Discharge Patterns of Neurones Supplying Tonic Abdominal Flexor Muscles in the Crayfish (original) (raw)
Related papers
Extensor motor neurons of the crayfish abdomen
Journal of Comparative Physiology ? A, 1975
The somata of five deep extensor motoneurons of the third abdominal ganglion of the crayfish (Procambarus clarkii) were located and identified. The positions of these somata within the ganglion and their distal distribution to muscles have been mapped and were constant. The soma of the extensor inhibitor was noted to touch the soma of the flexor inhibitor. Three of the excitatory neurons were clustered near their exit route. Sensory and cord routes of activation of the extensor motoneurons were also found and were constant from preparation to preparation. Sub-threshold recording showed that these motoneurons exhibited radically different types of post-synaptie response to stimuli at different sites in the nervous system. No interaction between extensor motoneurons or between the extensor and flexor motoneurons was observed.
Differentiation of Nerve Terminals in the Crayfish Opener Muscle and Its Functional Significance
The Journal of General Physiology, 1968
Junctional potentials (jp's) recorded from superficial distal fibers of the crayfish opener muscle are up to 50 times larger than jp' in superficial central fibers when the single motor axon that innervates the muscle is stimulated at a frequency of 1/sec or less. At 80/sec, in contrast, central jp's are up to four times larger than those observed in distal fibers. The tension produced by single muscle fibers of either type is directly proportional to the integral of the time-voltage curve minus an excitation-contraction coupling threshold of 3 mv. Distal fibers therefore produce almost all the total muscle tension at low frequencies of stimulation and central fibers add an increasingly greater contribution as their nerve endings begin to facilitate in response to increased rate of motor discharge. Differentiation of muscle membrane characteristics (input resistance, space constant, time constant) cannot account for these differences in facilitation ratios. The mechanism of neuronal differentiation is not based upon the size or effectiveness of transmitter quanta, since equal sized jp's have equal variances;: mjp sizes and variances are also equal. No differences were found between fiber types in rates of transmitter mobilization, density of innervation, or the relationship between transmitter release and terminal depolarization. Single terminals on distal fibers were found to release transmitter with a greater probability than central terminals. More effective invasion of distal terminals by the nerve impulse at low frequencies can account for the difference.
The structure of tonic flexor motoneurons in crayfish abdominal ganglia
Journal of Comparative Physiology ? A, 1974
1. The tonic flexor motoneurons were filled with cobalt dye via the cut ends of their axons. All six physiologically defined cells were identified anatomically (Figs. 2-4). 2. The cell somata are widely scattered in the ventral rind of the ganglia; three cells have ipsilateral and three cells have contralateral somata in reference to their axons; cells with contralateral somata tend to be more rostral in the ganglion (Figs. 2, 11). 3. All ceils have bilateral dendritic domains (Figs. 5, 6, 8, 10). Each soma is connected to a long, thin neurite which travels dorsally and enlarges into a thick process (neuropilar segment) that crosses the midline in the posterior outer commissure (Figs. 8, 9) except for fl, which crosses anteriorly (Fig. 10). Many branches emerge from the neuropilar segment; the proximal portions of these branches and the ncuropilar segment contribute to the coarse dorsal neuropile. Distal branches are found in the fine ventral neuropile (Figs. 9, 10). No recurrent collaterals were observed. 4. Most of the neuropilar segments converge into a narrow arc that sweeps across the dorsal neuropile (Figs. 8, 9). The close correspondence of the processes, especially of contralateral homologues (Figs. 10, 12) provides an anatomical basis for functional interactions among the tonic flexors. The main masses of finer processes that run along the longitudinal axis are located laterally. 5. Bilateral, serial and interanimal homologies of soma position all showed similar degrees of variation. Positions were relatively constant but might vary by up to 100 ,~ relative to external landmarks (Fig. 11). 6. Dendritic geometries were sufficiently similar to permit unambiguous identification of homologues, but variability in the number and shape of branches is common.
General physiology and biophysics, 2002
Action potentials (APs) and impulse responses in the soma and axon of the rapidly and slowly adapting (SA) abdominal stretch receptor neurons of the crayfish (Astacus leptodactylus) were recorded with single microelectrode current-clamp technique. Impulse frequency response to constant current injection was almost constant in the SA neuron while the response decayed completely in the rapidly adapting (RA) neuron. Mean impulse frequency responses to current stimulations were similar in the receptor neuron pairs. In the RA neuron additional current steps evoked additional impulses while a sudden drop in the current amplitude caused adaptation. Impulse duration was dependent on the rate of rise when current ramps were used. Adaptation was facilitated when calculated receptor current was used. Exposing the neuron to 3 mmol/l TEA or scorpion venom resulted in partly elongated impulse responses. SA neuron could continuously convert the current input into impulse frequency irrespective of ...
Journal of Experimental Biology, 2008
SUMMARY According to the size principle the fine control of muscle tension depends on the orderly recruitment of motor neurons from a heterogeneous pool. We took advantage of the small number of excitatory motor neurons (about 12) that innervate the depressor muscle of the crayfish walking leg to determine if the size principle applies to this muscle. We found that in accordance with the size principle, when stimulated by proprioceptive input, neurons with small extracellular spikes were recruited before neurons with medium or large spikes. Because only a small fraction of the motor neurons responded strongly enough to sensory input to be recruited in this way, we extended our analysis to all neurons by characterizing properties that have classically been associated with recruitment order such as speed of axonal conduction and extracellular spike amplitude. Through a combination of physiological and anatomical criteria we were able to identify seven classes of excitatory depressor m...
