Terms in this set (47)
Where in your body does 'hearing' take place?
right under eyes
-A hairlike appendage of a cell involved in transducing sensory information
-found on the receptors of the auditory or vestibular system
-made of microtubules in a 9+2 arrangement
This is a large hair cell important in the detection of the head's position. Whether the displacement of the stereocilia is towards or away from this determines whether it is excitatory or inhibitory.
Afferent vs Efferent synapses
in fish and aquatic amphibians principally monitor mechanical stimuli from water.
has 30-60 hair cells coming from it
A small gelatinous column that forms part of the lateral-line system of aquatic animals and also occurs within the vestibular system of mammals.
How do fish hear?
-only difference in density of fish and water is in the bones and swim bladder (very low density)
-sound waves hit swim bladder and vibrate gas inside->vibrates into the bones->Weberian ossicles (modified vertebral column conducts sound to brain)
How do sharks hear?
don't have swim bladders
can hear very well, but don't really know how
may be orientation of hair cells
How does sound move?
in a sine wave
fluctuates from positive to negative atmospheric pressure
-unit used to measure the loudness of sound
-lowest sound pressure you can hear is defined as 0 dB
Decible level and safety
-0-90 dB can handle 24/7 with no problems
-90-130 dB the longer you stay at this level the more damage to cilia
130< immediate danger
Sound pressure equation
20 log (P/Po)
Po = threshold
if P=Po -> 0 dB
if P= 10 x Po -> 20 dB
hair cell transduction
outer ear (pinna), middle ear ear (hammer, anvil, stirrup), inner ear (oval window, cochlea, basilar membrane, auditory nerve)
Why do we have outer ears?
configuration of the outer ear selectively boosts sound P 30-100X for frequencies at ~3kHz (human speech)
What nerve goes to the cochlea and vestibular system?
VIII cranial nerve
Plasticity of hearing vs seeing
-pinnae help the brain discern where sounds come from, each person learns to hear with their own pinnae
-it took several weeks to learn where sounds came from with 'new' ears, but after learning, participants could switch between either set of ears with ease (similar to learning a new language)
-people need the same amount of time to adjust to 'new' vision every time it is encountered
How does hearing work?
Sound enters the ear canal and hits the tympanic membrane (ear drum). The tympanic membrane vibrates causing the small bones in the ear to vibrate. These bones focus and amplify the vibrations onto the oval window on the cochlea. The cochlea is a fluid filled coiled membrane. The vibrations shake the fluid in the cochlea.
Auditory portion of the inner ear. The cochlea is filled with a watery liquid, which moves in response to the vibrations coming from the middle ear via the oval window. As the fluid moves, thousands of "hair cells" are set in motion, and convert that motion to electrical signals that are communicated via neurotransmitters to many thousands of nerve cells.
has ~16000 hair cells that cannot be replaced
boosts pressure at tympanic membrane by 200X
How are sharks relevant to the human middle ear?
the jaw support bone in fish/sharks transformed into human stapes
smallest bones in the body
-Malleus (hammer): attaches to the ear drum
-Incus (anvil): between the malleus and stapes
-Stapes (stirrup): vibrates against oval window
cochlea semi circular canals
-dark pink is endolymph
-light pink is perilymph
-resembles intracellular fluid
-high in K+
-resembles interstitial (extracellular) fluid
-high in chloride
How many times does the cochlea coil?
2.5 in humans
VIII cranial nerve location and functions
innervates semicircular canals and cochlea
-top part vestibular nerve
-bottom part auditory nerve
-stapes pushed in right in between vestibular part and auditory part
cochlea cross section
1) cochlear duct (contains endolymph); purple is where hair cells are
2) Scala vestibuli (perilymph)
3) Scala tympani (perilymph)
5) vestibulocochlear nerve (VIII)
organ of corti
-located in the cochlea; contains receptors (hair cells) that receive vibrations and generate nerve impulses for hearing
-structures to know: tectorial & basilar membrane, inner vs outer hair cells
Inner hair cells
~3000 hair cells
-90% of innervation by afferent fibers (primarily sensory in function) & much more innervated than outer
-hairs are free; not embedded in tectorial membrane
Outer hair cells
~12000 hair cells
-90% of innervation by efferent fibers
-associated with amplification rather than directly sensory
-amplify vibrations in basilar membrane
-hairs are embedded into tectorial membrane
How do sound waves affect the organ of corti?
sound waves cause the basilar membrane to move up & the tectorial membrane to move forward
Inner vs outer hair cells
outer: V or W shaped; different angles along the membrane
Efferent vs afferent nerves
Efferent: from brain to hair cell; NTs in nerve fiber
Afferent: from hair cell to brain; NTs in hair cell
-Function: pitch perception
-stiff & thick near oval window
-narrow & flexible near distal end
-brain translates location on membrane into pitch
Outer hair cells & frequency
-OHCs have uniform diameter (8-10µm), but graded lengths (20-100µm)
-High freq: shorter, stiffer 0.6µm length
-Low freq: taller, less stiff 6 µm length
Basilar membrane and frequency
as frequency spreads out, focal area for displacement moves further from inner ear
-cerebral cortex has a 'map' of cochlea
-symmetry with how the cochlea registers pitch
Why is the cochlea snail shaped?
-increasing curvature shunts energy to the outer wall-> adds to shearing of basilar and tectorial membranes
Fibrous connections between stereo cilia that pull open mechanically gated cation (K+) channels due to shearing of tectorial membrane, causing depolarization
How are hair cells depolarized?
-tip link opens mechanically gated ion channel
-allows K+ influx
-opens Ca++ channels, Ca++ influx
-depolarizes cell & releases NT vesicles
Soft Spring Model
-no longer used
-tip link made out of ankyrin & is elastic
Stiff Spring Model
-Tip link made of cadherin, stiff connection between sterocilia
-elasticity is within the cell (ankyrin)
tip link molecular anatomy
TMC proteins form transduction channel pore
PCDH15 & TMC proteins couple the tip link to the transduction pore
audtior channel (article)
-don't really know what it is, modified TRPA1 (skin sensing) channel
-without it, you'd be deaf by five
-have actin cytoskeleton and myosin to reduce membrane tension
How do outer hair cells amplify sound?
-somatic electrically induced motility of OHCs mediated by protein prestin as energy for amplification
-anions act as extrinsic voltage sensors
-OHC elongate when hyperpolarized
-shorten when depolarized (~5% change in length)
-amplification is non-linear
role of basolateral membrane
OHC efferent innervation
-doesn't relate to amplification
-protective device, transient way to modulate displacement
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