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Actions on gamma‐motoneurones elicited by electrical stimulation of joint afferent fibres in the hind limb of the cat.
Author(s) -
Johansson H,
Sjölander P,
Sojka P
Publication year - 1986
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1986.sp016110
Subject(s) - excitatory postsynaptic potential , stimulation , inhibitory postsynaptic potential , spinal cord , chloralose , hindlimb , chemistry , anatomy , cats , neuroscience , biology , medicine
Effects on seventy‐one single lumbar gamma‐motoneurones, evoked by graded electrical stimulation of fibres running in the posterior articular nerve of the ipsilateral knee joint (p.a.n.), were studied by micro‐electrode recording in twenty‐one cats anaesthetized with alpha‐chloralose. Sixty‐seven of the gamma‐cells were classified indirectly as dynamic (thirty‐seven) or static (thirty) using the method of mesencephalic stimulation (cf. Appelberg, Hulliger, Johansson & Sojka, 1982). A high general responsiveness (i.e. number of cells with effect/number of cells tested) was found for the whole sample of gamma‐cells (91.9% for dynamic and 93.3% for static cells). The thresholds for the effects were related to the stimulation intensity at which the early negative cord dorsum potential appeared (T). For all subpopulations of gamma‐cells (dynamic and static, flexor and extensor cells) excitatory as well as inhibitory effects were observed at 0.9‐1.1 T, probably corresponding to 1.1‐1.4 times the threshold for evoking a compound action potential in p.a.n. (cf. Discussion). In addition, a considerable number of high‐threshold effects were found. Some cells were influenced only from low‐threshold joint afferents, some only from high‐threshold joint afferents and some cells were influenced from both low‐ and high‐threshold joint afferents. No statistically significant differences in thresholds were found between dynamic and static cells. Among flexor gamma‐cells excitatory effects were found to predominate, while for extensor gamma‐cells excitation and inhibition occurred with about equal frequency. The shortest latencies for excitatory effects on dynamic gamma‐motoneurones were compatible with a trisynaptic pathway, while the routes for excitation of static units and for inhibition of both types of gamma‐cells seemed to be longer. The possible functional significance of the findings is discussed. The findings seem to support the idea, as suggested by Freeman & Wyke (1967b), that the joint receptors may contribute to the 'co‐ordination of muscle tone in posture and movement' via the gamma‐loop. It is furthermore suggested that the latter mechanism may serve to regulate joint stiffness and joint stability.