self assessment two Flashcards
Draw and label all major structure of the outer and middle ears (refer to red rectangles in slides)
- outer: helix, tragus, antihelix, antitragus, cavum concha, external auditory meatus, lobule
- ear canal: outer 1/3 is cartilaginous, inner 2/3 is osseus, where it changes is the isthmus
- tympanic membrane: lateral process of malleus, manubrium of malleus, umbo, cone of light
- middle ear: ossicles (their parts), ligaments^, tensor tympani muscle, stapedius muscle, mastoid air cells, eustachian tube, promontory, aditus to the mastoid antrum, round window, oval window, epitympanum
- malleus: head, neck, anterior process, lateral process, manubrium, umbo
- incudomalleal articulation
- incus: body, short process, long process, lenticular process
- incudostapedial articulation
- stapes: head, posterior crus, obdurator foramen, footplate, anterior crus
^superior malleus ligament, anterior malleus ligament, lateral malleus ligament, superior incus ligament, posterior incus ligament
Explain the overall process of sound transduction from movement of air molecules to brain signal, using correct anatomical and physiological terms
Explain what the two main functions of the outer ear are and how the anatomy and physiology of the outer ear accomplishes those tasks
- sound transmission
-Sounds reaching a listener are affected by the body, head, and outer ear
-The ear canal cavity is the primary resonance cavity and it acts as a one-quarter wavelength resonator
-pinna acts as a funnel
(i.e., an open-closed tube) - middle ear protection
-cerumen traps things
Describe the various disorders of the outer, middle, and inner ears discussed in class and what their impacts on hearing and health might be
- otitis media: inflammation leads to narrowing of the eustachian tube, increasing negative pressure sucks the TM in, muscousal secrections create bacteria and that creates pus
Explain the sound transmission function of the middle ear, including all the ways the middle ear helps us overcome the impedance mismatch
- pressure transformer: the area of the tm is way bigger than the oval window so the pressure on the oval window goes up (boosts by 25 dB)
- ossicular lever: when sound hits the tm it gets the malleus moving and it’s big, and since the stapes is so much smaller the force with which the stapes is moving is much greater (boosts by 1.2 dB)
- catenary lever/buckling effect: the tm is pulled back a bit at the umbo which is where all the sound is focused (focuses distributed force into center)
- if you add all the dB together you get 32 dB -about 40x (which almost overcomes the impedance mismatch)
Explain how middle ear anatomy and physiology allows pressure equalization between it and the external environment
eustachian tube: the levator veli palatini muscle and tensor veli palatini muscle open it
Explain the ear protection function of the middle ear, using appropriate anatomical and physiological principles
- tensor tympani and stapedius muscles are activated (constrict when we hear loud sounds)
- 75-85 dB SL (above our threshold)
- the muscles pull the ossicles tighter which limits their movement (and therefore transfers less energy)
- but not loud sounds that are really fast (like a gunshot etc)
Draw and label all structures of the inner ear from general anatomy of the cochlea and organ of corti down to IHC and OHC and how they connect to the auditory nerve
i think i can do this
Explain where and what the modiolus is
the modiolus is in the center of the cochlea and it is where the spiral ganglion (nerve cell bodies) is located.
