Function and structure of the avian peripheral auditory system Free

Studies of the function of the avian peripheral auditory system originated with cochlear microphonic recordings from pigeon by Wever and Bray in 1936. More recently, there have been several studies of the response properties of avian auditory‐nerve fibers; these will form the basis of our review of the function of the avian periphery. In many respects, the characteristics of avian auditory‐nerve fibers are quite comparable as is the precision of phase‐locking to low‐frequency tones. On the other hand, there do appear to be significant differences. For example, tuning curves of avian auditory‐nerve fibers seem to lack the low‐frequency tails found in tuning curves of mammalian fibers. Rates of driven and spontaneous activity are higher in birds than in mammals. Spontaneous activity of many avian fibers can be suppressed by appropriate single tones, whereas single‐tone suppression has rarely been reported in mammalian auditory‐nerve fibers. In light of these similarities and differences in function, it is instructive to consider similarities and differences in the structure of avian and mammalian inner ears. The bird's receptor organ is small and covered with a compact mass of sensory cells. Different kinds of hair cells with afferent and efferent nerve endings have a distinctive organization on the basilar membrane. The dimensions of the short basilar membrane (2–4 mm) and locations of hair cell types varies in parakeet, sparrow, pine siskin, pigeon and chicken. Their behaviorally derived audibility curves have short frequency ranges each with a sharp sensitivity peak. The barn owl's sensitivity is good over a considerably wider range; it has a 12‐mm‐long basilar papilla with an unusual hair cell arrangement.