Behavior of cutaneous mechanoreceptors recorded in mandibular division of Gasserian ganglion of the rabbit during movements of lower jaw

Abstract

1. The activity of cutaneous mechanoreceptors was recorded extracellularly in the mandibular division of the Gasserian ganglion of hemidecerebrate anesthetized rabbits. Fifty-four hair follicle afferents and 80 skin mechanoreceptor afferents were functionally identified. Their receptive-field characteristics were described and their activity patterns were recorded while the jaw was displaced by hand in the vertical, horizontal, and anterior-posterior directions, and during masticatory movements. 2. All hair follicle afferents were classified as rapidly adapting, whereas skin afferents could be divided into two categories: rapidly adapting and slowly adapting. Rapidly and slowly adapting receptors were found in all regions of the mandibular skin. Only one hair follicle afferent and four skin afferents fired spontaneously with the jaw at rest. 3. Fifty-eight percent (29/50) of the hair follicle afferents were activated by imposed displacement of the jaw and all of these tested also discharged during chewing. They were sensitive to movement in all three axes and their firing frequency was linearly related to the velocity, regardless of direction. 4. Only 10% (8/80) of the skin afferents were activated by imposed displacement of the jaw if their receptive fields were not directly contacted. Firing frequency was not well related to either the amplitude or velocity of movement. During chewing, the discharge frequency was variable but, in general, firing was restricted to the jaw-closing phase. Most skin afferents that were active during jaw movement had receptive fields close to the corner of the mouth. 5. The results are discussed within the context of a possible involvement of cutaneous afferents in kinesthesia and in the control of jaw movements. Hair afferents could make specific contributions to the appreciation of movement because their discharge pattern was clearly related to one of its parameters. The lack of activity of most skin afferents, as well as the absence of a strong correlation between the firing frequency of those that were active and the movement parameters, suggest that they do not make specific contributions to the awareness of movement. 6. Hair and skin afferents may also make different contributions to the control of ongoing movements. It is suggested that skin afferent activity during jaw closure may elicit a reflex reduction in the velocity or duration of this phase. Some evidence from other studies suggests that hair afferent activity may indirectly influence movement via effects on elevator fusimotor neurons.

Sensory transmission in cerebellar granule cells relies on similarly coded mossy fiber inputs

“…Although the primary afferents of both submodalities are excellent tactile event detectors, coded with bursts in the mossy fibers (7,18), they also function as proprioceptors, and then as rate-coding estimators operating at lower firing frequencies (22,23).…”

Somatosensory function in speech perception

“…Cutaneous afferents at the side of the mouth are also implicated in jaw movement. In particular, cutaneous mechanoreceptors at the oral angle have been shown to respond to passive jaw motion (26,27). Skin stretch at this location results in a compensatory reflex response that is normally evoked by unpredictable jaw position change (23).…”

Cutaneous afferents provide information about knee joint movements in humans

“…Appenteng et al (1982) demonstrated that hair follicle receptors in rabbits show vigorous responses during chewing and concluded that these receptors may contribute the 'perception of jaw movement, but not jaw position'. The most likely explanation for this discrepancy is the marked difference in the density of hair follicles between human and rabbit skin.…”