M3 L7 Flashcards
What does the outer ear include?
the pinna and auditory canal.
What does the pinna do? Why important?
The pinna directs sound waves into the ear.
The shape of the pinna makes us more sensitive to sounds coming from ahead than from behind. The convolutions in the pinna play a role in localizing sounds.
What does the auditory canal do?
helps channel sound towards the tympanic membrane (eardrum).
What does the middle ear include?
the tympanic membrane
what is the tympanic membrane? What is it attached to and what do they do.
it is the eardrum. it is the first structure that receives sound vibrations.
The eardrum is attached to three small bones called the ossicles (malleus, incus, and stapes). These bones amplify vibrations and transfer them from air (outer/middle ear) to fluid (inner ear).
What does the stapes do?
acts as the final step in converting air vibrations into fluid vibrations.
What two muscles does the middle ear contain and what do they do?
Tensor tympani muscle
Stapedius muscle
- prevent saturation
- regulate loud sound
Tensor tympani muscle
* function/purpose
* what is it attached to
* stimulated by what nerve?
The main role of the tensor tympani is to dampen loud sounds by pulling on the malleus. This reduces the vibration of the tympanic membrane (eardrum).
- attached to bone in cavity of middle ear on one end and malleus at other end
- stimulated by trigemninal nerve
The Stapedius muscle
* function/purpose
* what is it attached to
* stimulated by what nerve?
The stapedius muscle reduces excessive movement of the stapes by pulling it away from the oval window.
- attached to bone in the cavity of the middle ear on one end and stapes at other end
- stimulated by facial nerve
What does the inner ear contain? what is it
the cochlea, a fluid-filled structure responsible for sound transduction.
- also the vestibule and semicircular canals
What does the cochlea do
Vibrations in the cochlea cause movement in hair cells, generating action potentials (APs) that send auditory signals to the brain.
vestibule function?
These structures detect linear acceleration (e.g., moving forward in a car, going up in an elevator). Help maintain static equilibrium (posture and head position relative to gravity).
semicircular canals?
Detect rotational movements (e.g., turning your head left or right, tilting your head). Each canal is filled with endolymph which senses changes in head position.
Important for dynamic equilibrium (maintaining balance during movement).
What is the Attenuation Reflex
a protective mechanism of the ear that reduces the impact of loud sounds by dampening their transmission to the inner ear.
- makes sure sounds dont saturate the response of receptors in inner ear
Limit of the Attenuation Reflex?
Delay of 50–100 msec and therefore less protective when there is a very sudden loud sounds
What frequency does the attenuation reflex suppress?
Suppresses low frequencies more than high frequencies
* it tends to make high-frequency sounds easier to discern in an environment with a lot of low- frequency noise
Cochlea
* where located
* what filled with
* contains what structures
- located within the internal acoustic meatus
- filled with fluid that moves in response to vibrations, stimulating hair cells
- contains oval and round window and auditory vestibular nerve
Auditory-Vestibular Nerve
* function
* what connect to
Carries signals for hearing and balance to the brain.
Connects the cochlea (hearing) and the vestibular system (balance) to the central nervous system.
What is located at the base of the cochlea?
two membrane-covered openings: the oval window and the round window.
Oval window
* what do
* where is it
- Transfers vibrations from the stapes which push on the oval window which initiates movement of the fluid inside the cochlea eventually leading to hearing
- found on cochlea behind stapes and above round window
Round window
* what do
* where is it
Acts as a pressure release valve, allowing fluid movement inside the cochlea when the oval window is pushed inward.
- Positioned at the end of the scala tympani, a chamber of the cochlea.
how do round and oval window work together
The oval window bulges inward when it transfers vibrations from the stapes, creating fluid movement in the cochlea that stimulates hair cells for hearing. The round window acts as a pressure release valve, bulging outward to allow proper fluid movement and prevent pressure buildup
oval window push fluid in - round window push it out
Whats compression and rarefaction in the cochlea?
Compression (Pressure In) → At the oval window, where the stapes transmits sound vibrations.
Rarefaction (Pressure Out) → At the round window, which moves outward to relieve pressure.
How is the cochlea organized?
1) basilar membrane
2) base
3) apex
Basilar membrane
* what 2 things does it do?
