Vestibular Flashcards
Ex II
What are the different regions of the membranous labyrinth? Where are the perilymph and endolymph?
Semicircular ducts (sensitive to turning the head) Saccule and utricle (within vestibule, sensitive to lateral motion & head tilt) Endolymph: within cochlear duct and membranous labyrinth Perilymph: around cochlear duct and membranous labyrinth (scala tympani and vestibule plus area around semicircular ducts, saccule, and utricle)
What is Meniere’s disease and what causes it?
Transient vertigo and dizziness, nausea, vomiting, and abnormal saccadic movements due to excess endolymph secretion and resulting increased pressure.
Describe the structure and function of the crista.
Receptors located in the ampullae of semicircular canals (one each) stimulated by stopping and starting of rotary movements of the head.
Epithelium of hair cells and supporting cells make up a “cupula” (gelatinous mass), entire cupula bends with movement, bending stereocilia on receptor cells.
How does endolymph move? What is detected by the semicircular ducts?
Endolymph is secreted by the cochlear duct and drains into the dural sinuses via the endolymphatic duct.
Fluid fills semicircular ducts. When you turn your head there is some relative movement between the fluid and the ducts (fluid is more or less static), which moves the cupulae. Thus, semicircular ducts detect head rotation.
Describe the structure and function of the saccule and utricle. What do they respond to and what is the mechanism?
The sensory systems of these structures are called maculae. They consist of an epithelium with receptor cells and supporting cells. The stereocilia of the receptor cells project up into a gelatinous layer, which is topped by a layer of otoliths (Ca2CO3 crystals).
Saccule: vertical plane. Utricle: horizontal.
Respond to acceleration in the direction of hair cell alignment: otoliths shift during movement, bending hair cell stereocilia.
Briefly describe acoustic neuromas and their impact on vestibular function.
Acoustic neuroma is a benign tumor of the myelinating cells on vestibular nerve. Impinges on vestibular and cochlear nerves, resulting in unstable gait, vertigo, nausea, and vomiting for the former and deafness/tinnitus for the latter.
What causes benign paroxysmal positional vertigo?
Otoliths from the utricle fall into semicircular canals and stimulate the crista, telling your brain think you’re moving when you’re not. You feel funny because of the disparity between vestibular and somatosensory information.
To what structures do the vestibular nuclei project vestibular information?
Thalamus and cortex (make you conscious of movement)
Abducent, trochlear and oculomotor nuclei (eye movement)
Spinal cord (postural control)
Autonomics (vascular control–baroreflex)
Cerebellum (talks back to vestibular nuclei for reflexes)
Describe the vestibule-ocular reflex (VOR). How does the cerebellum impact this?
Adjusts eye movements so you can keep your eyes fixed on an object even when you move your head. Head rotation triggers inhibitory signal to muscles on one side of eye and excitatory signal to other side, so eyes turn to compensate.
Requires input from the vestibulo-cerebellum for precision.
What is nystagmus? Does it occur normally or only pathologically?
Another word for involuntary saccadic movements.
Normal (physiological): when eyeball is moving, part of VOR
Pathologic: when eyeball is at rest, problem with vestibular system.
What does the vestibule-sympathetic reflex do?
Vestibular nuclei project to the RVLM, which innervates the IML column of the spinal cord. Enhances vasoconstriction to keep you from fainting during postural changes or emotional stress.
Also makes you sweaty and pale when nauseous.
Where is the vestibular cortex? How does it relate to other sensory modalities? What is autoscopy?
Vestibular cortex is several cortical areas concentrated around the TPJ: temporal parietal junction.
The TPJ is involved in embodiment: the sense of being localized in one’s own body. This requires convergence of visual, auditory, somatosensory, and vestibular inputs.
Autoscopy is seeing one’s body separately, as in an out-of-body experience, caused by a lack of congruence between sensory inputs.
What impact does the vestibular system have on cerebral circulation, and under what circumstances?
Dilates cerebral blood vessels to enhance blood flow via sympathetic inhibition (inhibit vasoconstriction via RVLM) and pterygopalatine ganglion (vasodilate).
Maintains cerebral blood flow so you don’t faint when you stand up.
