What Is the Structure and Function of the Nervous System?
Learn how receptors, neurones, the brain and spinal cord coordinate rapid responses, with a GCSE Biology reflex arc example and a common exam mistake to avoid.
The nervous system detects changes in your surroundings and coordinates rapid responses. Its main parts are receptors, neurones, the central nervous system (CNS) and effectors. The CNS consists of the brain and spinal cord.
How a response works
A stimulus is a change, such as a bright light or heat. A receptor detects it and sends an electrical impulse along a sensory neurone to the CNS. The CNS processes the information and sends an impulse along a motor neurone to an effector. An effector is a muscle or gland that produces the response: a muscle might contract, or a gland might secrete a hormone.
The brain helps coordinate behaviour, while the spinal cord can coordinate a reflex action. At a synapse, the small gap between neurones, chemicals carry the signal from one neurone to the next.
Reflex example
If you touch a hot object, heat receptors in your skin detect the stimulus. An impulse travels along a sensory neurone to the spinal cord, passes through a relay neurone, then travels along a motor neurone to a muscle in your arm. The muscle contracts and pulls your hand away. This pathway is called a reflex arc.
A reflex is automatic and rapid, helping protect you from harm. It does not need a decision from the conscious part of your brain before your hand moves, although you can become aware of the heat afterwards.
Exam mistake to avoid: Do not say that every nervous response is a reflex, or that the brain must consciously decide to start one. For a reflex arc, give the pathway in the correct order and name the muscle as the effector, not the receptor.
