Lecture 7: Vestibular System Flashcards
(49 cards)
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
