A to Z of MS Nerve cells (neurons)
Nerve cells are called neurons. The human brain contains about 100 billion neurons, which carry messages between the central nervous system and the organs and limbs of the body.
The brain develops rapidly in the unborn child and in the first years of life. By the age of 2, a person has most of the neurons that they will have during their life. Although other cells die and are replaced, many neurons are never replaced when they die. The damage caused by MS can lead to the death of neurons, and thus can result in permanent disabilities.
Neurons have specialised extensions called dendrites and axons. A neuron usually has a number of dendrites but only one axon, although this axon may have extensive branching.
Information enters the neuron via the dendrites, passes through the cell body and then along the axon until it reaches the synapse. The synapse is the space between an axon and a dendrite of another neuron.
The axon can be as long as a metre, making neurons some of the longest cells in the body.
The axon is surrounded by a sheath of fatty protein called myelin. Myelin acts as insulation to the axon and prevents messages becoming interrupted. The myelin sheath has short gaps about one micrometre apart known as Nodes of Ranvier. Nerve messages leap along the axon from node to node. The thickness of the myelin sheath and the size of the gap between nodes determine the speed of messages, which can be as fast as 120 metres/second (268mph).
Nerve cells are surrounded by support cells.