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Biomedical subjects

C K Govind

Publications and source records attributed to C K Govind.

102 records · Page 6Linked to original sources
PubMed1977

Development of the dimorphic claw closer muscles of the lobster Homarus americanus: L Regional distribution of muscle fiber types in adults.

1. The closer muscles of the dimorphic claws (chelipeds) were studied for the presence and location of fast and slow muscle fibers. 2. Cutter claws were composed of about 60-70% short sarcomere (less than 4 mum) fast fibers; the remainder was longer sarcomere (greater than 6 mum) slow and intermediate (4-6 mum) fibers. 3. Crusher claws were composed of a uniform population of long sarcomere (6-13 mum) slow and intermediate (4-6 mum) fibers. 4. There was a regional distribution of fibers in the cutter claw. Ventral fibers were predominantly slow. Dorsal fibers and central medial fibers were fast. Proximal and distal fibers in the medial section were usually mixed. 5. The regional distribution of cutter fibers correlates with previous physiological studies on the distribution of the fast and slow motor axons to these muscle fibers.

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PubMed1976

Growth of lobster giant axons: correlation between conduction velocity and axon diameter.

The conduction velocity and axon diameter of medial and lateral giant axons in lobsters was followed during growth from early juvenile (13 mm) to adult (250 mm) forms. In both axons, conduction velocity increased more than 4-fold in the growth period examined. Correlated with the increase in conduction velocity is an increase in axon diameter and the relationship between these two parameters is expressed by the equation CV = krX, where X equals 0.5 for the lateral and 0.7 for the medial giant axons. The sheath surrounding the giant axons also increases in size during growth with that of the medial giant axon being considerably thicker than that of the lateral giant axon. The significance of the increase in axon diameters is to increase conduction velocity and thereby reduce the latency of the escape response mediated by these giant axons.

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PubMed1976

Ultrastructural diversity in motor units of crustacean stomach muscles.

The physiological and ultrastructural properties of muscle fiber.s comprising three motor units in the gastric mill of blue crabs are described. In their contractile properties muscle fibers in all motor units are similar and resemble the slow type fibers in crustacean limb muscles. The majority of fibers generate large excitatory post-synaptic potentials which do not facilitate strongly. Structurally two types of fibers are found. The one type has long sarcomeres (greater than 6 mum), thin to thick myofilament ratios of 5-6:1 and diads located near the ends of the A-band. The other type has shorter sarcomeres (less than 6 mum), thin to thick myofilament ratios of 3:1 and diads located at mid sarcomere level. Both types of fibers occur within a single motor unit and this differs from the vertebrate situation. Furthermore, the finding of fibers with a low thin to thick myofilament ratio of 3:1 demonstrates that they are not exclusive to fast type crustacean muscle but also occur in slow stomach muscles.

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PubMed1973

Synaptic differentiation in a regenerating crab-limb muscle.

Properties of synapses on regenerating nerve terminals of the single excitatory axon to the stretcher muscle were studied in the regenerating second walking leg of the shore crab, Grapsus. In the adult condition these synapses vary in physiological properties, ranging from high release, poorly facilitating types to low release, highly facilitating types. Synapses on regenerating stretcher-muscle fibers show a distinct temporal pattern of differentiation. In early limb buds, a characteristic fluctuating, excitatory postsynaptic potential, punctuated by failures of transmission, is seen, indicating a developmentally "naive" synapse with low quantal content. In these early stages proportionately more synapses are of the poorly facilitating type; the highly facilitating synapses appear increasingly in later stages. Thus, the type of synapse that will form seems likely to be related to the time of innervation. Synapses of early developmental stages found by electron microscopy are significantly smaller than those seen in adult muscles; thus, the synaptic contact area must increase during development. We postulate that contacts formed by the primary branches of the axon early in development differentiate into relatively large, poorly facilitating synapses, while contacts formed by secondary branches slightly later in development differentiate into smaller, highly facilitating synapses.

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PubMedDate not supplied

Neural factors influence the degeneration of muscle fibers in the chelae of snapping shrimps.

The asymmetric pincer and snapper claws in the snapping shrimp differ in external morphology and musculature. The snapper is a massive claw used for displays and defense; the pincer is small and slender, used for feeding and burrowing. The snapper has only slow muscle fibers; the pincer has both slow and fast. Removal or denervation of the snapper claw induces transformation of the contralateral pincer to a snapper type of claw at the subsequent molt. A removed claw regenerates as a pincer type, as long as the innervation of the remaining claw is intact. Fast muscle fibers, found exclusively in the pincer claw, normally degenerate completely within 10 d after the moult, which transforms the pincer to a snapper. Morphological transformation of the pincer following removal of the snapper claw can occur even if the pincer claw is denervated. Denervation of the pincer, however, delays degeneration of the fast fibers, increasing the estimated half-time of muscle degeneration, for 4.4 +/- 0.2 to 19.5 +/- 0.8. d after the transforming moult. Neural influences therefore are involved both in the determination of the morphology of the claw and in the induction of degenerative changes during the remodeling of an existing claw.

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