Hearing CN8 Flashcards by Katie Judd

Inner ear functions

AKA labyrinth, functions in both hearing and equilibrium. Respond to separate stimuli and are activated independently

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Bony labyrinth

Tortuous channels in the temporal bone

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Membranous labyrinth

Suspended within bony labyrinth

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What are the 3 main parts of the inner ear?

Vestibule, semicircular canals and cochlea

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Vestibule contains 2 enlargements of the membranous labyrinth known as?

Utricle and Saccule. Detect linear acceleration

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Where do the semicircular canals attach?

utricle

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Where does the saccule connect to?

Cochlear duct and utricle

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What substance is found in the bony labyrinth?

Perilymph

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Which substance has a LOW K+ and HIGH Na+ concentration?

Perilymph

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What substance is found in the membranous labyrinth?

Endolymph

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Which substance has a HIGH K+ and LOW Na+ concentration?

Endolymph

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Which space is continuous with subarachnoid space?

Perlymphatic space

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Which fluid-filled labyrinth is a closed system?

Membranous labyrinth filled with endolymph

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From what is endolymph continuously produced?

Blood plasma

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Which structures drain into the endolymphatic sac?

Cochlea drains to saccule

and semicircular canals drain to utricle. Both drain into the endolymphatic sac

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How does the lymph drainage connect to the venous blood supply?

Through the dura

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Stereocillia is found where?

Cochlea and semicircular canals, project from apical surface and bases synapse on CN8

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How is stereocillia arranged?

In graduated steps: largest (kinocilium) to smallest

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Organ of corti (part of labyrinth, gelatinous material, stimulus transduced)

Cochlea, Tectorial membrane, Sound

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Cristae (part of labyrinth, gelatinous material, stimulus transduced)

Semicircular canals, Cupula, Angular acceleration

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Maculae (part of labyrinth, gelatinous material, stimulus transduced)

Utricle/Saccule, Otolithic membrane, Linear acceleration

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Why is stereocilia rigid?

They are packed full of cross-linked actin filaments

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How does microvilli respond to mechanical deformation?

They do not bend–they pivot at their bases where they are attached to the hair cell. The whole hair bundle moves as a unit in response to mechanical stimuli

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Describe the function of Tip-Links

Tip-links extend from the tip of each stereocilium to its next tallest neighbor. Mechanically gated cation channels are located at each tip-link. Deflecting the hair bundle toward the tallest stereocilia stretches the tip links, increasing the probability of channel opening. Inward K+ current depolarizes the hair cells.

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Resting membrane potential is ____mV but opening of channels brings it towards ____mV

-65 mV, 0 mV

Shift stereocilia toward tallest stereocilium and opening of channels causes?

Increase depolarization, increase frequency of AP's

Shift stereocilia toward shortest stereocilium and closing channels causes?

Hyperpolarizarion, decrease frequency of AP's

If a perpendicular effect (parallel to rows) occurs, what happens?

No effect. Channels remain at semi-open state and no change in frequency of AP's occurs

Depolarization of hair cells causes the opening of which voltage-gated channel?

Ca2+ channels and release of glutamate

When glutamate is released, what type of graded-potential occurs?

EPSPs (local, graded) in neurons of vestibulocochlear nerve. Causes subsequent change in AP frequency

Define sound.

A pressure disturbance, alternating areas of high and low pressure, produced by a vibrating object

Which direction does a sound wave move?

Outward in all directions (Sin wave)

What happens to air molecules in areas of high pressure?

Compression

What happens to air molecules in areas of low pressure

Rarefaction

How does sound transfer through the ear?

1. Sound waves collected by external ear (auricle/pinna) and 2. funneled into external auditory meatus and 3. onto the tympanic membrane which vibrates with sound 4. back side of eardrum has ossicles which transfer sound vibrations to the fluid filled inner ear

Which structure marks the point where the external ear becomes the inner ear?

Tympanic membrane

Where does the transfer from sound to vibration to liquid occur?

At ossicles

Movement of which structure results in pressure waves within perilymph of cochlea?

