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46 Cards in this Set
- Front
- Back
the ear is an energy transducer
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changes energy from acoustic to mechanical, to hydraulic (fluid) to electrochemical. some energy is lost in the process of transducing
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initial considerations about hearing
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hearing is not an overlaid function as is speech, it is a specialized sense. audition is a telereceptor sense like vision, it that theres no direct contact with the stimulus source.
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outer ear
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collector and channeler of sound (air)
auricle or pinna EAM tympanic membrane |
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middle ear
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impedance matcher between air conduction and fluid conduction media (air)
middle ear space (tympanic cavity) |
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inner ear
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contains sensory receptors for hearing and balance (H2O) more resistant to stimulation so stimuli must be intensified
cochlea-auditory system (technically a space not an object) vestibular system |
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eustachian tube
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no clear division btw hearing and balance systems
e. tube communicates with nasopharynx and opens every time we swallow (via tensor veli palatini m.) |
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pinna (auricle)
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collects sound and adds 3-5 dB mainly in high freqs. made of cartilage (fairly rigid, maintains shape) covered with epithelium. stabilizes hearing aids/glasses.
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external auditory meatus
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(ear canal) 7 mm in diameter, 25-35 mm in length. elongated S on it's side that provides insulation and protection.
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cerumen
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production is normal, natural and necessary. traps insects and dirt, which is swept outward by cilia to entrance of EAM where it dries and falls out. impacted cerumen occurs when you produce it faster than cilia can sweep it out.
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lateral 1/3 of EAM
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lateral 1/3 cartilaginous, covered with epithelial cells, many having cilia. sabecous glands produce oil and ceruminous glands produce cerumen. innervated by CN V: trigeminal.
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medial 2/3 of EAM
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osseus portion, surrounded by temporal bone, canal narrows at juncture of cartilagious and osseus portions
no cilia, or glands innervated by CN X (vagus) also controls cough reflex. no lining btw epithelium and bone. skin is thin 1/10mm, and has many pain sensors and blood vessels. |
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tympanic membrane
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concave medial boundary of the outer ear. converts acoustic to mechanical energy.
55mm2 in area, 10mm in diameter, 55 degree angle to floor of EAM three layers:external (continuation of epithelial lining of the EAM), middle (fibrous and tough, circular and radial fibers), inner (continuation of mucous membrane lining of the middle ear). |
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TM landmarks
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pars tensa: 4/5 of TM, held taut and pulled medially by manubrium of malleus (points to left in left ear, and right in right ear)
umbo: inferior end of the manubrium, most medial pt. cone of light: always in anterior/inferior quadrant in normal TM pars flaccida: sup/ant 1/5 of TM, no fibrous layer, lateral process of malleus. |
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middle ear (tympanum)
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air-filled cavity, 1/3in h and wide, 1/6 in deep. increases pressure of sound waves hitting TM. besides air, it contains the ossicular chain, tendons of 2 muscles and ossicular ligaments. biggest purpose is to match impedance of the air to the fluid-filled inner ear.
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malleus
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most lateral of the bones, connects with the manubrium to the TM. head: ligament and attached to incus.
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incus
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body attaches to head of malleus. ends in a medial bend called the lenticular process, which attaches to the stapes. incus moves as a unit with the malleus.
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stapes
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smallest bone in the body. incudostapedial joint: head attaches to lenticular process of incus here. necks of stapes bifurcates into anterior and posterior crura, which attach to the footplate. the footplate fits into the oval window of the temporal bone and is held into place by the annular ligament.
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ligaments
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all ossicles are held into place by ligaments to the walls of the middle ear. this way we can hear upside down.
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impedance-matching
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area of the footplate in oval window=3.2mm2. TM=55mm2. TM is 17x bigger. the concentration of this amount of pressure on a small area amplifies it 25dB. motion of the ossicles adds 2dB. 27dB boost given by middle ear (needed to match high impedance of water in inner ear.
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stapedius muscle (tendon in the middle ear)
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tendon arises from the pyramidal eminence on the posterior wall of the middle ear. innervated by CN VII (facial) (close to aud nerve VIII). inserts at neck of stapes, pulling it posteriorly, keeping it tense.
