13: Vestibular System Flashcards
What is the peripheral receptor apparatus responsible for?
Transducing head motion/position in the inner ear
What is the central vestibular nuclei responsible for?
Integrating and distributing info that controls motor activities and spatial orientation in the brainstem
What is the vestibuloocular network responsible for?
Control of eye movements
What is the vestibulospinal network responsible for?
Coordinates head movements, axial musculature, and postural reflexes
What is the vestibulothalamocortical network responsible for?
Conscious perception of movement/spatial orientation
What is the function of semicircular canals?
Sense angular accelerations (via rotational head movements)
What are the three semicircular canals?
Horizontal
Anterior
Posterior
What is the function of the otolith organs?
Sense linear accelerations (via translational head movements)
What are two otolith organs and what do they specifically sense?
Utricle: Horizontal linear acceleration
Saccule: Vertical linear acceleration
What innervates receptor cells in vestibular organs?
Primary afferent fibers of Vestibular/Scarpa ganglion
Where do the vestibular pathways eventually terminate?
Ipsilateral vestibular nuclei and cerebellum
Where is perilymph located?
Between membranous and bony labyrinths
What is membranous labyrinth filled with?
Endolymph
What is endolymph “bathing?”
Auditory and vestibular systems
What does the movement of endolymph allow?
Responses in vestibular organs, either excitation or inhibition
What are the vestibular labyrinth organs?
Semicircular Canals
Otolith Organs
What supplies the labyrinth structures?
Labyrinthine Artery from AICA
Stylomastoid Artery
What can cause Meniere’s Disease?
Disruption (increase) of endolymph volume that can lead to endolymphatic hydrops, which is an abnormal distention of membranous labyrinth
What are the symptoms of Meniere’s Disease?
Fluctuating hearing loss Vertigo Positional Nystagmus Nausea Vomiting Tinnitus
What are some treatments for Meniere’s Disease?
Diuretics
Salt-restricted diet
Implantation of a shunt to drain excess endolymph
What activates hair cell movement?
Endolymph
What happens when stereocilia move towards or away from kinocilium?
Towards: Depolarize –> activation
Away: Hyperpolarize –> inhibition
What structure is found within the semicircular ducts?
Ampulla that extends into cupula
Where are hair cells found in semicircular ducts?
Embedded in cristae (base of ampulla)
What structure is found in the otolith organs?
Macula
How do hair cells in the macula receive input?
Otoconia on the otolith membrane will move depending on head movement, bending hair cells underneath
How is information relayed from the semicircular canals and otolith organs?
Primary afferents from the vestibular labyrinth organs form CN VIII and enter at the pontomedullary junction.
CN VIII then synapses to either superior, medial, lateral, and inferior vestibular nuclei.
How does the vestibular system send information to the cerebellum?
Vestibulocerebellar fibers go through the juxtarestiform body in the inferior cerebellar peduncle
What is the function of cerebellovestibular fibers?
Regulatory Mechanisms for eye and head movements + posture
What is subjective vertigo?
Patient experiences spinning sensation
What is objective vertigo?
Objects are spinning and patient is still
What is benign paroxysmal positional vertigo?
Brief episodes of vertigo that coincide with particular changes in body position
What can cause cupulolithiasis?
Otoconial crystals from utricle separate and get lodged in cupula of semicircular canal
What is a vestibular schwannoma?
Benign tumor from Schwann cells of vestibular root that impinges on structures traversing the internal acoustic meatus
What is vestibular neuritis?
Inflammation of vestibular nerve that can cause vertigo, nausea, and vomiting but not hearing loss
Where does the lateral vestibulospinal tract arise from?
Lateral and Inferior vestibular nuclei
What is the function of lateral vestibulospinal tract ?
Powerful control over extensors for maintenance of posture
Where does the medial vestibulospinal tract arise from?
Medial vestibular nucleus
What is the function of medial vestibulospinal tract ?
Stabilizes head via activation of neck musculature
Where do all vestibular nuclei project to?
Ventral posterior nuclear complex
What is the specific function of the vestibuloocular reflex?
Stabilizes retinal images during head movements
How does the vestibuloocular reflex work?
Movement in the semicircular ducts activate vestibular nuclei that stimulate the lateral and medial rectus muscles
If you are focusing on an object and turn your head to the left? Which CN nuclei are activated? What is inhibited?
Activated: Ipsilateral CN III (oculomotor), contralateral abducens
Inhibited: Ipsilateral abducens N.
Describe the two phases of nystagmus.
Slow phase: Vestibuloocular reflex directs eyes slowly in direction opposite to head motion
Fast phase: Eyes rapidly spring back to central position to the same direction as the head
(Named for direction of fast phase)
How is the caloric test performed?
What is a normal result?
Warm water: Nystagmus beats toward ear which warm water was poured
Cold water: Nystagmus beats away from cold water
Should be equal bilaterally
What is an abnormal result of a caloric test?
Reduced/absent nystagmus ipsilaterally
An unresponsive patient arrives in the ED. In order to evaluate the condition of the brainstem, you perform a Doll’s Eyes maneuver. What result would indicate that the patient’s brainstem was intact? What part of the brainstem?
Pt’s eyes move in opposite direction of the head turn
Reticular formation intact
