Auditory, Vestibular & Visual Pathways Flashcards
Most visual info is in OneNote Ophthalmology notes
What foramen does the cochlear nerve travel to the brain from the cochlea?
Internal acoustic meatus
Where are the spiral ganglion located and what is their function?
- Located along inside of cochlea
- stimulated by hair cells and carry APs from organ of Corti to cochlear nuclei
Where in the brainstem are the dorsal and ventral cochlear nuclei?
Pons
What makes up the Organ of Corti and what membrane does it sit on?
- Inner and outer hair cells
- basilar membrane
At what junction does cochlear nerve enter brainstem?
Pontomedullary junction
Superior to the cochlear nuclei input is ipsilateral/contralateral/bilateral. What significance does this have clinically?
- input is bilateral cos some fibres cross and some don’t
- clinically this means if patient presents with one sided hearing loss, problem will be from cochlear nuclei outwards because there are fibres from both ears on both sides so won’t be caused by central lesion
What are functions of superior olivary nuclei and nuclei of lateral lemniscus?
- sound localisation
- stapedial and tensor tympani reflexes
How do superior olivary nuclei & lateral lemniscus localise sound?
By comparing intensity and timing of arrival of signals from two different cochlear nuclei
Through what do the fibres from cochlear nuclei travel from pons to midbrain?
Lateral lemniscus
Where do cochlear nuclei fibres synapse in the midbrain?
In the inferior colliculus
Where is the primary auditory cortex?
Superior temporal gyrus
What is the trapezoid body?
Decussating fibres from both cochlear nuclei (R+L)
Where do the cochlear nuclei fibre synapse after coming from the inferior colliculi before they travel to primary auditory cortex?
What is the name of the pathway between the inferior colliculus and this structure?
- Medial geniculate nucleus of the thalamus
- inferior brachium
The auditory cortex is organised tonotopically. Fibres carrying low frequency info end in the _______ part of auditory cortex. Fibres carrying high frequency info end in the _______ part of auditory cortex.
- Low frequency in anterolateral part
- High frequency in posteromedial part
In the cochlea, the base of the basilar membrane detects _____ frequency sounds and the apex detects _____ frequency sounds. The base of basilar membrane is thinner/wider and more flexible/stiffer while the apex is thinner/wider and more flexible/stiffer.
- base = low frequency, thinner and stiffer
- apex = high frequency, wider and more flexible
What is aphasia? Damage to what two parts of the brain can cause this?
- Inability to use language
- Broca’s area (inferolateral frontal lobe)
- Wernicke’s area (adjacent to primary auditory cortex)
Damage to Broca’s area leads to expressive/receptive aphasia and damage to Wernicke’s area leads to expressive/receptive aphasia.
- Broca’s -> expressive AKA motor
- Wernicke’s -> receptive AKA sensory
What is the sensory cell of the auditory and vestibular system?
Hair cell
What ion enters through the TMC1 channels on cilia of hair cells and how are they opened and closed?
- K+
- opened and closed depending on tilt of the cilia
What substance is released from hair cells to efferent nerve fibres when hair cells depolarise?
Glutamate
At different levels of loudness, amplitude/frequency remains same but amplitude/frequency differs. At different pitches, amplitude/frequency remains same but amplitude/frequency differs.
- Loudness - frequency is same but amplitude differs
- Pitch - amplitude is same but frequency differs
What are the 3 mechanisms for impedance matching? (Amplification of sound force by middle ear)
- Area ratio of the eardrum to the stapes foot plate (bigger to smaller)
- Lever action of the ossicles - because they’re arranged as levers this makes additional force
- Buckling of eardrum
Endolymph/perilymph flows in the scala vestibuli and scala tympani and endolymph/perilymph flows in the scala media.
Perilymph flows in scala vestibuli and scala tympani and endolymph flows in scala media.
What does the Reissner’s membrane in the cochlea separate?
Scala vestibuli from scala media
What does the basilar membrane in the cochlea separate?
Scala media from scala tympani
At what point of the cochlea do the scala tympani and scala vestibuli meet?
Helicotrema
What separates the inner hair cells from the outer hair cells and which are more numerous?
- Separated by Rods of Corti
- outer more numerous
What connects to the tectorial membrane and what is the membranes function?
The tip of the cilia of the hair cells connect and the function is to show tilt. The relative position of tectorial to basilar membranes shows tilt
What additional ions enter the hair cell along with K+ ions that cause it to depolarise?
Ca2+ ions
Why is the hair cell K+ current inwards? (2)
- concentration of K+ in endolymph is really high
- potential gradient from endolymph to hair cell of 120mV
Mutations in what channels in the cochlea can lead to deafness?
K channels, transporters and gap junctions that recycle K+ back from hair cells into scala media
Inner hair cells get multiple afferent nerve fibres per cell while many outer hair cells are innervated by one afferent nerve fibre. True/false?
