Vestibular Anatomy and Physiology Flashcards
What is the primary role of the balance system?
To allow us to interact and maintain contact with out surroundings
As we move through our environment, information is gathered through the visual, somatosensory, and vestibular senses and sent to the brain for integration, perception and processing
What percentage does vestibular information contribute to body stability?
65%
Main contributor
Standing balance, however, does not rely on primarily on vestibular information
Proprioception is the major contributor to standing balance
When proprioceptive input is not helpful vision becomes the primary source of information
What is the bony labyrinth filled with?
Perilymph
What is the membranous labyrinth filled with?
Endolymph
What are the 5 sensory organs housed within each membranous labyrinth (10 total)?
Utricle macula
Saccule macula
Three cristae ampullaris
What are known as otolithic structures?
Utricle and saccule
What does the utricle do?
Plays a large role in postural control and primarily senses changes in orientation with respect to gravity. Such as moving forward in a car
What do gravity and linear motion exert forces on?
The otolithic sensory structures
What hair cells in the vestibular system stimulated by?
Mostly motion of the fluid
Sometimes sound
Does the utricle have a direct route to the SCCs?
Yes, the saccule does not
What are otoconia?
A layer of calcium carbonate crystals on the otoconial membrane (also known as the macula)
Protein matrix that holds all of the crystals together (continuously generated throughout life)
Just below the otoconia lies a
gelatinous membrane through which
the hair cells project the stereocilia
What does movement of the otoconia result in?
Stimulation of the sensory cells
Otoliths respond transiently to linear acceleration and to head tilt
With a sudden forward movement, the supporting structures will move synchronously with the head
The density and weight of the otoconia cause them to lag behind head movement than they catch up after several seconds of linear movement (utricular response is exhausted)
A tilt of the head causes a prolonged response from the utricle (why we think that the utricle is the primary sensor for orientation to gravity and plays an important role in postural stability)
What stimulates the saccule?
Up/down
Vertical stimulation
Debate on whether the saccule can be stimulated in a lab
What is orthogonal?
Right angles to each other
Describes orientation of SCC
This arrangement causes the endolymph to flow toward or away from the ampullated end of the canal in at least one canal on each side
What is pitch?
Shaking head yes
What is yaw?
Shaking head no
What is roll?
Tilting head to the side
What are the sensory cells in the SCC?
Cristae and are housed in the ampulla
What is sitting on the cristae ampullaris?
Cupula (extends across the ampulla to close off the lumen of the canal)
Has a density that is similar to the endolymph (not sensitive to gravity)
What will movement that causes the stereocilia to flow toward the kinocilium result in?
Depolarization and an increase in electrical potential
Does ampullopetal always mean excitation?
No, only in the horizontal SCC
Other canals result in inhibition
Are there 2 vestibular nerve branches?
Yes
What are the three functions of the vestibular apparatus?
To provide a subjective sensation of movement and/or displacement in 3-dimensional space
To maintain upright body posture (balance)
To stabilize the eyes during head and head and body movement
Where are the cell bodies for the superior and inferior vestibular nerves?
Scarpa’s ganglion
What does the posterior canal share a plane with?
The contralateral anterior canal
Are the different vestibular hair cells completely understood?
No
We know there are 2 types, but don’t really know what is different about them
What is type 1 vestibular hair cells?
Spherical shape with 60 to 70 small hairs emerging from the cuticle
What are type 2 hair cells?
Cylindrical in shape
stereocilia and kinocilia are identical to type 1
Are low frequencies more affected for vestibular deficits?
Yes
Shaking head slow vs fast
How are the hair cells oriented in the utricle and saccule
Toward striola in the utricle
Away in the saccule
Does constant low level current flowing through hair cells cause a resting discharge in the vestibular nerve?
Yes
Stimulation towards kinocilium leads to cell depolarization and increased nerve activity
Stimulation of hair cells away from kinocilium leads to hyperpolarisation and decreased activity in vestibular nerve
How are the kinocilia oriented in the anterior and posterior canals?
Toward the canal side of the ampulla
How are the kinocilia oriented in the horizontal canals?
Toward the utricle
Similar to hear, can you have a decent amount of hair cells loss without seeing it affect the vestibular system?
Yes
For the majority of people who have a significant amount of vestibular loss, is the loss permanent?
Yes
If you have one intact vestibular system, will you probably recover function in the affected side?
Yes
Through time and recovery through rehab
What were the vertebral artery screenings?
Looking for the possibility of stroke
Stand against the wall and turn head
Report if they get dizzy
Raises a red flag
Not a very good screening
How do we loos vestibular hair cells?
Prebystasis (age related loss)
Infections
Toxicities (both peripheral and central)
Many of the same things that impact the auditory system
Cancer
What does the superior division of the vestibular nerve connect to?
Utricle, anterior part of saccule(?), and horiz & anterior canals
What does the inferior division of the vestibular nerve connect to?
Posterior part of saccule, and posterior canal
Where does the vestibular nerve lead to?
Vestibular nuclei and cerebellum
For most normal head movements, is the firing rates in phase with the head velocity?
Yes
What are the other inputs to vestibular nuclei?
Cerebellum: primarily inhibitory
Spinal cord
Pontine reticular formation
Contralateral vestibular nuclei
What is the vestibulo-oculomotor pathways?
Direct: to oculomotor nuclei
Indirect: via reticular formation to oculomotor nuclei (III IV and VI)
What is the vestibulo-spinal pathway?
Lateral V-S-throughout spinal cord
Medial V-S-cervical & thoracic
Reticulospinal tract-via brainstem reticular formation
What happens in the brainstem with vestibular information?
Vestibular inputs undergo integration
Integrated signal is combined with original (velocity driven) signal
Processing to reset spatial map for eye musculature
How fast do we typically move our heads?
0.8-5 Hz
What are saccades?
Rapid shifts in gaze
What are pursuits?
Stabilize image of moving object
What is fixation?
Stabilize image of still object
What is VOR?
Stabilize image during head motion
What is OKN?
Backup for when VOR decays to continued head rotation
What is vergent movements?
Change depth of focus
Bringing things toward or away
