2.85 - Reflex arc

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

stimulus - the hot flame 

receptor - heat sensor in the skin 

- The impulse travels to the spinal cord along the sensory neurone 

- In the spinal cord the impulse is passed on to the relay neurone 

- This passes the impulse on to the motor neurone 

- The motor neurone carries the impulse to a muscle in the arm. The muscle is the effector. 

- The muscle contracts to remove the and from the hot object. This action is the response. 

There is a total of 3 synapses in this reflex arc: 

- sensory neuron and relay neurone 

- motor neurone and muscle