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Key terms from Edexcel IGCSE Biology on the topic of The Nervous System


A change in an animal's surroundings


A reaction to a change in one's surroundings


When energy is changed from one form to another

Central Nervous System (CNS)

Consists of the brain and spinal cord and is linked to sense organs by nerves

Reflex action

A rapid automatic (or involuntary) action in response to a stimulus that is not started by impulses from the brain

Reflex arc

The nerve pathway of a reflex e.g. stimulus > receptor > sensory neurone > CNS > relay neurone > motor neurone > effector > response

Dorsal root

Where sensory neurones enter the central nervous system

Ventral root

Where motor neurones emerge from the central nervous system

Dorsal root ganglion

A swelling in the dorsal root where the cell bodies of sensory neurones are located

White matter

Composed mainly of nerve axons. Forms the outer part of the spinal cord and the middle part of the brain.

Grey matter

Composed of mainly nerve cell bodies. Forms the middle part of the spinal cord and the outside of the brain.

Sensory neurone

A neurone conducting impulses from receptors to the brain or spinal cord

Motor neurone

A neurone transmitting impulses from the brain or spinal cord to a muscle or gland


The long threadlike part of a nerve cell that carries impulses

Myelin sheath

Fatty insulation that surrounds axons and helps to speed up the conduction of impulses


The fine cytoplasmic extensions of a nerve cell body


A junction between two nerve cells

Nerve-muscle junction

A special type of synapse where nerve endings from an axon connect with a muscle


A chemical substance released from a nerve cell, allowing an impulse to travel from a nerve cell to another nerve, muscle, organ or tissue


Consisting of two hemispheres, it is the largest part of the brain and is the source of all conscious thought

Cerebral cortex

Folded layers of grey matter covering the cerebral hemispheres


Region of the brain concerned with coordinating the contraction of sets of muscles, as well as maintaining balance.


Connects the spinal cord with the rest of the brain. Is responsible for controlling basic body activities such as heartbeat and breathing rate.

Pituitary gland

Located at the base of the brain. It secretes a number of different hormones into the blood, including those that regulate reproduction.


A region of the brain that coordinates the activity of the pituitary gland


Chemical messenger

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