Understanding the Nervous System

The brain communicates messages through a complex network of nerves that travel throughout our body. Together, the brain and nerves are known as the nervous system, while the spinal cord and the brain make up the central nervous system.

On their own, the nerves that run throughout our body are called the peripheral nervous system (PNS). They relay information from our brain through our spinal cord to the body, and back again.

The autonomic nervous system (ANS) is part of the peripheral nervous system. It communicates messages from all the organs in our chest, abdomen and pelvis. For example, it manages our “fight and flight” responses, our “rest and digest” responses. It looks after the automatic activities of our heart and blood vessels and plays an important part in sexual response and bladder control.

The basic building blocks of the nervous system are nerve cells or neurons. We are born with about 100 billion neurons. Neurons are connected by synapses which carry electrical signals and chemical neurotransmitters.

Grey matter is formed when neurons cluster together on the outer part of the brain and inner part of the spinal cord.

White matter is found on the inner part of the brain and outer part of the spinal cord. It is made up of bundles of nerve fibres called axons, which are long thin extensions of neurons. Axons are covered by a white, fatty substance called myelin which insulates them, like the plastic coating of an electric wire. The axons then bundle together, like the individual telegraph wires in a cable, to form a nerve.

The brain is in constant contact with all parts of the body, sending instructions and receiving feedback from the senses. The axons carry these messages as tiny electrical currents or nerve impulses.

Outgoing messages are sent from the brain along the motor pathways to activate the muscles of the body. The neurons that make up these pathways are called motor neurons.

Incoming messages sent from the senses back to the spinal cord and brain come along the sensory pathways. These are called sensory neurons.

The various causes of brain injury can affect the way the nervous system functions by:

• affecting brain function itself
• affecting the brain’s ability to communicate with the rest of the body
• affecting the ability of muscles to respond to the brain’s orders (nerve impulses).