Session 1: Anatomy & Physiology Flashcards
what is the purpose of vestibular assessment?
- History-taking forms a provisional diagnosis, and objective tests are used to confirm it.
- VA distinguishes between central and peripheral pathologies.
- VA quantifies residual vestibular function, tracks disease progression, and monitors treatment effects.
what are the 3 main components that maintain balance?
1-input
2-procesing
3-output
what are the main inputs for maintaining balance
1- vestibular system
2- visual system
3-propriopecption
what does the vestibular system do?
its a sensory system in inner ear responsible for:
-sensing head motion
-spatial orientation
-stable vision
-coordinating movements
what is the structure of the vestibular system?
it has semicircular canals which detect rotational head movement
-it has otolith organs which sense linear acceleration and gravitational forces
-hair cells within these structures respond to movements—-> and send signals to the brain
- the brain the processes info & maintain equilibrium
what does the visual system do?
provides info about environment
what does the proprioception do?
provides info about neck muscles, joint positions and foot pressure
what does the brainstem do in processing?
integrates info from vestibular, visual and proprioceptive systems.
what does the cerebellum do in processing?
coordinates and fine-tunes movements, including balance
what does the cerebral cortex do in processing?
involves higher level decision making and processing related to balance
How do reflexes contribute to maintaining stability in the body?
reflex like the VOR, VSR and VCR help maintain stability by coordinating eye and body movements in response to changes in head position and motion.
what is the VOR?
-a reflex that stabilises vision by moving the eyes in the opposite direction to head movement
-this maintain a clear visual focus during head movements
How does the VOR work? what happens in our balance systems when we move?
1- input head movements cause the bony & membranous
vestibular labyrinth to move
2- Endolymph in the semicircular canals (which are in the vestibular labyrinth) lags behind producing a relative flow of endolymph in a opposite direction to the movement, causing deflection of cupula causing deflection hair cells, in turn causing excitation or inhibition depending on direction of hair cell movement
3- hair cell deflection triggers neural signals via superior and inferior branches to the vestibular nerve and central processing occurs at the vestibular nucleus complex (inside the brainstem) and cerebellum
4- output mechanisms control the way the body responds to this movement, these signals generate compensatory eye movements, this ensures the eyes remain focused
what is normal VOR function?
eye movements are equal and opposite to head movements maintain a 1:1 ratio for clear vision during motion
what is an impaired VOR function?
- retinal slip caused by eye movements being slower than head movements, causing blurred vison and postural instability
- patient may report difficulty maintaining visual clarity during movement
what is a nystagmus?
a condition where eyes make uncontrolled repetitive movements which can effect vision & balance
how do we classify nystagmus?
1- direction of eye movements
2- characteristics of eye movements
what can cause nystagmus?
1- vestibular disorders: dysfunction of inner ear or vestibular system
2- neurological condition: issue with brain or nervous system e.g. MS or stroke
3- medication or alcohol: affects the CNS
4- vision impairment: poor vison or abnormal eye structures
what is the purpose of a nystagmus and is it there only when there’s an issue?
-the purpose is so the visual system adapts & stabilises quickly so the eyes can continue tracking the target
-nystagmus occurs temporary in healthy individuals and stabilises once the head is still. BUT ITS NIT NORMAL
what is a nystagmus fast phase?
- rapid corrective eye movements which help clinicians diagnose the underlying cause of the nystagmus
- these movements quickly shift in one direction followed by slower movements that return them to a resting position helping maintain visual stability
e.g. if you turn your head to the right, after the slow phase, your eyes quickly move back to the right, away from the target for an instant, before they start moving back to regain focus on the target
What happens during the slow phase when turning the head?
During the slow phase, when the head is turned (e.g., to the right), the eyes move slowly in the opposite direction (e.g., to the left) to keep the target in focus.
How do we assess the functioning of the peripheral
vestibular system?
1- eye movement recordings: directly measure eye movements during head motion to evaluate VOR function (VOR)
2 - video Head Impulse Testing(vHIT): assess VOR by tracking eye movements during quick, small head turns. (VOR)
3 - caloric irrigation: stimulates the vestibular system by introducing temperature changes in the ear to provoke eye movements (VOR)
4 - Vestibular Evoked Myogenic Potentials (VEMP): evaluates the function of the otolith organs by measuring muscle responses to sound or vibration stimuli. (VOR & VCR)
5 - posturography: measures the body’s ability to maintain balance under diff conditions (VSR)
6 - rotational chair: evaluates vestibular function by rotating the patient and measuring eye movements in response (VCR & VSR)
*tests 1-3 test the VOR, tests 4-6 test VOR, VCR and VSR
what is the role of the VOR?
