Reflex Arc
Biology: Cambridge International GCSE Supplement, topic 14.1.3
The Reflex Arc
For reflex actions, the nervous system responds to stimuli (events or things) via a reflex arc. The different parts of a reflex arc are:
Stimulus
- A stimulus can be any change in the environment to which the body needs to respond.
- The stimulus is detected by a receptor.
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).
Neurones
- 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.
Effector
- An effector is a muscle or gland that brings about an action in response to the change in the internal or external environment.
Response
- The response can be any action that helps the organism to avoid the harmful situation.
Test yourself on Reflex Arc
Which part of a reflex arc carries the signal to the CNS?
What happens when a motor neurone carries a signal to an effector?