmit motor impulses
(d) axons and transmit impulses from cyton to effectors
(b) dendrites and receive sensory impulses
Neurons that conduct impulses from the brain or spinal cord to a muscle or gland are
(a) Motor neurons
(b) Sensory neurons
© Association neurons
(d) Mixed neurons
(a) Motor neurons
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B. Assertion-Reason Type Questions
Assertion [A]: In brain, the gray matter forms the outer layer and white matter lies inside. ​Reason [R]: The gray matter is formed of cell bodies of neurons and white matter has axon fibres of neurons.
(a) Both Assertion [A] and Reason [R] are true. (The Reason correctly explains why the outer layer has a gray appearance and the inner layer has a white appearance).
Assertion [A]: Cerebrum is called little brain whereas cerebellum is the most highly developed part of the brain. ​Reason [R]: Cerebrum has folds and grooves, called the gyri and sulci respectively.
(d) Assertion [A] is false but Reason [R] is true. (The cerebellum is called the little brain, and the cerebrum is the most highly developed part. The Reason statement is independently true).
Assertion [A]: Medulla oblongata controls voluntary activities of visceral organs. ​Reason [R]: Medulla oblongata is the largest part of human brain.
(b) Both Assertion [A] and Reason [R] are false. (Medulla oblongata controls involuntary activities of internal visceral organs, and the cerebrum is the largest part of the human brain).
Assertion [A]: Heartbeat is an involuntary activity. ​Reason [R]: It is coordinated by the spinal nerves.
© Assertion [A] is true but Reason [R] is false. (Heartbeat is indeed an involuntary activity, but it is coordinated by the autonomic nervous system/medulla oblongata, not the spinal nerves).
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C. Fill in the blanks with suitable words.
Coordination in body activities is achieved through nervous and endocrine systems.
The cerebrum is the seat of memory, intelligence and reasoning in human.
Basic unit of nervous system is neuron.
Receptors of pain and pressure are present in skin.
Gyri and sulci are present in the gray matter of cerebrum.
The cranial and spinal nerves constitute peripheral nervous system.
The breathing movements are controlled by medulla oblongata.
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D. State whether these statements are true or false. If false, rewrite the correct form of statements.
Spinal cord is part of autonomic nervous system.
False. Correct Statement: Spinal cord is a part of the central nervous system (CNS).
Response to a stimulus is reflected by a receptor.
False. Correct Statement: Response to a stimulus is shown by an effector organ (or, A stimulus is detected by a receptor).
The gray matter is formed of axons of nerve cells.
False. Correct Statement: The gray matter is formed of cell bodies (cytons) of nerve cells.
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E. Define these terms.
Stimulus
Stimulus: Any change in the environment (either internal or external) of an organism that is detected by the nervous system and evokes a physiological or behavioral response.
Receptor
Receptor: Specialized nerve cells or sensory cells/organs that are stimulated by changes in the surroundings and generate a sensory nerve impulse.
Synapse
Synapse: The point of contact or microscopic gap between the terminal branches of an axon of one neuron and the dendrites of an adjacent neuron, through which nerve impulses pass as chemical messages.
Gyri and sulci
Gyri and sulci: The folds (gyri) and grooves (sulci) present in the outer layer of gray matter of the cerebral hemispheres that increase its surface area to accommodate more neurons.
Neuron
Neuron: The structural and functional unit of the nervous system, consisting of a cell body (cyton), dendrons with dendrites, and a single long extension called an axon.
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F. Give one word for the following.
Structural and functional unit of nervous system.
Neuron
Spiral sheath around axon.
Myelin sheath (or Medullated sheath)
The nerve fibres that transmit impulses from receptors to brain.
Sensory nerve fibres
The automatic response by the body towards a stimulus.
Reflex action
Centre of reasoning, instinct and intelligence.
Cerebrum
Membranes which surround and protect brain.
Meninges
Chain of ganglia on either side of vertebral column and connected to spinal cord.
Sympathetic trunk (or Sympathetic chain of ganglia)
Process of neuron that transmits impulses from cyton to effector organ.
Axon
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G. Encircle the odd one out. Give reasons for your choice.
Axon, receptor, dendron, cyton, dendrites
Odd one out: Receptor
Reason: Axon, dendron, cyton, and dendrites are anatomical parts of a single neuron, whereas a receptor is a specialized sensory cell or organ.
Cerebrum, cerebellum, hypothalamus, medulla
Odd one out: Hypothalamus
Reason: Cerebrum, cerebellum, and medulla oblongata are the three main structural parts of the brain, while the hypothalamus is principally associated with the diencephalon and links the nervous system to the endocrine system.
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H. Differentiate between the following.
Cerebrum and cerebellum
Feature
Cerebrum
Cerebellum
Size & Location
Largest and most highly developed part of the brain, occupying the front and upper regions.
Smaller part of the brain (“little brain”), located at the back of the cerebrum.
Structure
Outer wall has folds (gyri) and grooves (sulci).
Outer surface is furrowed but lacks distinct gyri and sulci.
Functions
Controls intelligence, consciousness, willpower, memory, thinking, reasoning, and sensory perceptions.
Coordinates voluntary movements, controls voluntary muscle activity, and maintains body balance.
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Gray matter and white matter
Feature
Gray Matter
White Matter
Composition
Formed mainly of cell bodies (cytons) of neurons.
Formed mainly of myelinated axons of neurons.
Location in Brain
Forms the outer layer of the brain.
Forms the inner layer of the brain.
Location in Spinal Cord
Centrally located in an H-shaped region.
Forms the peripheral/outer layer.
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Sensory and motor nerve
Feature
Sensory Nerve
Motor Nerve
Fibre Type
Contains only sensory nerve fibres.
Contains only motor nerve fibres.
Direction of Impulse
Carries impulses from sense organs (receptors) to the brain or spinal cord.
Carries impulses from the brain or spinal cord to effector organs (muscles/glands).
Example
Optic nerve of the eye.
Nerves supplying eye muscles.
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I. Answer these questions.
What is a nerve? How many types of nerves are found in human body?
A nerve is a bundle of nerve fibres (axons) wrapped in a protective sheath of connective tissue. Based on the impulses they conduct, there are three types of nerves in the human body:
Sensory nerves: Contain only sensory nerve fibres that carry impulses from sense organs to the CNS.
Motor nerves: Contain only motor nerve fibres that carry impulses from the CNS to effector organs like muscles or glands.
Mixed nerves: Contain both sensory and motor nerve fibres.
Name various divisions of human nervous system. How are they related to each other?
The human nervous system is divided into:
Central Nervous System (CNS): Comprises the brain and spinal cord. It integrates, processes, and interprets incoming information.
Peripheral Nervous System (PNS): Comprises 12 pairs of cranial nerves and 31 pairs of spinal nerves.
Autonomic Nervous System (ANS): Comprises paired chains of ganglia close to the spinal cord, split into sympathetic and parasympathetic divisions.
Relationship: They form a continuous communication and regulatory loop. Receptors collect environmental stimuli and send them through the sensory fibers of the PNS to the CNS. The CNS acts as the coordinator, processing and interpreting these signals. It then sends response signals back through the motor fibers of the PNS to the effectors (muscles or glands) to produce a response. Meanwhile, the ANS acts alongside the CNS and PNS to coordinate and regulate involuntary visceral functions (like heart rate and digestion) dynamically.
Summarise functions of cerebrum.
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