THE BODY'S DETECTORS OF MATTER WAVES 57 



Notes on the Ear 



The structure of the ear can be pictured, in simplest terms, as consisting 

 of three main parts: the pinna (lobe) and external canal, the middle ear, 

 and the cochlea. The canal and the middle ear are separated by the tym- 

 panic membrane (ear drum) which covers and protects the latter. The 

 middle-ear cavity contains a system of three bony levers, the ossicles (the 

 malleus, incus, and stapes) whose main job seems to be to act as a matching 

 device transmitting matter vibrations between the two fluids: the air outside 

 in the external canal, and the perilymph inside the cochlea. The cochlea 

 is a spiral canal within the bone of the skull. It is divided axially into three 

 channels by membranous partitions. Into one of these, the scala vestibuli, 

 is inserted the end of the stapes; this chamber, then, receives directly the 

 transmitted vibrations. Through the membranes, vibrations are passed 

 laterally into the other two canals, the scala media and the scala tympani. 

 These two are separated by the basilar membrane, which receives the end- 

 ings of the auditory nerve, and the cells of which are the transducers that 

 convert the mechanical energy of vibration into the electrical energy trans- 

 mitted along the nerve. Most recent work has been aimed at the mechanism 

 of action of the region of the basilar membrane, the transducer. Some of the 

 cells on the membrane have hair-like processes projecting from their upper 

 ends and attached to the overhanging, tectorial membrane. Relative move- 

 ment between the tectorial and basilar membranes distorts the cells of both. 

 Note Figure 3-5. 



The analogy with piezoelectric crystals is usefully drawn at this point: 

 distortion of the shape of the transducer in both cases leads to change in the 

 potential difference between two points on the surface of the transducer — in 

 one case the surface potential of the crystal, in the other case the membrane 

 potential of the cell. 



An accumulation of evidence now exists — Von Bekesy 13 received the 1961 

 Nobel Prize in Physiology and Medicine for this work, done at Harvard — 

 that a traveling wave passes along the basilar membrane during excitation. 

 The position at which the wave achieves its highest amplitude (think of 

 the whip) is dependent upon the frequency of the wave being detected. 

 Therefore, nerve signals from different tones arise at different spots, each 

 spot associated with specific nerve endings. At low frequencies the whole 

 basilar membrane vibrates in sympathy with the incoming matter wave. 



The question of membrane potential change will be considered in Chap- 

 ters 7 and 10, in reference to erythrocytes and nerve cells, upon which 

 voltages have been directly measured in vivo. 



Deformations in the structure, or failure of the ear to respond to matter 

 waves, is the subject matter of the otologist. Corrections are applied some- 



