The Innervation of Mammalian Skeletal Muscle. In: de Reuck AVS, Knight J, editors. Ciba Foundation Symposium - Myotatic, Kinesthetic and Vestibular Mechanisms. Chichester: John Wiley & Sons, Ltd.; 1967. pp. 3-19. [DOI: 10.1002/9780470719565.ch2]

Jaw-tongue reflex: afferents, central pathways, and synaptic potentials in hypoglossal motoneurons in the cat

The tongue position is reflexively controlled by the jaw position (the jaw-tongue reflex). The purpose of this study was to clarify the mechanism of this reflex in terms of afferents, central pathways, and synaptic potentials in hypoglossal motoneurons in the cat. Intracellular recordings from hypoglossal motoneurons revealed that electrical stimulation of the temporalis muscle nerve evoked excitatory and inhibitory post-synaptic potentials in hypoglossal motoneurons. The threshold of temporalis muscle nerve stimulation for evoking the synaptic potentials was higher than 2.0 times the nerve threshold. The amplitude of the potentials increased with stimulus intensity up to 5.0 times the nerve threshold. Punctate light pressure applied to the temporalis muscle induced a tonic depolarizing potential in hypoglossal motoneurons on which action potentials as well as depolarizing synaptic activation noise were superimposed. On the other hand, electrical stimulation of the temporalis muscle during jaw-opening could slightly inhibit the electromyographic activities in the genioglossus and styloglossus muscles. Lesions including the Probst's tract at the level caudal to the trigeminal motor nucleus abolished both excitation and inhibition in hypoglossal motoneurons induced by tonic depression of the lower jaw, but exerted no effects on either the tonic stretch reflex or the trigemino-hypoglossal reflex. In contrast, lesions including the trigeminal spinal tract produced no changes in either excitation or inhibition of hypoglossal motoneurons induced by temporalis muscle afferents, whereas the excitation of hypoglossal motoneurons was abolished by the lesions. We conclude that the group II muscle spindle afferents from the temporalis muscle are primarily responsible for evoking the jaw-tongue reflex.

Two groups of Golgi tendon organs in cat tibial anterior muscle identified from the discharge frequency recorded under a ramp-and-hold stretch

Twenty Golgi tendon organs (GTOs) from the tibial anterior muscle of the cat were investigated under a ramp-and-hold stretch of the passive muscle. The stretch rate was varied between 1 and 100 mm/s, the stretch amplitude between 0.1 and 7 mm, the prestretch of the muscle between 0 and 12 mm. The action potential sequences of the GTOs were recorded, and discharge patterns derived from them. The basic discharge frequencies, namely the initial frequency, the peak dynamic discharge, the maximum static value, and the final static value, were read from each discharge pattern. The tension of the muscle was determined at the same points in time at which one of the basic discharge frequencies was read from a discharge pattern. The static and dynamic properties of the GTOs were determined from the basic discharge frequencies. Two groups of GTOs were identified. Four GTOs discharged with an initial frequency and at the same time had static properties of small magnitude. Sixteen GTOs showed no initial activity and had static properties of large magnitude. The two groups of GTOs did not differ in their dynamic properties. The number of alpha-fibers activating a single GTO was determined from a further 11 GTOs. Eight GTOs without initial activity were activated by a mean number of 9.7 alpha-fibers. Three GTOs discharging with initial activity were activated by a mean number of 15.3 alpha-fibers. The two mean values were significantly different (p=0. 02). The identification of two groups of GTOs is explained by the GTOs being positioned differently within the muscle and its tendon.

Form and classification of motor endings in mammalian muscle spindles

The presynaptic features of 234 motor endings supplied to cat hindlimb muscle spindles have been studied in teased, silver preparations, and the postsynaptic features of a further 27 endings have been studied in serial, 1 micron thick, transverse sections. In the presynaptic study motor endings received by the three types of intrafusal muscle fibre were compared with the endings supplied to spindles by the various functional categories of motor axon. Three forms of motor ending were found that had significantly different presynaptic features. These forms correspond closely to those previously identified in the literature as p1 (beta), p2 (dynamic gamma) and trail (static gamma). The results of the postsynaptic study showed that the degree of indentation of the intrafusal muscle fibres by motor axon terminals increases with greater distance from the primary ending, irrespective of muscle-fibre type. We conclude that the postsynaptic form of intrafusal motor endings is determined by distance from primary ending and muscle-fibre type. It is not determined by type of motor axon, and cannot be correlated with presynaptic form so as to produce a unified classification of intrafusal motor endings.

Autonomic innervation of receptors and muscle fibres in cat skeletal muscle

Cat hindlimb muscles, deprived of their somatic innervation, have been examined with fluorescence and electron microscopy and in teased, silver preparations; normal diaphragm muscles have been examined with electron microscopy only. An autonomic innervation was found to be supplied to both intra- and extrafusal muscle fibres. It is not present in all muscle spindles and is not supplied at all to tendon organs. Fluorescence microscopy revealed a noradrenergic innervation distributed to extrafusal muscle fibres and some spindles. On the basis of the vesicle content of varicosities the extrafusal innervation was identified as noradrenergic (32 axons traced), and the spindle innervation as involving noradrenergic, cholinergic and non-adrenergic axons (14 traced). Some of the noradrenergic axons that innervate spindles and extrafusal muscle fibres are branches of axons that also innervate blood vessels. We cannot say whether there are any noradrenergic axons that are exclusively distributed to intra- or extrafusal muscle fibres. The varicosities themselves may be in neuroeffective association with striated muscle fibres only, or with both striated fibres and the smooth muscle cells in the walls of blood vessels. The functional implications of this direct autonomic innervation of muscle spindles and skeletal muscle fibres are discussed and past work on the subject is evaluated.

An autoradiographic study of the sensory innervation of teeth. I. Dentin

Autoradiography of axoplasmically transported proteins revealed that the coronal dentin of rat molar teeth receives sensory innervation from the trigeminal ganglion. The labeled processes appear to run in dentinal tubules and sometimes reach the peripheral dentinal region near the enamel.