Neuro: Auditory & Vestibular Systems Flashcards
Describe the structure of the hair cells in the auditory system
- Sterocilia bundles on top of a hair cell
- Hair cell synapses with auditory nerve fibres
- On top of stereocilia bundles is a overlying extracellular matrix
Why are the stereocilia arranged into bundles?
Stereocilia arranged into bundles because they are connected by a number of different links
What are the different types of link that connect the steroecilia together?
- Connectors: Lateral-links, top connectors, ankle links and shaft connectors
- Tip-links: Found at top of the cilia
How do the tip-links respond to tension that’s applied to them via sterocilia movement?
- Sterocilia moves in a particular direction creating tension within the tip-links
- Tension in tip-links causes them to strectch and pull on the top of the sterocilia
- This distorts the top of the sterocilia which opens ion channels on sterocilia
- If sterocilia moves in opposite direction the tip-links get compressed and ion channels close
Explain the transduction mechanism of a hair cell?
- Tip-links’ open ion-channels which results in K+ influx from K+- rich endolymph
- This K+ influx leads to depolarisation which activates voltage-gated Ca2+ channels
- This leads to Ca2+ influx which causes neurotransmitter release from vesicles
- Neurotransmitter binds to post-synaptic nerve fibre which triggers an action potential
What is the lateral line system?
A series of mechanoreceptors (neuromasts) along the sides of most fish and amphibians that provide information about movement through water
Explain how the lateral line system provides information about movement?
- Neuromasts within lateral line canals on surface of skin
- Water enters lateral line canals and pushses against cupula that surronds stereocilia
- This causes stereocilia to either be pushed towards or away from tallest stereocilia
- If they are pushed towards tallest one then ion channels of hair cell open
- If they are pushed away from tallest one then ion channels of hair cell close
What are the 2 main structures found within the inner ear?
- Semicircular canals - Vestibular system
- Cochlea - Auditory system
What is the name of the nerve formed from the axons of the vestibular and cochlea?
Vestibulocochlear nerve or 8th Cranial nerve
What are the different types of motion?
- Linear motion - up/down, left/right, backwards and forwards
- Rotation: roll, pitch and yaw
Different types of rotation lead to fluid movement in the different canals of the semicircular canals of vestibular. For each type of rotation name the semicircular canal that responds to it
- Roll - Posterior semi-circular canal
- Pitch - Anterior semi-circular canal
- Yaw - horizontal semi-circular canal
What structure within the semicircular canals is able to respond to the movement of the fluid (endolymph) inside them due to rotational movement?
Hair cells surronded by cupula within the Ampulla
How are the hair cells able to respond to movement of the endolymph within the semicircular canals of the vestibular as result of rotational movement?
- Under motion, fluid in the semicircular canals lags to due to inertia, pulling the cupula in the opposite direction to the rotation of the head.
- Movemnet of the cupula causes the stereocilia of the hair cells to be displaced
- This causes the opening of K+ channels allowing infux of K+ ions leading to depolarisation of haircells.
What areas of the vestibular respond to changes in linear motion?
- Utricular macula
- Saccular macula
What type of linear movement do the saccular macula and utricula maccula respond to?
- Saccular macula - responds to left/right movement
- Utricular macula - responds to up/down and forward/backward movement
How do hair cells within the saccular macula and utricular macula respond to linear movement?
- Otolithic membrane sits on top of Stereocilia on top of hair cells
- On the otolithic membrane there are otoconia crystals
- These crystals move in a particular direction during linear movement which causes otolithic membrane to cause movement of stereocilia
- This causes the opening of ion channels eventually leading to depolarisation of auditory neurons
Briefly describe auditory system pathway
- Ear
- Cochlear
- Cochlear nucleus
- Olivary complex
- Lateral lemniscus
- Inferior colliculus
- Medial geniculate body
- Auditory cortex
How does the outer ear (pinna) contribute to hearing?
- Gathers sound from the environment and funnels it to the eardrum
- Various parts of the pinna amplify sounds at particular frequencies
What are the names of the bones that connect the tympanic membrane to the oval window of Cochlea?
Ossicles (middle ear bones)
- Malleus (Attached to tympanic membrane)
- Incus (bridge between Malleus and Stapes)
- Stapes (attached to oval window of cochlea)
Describe the structure of the cochlea of the inner ear
- Scala vestibuli
- Scala media
- Scala tympani
- Membrane between scala vestibuli and scala media
- Membrane between scala media and scala tympani (basilar membrane)
Explain how the properties of the basilar membrane of the cochlea contributes to hearing
- Basilar membrane is narrow and stiff at one end (towards oval window) and wide and compliant at other end
- This means narrrow and stiff end of basilar membrane responds more to compression of cochlea fluid caused by higher sound frequencies
- Wide and complient end of basilar membrane responds more to compression of cochlea fluid caused by lower sound frequencies
- This allows different parts of cochlea respond selectively to particular frequencies of sound
What is the name of the structure that sits on top of the basilar membrane?
Organ of corti
What is the difference in function of the inner and outer hair cells?
- Inner hair cells go through transduction (send signals to brain)
- Outer hair cells only act as amplifiers
Explain how the influx of positive ions, as a result of the movement of stereocilia cells on top of the outer hair cell, results in the outer hair cell acting as an amplifier
- Influx of positive ions leads to prestin proteins going into short conformation within the membrane of the outer hair cell
- This causes contraction of entire outer hair cell
- This contraction pulls basilar membrane closer to the tectorial membrane
- This places more pressure on tectorial membrane and causes it to move stereocilia cells on inner hair cells
- This causes influx of positive ions into inner hair cells which eventually leads to action potential being produced in auditory nerve
Explain the concept of the “battery” of the cochlea and how it amplifies sound waves
- Endolymph (K+ rich) in scala media makes the membrane potential in it +80 mV
- Membrane potential of inner and outer hair cells have membrane potential of -60 mV
- This difference of +140 mV makes the movement of K+ into hair cells very fast and means more can diffuse into hair cells when ion channels are opened due to large gradient between scala media and hair cells
