Vestibular Anatomy and Overview Flashcards
What is the primary function of the vestibular system?
Awareness of body position in space, maintaining postural control, and coordinating eye and head movements.
Where is the vestibular system located?
Deep in bilateral temporal bones with both peripheral and central components.
What are the three main functions of the vestibular system?
- Gaze stability
- Postural stability
- Orientation in space
What reflex is responsible for maintaining clear vision while the head is in motion?
Vestibulo-Ocular Reflex (VOR): Generates eye movements which enable clear vision while head is in motion
- Gaze stability
What reflex helps maintain balance during head movements?
Vestibulo-Spinal Reflex (VSR).
What are the two main components of the peripheral vestibular system?
- the cochlea
- the vestibular apparatus
What structures make up the vestibular apparatus?
(5)
- Three semicircular canals
- Two otolith organs (utricle and saccule)
What do the semicircular canals detect?
Angular acceleration of the head.
What do the otolith organs detect?
Utricle
- Sits in a horizontal plane
- Responds to horizontal linear acceleration and/or lateral head tilt
Saccule:
- Sits in a vertical plane
- Responds to vertical linear acceleration (Eg. Detecting up/down movement in an elevator)
- Linear acceleration and static head tilt.
Which semicircular canal detects head rotation with forward motion?
Anterior (superior) canal.
Which semicircular canal detects posterior rotation of the head?
Posterior (inferior) canal.
Which semicircular canal detects lateral rotation of the head?
Horizontal (lateral) canal.
What is the function of endolymph in the semicircular canals?
It moves in response to head rotation, causing deflection of the cupula and hair cells.
Where are the sensory hair cells located within the semicircular canals?
In the ampulla, embedded in the gelatinous cupula.
What happens when the hair cells in the semicircular canals are deflected?
An action potential is generated, sending excitatory or inhibitory signals via the vestibular nerve.
What are the ‘functional pairs’ in the semicircular canals?
Coplanar pairs where one canal increases signals while the partner decreases signals.
- R/L horizontal canals are a functional, coplanar pair
- “LARP”= Left anterior/right posterior make acoplanar pair
- “RALP”= Right anterior/Left posterior make a coplanar pair
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What results from an acute disturbance in the semicircular canals?
Vertigo and imbalance.
Which otolith organ senses horizontal linear acceleration?
Utricle.
Which otolith organ senses vertical linear acceleration?
Saccule.
What is the function of the otoconia in the otolith organs?
They act as ballast, accentuating the bending of hair cells during head movement.
What can happen if otoconia become displaced into the semicircular canals?
It can lead to Benign Paroxysmal Positional Vertigo (BPPV).
Where is the information from the SCCs and otoliths sent?
To the cerebellum and vestibular nuclei in the brainstem via CNVIII.
How many vestibular nuclei are there on each side of the brainstem?
Four.
What role does the cerebellum play in the vestibular system?
It helps with the smoothness of movement by processing vestibular input.
What does the vestibulospinal tract help maintain?
Postural stability.
To which cranial nerves does the vestibular system send information to coordinate eye movements?
- CN III
- CN IV
- CN VI
What is the role of the tonic firing rate in the vestibular nerve?
It allows detection of head motion through changes in firing rate.
What happens when there is an asymmetry in tonic firing rate between the vestibular nerves?
It leads to vertigo and nystagmus.
What is the VOR phase?
As the head moves in one direction, the eyes move in the opposite direction with equal amplitude.
What is the VOR gain?
The ratio of eye velocity to head velocity, ideally 1:1.
What are the consequences of VOR dysfunction?
Difficulty with fast head movements, dizziness, nausea, and blurry vision with head movement.
What is oscillopsia?
Blurry or bouncy vision with head movement due to decreased gaze stability.
What are the primary functions of the central vestibular system?
(2)
Integration of sensory information and coordination of motor output.
What is the role of the medial and lateral vestibulospinal tracts?
They help maintain postural stability (VSR).
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What might result from damage to the central vestibular system?
Impaired coordination, dizziness, and balance issues.
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What is the function of the vestibular nucleus complex?
Integration of sensory input from vestibular, visual, and somatosensory systems.
Which sensory systems are involved in maintaining equilibrium?
- vestibular system
- visual system
- somatosensory system
What are the three components of motor output in the vestibular system?
- Eye movements (VOR)
- Postural movements (VSR)
- Head movements
What can cause vertigo?
Acute disturbances in the semicircular canals or otolith organs.
How does the brain detect the direction of head movement?
By comparing the input from the partner coplanar receptors in the semicircular canals.
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What is BPPV?
Benign Paroxysmal Positional Vertigo, a condition caused by displaced otoconia.
How do the semicircular canals detect angular acceleration?
Through the movement of endolymph and deflection of the cupula.
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What is the significance of coplanar pairs in the semicircular canals?
They allow the brain to detect the direction and speed of head movement accurately.
What is the result of non-reciprocal signals between coplanar pairs?
- abnormal eye movements
- balance issues
- dizziness
- vertigo
