Showing papers on "Motor neuron published in 1979"
TL;DR: Aplysia promises to be useful for investigating the mechanisms underlying both the generation and modulation of a central program of escape locomotion and has large neurons favorable for cellular analysis.
92 citations
TL;DR: It is proposed that graded interactions between pairs of nonspiking, local interneurons in the metathroracic ganglion of the locust are an essential element in the generation of motor patterns.
Abstract: 1. Graded synaptic interactions are revealed between pairs of nonspiking, local interneurons in the metathroracic ganglion of the locust. These interneurons drive motor neurons innervating muscles of a hindleg. 2. All the interactions found between the interneurons are inhibitory and one way. Synaptic transmission is effected by the graded release of chemical transmitter. Some of the connections are apparently direct. One local interneuron can, therefore, exert a graded control over the membrane potential of another local interneuron. 3. There are inhibitory connections between local interneurons that excite the same motor neuron, between local interneurons that excite antagonistic motor neurons, and between local interneurons that excite motor neurons to muscles moving different joints of a hindleg. 4. Other pairs of interneurons, which are not connected, may be driven by common synaptic inputs. Their outputs add together at the level of the motor neurons to produce effects that are greater than the sum of their individual effects. 5. It is proposed that graded interactions between these local interneurons are an essential element in the generation of motor patterns.
89 citations
TL;DR: Hereditary canine spinal muscular atrophy is a new genetic, clinical, and pathological entity, and, at present, it appears to be the best currently available animal model of motor neuron disease.
Abstract: Hereditary canine spinal muscular atrophy is a newly recognized motor neuron disease occurring in Brittany Spaniels. The clinical manifestations, pattern of inheritance, electrodiagnostic findings, and muscle biopsies have features in common with human spinal muscular atrophy. Neuropathological examination discloses some loss of motor neurons in the spinal cord and brainstem. Many of the surviving motor neurons have neurofibrillary swellings in proximal axons, an abnormality similar to that which occurs early in the course of human amyotrophic lateral sclerosis. These axonal swellings are filled with maloriented skeins of neurofilaments. Since the proteins comprising neurofilaments are carried by slow axonal transport, their accumulation within axons suggest that the swellings may result from impaired slow transport, a hypothesis that can be tested in affected Brittany Spaniels. Hereditary canine spinal muscular atrophy is a new genetic, clinical, and pathological entity, and, at present, it appears to be the best currently available animal model of motor neuron disease.
87 citations
TL;DR: It is suggested that all fibers were capable of generating action potentials when hyperpolarized, and that allaction potentials were blocked by tetrodotoxin, suggesting the relative intactness of the regenerative sodium conductance mechanism in the disease studied here.
Abstract: Electrophysiologic properties of biopsied normal and diseased intercostal muscle fibers were examined using intracellular microelectrode techniques The resting potentials of all diseased muscle fibers were found to be depolarized Those from Duchenne dystrophy patients showed the largest depolarization, followed by those from patients with myotonic muscular dystrophy, myotonia congenita, and motor neuron disease All of the diseased fibers except those from myotonia congenita patients demonstrated an imparied ability to generate action potentials In the latter fibers, the higher-than-normal membrane resistance was associated with hyperexcitability When the membrane was hyperpolarized to the normal range, however, action potential characteristics in all fibers were near normal, except in motor neuron disease All action potentials were blocked by tetrodotoxin These findings--ie, that all fibers were capable of generating action potentials when hyperpolarized, and that all action potentials were blocked by tetrodotoxin--suggest the relative intactness, in the disease studied here of the regenerative sodium conductance mechanism
48 citations
TL;DR: Central projections from the auditory and tensor nerves support evidence of a structural “layering” within the CNS of insects.
Abstract: The auditory and tensor nerves of cicadas are mixed nerves containing both afferent and efferent elements. In 17-year cicadas, and in Okanagana rimosa, the auditory nerve contains afferents from body hairs, from the detensor tympani-chordotonal organ, and some 1300--1500 afferents from the hearing organ. Within the fused metathoracic-abdominal ganglionic complex the receptors from both the auditory and tensor nerves form a neuropilar structure that reveals the metameric organization of this complex. A few fibers run anteriorly, projecting into the meso- and prothoracic ganglia. Within the ganglionic complex a division of auditory nerve afferents into a dense intermediate and a more diffuse ventral neuropile is observed. In addition, a dorsal motor neuropile is outlined by arborizations of the timbal motor neuron. This neuron is one of several efferent cell types associated with the auditory nerve, and there is an indication that several efferent fibers innervate the timbal muscle. There is anatomical evidence for a possible neuronal coupling between the bilaterally symmetrical large timbal motor neurons. In general, central projections from the auditory and tensor nerves support evidence of a structural "layering" within the CNS of insects.
