Neuroanatomy: Block 3, # 48 - Ear Histo Wang

Front 1

we know the ear is divided into an outer, middle, and inner - talk about what makes up the outer:

Back 1

the pinna, which is elastic cartilege.

the external auditory meatus - originally cartilege on the outside (1/3), becomes bone as you get inside. lined by thin skin with no glands on the inside.

also, the tympanic membrane has 2 faces - the outer one is part of the outer ear and is lined by epidermis on the outer face.

the inner face, which is probably part of the middle ear, is covered by simple cuboidal epithelium.

Front 2

what's in the middle ear? what medium fills it?

Back 2

the inside of the tympanic membrane and the bones:

malelous, incus, and stapes.

these attach to the oval window.

note that it's full of air, while the inner ear is full of fluid.

also has the auditory tube, which goes to the pharynx.

ALSO - there are muscles! tensor tympani attaches to the malelous.

stapidius attaches to the stapies.

if tone in the muscles is too low, sounds appear too loud.

Front 3

what components are under the heading of "bony labyrinth" and which are "membranous labyrinth?"

Back 3

bony: choclea, vestibule, and semicircular ducts.

membranous: chocolear duct, vestibular duct, and the utricle/sacule.

Front 4

between bony and membranous labyrinths, what do we have?

Back 4

the outer layer is bony and the middle layer is membranous.

note that the membranous labyrinth is coated with simple squamous epithelium. the bony labyrinth has periosteium on the outside.

note that the bony labyrinth is full of parilymph and the membranous labyrinth is full of endolymph

Front 5

describe the differences between perilymph and endolymph:

Back 5

endolymph is like intracellular fluid - it has really high K and really low Na+

perilymph is like the rest of body fluid - the K+ is very low, the Na+ is very high.

Front 6

what are the 3 hair organs in the ear?

Back 6

christa ampularis - this is in the ampule of each of the 3 semicircular canals.

note that this is useful for detecting angular acceleration.


the macula - there's one in the utricle, one in the sacule. these are for detecting linear acceleration and head position.

the spiral organ of corti - these are in the choclea and are for hearing.

Front 7

talk in more depth about the hair cells. efferent or afferent? main cilia called what?

Back 7

in the vesitbular system, the main big hair is called a KINOCILIUM (not present in the choclea, though its basal body is).

called neuroepithelia. also STEREOCILIA.

have efferent and afferent innervation.

they're all transducers in that mechanical information is converted into electrical information.

they all ascend up Cn 8 - the vestibulochoclear nerve.

Front 8

differences between type 1 and type 2 hair cells?

Back 8

type 1 and type 2 are in both the vestibular and choclear system. no functional difference. note that the vestibular ones will have the big kinocilium.

type 1's have 1 afferent nerve coming out of them and a rounded base.

type 2's have several afferent nerves coming out and have a slender, straight base.

Front 9

do hair depolarize or hyperpolarize when stimulated?

Back 9

can do either.

if the hairs bend toward the kinocilium in the vestibular system or the basal body in the choclear system, get depolarization.

if they bend away, get hyperpolarization. activation happens when it's depolarized. inhibition happens when it's hyperpolarized.

Front 10

describe the components of the choclea a little more precisely:

also, where are the oval and circular windows?

Back 10

MTV:

the scala media, scala tympani, scala vestibuli.

note that the media is in the middle, the scala vestibuli is on the outside, and scala tympani is on the inside.

the scala tympani and scala vestibuli both have PERILYMPH (high Na+, low K+) and the scala media has endolymph (high k+, low Na+).

the oval window is on the scala vestibuli, while the circular window is on the scala tympani.

Front 11

what else that's really important is in the scala media?

Back 11

the organ of corti. note that this is also called the choclear duct and represents membranous labyrinth.

Front 12

describe the organ of corti in detail

Back 12

remember that it sits in the scala media.

it has inner and outer hair cells. outer hair cells have 3-5 rows, inner cells have 1.

these all rest on a basilar membrane.

have supporting inner and outer phalangeal and pilar cells.

also a tectorail membrane over the whole thing - kinda like keratin.

Front 13

briefly, how does the organ of corti function?

Back 13

basalar membrane moves up and down in response to the oval window being bashed on.

pilar cells change this to a side to side motion.

this causes the hair cells to move.

if more away from modius, same as moving toward the kinocilia or basal body - this depolarizes the cell.

this is perceived by the spiral ganglion and transmitted.

Front 14

how are frequencies detected?

Back 14

the basalar membrane has different resonances along its length.

toward the bottom it's pretty stiff - specialized for high frequency detection.

at its apex, it's loose and flacid - better for picking up low frequencies.

Front 15

describe the two kinds of hearing loss. what does having a too loud iPod cause?

Back 15

conduction and receptor/CNS problem.

damage from the outer ear to the choclear duct = conduction

chocolear duct to the brain = receptor/CNS problem.

an iPod that's too loud causes receptor/CNS problems by killing off hair cells of certain frequencies.

water in the ear is an example of a conduction problem as it sits in the outer ear.

Front 16

what do the sacule and utricle have in them, and what are they specialized for?

Back 16

utricule and sacule are part of the vestibular systen, here responsible for linear acceleration and head position.

note that the neuroepithalial cells are hair cells like everywhere else. above them, though, are something called "otoliths?"