-stabilises vision during fast head movements, compensating for movements of upto 550degrees per second
How fast does the VOR process information?
The VOR processes information in about 15 milliseconds due to a short neural pathway involving just three neurons from the vestibular organs to the eye muscles.
How are the semicircular canals connected to ocular muscles?
-there’s 6 semicircular canals (3 in each ear) which are paired with 6 ocular muscles to ensure compensatory eye movements to head movements
-superior (anterior) semi-circular canals <-> superior & inferior Rectus muscles
-inferior (posterior) semicircular canals <-> superior & inferior Oblique muscles
-lateral (horizontal) semicircular muscles <-> Medial & Lateral Rectus muscles
How can the VOR function be tested to determine vestibular dysfunction?
vHIT & VNG (VideoNystagmoGraphy) provide objective data about vestibular system performance helping clinicians identify vestibular dysfunction.
where in the body is the vestibular peripheral system and what effect does this have on testing?
entirely encased in temporal bone behind the ear making so we cant assess it directly therefore all of the vestibular testing is indirect
what do we assess in vestibular testing?
-eye movements (most common and we use VOR, the eyes are the most direct way of evaluating vestibular peripheral system)
- Postural control
-myogenic responses
how do we assess the functioning of the peripheral vestibular system?
- Eye movement recordings
- Video Head Impulse Testing
- Caloric irrigation
VOR - Vestibular Evoked Myogenic Potentials
- Posturography
- Rotational chair
What is the primary function of the Vestibulo-Ocular Reflex (VOR)?
The VOR is responsible for maintaining stable vision by producing eye movements that are equal in velocity and opposite in direction to head movements.
How does the VOR handle very fast head movements?
The VOR can respond rapidly to head movements with a maximum velocity of 550 degrees per second and maximum frequency components of 20 Hz. This is due to its short processing time of about 15 milliseconds and a direct three-neuron pathway from the inner ear’s receptors to the eye muscles.
When does the VOR maintain stable eye images?
The VOR maintains stable eye images during non-constant velocity head movements, such as acceleration or deceleration.
Which system helps maintain stable images during constant velocity motion?
The optokinetic system is used during constant velocity motion to maintain stable images, particularly focusing on objects of interest in the fovea.
What is the eye-to-head movement ratio in a normal VOR?
In a normal VOR, the eye movement is equal and opposite to the head movement, maintaining a 1:1 ratio for stable vision.
Why is the VOR important for us?
- impaired VOR comes up in the history taking as patients with this experience a retinal slip which in turn causes blurred vision and postural instability
- integrity of vestibular end organs can be assessed through functional measurement of the VOR
what do healthy balance systems rely on?
complementary and accurate sensory input from vestibular, vison and somatosensory systems to perceive and interpret the persons location with regard to gravity, the horizon and space?
what does the balance system detect?
whether we’re moving and the direction we’re moving in relative to surrounding.
-this info is then interpreted by the brain which sends info the visual
and postural centers so that counter or corrective action is made
- a breakdown anywhere in the system and imbalance or dizziness will be perceived
whats included in the structures in the inner ear related to the peripheral vestibular pathways?
- 3 semi-circular canals
-2 otolith organs: utricle and saccule
-connections to the 8th nerve via the superior vestibular nerve and the inferior vestibular nerve
how does the brain maintain balance using coplanar pairs?
- to maintain balance the brain relies on equal but opposite input from the peripheral vestibular pathways, to achieve this, the left anterior SCC is paired with right posterior SCC.
left posterior SCC paired with right anterior.
the left and right horizontal SCC are paired.
This push-pull dynamic ensures accurate detection of head rotation and balance.
what happens when the left side of the VS sends excitatory info to the brain?
in a healthy VS the right sends an equal amount of inhibitory info to the brain,
if one of the vestibular organs is weak or impaired the brain sends a mismatch resulting in the sensation of dizziness
what is the ampulla?
an endolymph filled swelling at the base of the SCC that houses the cuplla
what is the cupulla?
a gelatinous membrane that seals teh inner ear diameter of the ampulla
what is stereocilium and kinocilium?
stereocilium are hair cells that project into the cupula.
the kinocilium is the stereocilium that is larger than the rest
why is the direction of the hair cell movement important?
displacement of hair cells towards the kinocilium causes increased excitation
-displacement away from the kinocilium causes inhibition
what are the otolith organs?
-utricle: detects horizontal movements/ acceleration & head tilts (moving your head backwards and forwards (to me to you)
-saccule: detects vertical movements (e.g. jumping & riding in an elevator) (saccule=slide= up and down)
what is the otolithic membrane?
gelatinous web like structure that houses the weight and mass of calcium carbonate crystals
-its the mass and wight of the otolith that bend the hair cells within the utricle and saccule sending either excitatory or inhibitory info to the brain
what is meant by the neural pathways of the VS being afferent and efferent?
the system is continuously providing a loop of info to and from the brain to maintain a sense of balance
what happens with VOR when the head is turned to the left?