True
What type of fibre primarily innervates inner hair cells and what primarily innervates outer hair cells?
- inner hair cells primarily by afferent nerve fibres to cochlear nucleus
- outer hair cells primarily by efferent inputs to superior olivary complex
What is the function of the efferent nerve fibres input to the outer hair cells and how does it do this?
- Control stiffness and amplify membrane vibration
- it causes motor protein prestin in membrane to contract hair cell and so increases basilar membrane movement & hair cell bending thus amplifying sound
What loop diuretic inactivated the membrane motor of the outer hair cells?
Furosemide
What are the two mechanisms for frequency coding?
- place code (where basilar membrane is activated)
- temporal code (number of waves - action potentials are generated for every wave)
Tonotopy is only in the cochlea and frequencies get mixed up throughout auditory system. True/false?
False, tonotopy is preserved through system
If sound is closer to the contralateral ear of the lateral superior olivary nucleus, does it have net depolarisation or net inhibition?
Net inhibition
Where is the vestibular ganglion?
In the inner ear with the vestibular apparatus
Which has bigger nuclei in the brainstem - auditory or vestibular?
How many nuclei does it have in the brainstem?
- vestibular
- 4
The primary vestibular cortex is in the parietal lobe. True/false?
False - there is no primary vestibular cortex, it has several places in brain fibres go to
Which of the semicircular canals and the saccule and utricle detect linear (translational) acceleration and which detects angular acceleration (rotational)?
- linear -> saccule and utricle
- angular -> semicircular canals
What is the crista in the semicircular canals?
sheet of cells where hair cells are clustered
What is the name of the bulge along the semicircular canal that contains the crista?
Ampulla
What are the 4 connections the vestibular nuclei has in the CNS and what is each for?
- thalamus - for conscious perception of position and motion
- nuclei of CN III, IV, VI - for aiming eyes and maintaining fixed gaze as moving
- cerebellum - for position awareness for co-ordination
- spinal cord - alter state of tension of muscles e.g. someone shoves you - postural control
What is the cupula?
Gelatinous structure in which hair cells are embedded in at the bottom and it connects to roof of ampulla at the top.
What are the kinocili and what is their function?
- Kinocili are the tallest cilia on the vestibular hair cells. the rest of the cilia are stereocilia
- their function is that when stereocilia move towards the kinocili, the cell is depolarised and when the stereocilia move away from kinocili the cell is hyperpolarised
Kinocili are oriented in different directions in a cupula. True/false?
False!! they are oriented in same direction so all are excited or inhibited together
Which contralateral canal do the posterior canals on one side share plane with - the contralateral anterior or posterior semicircular canal?
posterior canals share plane with contralateral anterior canals
Describe what happens when head is rotated left and what nerves are fired.
if turning left, endolymph in canals are swooshed right and so left hair cells are depolarised - their afferent fibres increase in firing. endolymph swooshing right in the right canal causes hyperpolarisation which decreases firing of afferent fibres
Saccule detects movement in the vertical plane and utricle detects movement in the horizontal plane. True/false?
True
What part of the otolith organs do the hair cells lie in?
Macula
What are the striola of the sacule and utricle?
curved ridge through the middle of the otolith organ. it arranges the otoconia into narrow trenches. the hair cells on opposing sides of the striola are polarised in opposite directions so it allows the otolith organs to have multidirectional sensitivity
What sit on the otolithic membrane?
otoconia - small calcium carbonate crystals
What is the vestibulo-ocular reflex?
Allows eyes to keep gaze on something when head is turned by moving the eyes in the opposite direction to head movement at the same speed of the head movement
What is the vestibulo-colic reflex?
Keeps head still in space e.g. when you’re walking
What is the vestibular-spinal reflex?
Adjusts posture for rapid changes in position
Where do the ganglion cell axons of optic nerve synapse?
Lateral geniculate mostly and small amount to superior colliculus
Where do the optic nerves cross and then become optic tracts?
Optic chiasma
What does the superior colliculus receive input from? (4)
- optic nerves
- visual cortex
- frontal eye fields
- spinal cord
What is main function of superior colliculus and where does output from superior colliculus go to? (3)
- aiming eye
- nuclei of CN III, IV, VI (for eye muscles)
- motor nucleus of CN VII (for muscles around eye)
- spinal cord (for head and neck muscles)
Left lower visual field info is processed in right gyrus inferior to calcarine sulcus and left upper visual field info is processed in right gyrus superior to calcarine sulcus. True/false?
False.
Lower in superior and upper in inferior
What part (anterior or posterior) of the visual cortex does the macula project to?
Posterior pole how
What is Meyer’s Loop?
geniculocalcarine fibres from upper half of visual field (lower retinal fibres) looping around lateral ventricles on way to visual cortex after lateral geniculate body
What part of brain is responsible for “tracking” eye movements and what part is responsible for saccadic eye movements?
- visual cortex for tracking object (smoother)
- frontal eye field for jumpy movements
