the nervous system

humans have two systems to detect and respond to changes int he external and internal enviroments:

a) nervous system; this has a rapid and short lived response, it consists of two parts

1) central nervous system (cns) composed of brain and spinal cord, cranial nerves go from brain to eyes mouth ears oher parts of head.

2) peripheral nerves; composed of sensory nerve cells (detectors) and motor nerve cells (responders)

a typical nerve fibre contains hundreds of nerves (individual specialised cells called neurones)

damage to a nerve fibre will effect hundreds of individual nerve cells so lots of responses can be lost

this interconnected system of specialised cells called neurones allows us to respond to stimuli ( changes in the enviroment)

the sequence of envents are:

 stimulus (sound-request to raise hand) > receptor ( ear ) (via sensory neourones)  > co-ordinator (via relay neurones) (brain) (via motor neurones) > effector ( arm muscles) > response (arm is lifted)