Abstract
Publisher Summary This chapter describes the emission and control of acoustic signals, the directional sensitivity of the echolocation system, and the processing of acoustic signals by bats. Anatomical studies of the larynx of bats revealed disproportionate development of laryngeal muscles, the cricothyroid muscle (CTM) in particular. The CTM, which is innervated by a branch of the vagus nerve, that is, the superior laryngeal nerve (SLN), regulates the tension of the vocal membranes during the exhalation of a bat to produce the intense ultrasonic signals. In an experiment described in the chapter, in the CF–FM bat—such as, Rhinolophus ferrumequinum—unilateral denervation of the SLN reduced the CF frequency by 4–6 kHz, but bilateral denervation reduced it by as much as 30 kHz and introduced several strong harmonics into its orientation sounds. The neural connection between the CTM and middle ear muscles (MEM) is through a branch of the sensory nerve in the SLN, but sensory nerves of the MEM do not make contact with the CTM. The amount of attenuation of incoming acoustic stimulation by the MEM reflex varied with stimulus frequency and intensity. The threshold of single-unit activity generally varied as a function of the location of a sound source. The latency of single units is known to be affected by a change in stimulus intensity. The auditory cortex of a CF–FM bat is specialized for the fine analysis of the predominant CF component of the orientation signals. Each orthogonal electrode penetration of the cortex was characterized by binaural interaction in which all the units encountered were either EE units, EI units, or varied with depth of electrode penetration.
Published Version
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