Vestibular Flashcards
There are 3 semicircular canals that are perpendicular to each other. Together, they can measure rotation. What are they?
Anterior, Posterior, Horizontal Semicircular canals
How is motion transduced into neural firing?
There is an increase in the frequency of AP’s in VIIIth nerve afferents
Endolymph vs Perilymph
Perilympth
high sodium, low potassium
similar to extracellular fluid (CSF)
found between the bone and membrane labrynth
Fluid inside middle ear is called perilymph
receptors are bathed in perilymph
scala vestibuli and scala tympani
Endolympth similar to intracellular fluid fills inside of membranous labrynth hair cells are bathed in endolymph scala media
Bending steriocilia in which direction depolarizes the cell?
Bending of the cilia towards the kinocilium depolarizes the cell (increase in AP’s)
Bending of the cilia away from the kinocilium causes hyperpolarization (decrease in AP’s)
Describe the semicircular canals
Each canal has a swelling at it’s base, called the ampulla
The crista is a saddle shaped receptor epithelium that is covered with sensory hair cells
The stereocilia of the hair cells are embedded in a gelatinous membrane (the cupula) which forms a fluid tight seal across the ampulla
Each canal has a partner in the other labyrinth (i.e., SSC work in pairs). When one partner is maximally excited, the other is maximally inhibited (push-pull organization)
How do the SCC
detect rotational
motion?
When there is a change in head rotational speed, the endolymph lags behind due to inertia. This pushes on the cupula which displaces the stereocilia.
Excitatory response to
ipsilateral motion. Inhibitory
response to contralateral
motion.
Canals work in pairs as
push-pull system.
What are the otolith organs and describe them
two membranous sacs called the utricle and the saccule
The receptor epithelium (the macula) contains hair cells innervated by afferents of the VIIIth nerve
With the head upright, the macula of the utricle is horizontal and the saccule is on the side
Within each macula, hair bundles are oriented in all possible directions (indicated by arrows)
The direction of linear acceleration or gravity is determined by which hair cells are most active
How do otolith organs detect linear acceleration?
the inertia of the otoconia crystals in the otolith membrane
Where are the 2 VNC inputs?
Vestibular nuclei
cerebellum
There is strong convergence between what?
There is strong convergence between vestibular, visual and somatosensory signals on second-order neurons
What does the vestibular system do?
Important in the control of posture and equilibrium
Minimizes retinal image motion during head/body movements, by rotating the eyes and keeping gaze stable in space – maintains visual acuity
Critical for the perception of spatial orientation and self-motion
Autonomic nervous system (e.g., blood pressure and heart rate)
What does the Vestibulo-spinal system do?
Influences muscle tone
produces reflexive postural adjustments of the head and body
Gaze control
Stabilizes head in space
MVST Function
What is the path for the VOR?
The short latency simple VOR path consists of 3 neurons:
1) afferent fiber 2) central VNC neuron 3) eye muscle motor neuron
What happens with a left head rotation in the VOR?
1) Left afferents excited, right inhibited
2) VNC cells on left excited
3) VNC projects excitatory input to contralateral (right) abducens neurons
4) Abducens motor neurons excite right lateral rectus
5) Abducens interneurons project back across to excite left oculomotor neurons and left medial rectus
6) Opposite action inhibitory path from right canal and circuit
What is nystagmus?
Normal nystagmus is seen during large head rotation
the VOR generates the slow phases
when eye approaches the edge of the oculomotor range, a saccade (quick phase) is generated in the opposite direction
Nystagmus is also seen with lesions, such as head trauma or temporal bone fractures
