Central neuronal projections and neuromuscular organization of the basal region of the shore crab leg

Abstract

The musculature and associated skeleton, peripheral nervous system, and central projections of motor and sensory neurones of the two basal (thoracic and coxal) segments of the shore crab leg (fifth pereiopod, P5) were examined in vivo and with methylene blue or cobalt staining. Each of the four main basal muscles, promotor/remotor, levator/depressor, controlling the thoracico-coxal (T-C) and coxo-basal (C-B) limb joints, respectively, comprises several more or less discrete fibre bundles (total 14), with little morphological segregation of different functional groups. The innervation to the basal leg region is carried in two nerve roots arising from the thoracic ganglion. The anterior Th-Cx root carries both sensory and motor axons, while the posterior Th-Cx root is purely motor. Three previously undescribed sensory branches (two "epidermal" nerves and an "accessory" branch), in addition to that innervating the coxobasal chordotonal receptor, have been found in the distal part of the anterior Th-Cx root. Two clusters of 10 to 15 multipolar somata (diam. 30-125 micron) are located proximally at the bifurcation of the accessory nerve and distally where the latter enters the basipodite. The cell bodies (diameter 20-80 micron) of basal leg motoneurones (total ca. 30) lie in the dorsal cortex of the ganglion, with somata of functionally related motoneurones tending to form discrete structural groups. The morphology of individual motoneurones conforms to the general arthropod pattern. All are confined to the ipsilateral hemiganglion and their main neuropilar processes run parallel and in close apposition to each other with overlapping dendritic structures. Sensory projections arising from the CB chordotonal organ also ramify in the region of the neuropile invaded by motoneurones. The possible physiological significance of such structural associations within the CNS is discussed, as are the functional implications of basal limb anatomy in general.

Recruitment in a heterogeneous population of motor neurons that innervates the depressor muscle of the crayfish walking leg muscle

“…In the distal limb within each leg segment, two antagonistic muscles move the next distal segment in opposite directions with movement being restricted to a single plane (Cochran, 1935). In contrast, in the proximal limb, although movement is still restricted to a single plane, the musculature is more complex (Bévengut et al, 1983). Within the proximal limb, functional muscles, defined by the direction of movement they cause, may consist of multiple muscle bundles with multiple origins and insertions (Bévengut et al, 1983).…”

“…In contrast, in the proximal limb, although movement is still restricted to a single plane, the musculature is more complex (Bévengut et al, 1983). Within the proximal limb, functional muscles, defined by the direction of movement they cause, may consist of multiple muscle bundles with multiple origins and insertions (Bévengut et al, 1983). In the crayfish, the depressor muscle consists of two bundles: a rostral bundle with a single origin and a caudal bundle with four origins (Antonsen and Paul, 2000).…”

Active Motor Neurons Potentiate Their Own Sensory Inputs via Glutamate-Induced Long-Term Potentiation

“…Contrary to mammals, terminal motor nerves of crayfish are composed exclusively of M Ns, and the CBC O sensory nerve contains sensory fibers only (Bévengut et al, 1983). This anatomical feature allowed us to distinguish intracellularly recorded M Ns from sensory axons.…”

The Leg Depressor and Levator Muscles in the Squat Lobster <i>Munida quadrispina</i> (Galatheidae) and the Crayfish <i>Procambarus clarkii</i> (Astacidae) Have Multiple Heads with Potentially Different Functions

“…3). Bévengut et al [1983] proposed that separate muscles should be functionally as well as anatomically distinct. However, functional definitions are inherently more problematic than strictly anatomical ones because they are open to a greater degree of interpretation.…”

“…The muscles controlling the two proximal leg joints, the promotor, remotor, levator, and depressor muscles, have not received as much attention although these joints are functionally very important in postural and locomotory behaviors [Evoy and Ayers, 1982;Kelly and Chapple, 1990;Müller and Cruse, 1991;Jamon and Clarac, 1995]. Furthermore, although the anatomy of the proximal leg muscles is known in detail for only a few decapod species [Schmidt, 1915;White and Spirito, 1973;McVean and Findlay, 1976;Ayers and Clarac, 1978;Bévengut et al, 1983;Tse et al, 1983], it is clear that the proximal muscles are anatomically much more complex than the distal muscles and often comprise multiple heads, or fiber bundles, with widely separated origins and sometimes separate insertions.…”