8.6A. Physiology of equilibrium. Flashcards
I. Vestibular system
1. What is the role of Vestibular system?
The vestibular system is responsible for the sense of equilibrium – a form of proprioception.
I. Vestibular system
2. What is the role of vestibular apparatus?
The vestibular apparatus detects the position, linear acceleration, and rotation of the head.
- To accomplish this, it uses two different apparatuses involving hair cells.
-> It includes the anterior, posterior and horizontal Semicircular canals, as well as the Utricle and Saccule (otolithic organs)
I. Vestibular system
3. Will the endolymph fill vestibular system? What are the consequences?
The endolymph will fill the vestibular system, but it is far away from the place of the production
-> the [K+] remains the same, but the electric potential will disappear (0mV), because the distance is too large and it will be attenuated
II. Vestibule (vestibular apparatus)
1. Describe the structure of Vestibule (vestibular apparatus)?
- The vestibular portion of the membranous labyrinth in the inner ear
- The vestibular portion has 5 sensory structures: 2 otolithic organs and 3 semicircular
canals
II. Vestibule (vestibular apparatus)
2A. List the Otholotic organs
saccule and utricle (macula + otolithic membrane)
II. Vestibule (vestibular apparatus)
2B. What are the characteristics of Otholotic organs?
- Located near the center of the labyrinth
- Filled with endolymph, but surrounded by perilymph
- Between the endo and perilymph, we have the endothelial layer, where we can find
hair cells
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2C. What is the role of Vestibular dark cells?
secrete K+ into the endolymph
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2D1. What are the features of macula?
Macula: contains hair cells
- The stereovilli of the hair cells project into the gelatinous otolithic membrane
- Otolithic membrane = mass of mucopolysaccharides + otoliths (crystals/salts =
CaCO3)
- Otoliths make the otolithic membrane denser than the surrounding endolymph
- If we change the position of this system or have a gravity force, the otoliths will cause the otolithic membrane to move -> mechanical stimulus (deflecting stereovilli etc.)
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2D2. Where do The stereovilli of the hair cells project into?
The stereovilli of the hair cells project into the gelatinous otolithic membrane
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2D3. What is the structure of Otolithic membrane
mass of mucopolysaccharides + otoliths (crystals/salts =
CaCO3)
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2E. What is the orientation of macula?
- Saccule = vertical (hair cells towards striola)
- Utricle = horizontal (hair cells away from striola)
=> Get a 3-dimensional-system and this is why the entire otolithic organ will respond (whatever direction) to change of mechanical stimulus
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2F. What are the features of striola?
- The hair cells of the macula are oriented in relation to a groove called the striola (reversal line), which runs through the middle of each macula.
- The striola is useful, because APs from hair cells will increase on one side of the striola and decrease on the other side, which creates a strong contrast that makes interpretation easier
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2G. Explain activation of macula
(1) Change of position of head and (2) linear acceleration of head, will serve as a mechanical stimulus: cause movement of otolithic membrane
-> deflection of stereovilli
-> activation
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2H. What is the innervation of Otholotic organs?
Vestibular N (CNVIII)
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2I. Describe afferentation of Otholotic organs
- Innervate type 1 and type 2 hair cells
- Body of the cell forms ganglion: Scarpa’s ganglion
- Ipsilateral ending of nerve cells in the vestibular nuclei
II. Vestibule (vestibular apparatus) - Otholotic organs = saccule and utricle (macula + otolithic membrane)
2J. Describe Efferentation of Otholotic organs
- Innervate type 1 and type 2 hair cells
- Comes from CNS
- Effect on long-term sensitivity of entire system
II. Vestibule (vestibular apparatus)
3A. What does semicircular canal include?
crista ampullaris + cupula
II. Vestibule (vestibular apparatus) - Semicircular canal (crista ampullaris + cupula)
3C. What happen in semicircular canal if we change the position of the head/linear acceleration of body?
Because if we change the position of the head/linear acceleration of body
-> the cupula will move together with the endolymph
-> there is no difference in the movement of cupula and endolymph, so there will be no activation of the system
II. Vestibule (vestibular apparatus) - Semicircular canal (crista ampullaris + cupula)
3E. What happen in semicircular canals if the rotation of head occur?
If the rotation of the head occurs
-> the endolymph has inertia (tendency to remain at a current state of motion)
-> cannot start to rotate at the same time with the head
-> DELAY
-> relative endolymph flow, because of the inertia
-> will move the cupula
II. Vestibule (vestibular apparatus) - Semicircular canal (crista ampullaris + cupula)
3F. What happen in semicircular canals when the rotation of the head stops?
When the rotation of the head stops, there will be a relative endolymph movement to the opposite direction
(=> Both the ‘’start’’ and ‘’stop’’ of the rotation will generate an activation of hair cells)
II. Vestibule (vestibular apparatus) - Semicircular canal (crista ampullaris + cupula)
3G. What is the relative endolymph flow?
The relative endolymph flow is a transient process, after a while the endolymph will move together with the head
-> about 15 seconds delay
II. Vestibule (vestibular apparatus) - Semicircular canal (crista ampullaris + cupula)
3I. What happen if head is rotated to the left?
- As the acceleration to the left begins, the inertial forces shift the endolymph to the right in both of the horizontal canals
- In the left ear, this means that stereocilia of the hair cells bend toward the kinocilium, and that APs in the afferent nerve supplying the left crista ampullaris increases
- The opposite occurs in the right ear: stereocilia bend away from the kinocilium -> AP firing decreases
III. Innervation
1. Describe innervation of vestibular system,
- Primary afferent fibers from the vestibular apparatus reaches the brainstem by way of the vestibular nerve (part of CN VIII).
- Most afferents terminate in the vestibular nuclei. Through these connections, the vestibular system is part of the vestibulospinal reflex (help orient the body with extensor muscle contraction if falling) and vestibulo-ocular reflexes (help focus on moving objects or stationary objects while moving by a process called nystagmus)
III. Innervation
2. What does dysfunction of the vestibular system lead to?
Dysfunction of the vestibular system leads to vertigo and pathological nystagmus
- Pathological nystagmus: uncontrolled eye movement which can result in reduced vision and can affect balance and coordination
