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"hard and stony"- bony labyrinth and its system of canals and cavities is found here
petrous portion of temporal bone
present in fetal development, a bony capsule surrounding the membranous labyrinth, consists of 3 parts- vestibule, SC's and cochlea. With further ossification of the fetal cartilage- otic capsule becomes assimilated into petrous bone.
why are guinea pigs and chinchillas often used for ear research?
-their cochleas project INTO the middle ear, easy access to the turns of the cochlea
vestibule is continuous with...?
the SC's and the cochlea, forms the central part of the bony labyrinth
the medial wall of the vestibule has...?
-number of small perforations, orifice of the vestibular aqueduct
semicircular canals lie in 3 planes which are...?
perpindicular to each other, any two form nearly a right angle
what nerves and artery are carried via the internal auditory meatus?
auditory nerve, facial nerve, nervus intermedius, internal branch of the basilar artery, (vestibular nerve-combines with cochlear nerve=auditory nerve)
the cochlea is divided into how many parts?
base- followed by 2 and 5/8 turns which terminate at the apex or cupola
where is the round window exactly?
basal extreme of the scala tympani, opens into the tympanic cavity, but is actually closed off by a thin secondary tympanic membrane
perilymph is similar to what other fluid and where is it found?
-the free surface of the bony labyrinth is covered with epithelium that secretes "the ultrafiltrate of blood"-perilymph- clear, watery fluid, like cerebrospinal fluid of the brain
- fills the scala V. and scala T., perilymphatic spaces of vestibule and around the SCC's
This adheres the membranous labyrinth to the bony labyrinth in some areas?
delicate tabs of tissue
how many divisions in the membranous labyrinth?
3- SCC's, the utricle and saccule, and the cochlear duct-scala media
What forms the "base" of the crista ampullaris in the ampulla of the SCC's
-small aggregations of connective tissue
what type of crystals are found IN the gelatinous mass-cupola- of the crista ampullaris?
minute crystalline grains of carbonate of lime
what nerve fibers supply the macula of the saccule and utricle?
-terminal fibers of the saccular and utricular branches of the vestibular part of the acoustic nerve
by what means do the utricle and saccule communicate?
-indirectly by means of the utricular and saccular ducts which join to form the common endolymphatic duct-( which runs through the vestibular aqueduct ending in the endolymphatic sac)
the cochlear duct or scala media complies with the general shape of the?
osseous cochlea, and lies on its outer wall
Do some authorities think the Canal Reuniens does not exist in the adult human?
Yes, some believe it is obliterated- because of its small size, high frequency disturbances in endolymph are prevented from being transmitted from the cochlea to the structures of the vestibule
the scala T. is terminated basally at the? Does it commuicate directly with the vestibule?
bony wall of the vestibule, it does NOT communicate diretlcy with the vestibule proper
Is the cochlear duct an open or closed tube? How?
Closed, it is bounded above by the vestibular/Reissner's membrane
What comprises the vestibular/Reissner's membrane?
one layer of ectodermal epithelium that faces the cochlear duct and endolymph, and one mesothelial layer that faces the scala V. and perilymph
What comprises the spiral lamina?
-narrow shelf of bone at the apical end of cochlea
-gradually widens towards basal end
-two thin plates of bone, between which are canals for the peripheral fibers of the auditory nerve
Upper layer of bone in the spiral lamina is continuous with?
thickening of the periosteum known as the spiral limbus, gives rise to the vestibular lip
Lower layer of bone of the spiral lamina is continuous with?
tympanic lip (perforata habenula), basilar membrane
What exactly is the basilar membrane comprised of?
- 3 layers-1. Base of connective tissure 2. transverse fibers 3. Tympanic surface-vascular covering.-- series of extracellular transverse, or radially directed fibers that run perpendicular to the axis of the cochlear duct
The fibers of the basilar membrane are embedded in what type of substance?
"homogenous interstitial substance"
The thinnest and most fragile part of the basilar membrane is the?
zona arcuata or pars tecta, extends from the SPIRAL LAMINA past the outer rods of corti (fragile=OSL end)
The region of the basilar membrane with two layers of fibrous cells is?
pectinate zone, stronger and towards the spiral ligament (stronger=sprial ligament end)
The basilar membrane gets wider or tapers at the apex of the cochlea?
it WIDENS at the apex, which is opposite of the cochlea itself which narrows an tapers at the apex
The "negative space" that surrounds the basilar membrane as it tapers to the base, is filled in by?
the spiral lamina
Which end of the basilar membrane is narrower, stiffer, and under some tension?
the basal end (base)
The changes in the nature of the basilar membrane contribute to its?
stiffness gradient which permits "propagation of a traveling wave along its extent...and responsible for place coding of frequencies
What covers the surface of the vestibular lip of the spiral lamina?