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stapedial reflex
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contracts bilaterally when sound to one ear is 85-100 dB above threshold. protective device but ineffective with high frequency sound. used in testing.
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tensor tympani (tendon in the middle ear)
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arises from anterior wall of ME superior to opening of e. tube. innervated by CN V (trigeminal). inserts into upper part of manubrium. contraction reduces range of movement of ossicular chain, exact manner unknown. pulls in opposite direction of stapedius muscle.
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lateral wall of the middle ear
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made up by the tympanic membrane. chora tympani: travels from front to back behind the ear drum, a branch of CN VII medial to the TM and manubrium.
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top wall of middle ear
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thin bones separates ear from cranial cavity.
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medial wall of middle ear
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oval window
round window (inferior to promontory) promontory (bulge of basal turn of the cochlea, inferior to oval window) prominence of lateral semicircular canal canal of tensor tympani muscle prominence of CN VII (facial). |
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anterior wall of middle ear
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carotid artery beneath the surface. tendon of tensor tympani arises from medial-most aspect. entrance to the e.tube.
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eustachian tube (auditory tube)
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35-38mm in length. medial 1/3 is osseus, and always open. lateral 2/3 closest to nasopharynx is cartilaginous and normally closed. opens when we swallow or yawn via the tensor veli palatini m. ventilates the middle ear and equalizes pressure between middle ear and the environment. is e.tube doesn't open close, can result in negative pressure in the middle ear. horizontal in children, but at an angle as face grows down during adulthood.
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inner ear: annular ligament
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the footplate is attached by the annular ligament to the oval window (this ligament goes completely around the stapes).
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inner ear: oval window
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opens into the vestibule, which in the cochlea becomes the scala vestibuli.
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inner ear: round window
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between the middle ear space and the scala tympani
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inner ear: round window
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smaller than oval window and in between middle ear space and scala tympani. covered with membrane, presence allows footplate to displace inner ear fluid. (round staircase going up)
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scala vestibuli
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(round staircase going up), filled with the same fluid as scala tympani. both go around the scala media (different fluid)
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inner ear: sensory receptors
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receptors for hearing are in the cochlea and balance are in the vestibule and semicircular canals. receptors are in fluid-filled (endolymph) membranous sac. this sac is called the membranous labryinth because it has multiple passageways. the m.labryinth is surrounded by fluid (perilymph) within a series of tunnels through the temporal bone called the osseus labryinth.
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vestibular system: utricle and saccule
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utricle and saccule maintain balance and are located within the membranous labrynth in the vestibule. maculae are spots on the utricle and saccule that sense bodily acceleration and tilting (innervated by vestibular branch of CN VIII.)
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vestibular system: semicircular canals
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sense rotational movement of the body. anterior (superior): perpendicular to the plane of the temporal bone. horizontal (lateral): transverse plane. posterior: parallel to plane of temporal bone.
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nerve fibers for balance and hearing
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are in the same nerve
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cochlear duct
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section of the membranous labryinth housing the sensory receptors for hearing. looks like a snail shell, spirals 2 3/4 turns from basal to apical end. tunnel through the temporal bone filled with fluid. in the fluid is a membranous sac with the sense organs in it.
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modiolus
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central core in middle of the cochlear duct spiral
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osseus spiral lamina
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bony shelf that projects from the modiolus
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basilar membrane
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attached between the osseus spiral lamina and spiral ligmaent. divides the scala media (cochlear duct) from the scala tympani.
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organ of corti
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sensory organ of hearing, sits upon the basilar membrane. one row of inner hair cells from basal to apical turn. 3 rows of outer hair cells.
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reissner's (vestibular) membrane
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divides scala media from scala vestibuli
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helicotrema
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at apex of cochlea, scala vestibuli and scala tympani join
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inner hair cells (IHC)
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teardrop-shaped, 3500 in number, cilia in a shallow U configuration, innervated by many nerve fibers. more significant to hearing.
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outer hair cells (OHC)
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test tube-shaped, 12,000 in number, cilia in a W or V configuration, cilia imbedded in tectorial membrane and moved via shearing action. a single nerve fiber serves many OHC. damaged in noise exposure.
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lenticular process
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where the incus ends in a medial bend and attaches to the stapes
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