Vestibular Disorders Flashcards
(38 cards)
What makes up the central portion of the Vestibular System?
- 4 vestibular nuclei
- Cortex/Thalamus
- Cerebellum
- Tracts connecting to the muscles and nerves, reticular formation
What makes up the peripheral portion of the Vestibular System?
- Bony Labyrinth
- Membranous Labyrinth
- 5 Sensory Organs
- Receptors
What do the 3 semicircular canals do?
Detect angular acceleration
-Mediates dynamic functions
What do the 2 Otolithic Organs do?
Mediate STATIC FUNCTIONS
Saccule and Utricle
What does the Saccule do?
Detect VERTICAL translation of the head
What does the Utricle do?
Detect Horizontal translation of the head
What is innervated by the Superior Division of Cranial Nerve VIII?
- Utricle
- Anterior Semicircular Canal
- Horizontal Semicircular Canal
What is innervated by the Inferior Division of Cranial Nerve VIII?
- Saccule
- Posterior Semicircular Canal
What is the entrance and exit of CN VIII? (Sensory only)
Stemming from the lateral inferior margin of the left and right side of the pons and the cerebellum, exiting the skull via the internal acoustic meatus.
Role of Vestibular System?
SENSORY and MOTOR System
- Provides awareness of spatial orientation
- Helps influence muscle tone and balance
- Controls the position of the eye in orbit
Input –> Integration –> Perception –> Selection of Motor –> Refinement –> Output
Positional information for visual, vestibular, and proprioceptive input go through central processing in cerebellum and reticular system. The inputs are influenced and controlled by eye movements and posture & motor skills.
What is responsible for input?
Somatosensory, Labyrinths, and Vision
What is responsible for Integration?
Vestibular Nuclei and Cerebellum
What is responsible for Perception?
Cortex and Thalamus
What is responsible for Selecting Motor Responses?
Cortex
What is responsible for Refinement of Movement?
Vesibular nuclei and cerebellum
What is responsible for Output?
Vestibular spinal, vesibular occular, occular tilt response
What is the Push-Pull Mechanism?
Each Canal has a mate on the opposite side that lies in the same plane.
When your head is rotated, the cupula of the horizontal canal on the side you turn towards is facilitory, causing an increased rate of firing of Scarpa’s ganglion to the vestibular nuclei.
On the opposite side (the side you are turning away from), the cupula is inhibitory, causing Scarpa’s ganglion to SLOW is rate of fire to that vestibular nuclei
(Scarpa’s Ganglion = Constanty firing at 100 spikes/sec. at rest)
–
Head move R, Fluid move L (excite side going towards)
When one canal is stimulated, its corresponding partner on the other side is inhibited, and vice versa. This push-pull system allows us to sense all directions of rotation: while the right horizontal canal gets stimulated during head rotations to the right (Fig 2), the left horizontal canal gets stimulated (and thus predominantly signals) by head rotations to the left.
What are some key concepts of nystagmus?
Involuntary rhythmic oscillation of the eyes
- Slow phase - generated by the vestibular system
- Quick phase - generated by the saccade system
Named for QUICK PHASE
Causes retinal slip, giving the illusion of movement
Horizontal, Vertical, or Torsional movements
- Direction of torsional nystagmus is identified by the direction that the superior pole of the eye is moving towards
- Most of the time, you see a combo of the 3
Anterior canal = down-beat nystagmus
Nystagmus is normal in supine in the dark
Named by the direction of the FAST-PHASE
What are key concepts of Spontaneous Nystagmus?
Vestibular hypofunction - fast phase of nystagmus beats towards the strong and unaffected side (eye beats R, means L side is weak - may be opposite if a virus is involved)
Alexander’s Law: Gaze in direction of fast component causes increased frequency, gaze away from fast component has opposite effect.
Usually a peripheral lesion (can suppress with fixation)
What are key concepts of Central Nystagmus?
VERTICAL is often CENTRAL in origin
Purely vertical, horizontal, or torsional is central (pure=central)
UNABLE TO SUPPRESS WITH FIXATION
(Torsion + Downbeat = Peripheral) - combo is rare?
What is “vertigo?”
Sensation of movement of oneself or of the environment (rotation, translation, tilt)
-Sensation that the room is spinning (usually over-diagnosed)
What is “dizziness?”
Non-specific catch all
Have the patient use a different term
What is a “Head Fog?”
Lightheadedness (pea soup in head?)
What is dysequilibrium?
Static and Dynamic unsteadiness