Fast-axon synapses of a crab leg muscle
Journal of Neurobiology, 1978
Neuromuscular synapses of the "fast" excitatory axon supplying the main extensor muscle in the leg of the shore crab Pachygrapsus crassipes were studied with electrophysiological and electron-microscopic techniques. Electrical recording showed that many muscle fibers of the central region of the extensor muscle responded only to stimulation of the fast axon, and electron microscopy revealed many unitary subterminal axon branches. Maintained stimulation, even at a low frequency, resulted in depression of the excitatory junctional potentials (EJPs) set up by the fast axon but EJPs of different muscle fibers depressed a t different rates, indicating some physiological heterogeneity among the fast-axon synapses. Focal recording a t individual synaptic sites on the surfaces of the muscle fibers showed quantal contents ranging from 1.4 to 5.5 at different synapses; these values are relatively high in comparison with similar determinations made in the crayfish opener muscle. Synapse-bearing nerve terminals were generally relatively small in diameter and filiform, with many individual synaptic contact areas of uniform size averaging 0.6 pm2. All of the individual synapses had a presynaptic "dense body" at which synaptic vesicles clustered. If these structures represent release points for transmitter quanta, the initial high quantal content, would have an ultrastructural basis. The mitochondial content of the nerve terminals, the synaptic vesicle population, and the specialized subsynaptic sarcoplasm were all much reduced in comparison with tonic axon synaptic regions in this and other crustaceans. The latter features may be correlated with the relatively infrequent use of this axon by the animal, and with rapid fatigue.
Resistance reflexes and patterned discharge in motor neurons of the crayfish propus-dactylus joint
Comparative Biochemistry and Physiology Part A: Physiology, 1979
The slow closer motor (SCM) and opener inhibitor (01) neurons of Canbarus clarkii display both phasic and tonic activity in resistance reflexes of the propus-dactylus joint. 2. Phasic response latencies of both neurons diminish with increasing velocity of joint opening according to a power function. Interpulse intervals (IPIs) diminish according to an S function. 3. IPI distributions for both neurons are characterized by Gamma distribution functions. 4. Though the SCM neuromuscular junction is not pattern sensitive, both neurons display patterning, i.e. a more or less discrete class of short IPIs (doublets). 5. Patterning is discussed as a mode of activity which may or may not be associated with pattern sensitive neuromuscular junctions.
Abdominal positioning interneurons in crayfish: participation in behavioral acts
Journal of Comparative Physiology A, 1989
Premotor interneurons involved in the abdominal positioning behaviors of the crayfish, Procambarus clarkE, were studied intracellularly, along with motoneuron activity, in semi-intact preparations during episodes of fictive behavior. Each impaled cell was tested by injecting depolarizing current and examining the motor output. If a response was evoked then the cell was classified as a flexion-producing interneuron (FPI), extension-producing interneuron (EPI) or mixed output interneuron (MOI). A platform drop/rise procedure was then used to elicit abdominal extensionlike and flexion-like responses. Interneurons that were active during positioning behavior were silenced by hyperpolarization to determine their contribution in generating the underlying motor program. The data were used to assess the degree of participation of these interneurons in abdominal positioning behavior. Fewer than half of the FPIs, EPIs and MOIs became active during the behavioral episodes. Strength of response to depolarizing current was not correlated with the probability that a cell would fire during behavior. Hyperpolarization tests showed that typical FPIs, EPIs and MOIs were only responsible for a small part of the overall motor output. Also, interneurons, regardless of their FPI or EPI classification, were often observed to fire during both flexion-like and extension-like behaviors. Responses of FPIs, EPIs and MOIs to repeated platform movements suggest that these cells may fire according to a probability distribution depending on: (1) strength of the stimulus; (2) location Abbreviations: FPI flexion-producing interneuron; EPI extension-producing interneuron; MOI mixed output interneuron; SFMN superficial flexor motoneuron; SEMN superficial extensor motoneuron
Nonhomogeneous excitatory synapses of a crab stomach muscle
Journal of Neurobiology, 1978
Neuromuscular synapses of pyloric muscle PI in the blue crab Callinectes sapidus were examined using electrophysiological and electron microscopic methods. The muscle is innervated by a single excitatory axon of the stomatogastric ganglion. Excitatory postsynaptic potentials show striking facilitation at very low frequencies of stimulation, indicating very slow decay of the facilitation process after a single nerve impulse. Quanta1 content of transmitter release at a low frequency of stimulation averaged 1.5. Evidence was obtained that not all synapses on a muscle fiber are equivalent. This was particularly evident at the morphological level in serially sectioned nerve terminals. On each nerve terminal examined, a wide range of synapse sizes was found. Synaptic contact areas ranged from less than 0.5 pm2 to almost 10 pm2; the latter value is large compared with those obtained for other crustacean neuromuscular synapses. Most of the smaller synapses lacked the presynaptic dense bodies which are putative release sites for the transmitter substance. The larger synapses all had presynaptic dense bodies, and some showed evidence of splitting apart into smaller subunits. It is postulated that about half the morphologically identified synapses are relatively inactive. INTRODUCTION Crustacean stomach muscles innervated by the stomatogastric ganglion receive only excitatory neuromuscular synapses from the axons supplying them. The majority of these muscles are innervated by only one axon (Govind et al., 19741, and thus provide favorable material for attempts to correlate physiological performance and ultrastructural detail. In a previous study (Atwood et al., 1977), two of the gastric mill muscles (GM8b and GM9) were examined in the blue crab, Callinectes sapidus. The present study was undertaken to define the structure and function of synapses in a pyloric muscle of the same animal, and to compare these synapses with those of the gastric mill muscles and with