The Nervous System

The nervous system is very important because it relays all messages from the brain, which is the control center of the body, to the rest of the organs in the body. The nervous system is divided into two main systems much as the skeleton is divided into two main skeletons. The central nervous system is composed of the brain and spinal cord, which is a bundle of nerves that is contained within the vertebral column. The peripheral nervous system is composed of all the nerves that deliver the messages sent down the spinal cord to the appropriate destination.

The nerves of the body are composed of cells called neurons (pictured left). Sensory neurons relay sensory information gathered from a certain part of the body back to the brain. Motor neurons send messages to the correct muscle or gland that needs to be stimulated. Interneurons are neurons that serve as relays between other neurons.

Each neuron has three main parts: the body, axon, and a number of dendrites. The axon is the part of a neuron that transfers the appropriate message, information on potential, to another nerve, muscle, or gland. When a message from the brain is sent down the spinal cord to a peripheral nerve and finally to its destination, a quick relay process is used to deliver the message. The message is sent throught the appropriate nerves by passing the information from neuron to neuron. When the first neuron receives the message, it immediately passes the information to the next neuron in line. This is achieved through the action of neurotransmitters, chemicals which allow the message from the brain to cross the synapse between cells. This process continues down the spinal cord and through the other nerves until the message reaches its destination. In the case of a reflex action, the message provided by the sensory neurons never actually gets processed by the brain, but is actually returned by the spinal cord with a certain pre-determined response. This process happens very quickly, but slows with age and other factors. The time which information takes to be sent to the brain by sensory receptors, processed by the brain, and to have the appropriate return message processed is commonly referred to as a person's reaction time.

Major Nerves of the Body:



written by Matt Richards