Revision: Human Anatomy and Physiology >> The Nervous System Biology (English Medium) ICSE Class 10 CISCE

The path that an impulse takes in a reflex action is called a reflex arc.

Neurons are the building blocks of the nervous system and transmit information throughout the body.

The neurons which carry impulses from the brain or spinal cord to the body parts are called motor or efferent neurons.

The neurons which carry impulses from the body parts to the spinal cord or the brain are called sensory or afferent neurons. For example, the optic nerve of the eye.

A stimulus is an agent or a sudden change in the external or internal environment that changes an organism or body parts. e.g., light, sound, heat, pain, hunger.

Receptors are specialised sensory cells that receive stimuli and convert them into nerve impulses.

Effectors are muscles or glands that produce a response by contracting or secreting substances when stimulated by nerve impulses.

A neuron is a specialised cell that forms the structural and functional unit of the nervous system and is responsible for transmitting nerve impulses.

Neurolemma is the outermost thin protective sheath covering the myelin sheath of a nerve fibre.

Nodes of Ranvier are gaps present at intervals in the myelin sheath that help in faster transmission of nerve impulses.

A stimulus is any sudden change in the internal or external environment that brings about a response in an organism.

Axon terminals are closely placed near the dendrites of another one or more neurons but are not connected. Such gaps in between are called synaptic clefts.

Axon terminals are closely placed near the dendrites of another one or more neurons but are not connected. Such gaps in between are called synaptic clefts.

A nerve is a bundle of axons from numerous neurons encased in a protective sheath.

A response is the reaction or change in an organism produced as a result of a stimulus.

A nerve impulse is an electrical disturbance that travels along a neuron in response to a stimulus.

The polarised state is when the outer side of a nerve fibre carries a positive charge due to more Na⁺ ions outside the axon membrane in the resting condition.

The sodium pump is a cellular mechanism that uses energy from ATP to actively transport sodium ions out of the axon, helping restore the resting state after depolarisation.

Synapse (syn: together, apse: gap/window) is the point of contact between the terminal branches of the axon of a neuron with the dendrites of another neuron separated by a fine gap.

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The junction between two nerve cells having a minute gap called synaptic cleft through which nerve impulse is transmitted by neurotransmitters is called synapse.

Nerve is a bundle of nerve fibres (axons) of separate neurons, enclosed in a tubular sheath.

The aggregates of the cytons or cell bodies of nerve cells from which the nerve fibres may arise or enter into are called ganglia.

Inflammation of the meninges is called meningitis.

The brain is protected by 3 membranous coverings called meninges (meninx: membrane) which continue backwards on the spinal cord.

White matter is the inner region of the cerebrum that consists mainly of myelinated axons (nerve fibres).

The outer portion (cortex) of the cerebrum contains cell bodies of the neurons and, being grayish in colour, is called the gray matter.

The cerebrum is divided into two halves called the right and left cerebral hemispheres.

The subconscious or unconscious mind is a part of the cerebrum where past experiences are stored and may be recalled during dreams or hypnosis.

The corpus callosum is a thick band of nerve fibres that connects the two cerebral hemispheres and allows communication between them.

Sulci are the grooves or depressions between the gyri on the surface of the cerebrum.

Gyri are the raised folds or ridges on the surface of the cerebrum.

It is an automatic/quick/immediate, involuntary action in the body brought about by a stimulus.

Reflex action is an automatic/quick/immediate, involuntary action in the body brought about by a stimulus. This mechanism prevents injury to the body by triggering a rapid and automatic response.

An involuntary, spontaneous automatic response brought about due to a previously learned experience is called a conditioned reflex.

A reflex which develops during lifetime due to experience or learning is called a conditioned (acquired) reflex.

A reflex in which no previous experience or learning is required and is inherited from the parents is called a natural (inborn) reflex.

A reflex arc is the shortest route that can be taken by an impulse from a receptor to an effector.

1. The cerebrum is the largest part of the brain and is divided into right and left hemispheres.
2. Its surface is highly convoluted with gyri (ridges) and sulci (grooves), increasing the surface area for more nerve cells.
3. The outer cortex consists of gray matter (cell bodies of neurons), while the inner portion contains white matter (nerve fibres).
4. The corpus callosum connects the two cerebral hemispheres and transfers information between them.
5. The cerebrum is the seat of intelligence, reasoning, memory, consciousness, and voluntary actions, and also stores subconscious experiences.

1. The cerebellum is located at the base of the brain beneath the cerebrum.
2. It has an outer gray matter cortex and inner white matter, with a tree-like appearance in section.
3. It lacks convolutions but has numerous furrows.
4. Its main function is to maintain balance and coordinate muscular movements.
5. It does not initiate movement, but ensures timing and coordination of muscle actions; alcohol affects its function, causing unsteady movements.

1. It is the lowest part of the brain, connecting the brain to the spinal cord.
2. It controls involuntary activities such as heartbeat, breathing, and peristalsis.
3. Damage to the medulla is usually fatal due to its role in vital functions.

1. Voluntary actions are performed consciously, while involuntary actions (reflexes) occur automatically without conscious control.
2. A stimulus is any change in the environment that initiates a reflex action.
3. Reflex actions are quick, automatic responses to stimuli and do not require conscious thought.
4. Examples of reflexes include withdrawal of hand from a hot object, shivering in cold, and sweating in heat.
5. All reflexes are triggered by sensory stimulation and result in either muscular movement or glandular secretion.