Innervation, synaptic physiology, and ultrastructure of three muscles of the second maxilla in crayfish

Abstract

SUMMARYInnervation patterns, synaptic properties, and fiber ultrastructure were studied in three muscIes of the second maxilla of Procambarus clarkii and Orconectes uirilus. All three muscles, ASDM (anterior scaphognathite depressor muscle), CFM (coxopodite flexor muscle), and SFM (scaphognathite flexor muscle), were polyneuronally innervated, receiving two, three, and four excitors, respectively. Two of the four excitors innervating SFM were branches of the two excitors supplying ASDM. No muscle received inhibitor axons. Synapses tended to be low output and show a high degree of facilitation as measured by the facilitation index of Atwood and Bittner. Ranges of EPSP amplitudes and facilitation indices were common to all excitors. Muscle fibers uniformly showed short sarcomere lengths and low thin-to-thick filament ratios. These physiological and ultrastructural peripheral features are consistent with the nature of the motor score from the central rhythm generator.

Effects of scaphognathite nerve stimulation on the acutely deafferented crab ventilatory central pattern generator

“…Our histological and physiological observations confirm previous reports (Pasztor 1968(Pasztor , 1969Young 1975;Pilkington and MacFarlane 1978;Moody-Corbett and Pasztor 1980) that the levator nerve which carries the motor neurons to the SG levator and D2a depressor muscles also contains virtually all of the small diameter afferent axons to the SG. The LNa branch carries all of the levator motor neurons and very few small diameter afferent axons.…”

“…The LNb branch carries in order of decreasing size, the three giant axons innervating the oval organ proprioceptor, the two D2a motor neurons and the majority of small diameter afferent axons. The count of axons in the size class thought to represent motor neurons (greater or equal to 6 lam diam) agrees reasonably well with estimates of the numbers of motor neurons based on size classes of excitatory junction potentials recorded from the SG muscles (Pilkington and MacFarlane 1978;Moody-Corbett and Pasztor 1980). All of the afferent neurons except the three OOAs have their somata located at the periphery in the SG (Pasztor 1969).…”

Inhibitory motoneurons in arthropod motor control: organisation, function, evolution

“…This is true for the scaphognathite, an appendage that is used in malacostracans to ventilate the respiratory cavity below the carapace (Moody-Corbett and Pasztor 1980). In this function, the scaphognathite performs constant slow ventilator strokes.…”

Analysis Of The Scaphognathite Ventilatory Pump in the Shore Crab Carcinus Maenas III. Neuromuscular Mechanisms

“…The SC muscles are innervated by two to four excitatory (and no inhibitory) axons and possess highly facilitating synapses (Moody-Corbett & Pasztor, 1980;Pilkington & MacFarlane, 1978). It has been proposed that the force generated by the SC muscles is varied mainly through changes in the firing frequencies and axonal recruitment of the motor neurones (Moody-Corbett & Pasztor, 1980). To date, there has been no rigorous analysis of the motor neurone firing pattern as a function of bursting rate.…”

“…To date, there has been no rigorous analysis of the motor neurone firing pattern as a function of bursting rate. Moreover, facilitation in the SC muscles has been studied largely at frequencies of 1-10Hz (Moody-Corbett & Pasztor, 1980), which are considerably lower than recorded firing frequencies of the motor neurones (60-140 Hz, cf. Pasztor, 1968).…”