Audio vestibular system Flashcards
What does the vestibular organ do
capture low frequency motion (movements)
What does the hearing organ do
capture high frequency motion (sound)
What is sound made up of
Frequency/pitch (Hz): Cycles per second, perceived tone
Amplitude/loudness (dB): Sound pressure, subjective attribute correlated with physical strength
Human range of hearing
Frequency: 20–20,000Hz
Loudness: 0 dB to 120 dB sound pressure level (SPL)
What are the function of the outer ear
Ear and canal helps to
capture and amplify sound (amplifies it by 10db)
Protect ear from external threats
By how much is sound amplified in ear canal
Modest amplification (10DB) of upper range of speech frequencies by resonance in the canal
what is the middle ear
From tympanic membrane to oval window
What is outer ear
Upto tympanic membrane
What changes in the middle ear
vibrations in air change to mechanical movement in inner ear
Tympanic membrane moves at exact frequency as you are hearing sounds
Tympanic membrane connected to malleus , incus and stapes (3 smallest bones)
What is the main function of the inner ear
The main function of the middle ear is mechanical amplification (can provide an additional 20-30dB
What are the muscles in the ear
Tensor tympani
Stapedius muscle
What does tensor tympanii do
When sound is loud, tensor tymapni will contract and make the tympanic membrane stiff decreasing vibration
what does Stapedius muscle do
contracts and prevent stapes from vibrating fast (reduces vibrations)
What is the chochlea
Hearing part of inner ear
What is function of inner ear
Its function is to transduce vibration into nervous impulses
It does so in a way that captures the frequency (or pitch) and intensity (or loudness) of the sound,
(when stapes vibrates, it makes the fluid in the chochlea vibrate at the same frequency. THis now needs to be converted to nervous impulses)
How many compartments in cochlea
3 Scala vestibuli and scala tympani Scala media:
What do the 3 layers contain
Scala vestibuli and scala tympani: Bone structures, contain perilymph (high in sodium)
Scala media: Membranous structure, contains endolymph (high in potassium). Here is where the hearing organ or Organ of Corti is located.
Where is the Hearing organ or Organ of Corti located
Scala media
Wherr does the organ of corti lie
In the basilar membrane
How is the basilar membrane arranged
Tonotopically using th esame prinicple as a xylophone
What part of the membrane do high frequencies move
High frequencies move the first part of membrane that is narrow and tight (BAase)
Each part of the membrane hair cells that are connected to nerves so the signal that will go through that will correspond to the frequency that is heard
What part of the membrane do low frequencies move
Low frequencies move the laterpart of membrane that is wide and loose (APex)
Each part of the membrane hair cells that are connected to nerves so the signal that will go through that will correspond to the frequency that is heard
what is tonotopical
Arranged on a way that is frequency based
What types of hair cells are in the organ of Corti
The organ of Corti contains two types of hair cells:
Inner hair cells (IHC) and (arranged in one line)
Outer hair cells (OHC) (arranged in 3 lines)
Not really hair just look like hair
where is the tectorial membrane
The tectorial membrane is above the hair cells and allows hair deflection, which in turn will depolarise the cell.
(basically rubs against the hair cells
where is the tectorial membrane
The tectorial membrane is above the hair cells and allows hair deflection, which in turn will depolarise the cell.
What is the function of IHC
IHC carry 95% of the afferent information of the auditory nerve. Their function is the transduction of the sound into nerve impulses
(so sound has now gone from motion to a neuronal signal)
IHC- Spiral ganglion-Auditory Nerve-brain
What is the function of OHC
OHC carry 95% of efferents of the auditory nerve. Their function is modulation of the sensitivity of the response.
What are sterocilia
The hairs of the hair cells are called stereocilia.
What is the function of the sterocilia
The deflection of the stereocilia towards the longest cilium (kinocilium) will open K+ channels
This depolarises the cell releasing the neurotransmitter to the afferent nerve which then depolarises.
