Auditory & Vestibular System Flashcards
What is the principle structure of the auditory/vestibular systems?
Hair cell
Describe the structure of a hair cell
Stereocilia form TMC1 channels which open when stereocilia tilt towards the kinocilium
Name the structure that acts as a ligand to these channels
Tip links
What happens when the TMC1 channels open?
Potassium entry causes the cell body to release glutamate onto efferent nerve endings to generate AP
State the 6 steps involved in hearing
- Sound waves his the tympanic membrane causign it to vibrate
- Vibrations pass from malleus to incus to stapes and end on the ovale window
- Travel through perilymph in bony labyrinth (scala vestibuli and scala tympani)
- Movement through perilymph causes basilar membrane to vibrate which moves the hair cells in organ of corti
- Ion channels open and depolarisation occurs leading to action potentials
- APs travel to the spiral ganglion and the cochlear nerve
Once the AP reaches the cochlear nerve where does it travel?
Cochlear nucleus Superior olivary nucleus Inferior colliculus (via lateral lemniscus) Medial geniculate body Superior temporal gyrus
Which process is the superior olivary nucleus important in?
Stapedial and tensor tympani reflexes
Is the input from the cochlear nerve bilateral or unilaterla
Bilateral
Name the two types of hair cell
Inner and outer
What separates the inner and outer hair cells?
Rods of corti
Describe the difference between inner and outer hair cells
Inner - increased convergence, afferent signals
Outer - efferent signals from olivary complex, stiffness and vibration
Are there more inner or outer hair cells?
Outer
Where are stereocilia tips embedded?
Tectorial membrane
What does the organ of corti sit on?
Basilar membrane
What ion is important in transduction and what direction does it move?
Potassium ion current is inwards
Why is potassium movement inwards and not outwards?
Due to high potassium ion concentration in the endolymph
What structures are vital in the re-entry of potassium in the endolymph?
Channels
Transporters
Gap junction networks
Define tonotopy
Ability of the brain to identify pitch
How does the basilar membrane allow tonotopy?
It has variable flexibility/width and vibrate in sync with fluid motion
Describe the shape of the basilar membrane
Narrow towards the ovale window and wide towards the helicotrema
Where do high frequency sound signals terminate?
Posteromedial cortex
Where do low frequency sound signals terminate?
Anterolateral cortex
What is special about the structure of outer hair cells?
Have a motor protein present that can alter the length of the cell
What is the place code?
Location along the membrane where glutamate is released
What is the temporal code?
Correspondance of action potentials to peaks of frequency
Name the three cochlear nuclei
- dorsal
- posteroventral
- anteroventral
What structure is most important for locating sound?
Lateral and medial superior olive
Name the huge post-synaptic density which is almost as big as a cell body
Calyx of Held
What is the function of the vestibular system?
Information about gravity, rotation and acceleration
Name the three key parts of the vestibular system
- peripheral sensory apparatus
- central processing system
- motor output system
What is the function of the sensory apparatus?
Detects and relays information to the vestibular nucleus about head angular and linear velocity
Orientates the head respective to gravity
What is the function of the semicircular canals?
Act to detect movements via rotary acceleration
Describe the structure of the semicircular canal
Crista - sheet of cells where hair cells cluster
Capula - stereo cilia are embedded
Ampulla - bulge along the canal with capula and crista
What does movement of fluid in the endolymph cause?
Displacement of capula
What is the function of otolith organs?
Sense linear acceleration and gravity
Name the two otolith organs
Saccule and utricle
What is the macula?
Structure where the hair cells and supporting cells are embedded
What is otoconia made of?
Calcium carbonate
What is the striola?
Subdivides the saccule and utricle and arranges the otoconia into narrow trenches dividing each otolith
Name three vestibular reflexes
Vestibulo-ocular
Vestibulo-colic
Vestibulo-spinal
