Saturday, 23 February 2013

2.86 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object

A reflex is an automatic reaction, for example removing your hand from extreme heat. A reflex arch is the path of the reaction.
It starts at a sense organ e.g a finger;
receptors pick up stimuli e.g heat;
Sensory neurones carry an electrical impulse to the CNS;
A relay neuron carries the impulse through the CNS where a response is decided;
The new impulse is sent through a motor neurone;
This makes an effector carry out a response e.g muscle contracts to bring finger away from heat.


  1. Might be worth noting that the sensory and motor neurone form synapses with the relay neurone

  2. The Biology Syllabus has changed.... New Syllabus Blog:

  3. more at