The Nervous System
The nervous system controls all body functions.
It receives information from inside and outside the body and then sends out messages to appropriate organs in the body in response to this information.
The organs of the body that receive such information are known as receptor organs and include the eyes, ears, skin and nose.
Organs in the muscles and joints provide further information.
The nervous system has three main parts:
- the brain
- the spinal cord
- the merves
The brain is the control centre for every activity of the body, conscious as well as involuntary actions. It is suspended in clear (cerebrospinal) fluid and surrounded by the skull (cranium) for its protection.
The spinal cord is about 1 cm wide when it leaves the base of the brain through an opening at the base of the skull.The vertebrae of the vertebral column protect it.
It is made up of nerve cells and fibres and carries messages to and from all parts of the body through a series of branching nerves situated in gaps between the vertebrae.
Nerves are thread-like substances made up of a large number of neurones, which are enclosed in an outer coat.
Neurones consist of three parts:
- nucleus: the main cell body
- dendrites: pick up and receive messages or impulses
- axons: transmit messages or impulses
The nerve impulses or messages are carried along neurones that are not directly connected to each other.
The gap between them is known as the synapse or synaptic joint.
Neurones can be divided into two types:
- Sensory neurones carry information to the brain and central nervous system.
- Motor neurones carry information from the brain or the central nervous system to other parts of the body.
There are three types of receptor or sense organs depending on where they are found.
Exteroceptors receive information from outside the body. Examples of these are the eyes, ears and skin.
Interoceptors receive information from organs inside the body including the lungs and digestive system.
Proprioceptors are found mainly in the muscles, tendons and joints. They respond to the degree of stretching in their particular body part and so give information about relative positions of different parts of the body. Proprioceptors enable us to move our limbs with great accuracy and speed without the need to actually watch them.