The Vestibular System Flashcards
What is the general orientation of the utricle and saccule?
Utricle is oriented in the horizontal plane
Saccule is in the verticle plane
How does the orientation of the utricle and saccule contribute to the perception of linear motion?
Each organ has a macula with hair cells embedded in a gelatinous membrane. The membrane has otoconia. When the body moves, the otoconia shifts due to gravity or inertia, which causes the hair cells to deflect and stimulate the organ.
How is the cupula stimulated by the rotations of the head?
When the head turns, the cupula moves against the flow of endolymph. This displacement deflects hair cells stereocilia within the cupula.
Describe how the three semicircular canals work in pairs.
The canals on each side of the head works in pairs. The horizontal canals work together and the left posterior canal works with right anterior canal
How does the orientation of three semicircular canals relates to the vestibulo-ocular reflex?
The canals are aligned to the planes of the eye muscles: horizontal canals are in the plane of the lateral and medial rectus, anterior and posterior are aligned with the superior/inferior recturs and oblique muscles. Once rotational movement occurs, this causes stimulation on one side and inhibits the other side.
Name the three cranial nerves involved in the vestibulo-occular reflex?
- Oculomotor (III)
- Trochlear (IV)
- Adbucens (VI)
What causes BPPV?
It’s a vestiblar disorder where the otoconia becomes displaced from the otolithic membrane and floats through the semicircular canals, causing vertigo.
How do we test for BPPV?
Dix-Hallpike
How can BPPV be treated?
Epley Maneuver
What does the two otolith organs sense?
Linear acceleration
Both the utricle and saccule contains:
Hair cells called macula
Which otolith organ is the largest?
Utricle
The otolith forms
The base of all three semicircular canals
The saccule is sensitive to:
Gravity while standing and acceleration
What is the macula?
Layer of supporting cells surroudning hair cells
Where are the hair cells of the macula embedded?
Gelatinous otolithic membranes
What does the surface of the otolithic membrane have?
A calcium carbonate called otoconia.
What does each otlith organ have?
A macula
What are three semicircular canals?
- Anterior (Superior) Canal
- Lateral (Horizontal)
- Posterior (Inferior)
What is the anterior canal sensitive to?
The rotation in the sagittal plane
What is the lateral canal sensitve to?
The rotation in the transverse plane
What is the posterior canal sensitive to?
The rotation in the coronal plane.
What is each semicircular canal connected to?
The utricle at a widened based called the ampulla
What’s within the ampulla?
Cupula
What’s within the cupula?
Sensory hair cells embedded in the crista ampularis.
When rotational movement of the vestibular-ocular occurs, what happens:
- Stimulation contracts one set of the eye muscles
2. Inhibition relaxes other set of eye muscles
What is the net result of vestibulo-ocular reflex?
Eyes shifting in unison to perfectly counteract the turn of the head
What happens when the vesitbular system detects movement of the head?
It reflexively activates the eye muscles to maintain visual fixation
What happens when someone has vertigo>
Their eyes move reflexively to counteract their perceived movement
What do e three cranial nerves involved in the vestibulo-occular reflex have in common?
- All motor nerves
2. All project to eye muscles
What is nystagmus?
Involuntary rhythmic motion of the eyes
What is vertigo?
False sensation of spinning
What causes nystagmus?
Stimulation of the vesitbular system while the head is stationary
