Molecular architecture of the neuromuscular junction

• Published in: Muscle & nerve Vol. 33; no. 4; pp. 445 - 461
• Main Authors: Hughes, Benjamin W., Kusner, Linda L., Kaminski, Henry J.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.04.2006; Wiley
• Subjects: acetylcholine; acetylcholine receptor; Animals; Biological and medical sciences; congenital myasthenic syndromes; Fundamental and applied biological sciences. Psychology; Humans; Lambert-Eaton myasthenic syndrome; muscle-specific kinase; myasthenia gravis; Neuromuscular Diseases - pathology; neuromuscular junction; Neuromuscular Junction - pathology; Neuromuscular Junction - physiology; Neuromuscular Junction - ultrastructure; neuromuscular transmission; Peripheral nervous system. Autonomic nervous system. Neuromuscular transmission. Ganglionic transmission. Electric organ; Receptors, Presynaptic - physiology; Striated muscle. Tendons; Synaptic Transmission - physiology; Vertebrates: nervous system and sense organs; Vertebrates: osteoarticular system, musculoskeletal system; Autoimmunity; Visualization; Nervous system diseases; Neuromuscular diseases; Program; muscle-specific kinase; Neuroglia; myasthenia gravis; Motor neuron; Striated muscle; Neuromuscular transmission; Muscle contraction; Neuromuscular junction; Protein; Complexity; acetylcholine receptor; Lambert-Eaton myasthenic syndrome; Schwann cell; Synaptic transmission; congenital myasthenic syndromes; Paraneoplastic syndrome; acetylcholine; Presynaptic
• ISSN: 0148-639X; 1097-4598
• DOI: 10.1002/mus.20440

The neuromuscular junction (NMJ) is a complex structure that serves to efficiently communicate the electrical impulse from the motor neuron to the skeletal muscle to signal contraction. Over the last 200 years, technological advances in microscopy allowed visualization of the existence of a gap between the motor neuron and skeletal muscle that necessitated the existence of a messenger, which proved to be acetylcholine. Ultrastructural analysis identified vesicles in the presynaptic nerve terminal, which provided a beautiful structural correlate for the quantal nature of neuromuscular transmission, and the imaging of synaptic folds on the muscle surface demonstrated that specializations of the underlying protein scaffold were required. Molecular analysis in the last 20 years has confirmed the preferential expression of synaptic proteins, which is guided by a precise developmental program and maintained by signals from nerve. Although often overlooked, the Schwann cell that caps the NMJ and the basal lamina is proving to be critical in maintenance of the junction. Genetic and autoimmune disorders are known that compromise neuromuscular transmission and provide further insights into the complexities of NMJ function as well as the subtle differences that exist among NMJ that may underlie the differential susceptibility of muscle groups to neuromuscular transmission diseases. In this review we summarize the synaptic physiology, architecture, and variations in synaptic structure among muscle types. The important roles of specific signaling pathways involved in NMJ development and acetylcholine receptor (AChR) clustering are reviewed. Finally, genetic and autoimmune disorders and their effects on NMJ architecture and neuromuscular transmission are examined. Muscle Nerve, 2005