The functional morphology of the uropod stretch receptor of the sand crab Emerita analoga : including a comparison with the uropod stretch receptor of the squat lobster Munida quadrispina

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dc.contributor.authorWilson, Linda Janeen_US
dc.date.accessioned2024-08-15T20:17:19Z
dc.date.available2024-08-15T20:17:19Z
dc.date.copyright1988en_US
dc.date.issued1988
dc.degree.departmentDepartment of Biologyen_US
dc.degree.levelMaster of Arts M.A.en
dc.description.abstractWhile much is known about the response characteristics and the central connections of crustacean primary afferents, the mechanism of stimulus transduction in stretch receptors remains enigmatic. I studied the morphology of a basal joint proprioceptor in two Anomura (Hippidae, Galatheidae) in order to better understand the mechanical aspects of the transduction process (the other aspects depend on the electrochemical properties of the membrane). The uropod stretch receptor (USR) complex in the sand crab Emerita analoga (Stimpson 1857) consists of an elastic strand innervated by four giant, nonspiking, mechanoreceptive neurons (NSRs) with central somata and a separate, parallel muscular strand innervated by two groups of neurons of unknown modality (Paul, 1972). Each of the NSRs has three morphologically distinct zones in the periphery. The Zone of Dendrite Entry for each NSR begins outside the strand at the first bifurcation of the dendrite into two primary branches which enter the strand at acute to right angles as thick ( 40 to 60µm) cylinders and immediately turn rostrally and caudally along the long axis of the strand and extend into the strand where further branching occurs. The Zone of Branching consists of 4 to 15 m diameter dendritic branches within the strand. Tiny (0.1-0.5 µm) cylindrical processes (dendritic tips) arise directly from all levels of this zone so that even the largest branches appear to be covered in the fine dendritic "hairs" of the Zone of Dendrite Termination. Each pair of branches is divided by a rod of extracellular matrix (ECM) running parallel to the long axis of the strand. These vacuolated strings are fusiform in shape and extend for the length of the dendritic branch with which each string is associated. Dendritic tips project into the strings and are probably the site of mechanosensory transduction because they are in direct contact with the ECM of the vacuolated string which is compressed by strand-stretching. Fibres in the ECM of the capsule and vacuolated strings of the elastic strand appear to belong to a special class of 'invertebrate elastic fibres' described by Elder and Owen (1967) and give the strand its resilience. Cross-sectional profiles of dendritic tips are significantly larger but significantly less numerous in stretched than in relaxed receptors. I propose a model in which distal tips are compressed until they are too small to be recognized in stretched strands. The large profiles are the proximal tip regions which have expanded by hydrostatic pressure. Like Emerita, the squat lobster, Munida quadrispina (Benedict 1902) has a USR complex consisting of parallel elastic and muscular strands. The strands are closely opposed to one another and lie in a single, ventral plane rather than running dorso-ventrally as they do in Emerita. The receptor complex receives its innervation from the receptor nerve which contains 10-13 profiles whose signal characteristics are unknown. Two of the smallest appear to innervate the receptor muscle, the remainder the elastic strand. The one or two largest profiles (10-20 µm), upon entering the strand transversely, turn longitudinally, and become associated with vacuolated strings into which they send tips as do the four NSRs in Emerita. Homologies between the two USRs and other basal joint proprioceptors are suggested and some functional and evolutionary consequences of USR morphology are discussed.
dc.format.extent113 pages
dc.identifier.urihttps://hdl.handle.net/1828/20158
dc.rightsAvailable to the World Wide Weben_US
dc.titleThe functional morphology of the uropod stretch receptor of the sand crab Emerita analoga : including a comparison with the uropod stretch receptor of the squat lobster Munida quadrispinaen_US
dc.typeThesisen_US

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