55° 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



species has added much to our understanding of the 

 function of the human labyrinth in spite of a number 

 of difficulties posed by the anatomical differences from 

 lower animals. Experiments on various members of 

 the animal kingdom have shown that some of the 

 responses will vary greatly from one species to another. 

 However, the use of electrophysiological techniques 

 for a more far-reaching study of the function, and the 

 refinement in recent years of the ultrastructural anal- 

 ysis made possible by the electron microscope may- 

 allow more precise experimental studies of the corre- 

 lation of function and structure. Some of our modern 

 ideas about this correlation rest firmly on experi- 

 mental facts; others, in the present incomplete state 

 of knowledge, are mere speculations. The remaining 

 ones ranee between these two extremes. 



AN.-SiTOMY OF LABYRINTH 



lar canal makes an angle of about 55°, open in front, 

 and with the posterior canal, an angle of about 45°, 

 open posteriorly (fig. 2). 



The semicircular canals run from and open into 

 the utricle by means of five apertures, one being com- 

 mon to the superior and posterior canals. At one end 

 of each canal, near its junction with the utricle, is the 

 swelling known as the ampulla. The horizontal and 

 superior canals have the ampulla forward and the 

 posterior canal has it backward. 



The utricle is the larger of the two sac-like struc- 

 tures. It has an irregularly oblong shape, slightly 

 compressed transversely. Its most caudal portion lies 

 posteriorly, wherefrom it slopes anteriorly and up- 

 ward (rostrally) at an angle of approximately 30°. 

 The utricle communicates with the utriculosaccular 

 duct and with the semicircular canals mentioned 

 above. 



For understanding the function of the semicircular 

 canals, the utricle and saccule, a clear concept of their 

 anatomical position and their relationship to each 

 other in space is paramount. 



The bony labyrinth comprises a series of ca\ities 

 tunneled in the compact petrous part of the temporal 

 bone. The whole memljranous labyrinth, consisting of 

 a system of thin-walled sacs and ducts with a clear 

 fluid, the endolymph, is enclosed within the osseous 

 labyrinth, separated from its wall by the perilymph. 

 In form it closely resembles the osseous labyrinth, ex- 

 cept in its middle portion (fig. i). 



The membranous semicircular canals, three in 

 number for each ear, are eccentrically suspended by 

 fibrous strands in the osseous semicircular canals. 

 They are smaller in diameter than the osseous canals 

 and fill only about one fourth of the lumen. The 

 canals are named according to their orientation in 

 space, the horizontal (external, lateral), superior 

 (frontal) vertical, and posterior (inferior) vertical, 

 lying approximately at right angles to each other, 

 one for each major plane of the f)ody. Considering 

 the two labyrinths together (right and left sides of 

 the head), the two horizontal canals lie in the same 

 bodily plane and form what may be termed a synergic 

 pair. The synergic partner of the right superior 

 vertical canal is the left posterior \ertical canal. The 

 left superior canal is parallel to the right posterior 

 canal. The horizontal canal is slightly inclined down- 

 ward and backward, so that it forms an angle of 

 about 30° with the horizontal plane when the head is 

 erect. The sagittal plane with the superior semicircu- 



PcriostGuTTv 



jcmicirCLilar- 

 Carval 



Utr.cle- 

 SacTjuIe" 



Oval window 

 Ductus reumens " 

 Round window and 

 secondary tynipanic 

 >T\embrane 

 Aouoduct oF the " ' 

 cochlea. 



Subdural 

 ondoVmphatiC? sac 

 -Dura nnatrcr 



Aqueduct of the 

 ~ vestibule 

 -Endolyrnphatic 

 duGtr 



Cochlear 

 duct 



■ -^Helicoti-enna 



— Peri09tCUTT\ 



5cala Cympani 

 Scala vestibuli 



FIG. I. Diagram of ppiilymphatic and endolymphatic spaces 

 of the internal ear. [From Larsell (57).! 



R.cochl.-sacc 



FIG. 2. The innervation and structural relations of liuman 

 vestibular apparatus and cochlea. [From Hardy (52).] 



