Flashcards in Vestibular System Deck (53):
What are the 5 components of the vestibular system?
- Peripheral receptor apparatus
- Central vestibular nuclei
- Vestibulo-ocular network
- Vestibulospinal network
- Vestibulo-thalamo-cortical network
What are the 2 portions of the peripheral vestibular labyrinth?
- Bony labyrinth
- Membranous labyrinth
In what bone is the bony labyrinth found?
Petrous portion of temporal bone
Where is the peripheral vestibular labyrinth located in relation to the cochlea?
- Posterior and lateral
Where is the membranous labyrinth found? What is it?
- A membrane of simple epithelium (the membranous labyrinth) is found within the bony labyrinth
Where is perilymph found?
Between the bony and membranous labyrinth
Where is the endolymph found?
Inside the membranous labyrinth.
What are the 5 portions of the membranous labyrinth?
- 3 semicircular canals
What structures make up the static labyrinth?
What type of structures are the utricle and saccule?
- Otolith organs
What are the 3 semi-circular canals?
What are the 3 functions of the static labyrinth?
- Monitor absolute position of head in space (posture/ balance)
- Maintain eye position
- Perception of linear acceleration and deceleration
Which otolith organ pertains to horizontal movement?
Which otolith organ pertains to vertical movement?
Which labyrinth pertains to pitch and roll of the head?
Which labyrinth pertains to yaw of the head?
What is the name of the specialized region within the otolith organs?
Describe the structure of the macula.
- Epithelial cells "hair cells" with special cilia called stereocilia and a single kinocilium on their apical surfaces
- Hairs extend upward into gelatinous substance containing otoconia (calcium carbonate crystals)
If the otoconia bend away from a kinocilia, what is the effect?
- Decreased Afferent Activity
If the otoconia bend towards the kinocilia, what is the effect?
- Increased afferent activity
What is the linear vestibulo-ocular reflex?
- Eyes are remain positioned as the head tilts (??)
What is a striola?
Structural land mark of small otoconia that define a narrow trench that divides each otolith organ.
How are the kinocilia arranged in reference to the striola in the utricle, and the saccule?
Utricle: Towards striola
Saccule: Away from striola
What is the tonic labyrinthine reflex for supine?
- Extension of UE and LE
What is the tonic labyrinthine reflex for prone?
- Flexion of UE and LE
What is the tonic labyrinthine reflex for side lying?
- Extension of limbs touching floor
- Flexion of limbs off floor
What is the trendelenburg position?
- Patient supine, but the body tilted so that the head is below the LE
What is the tonic labyrinthine reflex for the trendelenburg position?
- UE extension
- LE flexion
Which semi-circular tubule is the commonly used?
What are the 2 functions of the dynamic labyrinth?
- Track rotation of the head in space
- Perception of angular acceleration/ deceleration
How are the right and left semi-circular canals aligned?
- Right anterior canal aligned with left posterior canal
- Right posterior canal aligned with left anterior canal
- Semicircular canal mirror images of one another
What is the expansion at the end of each semicircular tubule called?
How are the semicircular canals oriented in relation to the horizontal?
Canted 30 degrees
What is the name of the sensory epithelium in the ampulla? (not sure if this is accurate)
What is the name of the gelatinous door that splits the ampulla into 2 compartments?
How does the endolymph function within the vestibular system?
- Endolymph has a high specific gravity, meaning it remain in place while structures around it move
- As the head rotates, endolymph will come into contact with the cupula on the side the head is rotating towards, facilitating the vestibular system
- Endolymph will also move away from the contralateral side pulling liquids out of the the ampulla causing inhibition
What are the 2 components of nystagmus?
- Slow component of eyes coming by to neutral to maintain fixation
What reflex causes saccades?
Describe the vestibulo-ocular reflex.
(Ipsilateral refers to side which the head is turning towards)
- Endolymph facilitates vestibular nuclei on ipsilateral and side, and inhibits vestibular nuclei on the contralateral side
On ipsilateral side:
- Lateral vestibular nucleus facilitates ipsilateral oculomotor nucleus
- Medial nucleus facilitates contralateral abducens nucleus
- CN VI sends a projection to ipsilateral oculomotor nucleus through medial longitudinal fasciculus
- CN VI facilitates the contralateral lateral rectus muscle through contralateral abducens nerve
- CN III through facilitation from the ipsilateral lateral vestibular nucleus and contralateral abducens nucleus activates ipsilateral rectus muscle
On contralateral side:
- Ipsilateral medial rectus and contralateral lateral rectus are inhibited through the same pathways
What is post rotatory nystagmus test?
- Pt seated at chair with head tilted 30 degrees
- Pt rotated 10 - 12 times
- Endolymph will be rotating in direction opposite to the rotation of the head
- Pt stopped
- Endolymph reverses direction of flow
- Slow component of nystagmus will be in the direction of the rotation, fast component will be opposite
- Since nystagmus is named by the fast component, nystagmus will be opposite to the direction of rotation
- In normal patients, nystagmus should stop within 20 - 30 seconds
What semicircular canals are tested by the post rotatory nystagmus test?
What is the Caloric test? What pathologies will it test?
- Flex head 30 degrees
- Irrigate external auditory canal with 20 - 30 mL of ice cold water
- Fast component of nystagmus should occur away from the irrigated side
- Supratentorial or memtabolic lesion will cause only the slow component to occur
- Unilateral brain stem disease will cause no reaction
What is the Doll's Eye Maneuver? What is indicated by a positive test?
- Head briskly turned to one side or another or tilted up and down
- Eyes should turn opposite the direction of the head turn
- Brain stem lesions are implicated if the eyes move with the head or stay still
What type of movements increase tone?
Phasic, quick movements
What type of movements decrease tone?
Slow, rhythmic movements
What autonomic responses can be affected by the vestibular system?
- Blood pressure
- Heart rate
- Body temperature
What nervous system is stimulated by quick movements?
What are the 4 most common symptoms of vestibular disease?
What are the 2 most common vestibular pathologies?
- Vestibular neuritis
- Benign Paroxysmal Positional Vestigo
What is vestibular neuritis?
Inflammation of the vestibulocochlear nerve
What is Benign Paroxysmal Positional Vertigo (BPPV)?
- Otolith pieces slip into SSCs
- These particles can create fluid waves that displace the cupula causing dizziness, vertigo, and nystagmus
Which canal is typically affected by BPPV?