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

2.75 •reflexes help prevent injury and do so automatically 

                  •the route taken (receptor to effector) is called a reflex arc

        •1.the neurones in reflex arcs go through the spinal cord 

       

        •2.when a stimulus (touching a hot object) is detected by the receptors, an electrical impulse is sent along a sensor neurone to the CNS  

        •3.in the CNS, the sensory neurone passes on the message to the relay neurone

                  •the gap in between the two neurones is called a synapse 

                            •messages are passed across synapses using chemicals 

        •4.relay neurones relay the impulse to the motor neurone 

        •5.the impulse travels along the motor neurone to the effector (here it’s a muscle)

        •6.the muscle then contracts and moves your hand 

        •7.because you don’t have to think about the response (which takes time), it’s quicker than normal responses