The cell body has many branches, called dendrites , which receive signals from other cells, and are often covered in dendritic spines . Extending from the cell body in one direction is an axon . The length of axons can be several centimetres or longer. Axons carry information from one neuron to another, and are terminated at the synaptic knob , which is attached to the dendrites or cell body of another neuron. Signals are transferred across the synapse by means of a chemical neurotransmitter .
Signals travel along the axon by generating and propagating an action potential.
This is produced by letting the delicate balance of sodium, potassium and chloride ions across the cell membrane be altered, thus generating an electrical signal that flows along the axon. If the axon is coated in a fatty sheath, called myelin , the signal travels at higher speeds of anything up to 120 ms -1 . The CNS contains a number of different types of neurons, which are tailored to the job they perform. Signals from sensory receptors over the body feed along the spinal cord to the brain, and signals are sent from the brain to make muscles contract. Many medical conditions are caused by the failure of the CNS to function correctly, for example in Parkinson's disease there is a deficiency of the neurotransmitter dopamine.