Vestibular System-Graf Flashcards
What is the vestibular system good for?
- compensatory movements (eyes, head, body)
- postural control (upright stance)
- spatial orientation
- self-motion detection and perception
- cardiovascular, pulmonary adjustment
Most of the time, we are unaware of the existence of our sense of balance.
We perceive our sense of balance only, when something goes wrong!
Examples: motion sickness, new glasses, Menière’s disease, influence of alcohol, vertigo, etc.
What are labyrinth?
- Vestibular system has 5 components: 3 semicircular canals (anterior, posterior, and horizontal) and 2 otoliths (utricle and saccule)
- there are 3 because they are oriented in 3 dimensions of space
- It is a complex structure in the inner ear which contains the organs of hearing and balance.
- It consists of bony cavities (the bony labyrinth ) filled with fluid and lined with sensitive membranes (the membranous labyrinth).
Receptor hair cells
- Stereocilia: oriented in a step like fashion from small to tall; there is still kinocilia on top
- when the stereocilia is bent towards to the tall stereocilia there is depolarization; if bent toward the small there is hyperpolarization
- the ion channels is a nonspecific mechanically gated ion channel; they are based in endolymph
- Type I hair cell
- Type II hair cell
- support cell
- calix
- afferent nerve ending
- receptor potential
What is the function of the kinocilia?
only there to ensure cell polarity that
Receptor systems: semicircular canals, otoliths:
What is covered over the other: bony labyrinth, membranous labyrinth?
membranous labyrinth is encased over with the bony labyrinth; the fluid in between the two is perilymph; the labyrinths themselves are filled with endolymph
Semicircular canals are oriented with their own coordinate system. How do the horizontal semicircular canal orient themselves?
on direction of the horizontal semicircular canal is backward rotation that will cause endolymph current towards the receptor system which is the cupula
Otoliths also have hair cells and are overlaid by the otolithic membrane which contains calcium and carbonate crystals? What is important about the crystals?
-they are necessary for sensory function
When we move our head, the endolymph in the semicircular canals have a so called endolymph current? What happens when this current pushes against the cupula?
we call it ampullopetal flow
In the horizontal canal, ampullopetal flow is necessary for hair-cell stimulation, whereas ampullofugal flow (flee) is necessary for the anterior and posterior canals.
When you tilt the head what do the otoliths do?
they will slide through the hair cells and bend the stereocilia in a certain direction or another which will cause opening of the ion channels
the otoconia slide across hair cells and thus exert a shear force which constitutes the adequate stimulus
What is the on direction of the horizontal and vertical canals?
- HORIZONTAL canals on direction (excitatory): ampullo-PETAL (towards the crista ampullaris)
- VERTICAL canals on direction (excitatory): ampullo-FUGAL (away from the crista ampullaris)
Semicircular canal activation is initiated by the so called what?
endolymph current
it is actually better to say the endolymph stays in place and the head turns around it
What is the push pull mechanism of the semicircular canals?
The semicircular canals are oriented in a way that each canal on each side of the head is mirrored with its counterpart on the opposite side. Each of these three pairs works in a push and pull way.
The stimulation of one canal (for example left side) results in the inhibition of the other on the other side of the head (for example right side). This mechanism makes it possible to be able to sense all directions of rotation when making movements with the head. It is important that both sides work in this push and pull mechanism but if there is a pathological predisposition to the canals it may result in affecting this mechanism as in those seen in vertigo.
How are the hair cells arranged in the semicircular canals?
The hair cells in the canals are arranged in such a way that they project into a gelatinous membrane called the cupula. When you turn your head in the plane of the canal, the endolymph causes it to splash against the cupula which then results in the deflection of the hair cells. But if you were to keep turning in circles without stopping, the endolymph fluid would catch up with the canal, and there would be no more pressure on the cupula. If you stopped spinning, the moving fluid would splash against a suddenly still cupula, and you would feel as though you were turning in the other direction.
What are the displacements of the otoliths?
- utriculus involves with displacements out of the horizontal plane
- sacculus involves with vertical linear displacements
the otoliths also project in a push-pull fashion with on and off directions
When happens to the utricles when you bend your head backwards?
the otoliths move backward and bend the stereocilia
The actual force hair cells are responding to are what?
ACCELERATION
-not constant speed
Semicircular canal hair cells respond to what type of accelerations?
angular accelerations (rotations)
Otolith hair cells respond to what type of accelerations?
translations
The ubiquitous linear acceleration force on earth is gravity which is?
9.82 m/sec^2
Experiments show that the system really detects acceleration.
A person is very rapid accelerated and a period of constant velocity.
cupula reacts to the acceleration not constant velocity
Tip link structure:
Cadherin 23 and Protocadherin 15 (configurs a spring-like structure)
Adaptation (motor): actin/myosin 1c
Fine thread-like tip links connect to trap doors in the adjacent cilium. Bending the hair cells stretches the tip link, causing an influx of K+ ions and the generation of neural impulses in the VIIIth cranial nerve.
What are tip link structures good for?
reflexes: eye movements and postural control
Postural reflexes
- tonic labyrinths reflexes (upon the extremities)
- tonic neck reflexes (upon the extremities)
Righting reflexes
Stato-kinetic reaction
to keep our neck upright
Stato-kinetic reaction: I can walk without falling over
postural reflexes go down the spinal cord
What are the two main vestibulospinal tracts that we have?
medial and lateral vestibulospinal tracts
Lateral vestibulospinal tract
lateral vestibular nucleus “Dieters” via ventrolateral medulla and spinal cord to ventral funiculus (LUMBO-SACRAL segments)
Medial vestibulospinal tract
medial, lateral, inferior, vestibular nuclei, bilateral projection via descending medial longitudinal fasciculus to CERVICAL segments
Reticulospinal tract
medial, pontomedullary reticular formation, bilateral projection via the lateral and ventral funiculi to lumbar segments
Vestibulo-collic reflexes
- they work on the whole head movement
- shows that when you stimulate the semicircular canals the cat will make head movements in the plane of a particular canal
Stimulation of one canal provokes compensatory eye and head movements in the spatial plane of that canal.
compensatory eye movements occur in these canal coordinates