Abstract
Evidence obtained by intracellular spike-triggered averaging has led to the belief that the monosynaptic excitatory connections of jaw-elevator muscle spindle afferents with jaw-elevator motoneurones may be weak. In the first such report, EPSPs were found of mean amplitude 18µV (range = 3.1 – 60µV: pentobarbitone anaesthetised cats: Appenteng, O’Donovan, Somjen, Stephens & Taylor, 1978). A subsequent study in the guinea-pig (ketamine anaesthesia) which gave a mean averaged EPSP amplitude of 21. 5µV, appeared to support this (Nozaki, Iriki & Nakamura, 1985). However, a more recent study in the rat (pentobarbitone anaesthetisia) gave a higher mean amplitude of 64µV (range = 7 – 289µV) and a connectivity of 52% (Grimwood, Appenteng & Curtis, 1992). Even with this revised estimate the steady depolarisation which might be caused by all the muscle spindles in masseter would only amount to some 2.2mV (see Harrison & Taylor, 1981; Munson, Fleshman & Sypert, 1982). This is based on 200 afferents (Gottlieb, Taylor & Bosley, 1984) firing at 100 impulses/s.
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Appenteng, K., Curtis, J.C., Grimwood, P., Min, MY., Yang, HW. (1995). Modulation of Transmission in Reflex Pathways of Trigeminal Motoneurones. In: Taylor, A., Gladden, M.H., Durbaba, R. (eds) Alpha and Gamma Motor Systems. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-1935-5_5
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DOI: https://doi.org/10.1007/978-1-4615-1935-5_5
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