The neuromuscular junction

Skeletal muscle fibres are innervated by large, myelinated motor neurons originating in the anterior horn of the spinal cord. The end of each motor axon branches into 20–100 thin terminal fibres, each of which has a terminal unmyelinated zone that innervates a single muscle fibre. The muscle fibres innervated by the terminal branches of a single motor neuron are called a ‘motor unit’. The neuromuscular junction is the chemical synapse that lies between the terminal ends of motor neurons and skeletal muscle fibres. It is unlike other synapses in the CNS because synaptic transmission is purely excitatory, there is only one type of post-synaptic receptor, and the synaptic (endplate) potential is usually large enough to generate a post-synaptic action potential. This contribution discusses the structure, development and function of the neuromuscular junction; causes of neuromuscular junction dysfunction and the scientific basis of envenomation, organophosphate poisoning and therapeutic neuromuscular blockade.