The Nervous System

The nervous system is made up of 3 main parts:

Brain

Spinal Chord

Neuones/ nerve cells

It has receptors in the:

Eyes (which are sensitive to light)

Ears (which are sensitive to sounds and changes in position. Thus helping us to balance)

Tongue and nose (which are sensitive to chemicals)

Skin (which are sensitive to touch, pressure, pain and temperature)

Receptors are cells that detect stimuli or changes in the environment.

Each receptor cell contains a nucleus and a cytoplasm surrounded by a cell membrane.

Information from receptors passes along neurones to the brain.

The information passes along the neurones as signals called impulses.

The brain then coordinates the response by sending information to the appropriate organs.

There are 3 main types of neurone.

Sensory Neurone (carries impulses from the receptor to the spinal chord)

Relay Neurone (carries impulses through the spinal chord and up to the brain)

Motor Neurone (carries impulses from the spinal chord to an effector)

An effector can be a muscle that is made to contract 

OR

A gland that secretes a chemical. (e.g. a hormone)

When pain is detected by a sensory receptor in your finger it sends an impulse along a sensory neurone to a relay neurone in your spinal chord. 

The relay neurone sends an impulse in an arc via a motor neurone to an effector (a muscle) which contracts  and pulls your hand away.

THIS IS CALLED A REFLEX ACTION.