271.The answer is e.(Young, pp 398–401. Junqueira, pp 471–474.)The
stria vascularis (D)is found in the lateral wall of the cochlear duct (scala
media, I) and is responsible for the ionic composition of the endolymph.
The organ of Corti is found within the cochlear duct and contains the hair
cells that are responsible for transduction of the sound to a nerve impulse.
It rests on the basilar membrane, which separates it from the epithelial lin-
ing of the tympanic cavity. The inner tunnel (H)of the organ of Corti sep-
arates the outer from the inner hair cells. The outer hair cells possess
microvilli that are attached to the tectorial membrane (C).In contrast, the
inner hair cells are unattached. Supportive cells include the phalangeal and
pillar cells, which are not labeled on the figure. The spiral lamina is a bony
structure that protrudes from the modiolus. The spiral limbus (B)is a con-
nective tissue structure superior to the unattached edge of the spiral lam-
ina. Along the outer wall of the canal of the organ of Corti is a thickened
projection of periosteum known as the spiral ligament (F).The spiral gan-
glion is labeled Aon the figure and contains bipolar cells. Peripheral
processes of spiral ganglion cells reach the organ of Corti, whereas central
processes terminate in nuclei located in the medulla. The internal spiral
tunnel is labeled Ein the figure.
272.The answer is a.(Junqueira, pp 471–474.)The vestibular mem-
brane, also known as Reissner’s membrane, maintains the gradient between
the endolymph of the scala media and the perilymph of the vestibular cav-
ity. The middle ear contains the auditory ossicles, which transmit sound to
the oval window and, therefore, serve in the conduction of sound waves to
the perilymph. The helicotrema represents the opening that allows com-
munication of the tympanic and vestibular cavities. The epithelium pos-
sesses extensive occluding junctions, which serve to maintain the
concentration gradient that is essential for sensory transduction. The
movement of the middle ear bones is dampened by the stapedius and ten-
sor tympani when an individual is exposed to a loud noise.
273.The answer is c.(Junqueira, pp 471–474. Sadler, pp 317–320. Moore
and Persaud, pp 476–478.)The semicircular canals, which extend from the
utricle, contain the cristae ampullares and detect angular acceleration. The
utricle represents the dorsal portion of the otocyst-derived inner ear; the sac-
cule represents the ventral portion. Both the utricle and saccule contain mac-
ulae that detect linear acceleration (answer a).The maculae of the utricle
406 Anatomy, Histology, and Cell Biology