Anatomy and Physiology of the Ear Flashcards
where do sound waves enter? what does this cause at the end of the canal to vibrate?
external auditory canal; tympanic membrane
within 4 cm or so occupied by the outer and middle ears, three distinct physical principles operate to magnify the weak vibrations in the ear, what are they? what is the result?
organ pipe increase air pressure
bone lever system can triple it
arrangement of the eardrum and oval window can increase it 30 fold
the result of the three is amplification of sound more than 800 times before it sets the inner ear in motion, like whispering, weak vibrations are amplified
what is the Tendon of stapedius muscle and the tensor tympani innervated by and their function?
the stapedius muscle attached to the stapes and innervated by the facial nerve
tensor tympani muscle attached to the malleus and innervated by trigeminal
both attempt to dampen loud noises before they are transferred to the inner ear
***what is the path of sound waves through the ear?
air waves hit the pinna pushed to the external auditory canal rattles the TM malleus, incus, stapes oval window cochlea perilymph in the scala vestibule all the way to the helicotrema scala tympani back to the round window in the mid ear vibrations dampen eustachian tube nasopharynx
***how is sound transmitted to the brain? (11 steps)
- Pinna reflects sound & affects ability to locate sounds
- Outer & middle ear turns air vibration into bone vibration
- Inner ear turns bone vibration into fluid vibration
- Cochlea turns fluid vibration into tissue movement
- Different parts of the cochlea resonate to different frequencies of sound
- The basilar membrane of the cochlea contains ciliated, mechanosensitive, receptor cells (which also resonate)
- The receptor cells release neurotransmitter on 1° auditory neurons
- 1° auditory neurons of the spiral ganglion project in the 8th cranial nerve to the medulla
- The place coding is preserved throughout the CNS (tonotopy)
- High & low frequency sounds are localized in the horizontal plane by interaural intensity & timing differences, respectively
- Sound is localized in the vertical plane, and back/front ambiguity is resolved by spectral differences
what is significant about the vibrating basilar membrane found in the cochlear duct?
the membrane is narrow and taut at the end near the stapes and wider and more pliant at the other and so hydraulic pressure waves in cochlea induce wave lie ripple in the basilar membrane which travels from taut(beginning) to loose end (apex)
high tones produce the greatest crests where the membrane is tight (beginning), low tones where the wall is slack (end)
the crests are important because it determines which nerve fiber will send signals to the brain
***why can’t elderly people hear high frequency sounds as well?
because the basilar membrane isn’t as taut at the beginning
T/F, the basilar membrane also picks up vibrations in the skull from such sources as teeth clicking
T
what part of the outer ear collects and focuses sound waves into the external auditory canal?
pinna and tragus which then transmit sound through the external auditory canal which ends up at the tympanic membrane
what bounds the middle ear? function of the middle ear?
TM and the oval window; it transfers vibrations from the TM to the oval window using three bones or ossicles known as the malleus, incus and stapes
what is the auditory portion of the inner ear? innervation?
cochlea innervated by auditory/cochlear nerve (branch of CN VIII)
what are the two membranes that divide the cochlea into 4 fluid filled compartments?
reissner’s membrane separating scala vestibuli from middle compartment (scala media)
basilar membrane separating the scala media from the scala tympani
***the scala has what type of lamina that meets with this type of ganglion eventually innervated by this nerve?
spiral lamina to spiral ganglion to cochlear portion of CN8
what is the function of the organ of corti?
contains the cells responsible for hearing
capillaries nearest to the organ of corti end at the wall of cochlea and nutrients on their way out are carried to and from capillaries by?
endolymph fluid that bathes the organ
the basilar membrane supports the organ which contains a mass of cells almost touching the branch endings of the _____?
auditory nerve
these cells embed in a thick overhang sheet called the tectorial membrane
as the basilar membrane bellies, it pushes and pulls the complex of tissues above it and the hair cells of the organ of Corti ride with the basilar membrane
what is the tectorial membrane?
the hairs located on here are transducers
how do the pressure waves travel through the cochlea?
the pressure waves exert energy that begin at the oval window and end at the round window so pressure can dissipate, note that pressure is applied to the oval window at stapes and all parts of cochlea
what is the most important membrane found in the cochlea duct?
vibrating basilar membrane which separates sound by frequency in between scala tympani and media where the organ of corti is found
where do the sensations in both auditory/vestibular systems begin?
inner ear and both use hair cells (mechanoreceptors specialized to detect minuscule movement along one particular axis)
the hair cells found in the auditory and vestibular systems are contained where?what is the stimulus for the hair cell
membranous labyrinth; bending of the hair, vibrating endolymph
the auditory portion of the labyrinth is what part of the structure?
spiraling cochlea
the vestibular portion of the labyrinth contains two structures called?
the otolith organs (gravity and head tilt)
semicircular canals (head rotation)
what does the hair bundle of the auditory/vestibular labyrinth consist of?
1 large kinocilium and stereocilia
