ABSTRACT

A skeletal muscle is covered by a connective tissue called the epimysium. Within the muscle lie thousands of muscle fibres, which are arranged in bundles or fascicles, surrounded by perimysium. Microscopically, muscle fibres have a striated appearance due to the presence of numerous myofibrils. Neuromuscular transmission occurs across the neuromuscular junction, which is composed of the a-motor neurone, synaptic cleft and motor end plate of the muscle fibre. The end terminals of the motor neurons are unmyelinated, with specialised sites for the storage and release of acetylcholine (ACh). Extra-junctional nicotinic acetylcholine receptors (nAChR) rapidly sprout after denervation and burns injuries. There are pre-junctional nAChR located on the nerve terminals, which form a positive feedback mechanism designed to increase the release of ACh during periods of high activity. These receptors are blocked by non-depolarising neuromuscular blocking drugs and this explains why fade on train-of-four stimulation is observed with these agents.