Nerve cell (neuron)
Special cells are required to construct an effective communication system (nervous system) within the body. The basic unit of the nervous system is the neuron or nerve cell. A simple neuron is shown below.

Neurons vary in size and shape, but all have four basic features:
- Cell body. This contains the nucleus and other cell organelles responsible for keeping the cell functioning perfectly.
- Dendrites. These are short projections originating from the cell body that receive signals from the nerve endings of other neurons.
- Axon. Is the long extension leading away from the cell body that transmits signals to muscles, glands or other neurons. The length of the axon can vary from 1mm to 1m.
- Axon ends. At these regions signals are transmitted to muscles, glands or other neurons.
Neurons are specialised cells that conduct electrical impulses in one direction only.
Two major types of neurons found outside the brain are sensory and motor neurons. Sensory neurons coduct signals from sensory organs. Motor neurons carry signals from the brain or spinal cord to muscles or glands. Click to see an animation
Most neurons in mammals are surrounded by a protective sheath called myelin. Myelin is a fatty material that insulates the nerve, much like plastic insulates the wire in electrical appliances. This protective sheath of myelin is actually a cell that is wrapped around the nerve as shown on the right. The image on the right shows a cross section through the myelin sheath revealing how the cell is wrapped several times around the nerve fiber.
Myelin allows the signal to travel through the nerve fiber 200 times faster than in an unmyelinated nerve. Damage to the myelin sheath results in a disease called Multiple Sclerosis.

Label the diagram on the right using the following words and give the function of each structure labelled.

Dendrites

Nucleus

Cell body

Axon

Myelin sheath

Axon endings

In which direction does a signal travel along the nerve cell?

What is the purpose of the myelin sheath?

 

 

Reflex arc

Continue