A comparison of peripheral and rubrospinal synaptic input to slow and fast twitch motor units of triceps surae
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TLDR
Post‐synaptic potentials evoked by electrical stimulation of a variety of input systems have been compared in triceps surae motoneurones innervating slow and fast muscle units, the speed of contraction of which was determined.Abstract:
1. Post-synaptic potentials (PSPs) evoked by electrical stimulation of a variety of input systems have been compared in triceps surae motoneurones innervating slow and fast muscle units, the speed of contraction of which was also determined.
2. Stimulation of high threshold afferents in both flexor and extensor muscle nerves, and of joint afferents, evoked polysynaptic PSPs which were predominantly hyperpolarizing in both fast and slow twitch motor units.
3. Volleys in cutaneous afferents in the sural and saphenous nerves evoked polysynaptic PSPs composed of mixtures of inhibitory and excitatory components. The inhibitory components were predominant in slow twitch motor units, while in fast twitch units there was a trend towards excitatory predominance.
4. Repetitive stimulation of the red nucleus caused predominantly inhibitory PSPs in slow twitch units and mixed or predominantly excitatory PSPs in fast twitch units. There was a correlation in the excitatory/inhibitory balance between PSPs of cutaneous and rubrospinal origin in those motoneurones in which both types of PSPs were studied.
5. The amplitudes of group Ia disynaptic inhibitory PSPs were found to be correlated with motor unit twitch type: IPSPs in slow twitch units were larger than those in fast twitch units. Rubrospinal conditioning volleys were found to facilitate group Ia IPSPs in both fast and slow twitch motor units.
6. The results suggest that there may be several basic patterns of synaptic input organization to motoneurones within a given motor unit pool. In addition to quantitative variation in synaptic distribution, there is evidence that qualitative differences in excitatory to inhibitory balance also exist in the pathways conveying input from cutaneous afferents and rubrospinal systems to triceps surae motoneurones. These qualitative differences are correlated with the motor unit twitch type.read more
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Functional significance of cell size in spinal motoneurons
TL;DR: The present paper is concerned with the central part of the motoneuron and the significance of its size in synaptic transmission and asks whether the cell bodies (and dendrites) connected with large and small motor fibers have different functional properties which can be recognized by their discharge characteristics.
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The convergence of monosynaptic excitatory afferents on to many different species of alpha motoneurones
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The specific ionic conductances and the ionic movements across the motoneuronal membrane that produce the inhibitory post-synaptic potential
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Neuron patterns controlling transmission of ipsilateral hind limb reflexes in cat
TL;DR: The results of experiments designed to resolve the segmental reflex into its functional components are described, finding that group I and group II fibers are the lowest threshold fibers in muscle and cutaneous nerves respectively, and may be excited in isolation by the simple expedient of selecting the appropriate nerves.
Journal ArticleDOI
Motor unit types of cat triceps surae muscle
TL;DR: Motor units, defined as including a motoneurone (cell body, dendrites and axon) plus the muscle unit innervated, have been examined in the triceps surae motor pool of pentobarbital anaesthetized cats.