. The biology of marine animals. Marine animals; Physiology, Comparative. 338 THE BIOLOGY OF MARINE ANIMALS The motor fibres innervate the muscle, and the accessory fibres form synapses with the dendrites of the receptor neurones. It has been observed that the sensory cells of the organs differ in the length and arrangement of their dendrites. The N-cells are somewhat similar sensory neurones, the processes of which are connected with ordinary muscles (those inserted on the epimeral plate of lobsters) (2, 3, 4, 4a, 48). Earlier conjectures that the muscle receptor organs are responsive to stre
. The biology of marine animals. Marine animals; Physiology, Comparative. 338 THE BIOLOGY OF MARINE ANIMALS The motor fibres innervate the muscle, and the accessory fibres form synapses with the dendrites of the receptor neurones. It has been observed that the sensory cells of the organs differ in the length and arrangement of their dendrites. The N-cells are somewhat similar sensory neurones, the processes of which are connected with ordinary muscles (those inserted on the epimeral plate of lobsters) (2, 3, 4, 4a, 48). Earlier conjectures that the muscle receptor organs are responsive to stretch have been confirmed physiologically. Stretching the isolated organ gives rise to a nervous discharge in its sensory axon (Homarus, Panulirus,. Fig. Responses of a Proprioceptor Organ in the Leg of the Crab Carcinus maenas to Vibration and Passive Movement of the Propodite- dactylus Joint Recording from nerves to propodite-dactylus organ. The lower beam indicates movement of the dactylus. (a) Passive extension, (b) (c) Passive flexion at different rates. (d) Two taps on preparation box. (From Burke (24).) Cambarus, etc.). The two organs differ considerably in their physiological characteristics (Fig. ). One has high threshold and adapts quickly to strong stretching in less than a minute. The other has low threshold and maintains continuous discharge for several hours under constant stretch. Furthermore, contraction of the receptor-organ muscle itself can initiate discharge in the sensory axon. The receptor muscle linked with the quickly- adapting neurone gives twitch-like contractions and has a high fusion frequency, whereas the receptor muscle connected with the slowly adapting sensory neurone gives slow contractions and has a low fusion frequency. One of the receptor organs thus acts as a phasic receptor signalling sudden flexion of the tail; the other is a tonic receptor, transmitting information. Please note that these images are extracted from scanned page ima
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