-specifically the tunnel in the center of the modiolus which is called rosenthal’s canal
Use your knowledge of how the cochlea works to explain how we process frequency, intensity and duration/timing of sound signals
Distance along the basilar membrane codes for frequency
Magnitude of displacement of the basilar membrane codes for intensity
-base high freq, apex low freq
- basilar membrane is a traveling wave , it’s transverse
- - a very fast sound has less action potentials than a prolonged one
- the louder the sound the more action potentials
Explain how IHC and OHC shearing works, how they’re similar and different, and why it matters to sound processing
- during upward phase of basilar membrane movement stereocilia are sheared away from the modiolus
- during downward movement of the basilar membrane stereocilia are sheared towards the modiolus
-cochlear amplifier is what happens when ohc are depolarized
-action potential is what happens when ihc are depolarize
inner hair cell shearing:
- shearing is the first step in turning movement into a brain signal
- when IHC stereocilia more away from the modulus positive ions enter the cell through tipo link gated channels
- when the tips links are moved its like a trap door
- ion flow leads to transduction of mechanical energy into brain signals
- when the ihc move towards the modiolus then the doors close
- the ions enter the cell at the frequency of the sound
Describe what happens within IHC and OHC as stereocilia are sheared
inner hair cells:
stereocilia bending out leads to rushing in of K+ which leads to depolarization of hair cells
- makes the cell more positive than the -40 mv
- depolarization: IHC
- - there are calcium gates that are voltage dependent, when they sense that the cell is getting more voltage they open up with allows calcium to flow into the cell
- when calcium flows in it interacts with neurotransmitter and it starts moving towards a synapse (where 2 cells connect)
- Neurotransmitter binding leads to a similar depolarization process in auditory neurons, which, in turn, leads to action potentials (i.e., nerve impulses)
———————————————–
- in ohc, depolarization = electromotility (expanding and contracting of the cells)
- aka the active process (tightened and amplified) of the cochlea
- cochlear amplifier
- The OHC acts as small motors that enhance the movement of the basilar membrane they amplify the movement of the basilar membrane at the narrow area where the BM is resonating with the traveling wave
- This increases the mechanic input to the IHC
- Greatest at lower intensities
- Loss of hair cells and cochlear amplifier results in a hearing loss of about 50 dBHL
- the outer hair cells expand and create a bouncing movement that amplifies the movement of the basilar membrane at the specific frequency it is vibrating at and not the surrounding frequencies
- this amplifies the sound and makes the signal louder than the noise so we can differentiate frequencies from each other
Explain the make up of endolymph and perilymph and why it matters
- endolymph: more potassium (k+) less: calcium and sodium
- stereocilia are in endolymph
- perilymph: more calcium and sodium less: potassium
- both are positively charged
- hair cell bodies are in perilymph
- inside the hair cells it is dominated by chloride (which is negatively charged)
- resting potentials:
- endolymph= +80mv
- perilymph= 0mv
- IHC= -40 mv
- OHC= -70 mv
stereocilia bending out leads to rushing in of K+ which leads to depolarization of hair cells - makes the cell more positive than the -40 mv
- depolarization: IHC
- there are calcium gates that are voltage dependent, when they sense that the cell is getting more voltage they open up with allows calcium to flow into the cell
- when calcium flows in it interacts with neurotransmitter and it starts moving towards a synapse (where 2 cells connect)
- Neurotransmitter binding leads to a similar depolarization process in auditory neurons, which, in turn, leads to action potentials (i.e., nerve impulses)
Describe the entire process of IHC and OHC depolarization
- basilar membrane moves and hair cells get sheared and potassium (positive) enters the cell (which is negatively charged inside)
- the cell is depolarized
- the voltage dependent calcium gates are opened and let calcium into the cell
- the calcium makes the neurotransmitter go to the synapse and send a signal to the brain (action potential)
while this is happening…
- in ohc, depolarization = electromotility (expanding and contracting of the cells)- aka the active process (tightened and amplified) of the cochlea
- cochlear amplifier
Talk intelligently about what the cochlear amplifier/active mechanism is, why it matters to typical cochlear function, and what happens when it’s damaged
- The OHC acts as small motors that enhance the movement of the basilar membrane they amplify the movement of the basilar membrane at the narrow area where the BM is resonating with the traveling wave
- This increases the mechanic input to the IHC
- Greatest at lower intensities
- Loss of hair cells and cochlear amplifier results in a hearing loss of about 50 dBHL - the outer hair cells expand and create a bouncing movement that amplifies the movement of the basilar membrane at the specific frequency it is vibrating at and not the surrounding frequencies
- this amplifies the sound and makes the signal louder than the noise so we can differentiate frequencies from each other
