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BLUK100-CalveyNovember 27, 20071013:46Drugs that Act on JunctionStructure of the nerve fibres are the axons of nerve cells that originate in the anterior horn of the brain stem and the . The axon terminals branch extensively, and each anterior horn cell normally innervates 10–150 muscle fibres.(the motor unit). As each terminal branch muscle it loses its myelin sheath, and the neuromuscular junction (the ‘final common pathway’ of ) commences at the non-myelinated that is distal to the last node of axon terminals are situated in a junctional fold on of the muscle fibre (the motor endplate). In muscles, each muscle fibre has a single near its midpoint (focal innervation). This usually forms an elevation on the surface of the fibre, which an en plaque neuromuscular junction. These supplied by fast conducting A. axons, and have of contraction and relaxationMultiple minority of muscle fibres are densely innervated sites by slower conducting A. axons. Multiple innervation occurs in extraocular, intrinsic some facial muscles where the termination of motor nerves resembles a bunch of grapes, and is called grappe neuromuscular junction. These fibres are unable to propagate action potentials and require a series to produce a muscle response. The resultant contraction and subsequent relaxation is thus slower than innervated fibres, and is sometimes described as and Practice of Pharmacology for Anaesthetists, Fifth Edition.© 2008 Norman Calvey and Norton Williams. ISBN: 978-1-405-15727-8The motor essential features of focally innervated motor endplates can be revealed by electron microscopy (Fig. )The axon terminal, which is enveloped by processes cell cytoplasm, lies in a cleft in the sarcolemmal membrane and contains numerous mitochondria vesicles. Many of these vesicles are associated zones in the axon membrane that sites of neurotransmitter release. The synaptic synthesized in anterior horn cells of the spinal cord transported to the motor nerve terminal by the microtubular system. The terminal axolemmal membrane from the postsynaptic membrane by the synaptic gap, which is approximately 50 nm wide. The synaptic gap includes a basement lamina approximately 20 , which mainly consists of mucopolysaccharidesAcetylcholine receptors are primarily present in discrete groups on the shoulders of the junctional folds. density at these sites is approximately 10, square micrometre (.m2 ). The distal valleys (AChE), which has a globular structure and is predominantly present in the synaptic gap. is firmly attached to the basement membrane fibres. Both acetylcholine receptors and also present at presynaptic sites on the motor of synthesis, storage and transmission depends on the synthesis,.storage and release of acetylcholine by the motor . At the motor endplate, choline is partly derived from plasma and partly produced by the . Calvey and . 27, 200713:46Chapter 10Fig. Electron micrograph of part of a normal neuromuscular junction. The axonal terminal (A) lies in a deep indentation of membrane and contains abundant mitochondria and synaptic vesicles. The external surface of the axon is covered of Schwann cell cytoplasm (S). There are numerous infoldings (arrowed) of the sarcolemma beneath the axon, and materi

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