How the Nervous System Coordinates a Response

The nervous system coordinates a response by detecting a stimulus, sending electrical impulses to the central nervous system, and activating an effector that produces a response.

The response pathway

The pathway can be summarised as:

stimulus → receptor → coordinator → effector → response

• A stimulus is a change in the internal or external environment, such as heat, light or sound.
• Receptors are cells that detect stimuli. For example, temperature receptors in the skin detect changes in temperature.
• Electrical impulses travel along sensory neurones to the central nervous system (CNS). The CNS consists of the brain and spinal cord.
• The CNS acts as the coordinator. It receives and processes the information before coordinating a response.
• Electrical impulses then travel along motor neurones to an effector.
• An effector is a muscle or gland. Muscles respond by contracting, while glands respond by secreting substances such as hormones.

Worked example: touching a hot object

When you touch a hot object:

1. Heat is the stimulus.
2. Temperature receptors in the skin detect it.
3. An electrical impulse travels along a sensory neurone to the CNS.
4. In a reflex arc, the impulse passes across synapses and through a relay neurone.
5. A motor neurone carries an impulse to an arm muscle.
6. The muscle contracts, moving the hand away.

This is a reflex action: an automatic and rapid response that does not involve the conscious part of the brain. Reflexes help protect the body from injury.

Common exam mistake

Do not say that electrical impulses travel through the whole body in the blood. They travel along neurones. Hormones are chemicals transported in the bloodstream.

This explanation assumes AQA GCSE Biology Higher tier and separate Biology, although this nervous-system content is assessed on both Foundation and Higher tiers and is shared with Combined Science.