Lecture 7: Vestibular System Flashcards
What are the 3 main functions of the vestibular system?
- gaze stability (VOR)
- sensing and perceiving motions (SCC hair cells or otoliths)
- Postural control (VSR)
What are the 3 main components of the vestibular system?
- peripheral sensory apparatus ( Membranous and bony labyrinth)
- a central processor ( Floculonodular lobe in cerebellum)
- Mechanism for motor output (ocular motor muscles)
What are the three components of the bony labyrinth?
three semicircular canals, cochlea and vestibule
contains perilymph fluid that resembles CSF
What are components of the membranous labyrinth?
membranous portions of SCC, utricle and saccule
filled with endolymph
What is the main role of the SCC?
detect angular head rotation and provide sensory input about velocity
What structure is at the beginning of each SCC?
ampulla which contains specialized hair cells as well as endolymph
What does the term contralateral co-planar mate mean in relation to SCC?
planes are perpendicular to one another so in a case of hypo function one plane can assist the other will a push pull mechanism
What are the otoliths ?
refer to both the utricle and saccule
What is the role of the otoliths?
detect linear acceleration and static head tilt
Utricle- horizontal acceleration
saccule- vertical acceleration
What important structure is located in the Otoliths?
sensory hair cells or macula- on the medial wall of saccule and floor of utricle
What is the role of the macula in the otoliths?
project gelatinous matrix which contains calcium carbonate crystals known as otoconia
What is the role of the hair cells located in the otoliths?
biological sensors than convert displacement due to head motion into neural firing
How is each hair cell in the otolith innervated?
each hair cell is innervated by an afferent neuron in Scarpa’s ganglion
What are the two different types of hair cells in the otoliths?
stereocillia and kinocillia
Which directions of the hair cells causes excitation and inhibition?
deflection of endolymph results in changes in membrane potential
stereocilia (short hair cells) towards kinocillia (long hair cells) = excitation
opposite direction= inhibition
What are the major components of the central processor of vestibular information?
- vestibular nuclear complex- located in pons and medulla
- cerebellum- major recipient of outflow from the VN, calibrates vestibular info
- floculonodular lobe- in cerebellum that is major role in vestibular system
What would happen if there was damage to the cerebellum?
vestibular reflexes would be both uncalibrated and ineffective
What are the two main mechanisms for motor output of vestibular system?
VOR and VSR- primary reflexes of vestibular system
Which tract is responsible for transmitting output to the VOR?
medial longitudinal fasciculus
Which tract is responsible for transmitting output to the VSR?
lateral and medial vestibulospinal tracts
What is the main role of the VOR?
functions to maintain stable vision/gaze stability during head motions
works closely with the ocular muscles and visual system
one of fastest reflexes in the bosy
What is VOR gain?
ratio of eye movement to head movement which should be 1.0
rate will be disrupted in vestibular pathology
What is the main role of the VSR?
functions to stabilize body using otoliths output
not as quick as VOR but still a primary vestibular reflex
“corrects body if you trip over stone”
What are three secondary vestibular reflexes?
- cervico ocular reflexes- supplements VOR, driven by neck proprioceptors
- Vestibulocollic Reflex- acts on neck musculature to stabilize head
- Visual reflex- influences vestibular circuitry
Wy does the VOR work so well?
due to the pull push mechanism in coplanar SCC, during an excitation of one side of hair cells the other side will inhibit so there is not an overload of excitatory saturation
What is vertigo?
issue with one’s vestibular system, sensation of motion such as spinning, tilting, translation of the either the environment or self
What is vertigo not?
vertigo is not the same thing as dizziness, which is a non specific term that describes altered orientation in space which can be due to a number of different things
sx like: light headed, fainting, floating, imbalance
What is dysequilibrium?
inability to maintain upright posture can result in lateral or retropulsion can be associated with non vestibular problems
What is nystagmus?
involuntary back and forth movements of eyes, damage to vestibular system will cause either vertical or horizontal nystagmus
What is a pure vertical nystagmus indicative of?
CNS pathology
What is a pure horizontal nystagmus indicative of?
peripheral pathology, but could also be in CNS pathology
What are two different specific types of pathological nystagmus?
- spontaneous
2. gaze evoked
What is spontaneous nystagmus?
occurs in acute phase of UVH or in brainstem/ cerebellar abnormality
if peripheral inhibited by fixation, opposite if CNS
What is gaze evoked nystagmus?
pt unable to main stable gaze
usually indicative structural brain lesion or med/ETOH induced (hair cells absorb ETOH)
What is BPPV?
benign paroxysmal positional vertigo
most common cause of vertigo due to peripheral vestibular disorders
How does BPPV occur?
occurs as a result of otoconia that become dislodged from gelatinous matrix and travels into SCC
What are two different results from traveling otoconia?
- canalathiasis- float freely in canal
2. cupulolithiasis- otoconia fix themselves in cupola
What is most common cause of BPPV?
unknown cause followed by post trauma
What canal is BPPV most likely to occur in?
posterior canal 85%
What population is BPPV more common in?
elderly and women, possible connection with osteoporosis and osteopenia
What is clinical presentation of BPPV?
presence of vertigo, nausea, imbalance with head turns,
commonly triggered by rolling in bed, showering, driving
What is presentation of canalathiasis?
onset of sx of 1-40 after moving into provoking position, horizontal, torsional upbeating CCW nystagmus
sx last less than 60 seconds
What is presentation of cupulolithiasis?
immediate onset of vertigo after moving into provoking position, horizontal and torsional nystagmus, sx lasting greater than 60 seconds
What is the gold standard test for BPPV?
Hall pike dix
What is procedure of Hall pike dix?
start in long sitting on plinth with head in 45 degrees of rotation, drop down into supine with 30 degrees of extension, hold for 60 seconds, return to sitting with head still rotated (check nystagmus)
test both sides
What are contraindications for a hall pike dix?
recent neck trauma or surgery, cervical myelopathy or radiculopathy, carotid sinus syncope, chiari malformation, severe RA, down syndrome, cervical spine instability
What are precautions for a hall pike dix test?
cervical stenosis, severe kyphoscoliosis, limited cervical ROM, pagets disease, AS, LBP, SCI, obesity glaucoma, torn or detached retina
What is alternative test for HPD?
side lying test used if limited cervical ROM or traditional HPD is not tolerated
subject briskly brought to side being tested with 45 degrees of rotation
What type of nystagmus is present in anterior canal BPPV?
downward and torsional
