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how does the ear develop?
- - ectoderm invaginates forming otic vesicle - invaginates - deeper and becomes the membranous labyrinth
- endoderm forms first pharyngeal pouch - cavity of inner ear
- - mesenchyme from first and second
- - first pharyngeal groove - has ectoderm - produces ear canal (external meatus)
- - arch tissue condenses and makes the bones of the middle ear
describe the ear canal?
- first third = cartilagenous
- last 2/3rds are in temporal bone and ends with tympanic membrane and then you get the ceruminous gland
what is the ceruminous gland?
- makes the ear wax, type of apocrine sweat gland, mix of waxes and fats, cuboidal or columnar (more active ones), mixes with sebum from esbacious glands and also exfoliated skin cells
- genetics: yellow liquidy or dry grayish white
- covered in thin skin
- elastic cartilage (hyalin with a bunch of elastic fibers)
what are the 2 functions of the ear?
auditory and vestibular
components of external ear?
- auricle (pinna)
- external acoustic meatus
- tympanic membrane (eardrum)
- ceruminous glands (not sweat)
middle ear? - structure and function?
- air filled space (tympanic cavity) that contains three small bones (ossicles)
- also has auditory tube (eustachian tube)
- contains two openings (oval vestibular window and round chochlear window)
- bounded by the tympanic membrane
- converts sound waves into mechanical energy
which window is what?
- vestibular (oval)
- round (cochlear)
which bone is it attached to?
- separates external acoustic meatus from the middle ear
- connect tympanic membrane to oval window
- convert energy
- malleus - attaches to tymp membrane
- incus - largest, links the malleus to the stapes
- stapes (stirrup)- footplate of which fits into the oval window, acts like a small piston on the cochlear fluid
- bony labyrinth - interconnected cavities and canals in the petrous part of the temporal bone, lined with perosteum
- membranous labyrinth - lies within bony lab, contains endolymph fluid
- perilymph fluid is between the two membranes
- structure: vestibule in middle, 3 semicircular canals (balance) and a cochlea (hearing)
- vestibule also attaches to the stapes
where are the windows located?
- oval window - attached to vestibule and stapes
- round - attached to the cochlea
three semicircular canals
tubes within the temporal bone that lie at right angles to each other
contains the utricle (branches into the semicircular canals) and saccule (goes into the cochlear duct)
6 sensory cells of the membranous lab:
- - 3 cristae ampullaris - located in semicircular ducts, angular acceleration of head
- - two maculae: macula of utricle and macula of saccule - position of head and linear movement
- - spiral organ of corti - projects into endolymph of cochlear duct - sound receptor
what is formation of hair cells within a bundle?
- rows of sterocilia (hair cells) that increase in height in one particular direction across the bundle
- they are gradated
- the one furthest away from the kinocilia/basal body is the shortest
kinocilium? where is it?
- each hair cell possesses a single true cilium = kinocilium - located behind the row of longest sterocilia
- - vestibular
- hair cells lose kinocilium but maintain basal body
- - defines polarity of assymetric hair bundle because it is next to the longest row of stereocilia
what is a stereocilia?
organization of sterocilia?
- tightly packed actin filaments crosslinked with fimbrin and espin, 9+2 arrangment,
- rigid and stiff, which makes precise movements
- - at the top of each stereocilia = MET channel protein (mechanoelectric transducer)
- - tip links connect the top of one sterocilia with the shaft of a longer stereocilia right next to it
what is a basal body?
microtubule organizing body, at the base of the stereocilia, it is what is in the auditory canal
where and what is the endolymph?
it is contained in the membranous labyrinth
where and what is the cortilymphatic space?
lies w/in the organ of corti, filled with cortilymph
what is the role of tip links?
- tip links activated when there is enough tension and bend
- to activate the K+ channels and the MET channels, gets its neigbors to get going!
- potasium moves into the cell adn you get an action potential
movement aawy from kinocilia?
movement towards kinocilia?
- towards - action potential (depolarization)
- away - MET channels close and you get hyperpolarization
what happens after depolarization?
- voltage gated calcium channels open up in the basolateral surface of the hair cells and cause secretion of a nuerotransmitter that generates AP in afferent nerve endings
- example of calcium mediated exocytosis
difference between type 1 and type 2 hair cells?
