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Biomedical subjects

J Noth

Publications and source records attributed to J Noth.

121 records · Page 7Linked to original sources
PubMed1976

Inhibition of extensor gamma motoneurons by anatagonistic primary and secondary spindle afferents.

About 2/3 of the gamma efferents isolated from the medial gastrocnemius nerve were inhibited by longitudinal high-frequency vibration applied to the tendons of the non-contracting pretibial flexors (decerebrate cats). The inhibition appeared at 15-25 mum amplitude of vibration and increased up to maximum at nearly 100 mum. Increasing the frequency of vibration from 100 to 300 Hz increased the inhibition. The reflex effects elicited by muscle vibration corresponded well in incidence and magnitude with those evoked by tetanization of the deep peroneal nerve at group I stimulus strength. The reflex disappeared when the nerve supply of the vibrated muscles was cut. The sensitivity of some pretibial proprioceptors to vibration was also tested. It is concluded that primary spindle endings of the pretibial flexors inhibit the extensor gamma motoneurons. Some findings hint at a spinal pathway involving Ia inhibitory interneurons. In addition, an inhibitory action of pretibial group II afferents, probably secondary spindle endings, on extensor gamma efferents was demonstrated. The described fusimotor inhibition by antagonistic muscle spindle afferents is a further example of alpha-gamma-linkage.

Animals↗
PubMed1976

Reflex responses of gamma motoneurones to vibration of the muscle they innervate.

1. High frequency vibration was applied to the tendon of the non-contracting triceps surae muscle while recording the background discharges of single gamma fibres only small nerve bundles were cut, leaving most of the nerve supply to the triceps intact. 2. 22% out of a total of sixty-three gamma efferents were tonically inhibited by vibration. The inhibition appeared between 25 and 50mum peak-to-peak amplitude of vibration and increased to a plateau for amplitudes of about 100mum. The dependence of the tonic vibration reflex of alpha-efferents on the amplitude of vibration was found to be similar. Increasing the frequency of vibration from 150 to 300 Hz increased the degree of inhibition. 3. 33% of the fusimotor neurones investigated responded to muscle vibration with an increase in discharge rate. The threshold amplitudes of this reflex ranged from 20 to 50mum. Some features of the reflex, in particular the parallel post-vibratory facilitation found in alpha and gamma efferents, pointed to a polysynaptic pathway organized in an alpha-gamma linkage. 4. All gamma efferents inhibited by vibration showed inhibitory responses to antidromic stimulation of the parent ventral root, and most of them were inhibited by ramp stretch of the triceps. The gamma motoneurones facilitated by vibration, however, were excited by muscle stretch and were less susceptible to antidromic inhibition, some lacking it completely. 5. Cutting the nerves to triceps abolished the inhibitory as well as the excitatory responses of gamma efferents to muscle vibration. Both fusimotor reflexes were preserved after spinal section and subsequent administration of L-DOPA. 6. It is concluded that both of the fusimotor reflex effects of vibration are caused by excitation of primary spindle endings within the triceps. The inhibition of fusimotor neurones is thought to be mediated by Renshaw cells activated during vibration. The significance of positive feed-back on to gamma motoneurones as a result of autogenetic facilitation by Ia afferents is discussed in connexion with stability in the stretch reflex loop.

Action Potentials↗
PubMed1973

Tension in isolated frog muscle fibers induced by hypertonic solutions.

The effect of hypertonic solutions on the tension of isolated twitch muscle fibers of the frog has been investigated. Increased tonicity up to about 1.7 times normal (1.7 T) caused a very small, graded, maintained tension increase. Above about 1.7 T a large, transient contracture response was superimposed on the small tension. The contracture response was graded with tonicity and reached a maximum at 2.5 T of 108 +/- 25 mN.mm(2) a third of the maximum tetanic tension in isotonic solution. Contracture tension developed with a delay which decreased with increased tonicity. The contracture threshold was lower and the delay shorter in small fibers than in large. Contractures were obtained equally well in depolarized as in polarized fibers. They were completely suppressed by 0.1-0.5 mM tetracaine. The possible mechanism responsible for the tension-inducing effect of hypertonic solutions is discussed in terms of the close similarity between the properties of these contractures and those caused by caffeine, and it is suggested that the effect is due to a release of calcium from internal stores.

Animals↗
PubMed1973

The effect of bathing solution tonicity on resting tension in frog muscle fibers.

Resting tension and short-range elastic properties of isolated twitch muscle fibers of the frog have been studied while bathed by solutions of different tonicities. Resting tension in isotonic solution at 2.3-microm sarcomere spacing averaged 0.46 mN.mm(-2) and was proportional to the fiber cross-section area. Hypertonic solutions, containing 0.1-0.5 mM tetracaine to block contracture tension, caused a small sustained tension increase, which was proportional to the fiber cross-section area and which reached 0.9 mN.mm(-2) at two times normal tonicity (2T). Further increases in tonicity caused little increase in tension. Hypotonic solutions decreased tension. Thus, tension at 2.3 microm is a continuous, direct function of tonicity. The dependence of tension on tonicity lessened at greater sarcomere lengths. At 3.2 microm either a very small rise or, in some fibers, a fall in tension resulted from an increase in tonicity. Hypertonic solutions also decreased the tension of extended sarcolemma preparations. In constant-speed stretch experiments the elastic modulus, calculated from the initial part of the stretch response, rose steeply with tonicity over the whole range investigated (1-2.5T). The results show that tension and stiffness of the short-range elastic component do not increase in parallel in hypertonic solutions.

Animals↗