-distinctive epithelium cells, arranged in parallel rows, serrated appearance when viewed from above="auditory teeth"
-may form the substance of the tectorial membrance
-continous with the lining of the internal spiral sulcus
How do the supporting phalangeal cells help support the inner hair cells of the organ of corti?
inner hair cells are supported at their bases by the bodies of the phalangeal cells, and at their apex by the phalangeal process-curticular extension
Inner rods of corti rest on?
-junction between the tympanic lip and osseous spiral lamina on the basilar membrane (INNER RODS=OSL side)
Outer rods of corti rest on?
-outer limit of arcuate zone of basilar membrane (OUTER RODS= side towards spiral ligament)
The order (line up) of supporting cells in the organ of corti for the INNER hair cell side is?
From outer towards the tunnel of corti= (large flat polygonal cells of internal spiral sulcus) BUT mostly- Border Cells of Held t> inner phalangeal cells >inner rod of corti
The order (line up) of supporting cells in the organ of corti on the OUTER hair cell side is?
From outer towards the tunnel of corti=cells of Claudius> cells of Boettcher > Cells of Henson>Cells of Deiters > outer rod of corti (CB, HD-outer Rod)
the inner and outer rods of corti form a tunnel by their overlapping _______ _________
The thin head plates of the outer pillar cells of the rods of corti are also known as...?
What makes Deiters cells soo extra special!?
its shape is modified to form a cup that snugly accomodates the basal end of an outer hair cell
Do the cells of Deiter directly connect or touch the outer rods of corti?
not completely, they are in contact with the bases of the outer rods, but separated from the body/shaft of the cells
the bases of Deiters cells rest where?
the pectinate zone of the basilar membrane (Pectinate=stronger=Spiral ligament side)
What function does the lamella of a Deiters cell have?
-contributes to the reticular membrane
-separates the apexes of the neighboring cells
What exactly comprises the reticular mebrane (lamina)?
-inner phalanges, headplates of the inner rods, phalangeal processes of the outer rod and Deiters cells
What is the most important function of the reticular membrane?
lend support to the apexes of the hair cells and the tufts of cilia that occupy space in it- helps keep cilia in place for contact with tectorial membrane
The supporting cells of Henson are located next to...?
-immediately adjacent to the outer row of Deiters cells
-are tall and columnar. 5-6 rows
-help create the outer tunnel space
Cells of Claudius and Boettcher
-columnal and cuboidal
-next to Henson's cells
-are continous with the vascular epithelium of the spiral ligament
Are the sterocilia of the inner hair cells a uniform size?
No, they vary in length and diameter within individual hair cells and among the turns of the cochlea
Are there more inner hair cells at the basal end of the basilar membrane or apical end?
-apical end=around 115 cells
-basal end=around 80 (Bredberg 1968)
Approx. how many steroclila on an INNER hair cell?
-apex of the cell is slightly concave and cuticle capped
-sterocilia arranged in 3-4 wavy rows
How are the cilia able "to move together as a unit when the longest one is bent?"
-the cilia are joined by very fine fibrils
How are the outer hair cells arranged?
-3 or more rows and in the shape of a 'V' or 'W'
-3 rows in the basal turn, 4 rows in middle turn, and maybe up to 5 in apical turn (increases towards the top)
The outer stereocilia of the OUTER hair cells is larger or smaller than the others?
-it is considerably larger
The tectorial membrane is completely NON-cellular- Yes/No?
Yes-has no true cell membrane or real metabolic function and its role is purely mechanical
the 3 parts of the tectorial membrane are?
1. the cover net , 2. fibrous main body, 3. homogeneous basal layer
The tectorial membrane most likely has how many attachment points?
-at least 2 that are known
1. to the longest stereocila of the outer hair cell
2. Henson's stripe which attaches to the Border cells of Held
Zones of the Basilar membrane
Arcuate Zone is?
Pectinate Zone is?
Arcuate zone=thin and fragile, near OSL
Pectinate zone=thick, rigid, near basilar crest of spiral ligament, 2 fibrous layers
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