Functional Anatomy

The functional unit of the nervous system is the neurone, with its cell body and axon, which terminates at a synapse. The specificity, size and type of each group of neurones varies greatly. For example, an ex motor neurone of the anterior horn cell of the lumbar spinal cord has an axonal length of over 1 m and innervates several hundred to 2000 muscle fibres-to form the motor unit. By contrast, a spinal or intracerebral internuncial neurone may have an axon under 100 /-Lm in length and terminate solely on one or other neuronal cell body. It is now generally agreed that transmission at most if not all synapses is mediated by chemical neurotransmitters.
These transmitters are released by action potentials passing down the axon. They then react with the receptors on the postsynaptic cell body, increasing its ionic permeability and propagating a further action potential within it.
This combination of electrical activity in the axon and chemical release at the synapse is the basis of all neurological function.
Important neurotransmitter substances are:
• Acetylcholine
• Noradrenaline
• Adrenaline
• 5-Hydroxytryptamine
• y-Aminobutyric acid (GABA)
• Opioid pep tides
• Prostaglandins
• Histamine
• Dopamine
• Glutamate
The exact role of these neurotransmitters in pathogenesis is being evaluated, but it is now thought that a wide variety of acute and chronic neurological disease may be mediated, at least in part, by a final common pathway of neuronal injury involving excessive stimulation of glutamate receptors. Effective glutamate antagonists are being used in clinical trials.