Higher amplitudes (louder) of sound will cause greater deflection of stereocilia and K+ channel opening
When potassium channels open, influx of potassium into cell and tthen there is influx of calcium into the cell which then releases excitatatory transmitter Glutamate
what is the kinocilium
logest cilium
IF hairs move towards kinocilium tehn different effect to if they move away from kinocilium
Transduction:
How does deploarisation happen
when basilar membrane goes up, the tectoral membrane goes forwards due to shearing force causes depolarisation sending a signal so you here a sound
what happens in hyperpolarisation
When the membrane goes down, shearing makes the tectoral membrane go backwards causing hyperpolarisation and decreasing the sound.
Hyperpolarisation closes the K chhannels
Auditory pathway
Auditory nerve combines with the vestibular nerve to make the vestibulocochlear nerve (8th cranial nerve) nerve .
the auditory parts from the cochlea go to the ipsilateral cochlear nucleus in the pons in the brainstem
From the cochlear nucleus sends message to the other side of the brain and to the superior olive which then communicate bilaterally
Clinical implication: if you have brain damage that involves small part of brainstem, very rare to loose hearing because if this bilateral communication. Hearing very rarely lost on bath sides in stroke.
What does this image show
Otitis. Bubbles can be seen through the ear drum, suggesting there is liquid inside the middle ear.
What does this image show
A patient presents with unilateral hearing loss what is the arrow point to?
acoustic neuroma (vestibular schwannoma
Bedside tests for hearing loss with tuning fork
Assess gross hearing loss
Weber test
Rinne test
Use tuning fork on top of head and they should hear in th emiddle (Weber)
Using tune fork on mastoid and then in air in front of ear. IF its Lounder from bone than air then its a problem with the conduction so outer or inner ear problem
How is Audiometry done
Patient clicks when they hear a sound
The audiogram is where the hearing thresholds are plotted to define if there is a hearing loss or not. A normal hearing threshold is located between 0 – 20dB
What does this pictiure demonstrate
Hearing loss at high frequency but one ear is worse than other so more likely to be sensorineural hearing loss
What do these patterns show
do hearing test with audiology with headphones and then putting it on bone.
If there is a disparity in line then its conductive hearing loss
what is - Otoacoustic Emissions (OAEs
The normal cochlea produces low-intensity sounds called OAEs
These sounds are produced specifically by the outer hair cells as they expand and contract
This test is often part of the newborn hearing screening and hearing loss monitoring.
What are otoliths
utricle and saccule
The hair cells are located on the maculae, placed horizontally in the utricle and vertically in the saccule
What are the parts of the vestibular organ
The utricule and saccule are located in the vestibule and are joined by a conduit. The saccule is also joined to the cochlea
There are three semicircular canals on each ear, anterior, posterior and lateral
The semicircular canals have an ampulla on one side, and they are connected to the utricle.
The hair cells sit on the ampulla
Describe the ampulla
The ampulla has the crista, where the hair cells are located. The cells are surrounded by the cupula which helps the hair cell movement
How are the canals oriented
The canals are arranged in a way to detect angular movement
The orientation of the canals in the head defines three planes.
Anterior and posterior canals form a 90° angle. Lateral canals are horizontal to the other canals.
Therefore they work in pairs
What are the two types of hair cells in the vestibule
Type 1 and type 2 . they both produce afferent signals
Vestibular hair cells have a kinocilium (the biggest cilium) and stereocilia.
Cilia allows the cells to depolarise the cell with movement of the endolymph generated by head movement
Hair cells have a resting potential which has a basal discharge to the nerve
Hairs moving towards the kinocilium generates depolarization and an increase in nerve discharge.
Hairs moving away from the kinocilium generates hyperpolarization and a reduction in nerve discharge.
Pathway
Primary afferents end in vestibular nuclei in the brainstem (pons)
Goes to the vestibular nucleus. After this it goes to various parts: 1.cerebellum
2.down to vestibulospinal tract (spinal reflexes to keep postural balance)
3. Nuclei of the eye movements (3. 6, 4 nerve) that control the muscles of the eyes
What is the Vestibular Ocular reflex (VOR)
Keeps images fixed in the retina
Connection between vestibular nuclei and oculomotor nuclei
Eye movement in opposite direction to head movement, but same velocity and amplitude