Stapes

Describe the route of sound waves through the ear

1. Sound waves vibrate the tympanic membrane 2. Auditory ossicles vibrate and pressure is amplified 3. Pressure waves created by the stapes pushing on the oval window move thru fluid in the scala vestibuli

Where do sounds with frequencies below hearing travel?

Through the helicotrema and do not excite hair cells

Where do sounds with frequencies in the hearing range travel?

Through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells

Which 2 muscles modulate movement of ossicles? How do they function?

Tensor tympani and Stapedius. Decrease transmission of vibrations when contracted to protect hair cells in response to loud sounds

Tensor tympani (attachment, innervation, action)

Malleus, CN 5, Contract bilaterally in response to something touching the face, being startled, and before speaking/chewing

Stapedius (attachment, innervation, action)

Stapes, CN 7, filtering out low frequency background sounds

What is the auditory part of the inner ear?

Cochlea

Where are sensory cell bodies for peripheral projections to hair cells found?

Spiral ganglion (which is located in the center of spiral structures)

What are the 3 chambers of the cochlea?

Scala media, Scala vestibuli, Scala tympani

Scala media (location, attachment, fluid)

Center section, Cochlear duct, Endolymph

Scala vestibuli (location, attachment, fluid)

Superior part, Vestibule (opens to oval window), Perilymph

Scala tympani (location, attachment, fluid)

Inferior part, Opens to round window, Perilymph

The basilar membrane separates which 2 chambers?

Scala media from scala tympani

What cells make the endolymph?

Stria vascularis

Sound is encoded based on what 3 factors?

Frequency, Intensity, and Location of stimulus

How does frequency impact movement of the basilar membrane?

Results in one portion of the basilar membrane moving the most (number of cycles/second). Only certain hair cells responding to vibration at peak amplitude

Which section of the basilar membrane detects high frequency sound?

The base, because it is narrow and stiff (thick)

Which section of the basilar membrane detects low frequency sound?

The apex, because it is broad and floppy (thin)

Auditory receptor cells are located in which structure?

Organ of Corti (which rests on the basilar membrane in the floor of the membranous labyrinth)

Which frequency is considered most sensitive hearing?

3,000 Hz

The primary auditory cortex has ____ organization

Tonotopic

Wernicke's area (location and function)

Lies within the secondary auditory area. Critical to the comprehension of human language

How is intensity (loudness) detects in the basilar membrane?

Amplitude and/or time of movements of the basilar membrane. Coded as the number of AP's per unit of time

How is the location of sound detected and processed?

Based upon which ear hears first and computation within brain. Coded for by which cochlea responds first and time difference btw each ear.

Where is localization processed primarily?

Superior olivary nuclei (bilateral innervation)

Where are sterocilia inserted into?

Tectorial membrane

We receive 90-95% of sounds from which hair cells?

Inner hair cells

Problems with sound conduction affect which portions of the ear?

External/middle ear and not reaching the inner ear

Sensorineural problems affect which structure in the ear?

Hair cells

Air conduction pathway involves with structures?

Eardrum (tympanic membrane), ossicles, and hair cells of cochlea. Involves outer, middle, and inner ear

What is normal air conduction (compared to bone conduction)

AC > BC (AC is about 2x BC)

Bone conduction bypasses which structures to set up vibrations directly in cochlear endolymph?

Tympanic membrane and ossicles (only involves inner ear)

Weber Test is used to determine?

Which side has a problem

Rinne Test is used to determine what?

Compares bone and air conduction

Conductive hearing loss is caused by?

Some form of sound conduction problem, most likely a middle ear infection, impacted wax or bony growth. (bigger issue with air conduction)

How does sensorineural hearing loss present?

Auditory deficits that have NO difference btw bone and air conduction

What causes sensorineural hearing loss?

Sensorineural problem with or without sound conduction problem. Caused by ototoxic drugs kill off hair cells, tumor or stroke affecting auditory pathway or crushing CN 8 (cochlear division), infection of inner ear, damage to hair cells from loud noises

Hearing CN8 Flashcards

(75 cards)