Electrophysiological properties of the acoustic middle ear and laryngeal muscle reflexes in the awake echolocating FM-bats,Myotis lucifugus

Abstract

The basic electrophysiological properties of the acoustic middle ear and laryngeal muscle reflexes inMyotis lucifugus are described. The discharge patterns and impulse-count functions obtained from the two middle ear muscles and laryngeal muscles are similar to one another. The response latencies of these two groups of muscle not only depend upon the stimulus amplitude but also upon the duration. The latencies of the tensor tympani fibers ranged widely from 3.1 to 14.6 ms and have been divided into two subgroups for comparison with the stapedius fibers whose latencies were within 3.0–6.6 ms. All the laryngeal muscle fibers have monotonously narrow tuning curves of triangular shape but those of the two middle ear muscles are very broad and can be divided into two types according to their shape. However, both the middle ear and laryngeal muscle fibers have their BFs mainly within 30–50 kHz. The thresholds obtained from the two middle ear muscle fibers are comparable and are mainly distributed between 30 and 80 dB SPL, but those of the majority of laryngeal muscle fibers were between 50 and 85 dB SPL. On the average, the laryngeal muscle fibers are 5 dB more sensitive to 4-ms FM signals sweeping downward 10 kHz across their best frequencies than to pure tones, but this is not true for the fibers of the two middle ear muscles. Electrical stimulation of the superior laryngeal nerve elicits action potentials from the two middle ear muscles. The middle ear and laryngeal muscles are apparently coupled through sensory fibers in the superior laryngeal nerve.