preprints.org > biology and life sciences > neuroscience and neurology > doi: 10.20944/preprints202305.0481.v1

Preprint Hypothesis Version 1 Preserved in Portico This version is not peer-reviewed

Version 1 : Received: 6 May 2023 / Approved: 8 May 2023 / Online: 8 May 2023 (08:47:47 CEST)
Version 2 : Received: 20 September 2023 / Approved: 21 September 2023 / Online: 21 September 2023 (10:29:32 CEST)

Background: Anterior-tooth (ANT) contacts induce short latency reflex inhibition of human jaw-closing muscles. Coincidental to the advent of vertebrate jaw, the mesencephalic ganglion (Vmes), neural myelin sheath, and muscle spindles also evolved to improve the velocity of proprioceptive and withdrawal reflexes. The vertebrate jaw is a rigid class 1 lever for pinpoint-targeting muscle force into a single bite-point, the pivoting food particle. See-saw reflex movements around the food particle fulcrum multiplicate the food-crushing force. Unpredictable jolts of reaction force are caused for the rostral and the two articulate ends of the jaw triangle. Compression/distraction strains of the three ends of jaw must be monitored and inhibited by ipsilateral withdrawal reflexes. Hypothesis: For food-crushing, the spindles of the taut motor units, stretched by the food-fulcrum send monosynaptic, excitatory feed for the ipsilateral, homonymous motor efferent neurons, via Vmes. In the Vmes, the spindle-inputs are coupled with excitatory feed from back-tooth (BAT) mechanoreceptors. The summated excitatory pulses are targeted precisely for the stretched motor units only. The afferent feed from ANT mechanoreceptors is also coupled with concomitant feed from spindles in the Vmes. The ANT feed, however, is inhibitory to negate the excitatory feed from stretched jaw-muscle units. The inhibitory feed from ANT protects the teeth and jaw-joints from inadvertent strains. Inhibitory inputs from ANT alternating with excitatory feed from BAT determine which jaw-closing muscle units are activated or inhibited at any given instant of food-crushing. The monosynaptic unilateral food-crushing reflexes (UFCR) overrun the coexisting bilaterally executed feed for jaw muscles from the central nervous system. Conclusion: The UFCR combines the monosynaptic food-crushing-reflex and its reciprocal inhibition. The UFCR is universally conserved for probably all jawed vertebrates.

vertebrate evolution; mesencephalic nucleus; primary afferent neuron; jaw movements; dental formulas; chewing reflexes; dental occlusion; brain stem; premaxilla; trigeminal nerve

Biology and Life Sciences, Neuroscience and Neurology

* All users must log in before leaving a comment