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At least 1,621 records · Page 90Linked to original sources
PubMed1984

Fine structure of primary afferent axon terminals projecting from rapidly adapting mechanoreceptors of the toe and foot pads of the cat.

Two Pacinian corpuscle afferents and two rapidly adapting afferents from Krause corpuscles were intra-axonally labelled with horseradish peroxidase in the lumbosacral enlargement of the cat's spinal cord. Tissue was prepared for combined light and electron microscopical analysis. Boutons from both classes of afferent had similar ultrastructural appearances. They both formed from one to three synaptic junctions with dendritic shafts and spines and received axo-axonic synapses. In addition, both categories of bouton were seen to be presynaptic to structures interpreted as vesicle-containing dendrites. It is concluded that both types of afferent fibre are subject to presynaptic control and that they synapse with dorsal horn neurones which are possibly interneurones involved in primary afferent depolarization and post-synaptic dorsal column neurones.

Adaptation, Physiological↗
PubMed2002

Toe flexor muscle spindle discharge and stretch modulation during locomotor activity in the decerebrate cat.

In order to investigate the nature (i.e. static or dynamic) of fusimotor drive to the flexor hallucis longus (FHL) and flexor digitorum longus (FDL) muscles during locomotion we recorded Ia and group II muscle spindle afferent responses to sinusoidal stretch (0.25 and 1 mm amplitude, respectively, 4-5 Hz) in a decerebrate cat preparation. FHL Ia and group II afferents generally had increased discharge rates and decreased modulation to stretch throughout the step cycle, compared to rest, suggesting raised static gamma drive at all locomotor phases. Although the modulation of Ia afferents was reduced during locomotion, most (13 of 18) showed a clear increasing trend during homonymous muscle activity (extension). This was consistent with phasic dynamic gamma drive to FHL spindles linked with alpha drive. In agreement with previous reports, FHL gave a single burst of EMG activity during the step cycle while FDL alpha drive had two components. One was related to extension while the other comprised a brief burst around the end of this phase. Typically FDL Ia and group II afferents also had elevated firing rates and reduced modulation at all locomotor phases, again implicating static gamma drive. Half the afferents (seven Ia, three group II) showed increased discharge during extension, suggesting phasic static gamma drive. There was no gamma drive associated with the late FDL alpha burst. In conclusion, the gamma drives to FHL and FDL differed during locomotion. FHL, which has the alpha drive of a classic extensor, received gamma drive that closely resembled other extensors. The gamma drive of FDL, which exhibits both extensor and flexor alpha synergies, did not match either muscle type. These observations are compatible with the view that fusimotor drive varies in different muscles during locomotion according to the prevailing sensorimotor requirements.

Animals↗
PubMed1980

Axonal refractory period of single short toe extensor motor units in man.

The aim of this study was to test the reliability of the commonly used blocking technique for measuring the conduction velocity spectrum of the peripheral motor nerve in man, as first described by Hopf in 1962. Electromyographic recordings were carried out with a selectivity permitting identification of single motor unit potentials. The conduction velocity of the single alpha motor axon was determined by a direct technique and by the blocking technique. the refractory period was determined by comparison of the results of these two techniques. The refractory period was studied in relation to the strength of the testing stimulus, axonal conduction velocity, skin temperature and age of the subject. When the strength of the test stimulus increased from 10% to 50% above the axonal threshold, the refractory period decreased from 1.7 to 0.6 ms. An inverse relationship between the axonal conduction velocity and the refractory period was observed. When skin temperature was 4 degrees C subnormal the refractory period was significantly prolonged; at 10 degrees C subnormal it was more than doubled. The same relationship between axonal conduction velocity and the refractory period was observed in both young and elderly subjects. The significance of these findings for the clinical application of the blocking technique is discussed.

Adult↗