39 citations
TL;DR: The voluntary discharge properties and axonal conduction velocity of single motor units were studied in patients with neuromuscular diseases with retained differentiation of the muscle fibers into type 1 and type 2, and in patients in which muscle fibers have only intermediate histochemical properties.
Abstract: The voluntary discharge properties and axonal conduction velocity of single motor units were studied in patients with neuromuscular diseases with retained differentiation of the muscle fibers into type 1 and type 2, and in patients with late-onset hereditary distal myopathy in which muscle fibers have only intermediate histochemical properties. In the patients with muscle fiber differentiation, the findings were similar to those in normal subjects; that is, there was a continuum between motor units which fired tonically at low rates and had a low axonal conduction velocity, and motor units which fired phasically at high rates and had a high axonal conduction velocity. In the patients without muscle fiber differentiation, all motor units had intermediate firing properties and a low axonal conduction velocity. It is suggested that in chronic pathologic states, the differentiation of the muscle fiber histochemistry remains only as long as the differentiation of the motor neurons remains.
31 citations
TL;DR: The results suggest that the cause of embryonic cell death may not be related to the availability of adequate numbers of synapses with the periphery, and that the physiologic activity of the embryo may play a significant role in regulation of cell number in the developing nervous system.
26 citations
TL;DR: It is concluded that several types of chordotonal organ receptors form an ensemble of parallel input channels, which modulates the activities of OI and CE and contributes to the generation of the spatial-temporal nonuniformities of their proprioceptive reflex responses.
Abstract: 1. Action potentials of crayfish propodite-dactyl (PD) chordotonal organ receptors and two claw motor neurons, the opener inhibitor (OI) and slow closer excitor CE) were simultaneously monitored during imposed step and ramp movements of the dactyl or while the dactyl was held at various positions. 2. The activities of the cells during imposed displacements were analyzed using peristimulus time histograms and response and contour planes. The proprioceptive fields (PFs) of individual receptors resemble components of the more complex motor neuron PFs. Some receptors are briefly active after each successive opening step, while others do not respond to steps near the closed position but respond as the joint angle increases, becoming active when the claw is held open. Another type of receptor responds to closing movements. 3. Interactions among the various types of receptors and the two motor neurons were detected and analyzed by various statistical methods and intracellular recording techniques. The results indicate that receptors activated during opening movements and when the dactyl is held at open positions excite OI and CE via divergent functional connections. The efficacies of the connections made by a receptor may differ. Receptors activated by closing movements produce hyperpolarizing synaptic potentials in both efferents, possible directly or via interneurons. 4. It is concluded that several types of chordotonal organ receptors form an ensemble of parallel input channels, which modulates the activities of OI and CE and contributes to the generation of the spatial-temporal nonuniformities of their proprioceptive reflex responses.
23 citations
22 citations
TL;DR: Evidence suggests that L9's modulatory effect is mediated in the periphery, in the gill and not centrally in the abdominal ganglion, and that motor neurons L7 and LDG1 were found not to possess this ability of L9 to modulate gill reflex habituation.
Abstract: Repeated tactile stimulation of the siphon in Aphysia normally results in habituation of the gill withdrawal reflex and a concomitant decrease in the amplitude of the excitatory synaptic input ot gill motor neurons in the abdominal ganglion. It was found, however, that induced low-level tonic activity in motor neuron L9, which does not itself elicit a gill withdrawal movement, prevented habituation of the reflex from occurring. Further, in preparations already habituated, this tonic low-level activity brought about a reversal of habituation. Although tonic L9 activity prevented the occurrence of habituation or brought about its reversal, it did not interfere with the synaptic decremental process which normally accompanies gill reflex habituation. Motor neurons L7 and LDG1 were found not to possess this ability of L9 to modulate gill reflex habituation. Evidence suggests that L9's modulatory effect is mediated in the periphery, in the gill and not centrally in the abdominal ganglion.
15 citations
TL;DR: It was found that L9 was a modulator of L7's effectiveness to elicit gill movements, and was the only neuron found to possess these modulatory abilities.
TL;DR: It is concluded that the dopaminergic motor neuron L9 is modulating habituation in the periphery and that the central nervous system facilitatory control of the peripheral nervous system may act via a dopamine pathway.
Abstract: We have studied the effects of dopamine on the gill withdrawal reflex evoked by tactile siphon stimulation in the margine mollusc Aplysia. Physiological concentrations of dopamine (diluted in seawater) were perfused through the gill during siphon stimulation series. The amplitude of the reflex was potentiated by dopamine and habituation of the reflex was prevented. This occurred with no change in the activity evoked in central motor neurons. These results lead us to conclude that the dopaminergic motor neuron L9 is modulating habituation in the periphery and that the central nervous system facilitatory control of the peripheral nervous system may act via a dopaminergic pathway.