Contributions to Sensory Physiology

Volume 5

William D. Neff, William D. Neff

• Publisher: Academic Press
• Year: 2013
• ISBN:
  9781483191584
• Topic: Social Sciences
• Subtopic: Physical Anthropology
• Index: Social Sciences

Contributions to Sensory Physiology: Volume 5 presents a theory about the physiological basis of sensation. It discusses some research made in microscopic anatomy and psychophysics. It addresses the functional significance and physiological mechanisms of the sensory systems. Some of the topics covered in the book are the simple cells of the striate cortex; the concept of a receptive field; definition of a unimodal simple cell; inhibitory components in the receptive field; stimulus contrast and mean level of luminance; specificity of inhibitory zones; and experimental procedures for recording average response histogram. The relation and possible importance of taste bud cells are covered. The comparison of foliate, vallate, and fungiform buds are discussed. The text describes the nature of taste receptor sites. A study of the location of receptor sites on taste cells is presented. A chapter is devoted to the mechanochemical model of taste excitation. Another section focuses on the proposals for molecular specificity. The book can provide useful information to scientists, doctors, students, and researchers.

Auditory Receptor Organs of Reptiles, Birds, and Mammals¹

Catherine A. Smith, Department of Otolaryngology, University of Oregon Medical School, Portland, Oregon

Tomonori Takasaka², Department of Otolaryngology, University of Oregon Medical School, Portland, Oregon

Publisher Summary

This chapter describes the auditory receptor organs of reptiles, birds, and mammals. Although reptiles have poor conduction of sound because of the low-grade sensitivity to their ears, some of them have great variations in their middle-ear structure. Birds have a more stable middle-ear structure but still have the columellar apparatus and the lagena that are found in reptiles. The ears of monotremes represent an intermediate stage between reptiles and mammals. They retain the lagena as well as the stapes with the single shaft. The reptilian papillae are all small and, except for the alligator, have a receptor cell population that is composed of nondifferentiated hair cells. The pigeon displays two populations of differentiated hair cells with a distinctive distribution of afferent and efferent nerve fibers. The location of tall and short hair cells is similar in part to that of inner and outer hair cells in the organ of Corti of mammals.

I Introduction

II Reptiles

A Morphology

B Physiological Data

III Birds

A Morphology

B Physiological Data

IV Mammals

A Organ of Corti of Monotremes

B Organ of Corti of Other Mammals

V Summary

References

I Introduction

The first comprehensive survey of the structure of the inner ear of vertebrates was made by Retzius in 1884. This work (Retzius, 1884) was written with such care for detail and so elegantly illustrated that it became a classic and is still a standard reference, often quoted some 85 years later. Within the half century that followed, many studies were made on the mammalian organ of Corti so that the histology of the membranous labyrinth of common laboratory animals is now well known. A large number of investigators, among whom Kolmer (1927) and Held (1926) were outstanding, contributed much to our present knowledge.

On the other hand, very little more was added to Retzius’ descriptions of auditory papillae in lower animals. One notable exception to this was Held’s (1926) study of the pigeon cochlea, in which some new and important features were described. Interest was centered on the middle ear and vestibule in lower vertebrates, an interest no doubt stimulated by the fact that the columellar apparatus which traverses the middle ear of lower animals is considerably different from the well-known three ossicles in mammals. Other features, such as relative ease of structural preservation and the greater variability in middle ear relationships, may also have influenced the investigators’ choice of areas for study.

Comparative studies on hearing (Katsuki, 1965; Schwartzkopff, 1967) rather than on structure have been more numerous in recent years. Functional studies coming from the laboratories of Schwartzkopff (1955) and Wever (1967a), as well as structural studies such as those of de Burlet (1934) and Shute and Bellairs (1953), have kept alive interest in the ears of lower animals. Within the past few years, many investigators have begun to realize that the specialized character of the mammalian organ of Corti which makes it such a fascinating structure for study also results in a complexity of function which makes understanding more difficult. This realization has been partially responsible for an increased interest in the ears of lower animals. The histological features of the ears of a number of lower animals have been reviewed and new findings have been added (Baird, 1960; Miller, 1966a, b). More important, ultrastructural studies have been initiated on amphibia (Flock and Flock, 1966), reptiles (Baird, 1969, 1970a; Mulroy, 1968), and birds (Cordier, 1964; Smith, 1968a; Takasaka and Smith, 1968). The ultrastructural studies have described structures or clarified cytological relationships which were previously ill defined. This seems to be an appropriate time to bring together this new information on structure and to add data on neurophysiology.

Van Bergeijk (1967) has covered some of the early stages of the evolutionary changes in the cochlea in his chapter in the second volume of this series. Despite his assertion that he was interested in hearing rather than structure, he found it necessary to describe histological relationships, and he very competently laid an excellent foundation for further work by others. It is our purpose to build upon this foundation, with a special emphasis on ultrastructural details. We shall begin with the ears of reptiles, the foundation from which both birds and mammals have evolved. From our recent electron microscopic studies of the pigeon’s ear, combined with a number of studies on mammals, we can visualize the contemporary results of two different evolutionary radiations.

II Reptiles

Several detailed reports on the structure of the reptilian auditory organ have been published recently, and the description that follows will be based on studies by Baird (1960, 1970a), Miller (1966a,b), and Wever (1965, 1967a,b,c, 1968), supplemented by information from others.

A Morphology

1 External Ear

The ears of reptiles are quite remarkable for their variability. Some have readily recognizable tympanic membranes with attached ossicles and well-defined middle ear spaces; others do not. None have the large moveable auricles that are so prominent a feature of mammals. The Ophidia (snakes), some Amphisbaenia, and the Chamaeleonidae, for example, have neither auricles, external auditory meati, nor tympanic membranes. The snakes as well as the amphisbaenians probably originated as burrowing animals, and it might be inferred that their smooth earless heads, covered by scales, are an adaptation for this burrowing behavior. The chameleons, however, live above ground, and their lack of auricles can hardly be explained in the same way. Some of the lizards (Holbrookia and Phrynosoma) have reduced external ears, but most have an elevated fold of skin posterior to a slight declevity which marks the position of a tympanic membrane which is free of scales. There seems to be no simple explanation for the presence or absence of external ears and of thin, flexible tympanic membranes. Baird (1970a) has recently written, “there is reason to question implications of direct cause and effect in statements relating morphology of the external ear solely to a given habit or habitat.” One example where environment seems clearly to have influenced structure is the adductable ear lids of the alligator. Wever and Vernon (1957) point out that these lids are closed when the animal submerges but are usually open when he is on land.

2 Middle Ear

Many lizards (Baird’s “typical” lizard, 1970a) and Sceloporus, described by Wever (1965), have well-defined middle ear structures analogous to those in mammals. The tympanic cavity is an air-filled space and widely open to the pharynx. It is traversed by the columellar apparatus; the major part of this is the stapes, whose slender central shaft expands into the stapedial footplate which is inserted in the oval window. The outer or lateral end of the stapes usually has an “extrastapes” which is generally a cartilaginous extension that is attached to the tympanic membrane (Fig. 1). There is some sort of secondary opening in the bony otic capsule over scala tympani, analogous to the round window. In such a system, transmissi...