L4 Audio System Flashcards
Sound transduction steps
- Sounds start as a pressure wave in the air
- External ear focuses sound waves onto the tympanic membrane
- Vibration of the tympanic membrane causes vibration of the bones of the middle ear
- Vibration is transferred to the oval window at the inner ear
- Oval window vibrates fluid within the cochlea
- Vibration of fluid is turned into electrical impulses via mechanoelectrical transduction
The cochlea…
converts sound into electrical signals
Cochlea makeup
spiral structure with basal and apical ends. basilar membrane splits it.
basal = oval and round window
Basilar membrane
divides the cochlea into half
has specialized epithelial cells called cochlear hair cells
cochlear hair cells have projections called stereocilia
Tectorial membrane
sits above the stereocilia
moves the stereocilia as vibrations travel through the cochlea
the movement of the stereocilia will cause the release of NT, causing an AP
Cochlear hair cells
found in the basilar membrane
contains bundles of stereocilia and one kinocilium
has one row of inner hair cells, three rows of outer hair cells
Stereocilia
causes the release of NT, which makes an AP
made up of actin, arranged shortest to tallest
attached to other stereocilia via tip links
What happens to stereocilia with sound vibrations?
bend, can either be towards or away from the direction of the tallest stereocilia
TOWARDS: causes tip links to stretch and open transduction channels, causing influx of ions into hair cell
AWAY: hair cells releases less NT
Inner hair cells
sensory receptors
95% of fibers of auditory nerve come from these
Outer hair cells
receive efferent axons that arise from cells in the superior olivary complex
help modulate movement of the basilar membrane
cochlear amplifier
Sound localization
Created through tonotopy and coincidence detection neurons in the MSO
Tonotopy
cochlea is organized topographically, lower pitched sounds will travel farther along the basilar membrane towards apex
different pitched sounds interact with the cochlea differently
apex = low frequency
baislar = high frequency
Coincidence detection neurons
located in the medial superior olive
set of neurons that respond more strongly when input arrives from separate pre-synaptic neurons,
detects interaural time differences; whatever side the sound is closer to will alert the neurons to sound
Medial geniculate complex
receives convergent frequency and temporal information from ascending pathways
DCN pathway
Spiral Ganglion
DCN
Decussates in trapezoid body in pons
Inferior colliculus
Medial geniculate complex
A1
Purposes: Localization of sound, auditory filtering, integration of multisensory information
VCN Pathway
Decussates in the trapezoid body, also splits in the pons, creating two pathways to the A1
Purposes: Auditory signal transmission, pitch perception, tonal discrimination
Labyrinth
consists of 2 otolith organs–utricle and saccule and 3 semicircular canals
filled with endolymph, also has a perilymph which is between osseous labyrinth and membranous lanyrinth
Otoconia
each otolith organ contains a membrane which is covered in calcium carbonate crystals (otoconia)
Otolithic membrane
located in the macula (uricle and saccule), horizontal and vertical movements
covered in otoconia
vestibular hair cells project into the membrane, rooted in the macula
thick, gelatinous sustance that can be displaced by forces
Movement of vestibular stereocilia
TOWARDS kinocilium (tallest) = increased NT release
AWAY kinocilium = decreased NT release
Utricle
oriented horizontally
responds to horizontal translational movements, sideways head tilts
Saccule
responds to vertical translational movements of the head, upward or downward head tilts
Striola
divides the utricle and saccule so that they can have separate actions
along the axis of striola = excite hair cells on one side and inhibit hair cells along the other
Semicircular canal pairs
Right and Left horizontal canal
Right anterior canal and left posterior canal
Left anterior canal and right posterior canal
Semicircular Canals Hair Cells
Ampulla = bulbous expansion at the base
Cupula = gelatinous mass in ampulla which contains hair cells
Endolymph = fluid fills each canal
Cupula Movements
AWAY from head movement. Displaces the hair bundles in the cupula towards movement
they are all organized with kinocilia pointed in the same direction
If the head turns to the left, what happens to the stereocilia in the left and right horizontal canals?
LEFT HC has stereocilia deflected towards kinocilium, cupula deflects right. Firing rate of L vestibular nerve increases
RIGHT HC has stereocilia deflected away from kinocilium, cupula deflects towards the right and firing rate of R vestibular nerve decreases
Can you have negative firing rate in the vestibular system?
No
vestibular system is always active
firing rate increases or decreases from the baseline (which is not 0)
vestibular system has a high activity at rest
What motions are the same in the otolithic membrane?
Backwards and Forward acceleration
Forward and Deceleration
Static movements and vestibular
sitting in a static position changes the baseline firing rate
Translational movements
transient increase or decrease of firing rate
Forward head tilt causes
occurs within the saccule
top hair cells to deflects towards, increasing activity
bottom hair cells deflect away, decreased activity
Left head tilts causes
occurs within the utricule
left hair cells deflect towards, increased activity
Right hair cells deflect away, decreased activity
Semicircular Canals Static vs Movements
SCC only detect changes in angular or rotational acceleration
constant velocity will produce a baseline firing
Vestibulo-ocular reflex
helps with producing eye movements that counter head movements, helping gaze to remain fixed on a particular point
plays a big role in vertical gaze stabilization in response to linear movements
Pathway of VOR
vestibular input from scarpa’s ganglion signals change in vestibular state
info is transmitted to vestibular nuclei
medial vestibular nucleus communicates with abducens nucleus, causing inhibition of ipsilateral lateral rectus, excitation of medial rectus of ipsilateral and lateral recuts of contralateral eye
How would turning your head to the right affect VOR?
- Turning head to the right increases firing rate of right vestibular nerve
- Right vestibular ganglion sends info to the right medial vestibular nucleus
- The medial vestibular nucleus sends excitatory fibers to the contralateral abducens nucleus
- The abducens nucleus has two outputs–> motor pathway that excites contralateral lateral rectus and an interneuron that excites the medial longitudinal fasiculus to oculomotor nucleus to excite ipsilateral medial rectus
- Oculmotor nucleus activates neurons that cause the medial rectus of the right eye to contract
Summary of excitation of VOR
Excites ipisilateral medial rectus
Excites contralateral lateral rectus
Inhibits ipsilateral lateral rectus
Inhibits contralateral medial rectus
Vestibulo cervical reflex
modulates head position with respect to what is happening in the SCC. Basically a reflex
Pathway: medial vestibular nucelus, MLF to upper cervical region
Vestibulo-spinal reflex
excites extensor muscles and inhibits flexor muscles to promote upright posture
mediated by medial and lateral vestibulospinal tracts and reticulospinal tract
input comes from otolith organs
Thalamocortical pathways
helps us to know where we are in space, whether an object is coming towards us or we are going towards an object
projects to many cortical areas
rostral fastigal nucleus helps with the distinguishing
