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CNMS ICSE - 7 Std
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Key Terms

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Chapter: 07. Nervous System

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Stimulus: Any change in the environment of an organism that evokes a response.
Response: A reaction shown by a living organism or its part to a stimulus.
Coordination: Normal control over the functioning of body tissues and organs at the correct speed and in correct sequence simultaneously within physiological limits.
Nervous System: The control centre of the body that receives stimuli, coordinates activities, and provides a fast communication network of neurons and nerve fibres.
Neurons (or Nerve Cells): The structural and functional units of the nervous system.
Cyton (or Cell Body): The main part of a neuron that receives impulses from dendrites and passes them to the next neuron through the axon.
Dendrons: Several finger-like projections branching out from the cyton of a neuron.
Dendrites: The fine branches of dendrons that receive impulses from neighbouring neurons and conduct them to the cyton.
Axon: The longest single extension from the cyton that transmits nerve impulses away from the cell body to other neurons or effector organs.
Myelin Sheath: A spirally-coiled sheath of fatty substance around an axon that insulates it and speeds up the conduction of nerve impulses.
Nodes of Ranvier: Regular constrictions present along the myelin sheath of an axon.
Synapse: The point of contact between the terminal branches of an axon of one neuron and the dendrites of an adjacent neuron.
Nerve Fibres: The long axons of neurons that form the pathways for impulses.
Nerve: A bundle of nerve fibres wrapped in a protective sheath of connective tissue.
Sensory Nerves: Nerves containing only sensory nerve fibres that bring impulses from sense organs to the brain or spinal cord.
Motor Nerves: Nerves formed of motor nerve fibres that carry impulses from the brain or spinal cord to effector organs like muscles or glands.
Mixed Nerves: Nerves that contain both sensory and motor nerve fibres.
Transduction: The process by which sensory cells or receptors convert stimuli into electrical nerve impulses.
Transmission of Nerve Impulse: The process in which receptors transmit sensory impulses to the sensory neurons present in the brain or spinal cord.
Meninges: Three membranes that surround and protect the brain.
Cranium (or Skull): The bony brain case that encloses and protects the brain.
Gray Matter: The layer of the nervous system composed mainly of the cell bodies of neurons, forming the outer layer of the brain and the inner H-shaped region of the spinal cord.
White Matter: The layer of the nervous system composed of axons, forming the inner layer of the brain and the peripheral layer of the spinal cord.
Cerebrum: The largest and most highly developed part of the brain, which acts as the seat of intelligence, consciousness, memory, reasoning, and sensory perception.
Cerebral Hemispheres: The right and left hollow halves of the cerebrum separated by a deep groove.
Gyri: Highly folded ridges in the gray matter wall of each cerebral hemisphere.
Sulci: Grooves located between the folds (gyri) in the gray matter wall of each cerebral hemisphere.
Cerebellum: The part of the brain, also called the little brain, associated with coordinating voluntary muscular movements and maintaining body balance.
Medulla Oblongata: The posterior-most part of the brain, or brain stem, which coordinates all involuntary activities of internal visceral organs.
Spinal Cord: The part of the central nervous system extending from the medulla through the vertebral column that controls reflex actions and conducts sensory and motor impulses.
Cranial Nerves: The 12 pairs of nerves that arise directly from the brain and supply different parts of the head.
Spinal Nerves: The 31 pairs of mixed nerves that arise from the spinal cord and supply different parts of the body excluding the head.
Autonomic Nervous System (ANS): The system consisting of paired chains of ganglia close to the spinal cord that controls involuntary actions of visceral organs and smooth muscles.
Sympathetic Nervous System: A division of the autonomic nervous system that has a stimulatory effect and prepares the body for violent action during adverse situations.
Parasympathetic Nervous System: A division of the autonomic nervous system that has an inhibitory or calming effect, bringing body activities back to normal.
Receptors: Nerve cells or sensory cells that are stimulated by changes in the surroundings and generate sensory nerve impulses.
Visceral Organs: Internal organs of the body.
Impulse: A wave of electric disturbance that passes along the axon of a neuron.
Reflex Action: An action that occurs automatically in response to a stimulus, independent of an individual’s will.
Neurotransmitter: A chemical substance, such as acetylcholine, that propagates a nerve impulse across the synaptic gap between two adjacent neurons.
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