Title: The biology of marine animals
Identifier: biologyofmarinea00nico (find matches)
Year: 1960 (1960s)
Authors: Nicol, J. A. Colin (Joseph Arthur Colin), 1915-
Subjects: Marine animals; Physiology, Comparative
Publisher: New York, Interscience Publishers
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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NERVOUS SYSTEM AND BEHAVIOUR 441 and muscle membranes, and depolarizes the muscle end-plate. The transient local depolarization of the latter is manifest as an end-plate potential (e.p.p.). This is not itself propagated, but it electrically discharges or stimulates a small surrounding region of muscle fibre, and so gives rise to a propagated wave of muscular excitation. Crustacean muscle fibres show a different functional pattern: here the end-plates are distributed widely over each muscle fibre, and the numerous end-plate potentials often produce local contractions, without propagated action potentials. Acetycholine exists in bound form at vertebrate motor nerve endings and is released on the arrival of a nervous impulse. It is rapidly destroyed (hydrolysed) by a specific enzyme, acetylcholinesterase, concentrated at c. br. m. com.ant. m
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n. Inf. ant Fig. 10.18. First-Order Giant Cell in the Brain of the Squid (Loligo pealei) ant. dendr., anterior dendrite of giant cell; ax., axon of giant cell; b, interaxonic bridge; com. ant. m., commissura anterior magnocellularis; c. br. m., brachio-magno- cellular connective; lat. dend., lateral dendrites of giant cell; n, nucleus; n. inf. ant., nervus infundibuli anterior; v. dend., ventral dendrites of giant cell. (From Young (132).) the end-plate, thus preparing the neuromuscular junction for the arrival of a new impulse. Nerve fibres which release acetylcholine at their terminals are designated cholinergic fibres. Apart from the end-plate of vertebrate striated muscle, transmitter action by acetylcholine occurs in the heart (vagus fibres), smooth muscle, peripheral ganglia and glands (autonomic fibres), and in central synapses (spinal cord) (31, 32, 33, 34, 36). Adrenergic nerve fibres form another category and their chemical trans- mitter is adrenaline or noradrenaline. Adrenergic nerve fibres supply heart, smooth muscle, glands, chromatophores, etc. Still other transmitters are suspected in invertebrates, e.g. 5-hydroxytryptamine as a neuro-cardiac transmitter in molluscs (94#, 122).

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