574 HANDBOOK OF PHYSIOLOGY ^ NEUROPHYSIOLOm' 1 



RETICULAR 



TECTORIAL 



FIG. 12. Movement of the organ of Corti and the tectorial membrane, based on descriptions by 

 von Bekesy. The shearing action between two stifT structures, the tectorial membrane and the 

 reticular lamina, bends the hairs of the hair cells. [From Davis (s)-] 



helicotrema 



stapes 



Hensen s 

 cells 



longitudinal 

 vibrations 



radial 



FIG. 13. The distribution of radial and longitudinal vibra- 

 tion along the organ of Corti for stimulation with a tone, seen 

 through Reissner's membrane. [From von Bekesy (20).] 



FLUIDS AND BLOOD SUPPLY OF INNER EAR* 



Blood Supply 



The cochlea is supplied by the cochlear artery 

 which enters the modiolus through the internal 

 auditory meatus. The spiral ganglion is richly sup- 

 plied with capillaries, and arterioles arch across the 

 roof of the .scala vestibuli to the spiral ligament. The 

 stria vascularis, facing the scala media, is, as its name 

 suggests, a veritable maze of small blood vessels with 

 many anastomoses. The limbus is fairly well supplied 

 with capillaries and a small arteriole often runs length- 

 wise on the tympanic surface of the basilar membrane. 



' See especially the papers of Davis (4) and of Smith et al. 

 (.0). 



The blood flow of the inner ear reflects, as would be 

 expected, major alterations in systemic circulation, 

 but it does not seem to be significantly aff^ected by 

 stimulation of the cervical sympathetic nerve. 



Fluids 



The perilymph, which fills the scala vestibuli and 

 the scala tympani, is chemically almost identical with 

 cerebrospinal fluid, and in fact the perilymphatic 

 space is anatomically continuous with the subarach- 

 noid space through the cochlear aqueduct. Essen- 

 tially the same fluid also permeates the modiolus, the 

 substance of the spiral ligament, and the tunnel of 

 Corti and other spaces within the organ of Corti. The 

 basilar membrane seems to be readily permeable to 

 ions, and, in contrast to Reissner's membrane, offers 

 little resistance to electrical current flow. The sensory 

 cells are probably nourished from the scala tympani, 

 not from the scala media. 



The endolymph, which fills the scala media, differs 

 sharply from perilymph in its ionic content. 

 Unlike all other extracellular body fluids, it is high 

 in potassium and low in sodium. It more nearly 

 resembles intracellular fluid in this respect. Typical 

 analyses of endolymph, perilymph and cerebrospinal 

 fluid are given in table i. The endolymph has some- 

 times been described as 'viscous,' but this is probably 

 true onlv for certain fish and perhaps other lower 

 forms. 



The endolymph is probably secreted h\ the stria 

 va.scularis. Whether it is also reabsorbed wholly or 

 onlv in part by the same structure is a matter of de- 

 bate. The saccus endolymphaticus, an intradural 

 extension of the endolymphatic system of the mem- 

 branous labyrinth, may participate in secretion, in 

 reabsorption or in both. 



