The main parts of the nervous system in a human being.
Your nervous system is divided into two parts: the central and the peripheral nervous system.
The central nervous system (CNS) is made up of the brain and the spinal cord.
The peripheral nervous system is all the other nerve fibres that connect to it.
Together, they take in information about the outside world through special receptor cells. Each cell responds to a specific stimulus.
They then pass the information on as electrical impulses to the billions of nerve cells (neurones) that make up the nervous system.
Receptors
Receptors are specialized nerve cells, which are adapted to respond to a stimulus. For example, each of our ‘senses’ has a particular group of receptors, which respond to a stimulus.
Each receptor is specifically adapted to the stimulus to which it is sensitive. For example, the eye (see ‘The Eye’) is beautifully adapted to receive light stimuli. It might surprise you to learn that your ear is responsible for keeping you in balance! How bizarre!
The following table tells you where the receptors for each stimulus are situated:
| Description of stimulus: | Location of receptors: |
| The lush smell of tasty food | Nose |
| The sound of your favourite music | Ear |
| The taste of your favourite food | Tongue |
| The feel of the shape of your computer mouse | Skin |
| The image on your computer screen | Eye |
Receptors pass electrical impulses to other neurones at tiny junctions called synapses.
These signals allow the nervous system to co-ordinate a response.
Neurones
These are specialized cell transmitting nerve impulses; a nerve cell.
The path taken by an impulse through a spinal reflex arc.
A reflex arc is a neural pathway that controls an action reflex. It is the pathway followed by sensory nerve in carrying the sensation from receptor organ to spinal cord and then the pathway followed by motor nerve in carrying the order from spinal cord to effector organ during a reflex action. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex is carried out. There are two types of reflex arc: autonomic reflex arc (affecting inner organs) and somatic reflex arc (affecting muscles).
