Eye and Ear Answers 405268.The answer is b.(Kandel, pp 597, 614–615, 803.)The vestibular hair
cells are the sensory transduction system of the inner ear and are responsi-
ble for the conversion of mechanical energy into an electrical signal for cra-
nial nerve VIII. These cells are called hair cells because their surface
contains stereocilia. These are modified microvilli that contain a large num-
ber of actin filaments and extend from the surface of the cell. The stere-
ocilia are different lengths and are arranged in order by size with a large
kinocilium at one end. The arrangement of the stereocilia is very important
because bending in one direction (i.e., toward the kinocilium) depolarizes
the cell and increases the rate of nervous discharge, whereas bending them
in the other direction (i.e., away from the kinocilium) results in hyperpo-
larization and decreased neural discharge. The classification of type of hair
cell (I or II) is based on the pattern of efferent and afferent innervation.
269.The answer is c.(Junqueira, pp 471–475.)Movement of the tectorial
membrane results in hair cell depolarization and the release of neurotrans-
mitter onto afferent endings of the auditory cranial nerve leads to initiation
of an action potential. Sound waves are directed toward the tympanic
membrane by the pinna and the external auditory canal of the external ear.
The vibration of the tympanic membrane is transmitted to the oval window
by way of the ossicles of the middle ear. Induction of waves in the peri-
lymph results in the movement of the basilar and vestibular membranes
toward the scala tympani and causes the round window to bulge outward.
The movement of the hair cells is facilitated because the tectorial mem-
brane is rigid and the pillar cells form a pivot. The stabilization of the pres-
sure between the middle ear and the nasopharynx is notdirectly related to
the mechanism of sound transmission.
270.The answer is e.(Junqueira, pp 471–474.)The scala tympani con-
tains perilymph. Endolymph is similar to extracellular fluid (high K+, low
Na+). It is found in the utricle, saccule, semicircular canals, and scala media
(cochlear duct), which are parts of the membranous labyrinth (answers a,
b, c and d).Endolymph is synthesized by the highly vascular stria vascu-
laris in the lateral wall of the scala media. The endolymphatic sac and duct
are responsible for absorption of endolymph and the endocytosis of mole-
cules from the endolymph.