Components of a Reflex Arc

Biology: AQA GCSE Higher, topic 5.2.5

The different parts of a reflex arc are:

A stimulus can be any change in the environment to which the body needs to respond.
The stimulus is detected by a receptor.

Receptors are found all over the body.
They detect the change in the environment and initiate (start) a signalling process within the body.
The signal is picked up by a neurone (nerve cell).

There are three types of neurone (nerve cell):
The sensory neurone, which carries the signal in the form of an electrical impulse to the central nervous system (CNS).
The relay neurone (in the CNS) relays the electrical impulse from the sensory neurone to the appropriate motor neurone.
The motor neurone is another type of nerve cell that carries the electrical impulse from the CNS to an effector.

An effector is a muscle or gland that brings about an action in response to the change in the internal or external environment.

The response can be any action that helps the organism to avoid the harmful situation.

Test yourself on Components of a Reflex Arc

Which part of a reflex arc carries the signal from a receptor to the CNS?
What happens when a motor neurone delivers a signal to an effector?
A person steps on a sharp stone and feels pain in their foot. Which part of the reflex arc first detects this change?
What does the relay neurone do inside the central nervous system?
A person's hand touches a hot object and they immediately pull it away. Which part of the reflex arc does the pulling away represent?