Separates the scala media (middle chamber) from the scala tympani.
Vibrates in response to sound, activating hair cells.
Base of cochlea
* width and flexibility
* location
* frequency detection
- narrow and stiff
- near oval and round windows and stapes
- detect high frequency
Apex of cochlea
* width and flexibility
* frequency detection
* distance from windows
- wide and floppy
- detects low frequencies
- far from windows
Scala vestibuli
* top or bottom chamber?
* contains what fluid
* connected to what
- top chamber
- periplymph fluid
- connected to oval window
Scala tympani
* top or bottom chamber?
* contains what fluid
* connected to what
- bottom chamber
- periplymph fluid
- conncted to round window
What is the helicotrema?
A small opening at the cochlear apex that connects the scala vestibuli and scala tympani.
ensures both chambers are continuous with fluid
Reissners membrane
* where is
* what do
* why important that its FLEXIBLE
- inside cochlea
- allows vibration of perilymph to also vibrate endolymph
- important because the perilymph movement will cause the endolymph to move as well.
Cochlear duct/Scala media:
* where is it
* what contain
- the middle chamber of the cochlea, located between the Scala Vestibuli (above) and the Scala Tympani (below)
- contains the organ of Corti, endolymph, tectorial membrane, stria vascularis
What is the stria vascularis
* where is it
maintains the ionic balance of endolymph by pumping K⁺ into the endolymph by active transport
- inside of Scala media
What is the endolymph and what does it do
extracellular fluid with high potassium (K⁺) (150 mM) and low sodium (Na⁺) (1 mM).
creates driving force for K+ to move into their hair cells
How is the organ of corti structured?
It sits on the Basilar Membrane and is covered by the Tectorial Membrane. The reticular lamina is in the middle, holding onto the hair cells.
What is the organ of corti
The Organ of Corti is the sensory structure inside the Scala Media (Cochlear Duct) responsible for converting sound vibrations into electrical signals.
What is the tectorial membrane? What do?
A gel-like structure that sits above the hair cells.
When sound vibrates the Basilar Membrane, hair cells push against the Tectorial Membrane, triggering electrical signals.
What does the reticular lamina do
A middle structure that holds the hair cells in place.
Inner hair cells:
* function
* how many arranged and how
* efferent or afferent?
* discuss hair bundles
- Send sound information to the brain.
- 4500 form a single row
- afferent (send info to brain)
- Hair bundles are free to move
Outer hair cells:
* function
* how many arranged and how
* efferent or afferent?
* discuss hair bundles
- Amplify sound and fine-tune hearing.
- 12k - 20k arranged in 3 rows
- efferent (receives input)
- Hair bundles are embedded in the tectorial membrane
Stereocilia
* what is
* what do
Hair-like Projections on Hair Cells
Bending of stereocilia opens ion channels, allowing K+ and Ca²⁺ to enter, creating an electrical signal.
What are Spiral Ganglion Cells and what do
Bipolar Neurons
Carry signals from hair cells to the auditory nerve, then to the brain.
purpose of modiolus?
use as a reference point for hair movement
whats transduction by hair cells?
how hair cells in the cochlea convert mechanical vibrations into electrical signals
whats a cochlear amplifier?
outer hair cells contain myosin and prestin which amplify sound by enhancing the movement of the basilar membrane.
also about 1000 efferent fibers projecting from the brain stem toward the cochlea.
What are tip links
Hair cells are connected by tip links (protein bridges) that ensure all the hairs move in the same direction.
What happens when stereocillia bend towards tallest hair
When the stereocilia bend toward the tallest hair, the mechanically gated channels open, allowing K⁺ to enter from the endolymph (which is rich in K⁺).
What happens when stereocillia bend away from tallest hair
If the stereocilia move away from the tallest hair, the channels close, preventing K⁺ entry.
This results in hyperpolarization, slowing down or stopping neurotransmitter release.
one spiral ganglion fiber receives input from HOW MANY inner hair cell
one spiral ganglion fiber receives input from only one inner hair cell
one spiral ganglion fiber synapses with HOW MANY outer hair cells.
The situation is the opposite with outer hair cells. Because they outnumber their spiral ganglion cells, one spiral ganglion fiber synapses with numerous outer hair cells.
