Characteristics of complex voluntary mandibular movements in the monkey before and after destruction of most jaw muscle spindle afferents

The control of orofacial movements in speech

Rapid, complex movements of orofacial structures are essential to produce the sounds of speech. A central problem in speech production research is to discover the neural sources that generate the control signals supplied to motoneurons during speaking. Speech movement production appears to share organizational principles with other motor behaviors; thus speech movements probably arise from an interaction of centrally generated command signals with sensory information. That speech movements are ultimately linked to the perception of language, however, has led many investigators to suggest that speech movement control involves unique features, features that may be linked to abstract linguistic units.

Monosynaptic connections between neurons of trigeminal mesencephalic nucleus and jaw-closing motoneurons in the rat: an intracellular horseradish peroxidase labelling study

In order to confirm the monosynaptic connections of muscle spindle-mediated jaw stretch reflexes, 8 neurons of trigeminal mesencephalic nucleus innervating masseteric muscle spindles were identified electrophysiologically and stained intracellularly with horseradish peroxidase. These axon terminals projected to ipsilateral dorsal and dorsolateral divisions of trigeminal motor nucleus and extensive premotor areas. Under electron microscope, labeled terminals made monosynaptic contacts predominantly with dendrites in the jaw-closing motoneuron pools. One labeled and many non-labeled terminals were frequently observed to converge simultaneously on one dendrite in the area. However, it was of particular interest that 28% of the labeled terminals constituted the intermediate component of axo-axodendritic synaptic triads. The present study confirmed, for the first time, monosynaptic connections between jaw-closing muscle spindle afferents and jaw-closing motoneurons. These findings also provided ultrastructural evidence for the monosynaptic excitation of muscle spindle-mediated jaw stretch reflexes which received presynaptic and postsynaptic inhibitions of the premotor neurons from other sources.