[Difference in responses of free nerve endings and Ruffini-type endings innervating the cat mandibular periosteum to square wave pressure stimuli, ramp mechanical stimuli and triangular vibrations].

Abstract

Unlabelled: The free nerve endings and Ruffini type endings in the cat mandibular molar buccal periosteum (posterior periosteum) were selectively stimulated with specific displacements of various velocities and frequencies and the afferent impulses generated by the nerve endings were recorded.

Results: 1. There were two types of fast-adapting free nerve endings, discharging on effects and off-effects in response to square wave pressure stimuli and ramp mechanical stimuli and on-effects only. 2. Unencapsulated endings were distributed near the mentale foramen and again there were two types of fast adapting endings, discharging on effects and off effects in response to square wave pressure stimuli and ramp mechanical stimuli, and on-effects only. 3. Slow-adapting free nerve endings were also observed through response to square wave pressure stimuli and ramp shaped pressure stimuli. These were difficult to differentiate from the slow adapting Ruffini-type endings. 4. Ruffini type endings were slow adapting types, exhibiting impulse frequency displacement velocity curves of F = 39.627V0.743 (F = impulse frequency, V = displacement velocity, r = 0.999, n = 12 and p less than 0.001). The number of impulse displacement curves was proportional to the displacement, with F = 1.024S0.767 (F = impulse frequency, S = displacement, r = 0.981, n = 6 and p less than 0.001). 5. Free nerve endings followed Stevens' power function law, dropping in order from fast-adapting units (10 units) to intermediate type sensory units (21 units) and slow-adapting sensory units (20 units), with 0.894 +/- 0.103, 0.684 +/- 0.022 and 0.650 +/- 0.023, respectively. Values for slow adapting Ruffini type endings followed the previous order. 6. Slow adapting free nerve endings responded to triangular vibration stimuli at 0.1 Hz to 240 Hz and the lower frequency limit of 0.1 Hz (actually it was below 0.1 Hz but this value was adopted in order to facilitate the recording of the difference to fast adapting free nerve endings) was considerably lower than the 0.6 Hz to 1 Hz range for fast-adapting free nerve endings. The structure and functions of the nerve endings in the cat posterior periosteum were investigated and it was found that the relationship between the impulse frequency and displacement velocities and displacement amplitude for slow-adapting Ruffini-type endings followed Stevens' power factor law. In conclusion, it was demonstrated that the slope constant follows the order of fast-adapting free nerve endings, intermediate type free nerve endings and slow-adapting free nerve endings.