Physiology of the Vestibular apparatus Flashcards
What is responsible for the detection of linear movement?
The Maculae of the Utricle and Saccule
What is responsible for detection of rotational movement?
The Cupulae in the ampullae of the Semicircular Ducts
What is the name of the longest cilium of the hair cells? and how does the rate of firing change with its bending?
Kinocilium
There is a steady rate of impulses
Bending away from KC → decreased rate of firing
Towards KC → increased rate of firing
What is the structure of the Macula?
- Neuroepithelium - hair cells located on epithelial wall, with cilia projecting
- Gel layer - floating in endolymph, tips of cilia are embedded here
- Otoconia - Calcium Carbonate pellets attached to gel to provide inertia
What is the mechanism of the maculae?
Linear motion of head → neuroepithelium movement
Gel layer and otoconia lag due to inertia
Cilia bend due to movement of neuroepithelium relative to gel
→ Modified firing rate
What is the structure of the cupulae?
Neuroepithelium - hair cells with cilia
Cupula - gel like structure with traversing duct, in which cilia are embedded
What is the mechanism of the cupulae?
Endolymph moves with rotation of the head
Distortion of cupula due to endolymph pushing against it
Cilia bend due to movement of cupula realtive to endothelium
Modifies the firing rate of hair cells → vestibular nerve
Explain functional pairing.
The semicircular canals work in pairs
If head turns to the left, in the L&R lateral semicircular ducts
Left vestibule - cilia move towards kinocilium - increased firing
Right vestibule - cilia move away from kinocilium - decreased firing
L Sup + R Inf
R sup + L Inf
How does the brain interpret the paired information? and how may malfunction lead to pathology?
It looks at the net movement of both ears.
If the head is not moving, but the R vestibule does not work, the brain only receives information from the left → spinning sensation
Explain the vestibulo-ocular reflex.
Movement of the eyes in the opposite direction to head rotation
Allows on to stare at a fixed object despite head movement
Connections between semicircular canals and extra-ocular muscles
What is nystagmus?
Involuntary eye movement - slow drift phase towards periphery of visual field and quick snap phase back to central visual field
What is the definition of physiological nystagmus?
Interaction of the VO reflex and the cerebral control mechanisms → ≤3 beats of nystagmus on head rotation
When does nystagmus become pathological?
When one semicircular canal becomes dominant/unopposed due to pathology in functional opposite
Eyes drift towards side of pathology, before cerebral control mechanisms correct drift with quick snap away from pathology
How is nystagmus named?
It is named after fast phase
e.g. Right beating nystagmus = fast phase towards right → pathology on left