If the head is turned to the left the acceleration of the head (1) causes fluid
movement in the horizontal SCCs(1). This fluid movement causes movement of the
cupula (1) which moves the stereocilia (1) and depolarises the sensory hair cell (1) in
the crista (1), causing a change in the firing rate along the vestibular nerves (1). As
the head accelerates to the left the firing rate in the left vestibular nerve increases (1)
and the firing rate in the right vestibular nerve decreases (1) Eyes will move to the right (1)
how would a patient fall into the category of central vestibular pathology?
a patient may have normal functioning visual and vestibular structures, but to still perceive imbalance
which of these words are interchangeable?
inferior, anterior, superior, lateral, horizontal, posterior?
horizontal= lateral
anterior= superior
posterior= inferior
what are the 3 processing components to maintain balance?
- Brainstem; vestibular and oculomotor nuclei
-cerebellum
-cerebral cortex
what are the 3 output components to maintain balance?
-vestibulo- spinal reflex (VSR)
-vestibulo- collic reflex (VCR)
-vestibulo- ocular reflex (VOR)
what is the purpose of the vestibular system?
responsible for detecting head movements in order to maintain balance, postural control and clear vison.
Name the 3 semi circular canals
-lateral
-anterior
-posterior
What type of head movements do the semi-circular canals detect?
The semi-circular canals detect angular changes in head velocity, such as rotational movements.
How are the semi-circular canals oriented, and why is this important?
-The semi-circular canals lie orthogonal (at right angles) to each other, allowing them to detect rotation in 3 different planes
Anterior: detects rotational movement in the vertical plane (moving head up & down)
Lateral: detects horizontal rotational movements (turning head left & right)
Posterior: detects tilting of the head to the side (moving head towards shoulders)
what are the types of vestibular hair cells?
Type I hair cells:
- flask shaped with a dense core terminal surrounding them.
-typically associated with afferent nerve fibres that are highly specialised for rapid and precise signalling.
Type II hair cells:
- cylindrical in shape with a clear core terminal.
-associated with both afferent and efferent nerve fibres, playing a role in both sensing and modulating signals.
Where are vestibular hair cells located?
in the cristae within the ampullae (in the SCC) and the maculae (in the utricle and saccule).
How do vestibular hair cells detect head movement?
by sensing deflections of their stereocilia (small hair-like projections) and kinocilium (a larger single projection)
What is the typical resting firing rate of vestibular hair cells’ primary afferents?
The typical resting firing rate is 70–100 spikes per second, allowing precise detection of increases and decreases in activity during head motion.
How does the movement of stereocilia and kinocilium affect the firing rate?
- Deflection toward the kinocilium excites the hair cell, increasing the firing rate.
- Deflection away from the kinocilium inhibits activity, decreasing the firing rate.
What is the role of supporting cells in the vestibular system?
Supporting cells surround the hair cells and provide structural and metabolic support.
What is the basal lamina, and what is its function?
The basal lamina provides a foundation for both hair cells and supporting cells, maintaining their structural integrity.
What do the otolith organs detect, and how are they arranged?
- Detect changes in linear
acceleration and gravitational
tilts - Arranged in different planes
which enable them to respond
maximally to motion in all
directions
What are the two branches of neural innervation and blood supply to the vestibular end organs?
1) Superior Vestibular Nerve (VN) and Anterior Vestibular Artery, which supply:
- Lateral Semi-Circular Canal (SCC)
- Anterior Semi-Circular Canal (SCC)
- Utricle
2) Inferior Vestibular Nerve (VN) and Vestibulocochlear Artery, which supply:
- Posterior Semi-Circular Canal (SCC)
- Saccule
What happens in our balance systems when we move?
- Deflection of hair cells located in the ampulla of the semi-circular canals and
macula of the otolith organs will result in excitatory or inhibitory responses - Afferent neural information is transmitted along peripheral vestibular nerve
- Central processing of information
- Reflex pathways control way body responds to these movements
what is the purpose of the Vestibulo-spinal reflex?
- Responsible for maintaining upright position and stabilisation of our bodies
- Helps maintain desired orientation
helps stabilize and reorient the head position relative to the body when there is a sudden movement or disturbance (perturbation).
what is the purpose of the Vestibulo-collic reflex?
Responsible for reorienting the head with respect to the body following a
sudden perturbation
what do the otolith organs detect change in?
linear acceleration and gravitational tilts