- type 1: flask shaped, rounded base and thin neck, surrounded by afferent nerve chalice and a few efferent
- type 2: clyindrical and have both afferent and efferent endings at the base
sensory receptors of the membranous labyrinth:
crista ampullaris - in each of the semicircular ducts and are receptors for angular movement, thickened epithelial cells, perpenidcular to long axis of duct, covered in hair cells
- gelatinous protein polysaccaride mass
- that coats the top of the hair cells of each crista, surrounded by endolymph
big pic of how neuronal impulses get transmitted to the brain?
rotational movement of the head - walls of semicircular canal and membranous semicircular ducts move, but endolymph lags behind - differential of movement causes the hair cells to move and then they send nerve impulses
what is function of maculae of saccule and utricle?
- innervated sensory thickenings of epithelium that face the endolymph
- has type 1 and 2 hair cells, supporting cells, and nerve endings
- they are right angles to each other
what is position of macula of S and U when a person is standing?
- M of S - vertical plane
- Mof U - horizontal
what is it analogous to?
how does it function?
- gelatinous polysaccharide material that overlies the maculae
- heavier than endolymph
- it is analogous to the cupula
- it drags on the stereocilia bc of inertia - activates MET channels and depolarizes hair cells
- contains otoconia
what are otoconia?
crystalline bodies of calcium carbonate and protein, apart of the otolithic membrane
divisions in cochlear canal?
- scala media - middle compartment (duct itself) - contains endolymph, has organ of corti on lower wall
- scala vestibuli (above media) - has perilymph, begins at oval window
- scala tympani (below media) - has perilymph, ends at round window
how do the scala vestibuli and the sc. tympani communicate with each other?
through the hiliocotrema
vestibualr membrane (Reissners)
upper wall of scala media, between sc. media and scala estibuli
lateral wall of scalar media - maintains the endolymph, ion concentrations, action potentials, complex capillary network
trend as it coils?
- lower wall (floor) of scala media - flaccid
- increases in width and decreases in stiffness as it coils from the base to apex, also number of hair cells increase
membranes near the organ of corti?
- basilar membrane is underneath
- and tectorial membrane is on top
how are diff frequencies heard by the ear?
diff fibers have diff resonance frequencies, and when you hit that sweet spot they vibrate very rapidly
higher frequency sounds target the base of the cochlea
hair cells of spiral organ of corti?
- complex epithelial layer on the floor of the scala media
- inner hair cells - close to spiral lamina
- outer hair cells (farther from lamina)
- inner phalangeal (supporting) cells and outer phalangeal cells
- pillar cells
inner hair cells (row #?)
outer hair cells row #?
in general ?
- goes from 3 (base) to 5 (apex)
fx of phalangeal cells?
- supporting cells
- surround inner hair cells completely
- surround only basal part of outer hair cells, but send up processes towards endolymphatic space, flatten at the top forming a plate (tight junctions between apical sides! - forming reticular lamina
how are sound waves conducted in the cochlea?
rigidity of basilar membrane gives fibers different thicknesses - so the sound waves jerk on the basilar membrane causing it to move, but at different speed than the endolymph so the hair cells move
muscles that attach to the ossicles?
tensor tympani muslce - next to mallus, contraction increases tension on tympanic membrane
stapedius muscle - connects to stapes, contraction dampens movement of stapes against oval window
division of membranous labyrinth:
cochlear labyrinth and vestibular labyrinth
function of eustacian tube?
equalizes pressure on inside and outside
apex of cochlea hears higher or lower frequencies?
- covers the organ of corti
- special glycoproteins
- touches the longest of the hair cells
how do the scala vestibuli and scala tympani work together?
they normalize the pressure difference between the two
big pic of hearing?
movement of stapes against the oval window of the vestibule - set up waves in the perilmph of the scala vestibuli - these waves are transmitted to the sc. media (contains endolymph) - go to perilymph of the sc. tympani - pressure differences move the round window of cochlea - soooo - sound vibes enter the inner ear - traveling wave set up in the basilar membrane - hit that sweet spot on the membrane - moving stereocilia of hair cells causes the basilar and tectorial membranes to move (different movement though) - deflection causes activation of MET channels - action potential to cochlear nerve
2 ways to get NIHL (noise induced hearing loss)
- short and intense
- or gradually developed
what happens to the hair cells when they get damaged?
- - overstimulation causes too much metabolism - release of too many reactive oxygen species (Free radicals) that do damage to cell and kill it
- - neuronal structures so they cant undergo mitosis, they can repair themselves but once they hit a certain point they decide to jsut die
which cells are the most prone to getting damaged?
why does current generation have so many hearing problems?
- little headphones
- long battery life
tips: time to recover, play music as loud as you are still able to hear someone speak
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