Physiology of Auditory and Vestibular Systems Dr. Pierce Flashcards
Where in the basilar membrane are high frequency sounds heard the best? Characteristic of the membrane at that point?
At the base nearest the oval windows, the membrane is stiff and narrow
Where in the basilar membrane are low frequency sounds heard the best and what are the characteristics of the membrane?
More apical near helicotrema Wider and more flexible near the helicotrema
Describe hair cells.
Polarized epithelial cells that are stiff and full of actin. They have stereocilia on the apical surface and neural synapses on the basal side
Describe the endolymph and what side of hair cells does it bathe?
Potassium rich sodium poor similar to ICF. Found in scala media made by stria vascularis Apical end of hair cells
Perilymph and what side of hair cells does it bathe?
- Potassium Poor
- Perilymph Potassium Poor
- Similar to ECF high sodium low K
- Found in scala vestibuli and scala tympani
- Basal end of hair cells
What causes depolarization of hair cells?
- Deflection of stereocilia allows K ions to enter the cell and depolarize it
- Mechanically gated K channels open flowing in
- The change in charge allows Ca Voltage gated TRPA1 channels to open
- The influx of calcium can cause depol of the hair cells allowing release of glutamate
What direction do stereocilia bend to depolarize and hyperpolarize?
- Deflection opposite of the tallest stereocilia causes hyperpolaraization
- Deflection toward tall stereocilia causes depolarization
What is the action of the stria vascularis?
- Maintains electrochemical properties of endolymph
- Blood labrynth barrier, pumps k from blood across membrane into endolymph
What is the primary function, arrangement, synspases and efferent activity of the Inner hair cells?
- Primary source of auditory info
- Arranged in a single layer
- Synapse with peripheral terminal of primary afferent sensory neuron
- Efferent neuron also modulates activity
Outer hair cells function, arrangement, synapses and efferent activity
- Primary cells responsible for amplilfying sound waves. Contractile epithelilal cell which boosts the vibration of basilar membrane acting like an amplifyer
- Three rows
- Synapse with sensor yafferent peripheral terminnls from spiral ganaglion
- FOrm synpse with terminals from efferent neurons
Where do motions of outer hair cells originate?
- Superior olivary complex called olivocochlear efferents
What innervates inner and outer hari cells?
Medial olivary complex innervate outer hair
Lateral olivary complex innervate innher hair cells
What are Otoacoustic Emissions
- Spontaneous or evoked
- evoked is the basis for newborn hearing test
- the outer hair cells generate a low intensity usually inaudible sound
What specifically do the anterior and posterior cochlear nuclei do?
- Anterior processes temporal and spectral features of sound
- Posterior integrates acoustic with somatosensory information
What isi the superior olivary complex and its divisions
First site where information from both ears meets. The binaural processesing is crucial for sound localization.
- Medial superior olivary nucleus generates a map of time differences to help localize the location and gets EAA input
- Lateral superior olivary nucleus looks at intensity differences to help localize where the sound is coming from
Inferior colliculus function
- Suppresses information related to echoes
- Information about sound time and intensity converge here and this along with suppression of the echoes allows for sound localization
Medial Geniculate Nucleus
- Precise info regarding intensity frequency and binaural properties are integrated and relayed on
- lots of converging from spectral and temporal paths occurs here allowing for processing of speech inflections
Primary Auditory Cortex (A1)
- Essential for perception of sound
- higher order processing of sounds
Secondary auditory complex
- Less specifically organized than primary AC
- Responds to more complex sounds, identifying a sound and speech
What are the three general Efferent input to auditory system
- Olivocochelar efferents
- Middle ear mm motorneurons
- Autonomic innervation of inner ear
What do the Olivocochlear efferents do
- Decrease basilar membrane motion reducing responses of inner hair cells and auditory nerve fibers, also reduces response to noise
- May protect hair cells from damage from intense sounds
Middle ear efferents
- Includes motor innervation to tensor tympani and stapedius attenuating the sound
- Bilateral responsne to high sound levels contractions decrease transmission of sound
- Acts at low frequencies
- Implicated in tinnitus
- May prevent damage
Autonomics to the inner ear
- Comes from CN 8 or superior cervical ganglion
- Caroticotympanic nerve off of SCG to innervate mucous glands of tympanum and blood vessels of tympanic membrane
- Acoustic nerve supplies blood vessels sympathetic regulates vasuclar tone
- Sympathetic Adrenergics
What causes sensorineural heraing loss and what cells are more succeptible to injury?
- Damage to hair cells nerve fibers or both
- Noise, ototoxic drugs, age, or unknown etiology
- Outer hair cells more succeptible to injury, this will cause a decrease in sensitivityy and broader tuning
- Inner hair cells cuts off auditory inputs to CNS if they are injured
What end of the cochlea is more succeptible to damage causing sensorineural hearing loss?
The base end which detects high frequencies
Cochlear implant can restore some hearing
How does a cochlear implant work
Multiple electrodes threaded through cochlea to stimulate surviving nerve fibers
What do the anterior semicircular canals do?
Detects rotation in the vertical plane forwards
Horizontal semicircular canal detects ___.
Rotation in horizontal plane
Utricle detects ____ and saccule detects ____
- linear acceleration forwards and backwards
- Linear acceleration up and down
Rotation in the verticlal plane backwards maximallly activates ________.
Posterior semicircular canal
