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The vestibular receptors are what structures?
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The utricle and the saccule each contain a sensory receptor. What is the name of this sensory receptor?
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Vestibular System
Neuroscience
| Question | Answer |
|---|---|
| The vestibular receptors are what structures? | the utricle and the saccule |
| The utricle and the saccule each contain a sensory receptor. What is the name of this sensory receptor? | the macula (otolith organ) |
| One end of each semicircular duct is dilated (ampulla) and contains a sensory receptor. What is the name of this sensory receptor within the ampulla? | crista ampullaris |
| Vestibular receptors transduce stimuli of movement and postition of the head into what that are then sent to the brain? | neural signals |
| True or False - The 3 cristae and the 2 maculae contain hair cells (sensory transducers) | True, the three cristae and the two maculae contain hair cells, which are also called sensory receptors. |
| What is the longest of all the finger-like projections? | kinocilium |
| Approximately how many hair cells are there? How are they arranged? | There are 60-100 stereocilia; arranged in rows of varying height. The longest stereocilia are next to the kinocilium. As one moves away from the kinocilium, the stereocilia become progressively shorter. |
| What does this type of arrangement do to the hair cell anatomically and physiologically? | This arrangement polarizes the hair cell anatomically and physiologically. |
| The bending of stereocilia causes changes in what across the cell membrane? | The bending of the stereocilia causes changes in the flow of ions across cell membrane. |
| When the stereocilia bends towards the kinocilium, what happens to the cell? What does the cell release? Is there an increase or decrease in the number of action potentials and firing rate of sensory nerve fibers? | -Cell becomes depolarized -Cell releases Neurotransmitter (glutamate or aspartate) -Increase in action potentials and firing rate of sensory nerve fibers. - |
| Bending of stereocilia away from the kinocilium causes what? | Cell hyperpolarization and decreased rate of firing. |
| The vestibular part of CN VIII also contains some efferent fibers from where? Where do these efferent fibers synapse? What may they control? | -From small collection of cells in pons, just lateral to abducens nucleus -Synapse w/ hair cells or their afferent fibers -May control sensitivity of hair cells. |
| Describe what the maculae are. | The Maculae are 2 patches of hair cells and supporting cells located in the walls of the utricle and saccule (one maculae is in each) |
| When the head is upright, the utricular macula is roughly _________ and the saccule macule is roughly _________. | utricle maculae is roughly horizontal; sacular macula is roughtly verticle. |
| Hairs are embedded in what? | The otolithic membrane, which is a gelatinous membrane with little crystals of Ca Carbonate (otoliths, otoconia) |
| Displacement of the otolithic membrane causes what? | bending of stereocilia, some cells are depolarized and some are hyperpolarized (polarity of all cells is not the same in all areas of the macula) |
| The otolithic membrane of each macula contains a small, curving depression which roughly bisects the underlying macula. What is this depression called? | striola |
| Hair cells in utricle macula are polarized so that kinocilium of each cell faces what structure? | the striola |
| Kinocilia of saccular hair cells are located on the side . . . | away from the striola (**memory trick --> two s's will repel each other, like two north ends of a magnet) |
| Because the strola curves through the macula, hair cells are polarized in many __________ directions. | different |
| Maculae respond to position of head with respect to what? | Gravity, Linear Acceleration, and tilting of the head |
| forward and backward tilting --> | pitch |
| side to side tilting --> | roll |
| What does the Crista Ampullaris respond to? | rotational/angular acceleration |
| Anatomically describe where/what the Crista Ampullaris is. | The Crista Ampullaris is a transversely oriented ridge of tissue (containing hair cells and supporting cells) located in the ampulla of each semicircular duct. |
| The hair cells of the Crista Ampullaris are covered by what? | Hairs of the Crista Ampullaris are covered by a gelatinous mass (cupula), which extends across ampulla as a partition |
| All hair cells in a crista ampullaris have the _______ polarization. | same. deflection of cupula in one direction causes all cells to depolarize and afferent fibers to increase firing rate. Deflection of cupula in opposite direction causes all cells to hyperpolarize and a decrease in firing rate of afferent fibers. |
| Each semicircular duct responds best to angular acceleration in a... | ... particular plane. Because ducts are arranged in roughly orthogonal planes, movements in any direction can be detected. |
| Lateral (horizontal) semicircular ducts are almost __________ (tilted backward ___ w/ respect to horizontal plane) | horizontal, 30 degrees |
| Anterior and Posterior semicircular ducts are roughly ________ & _________ to each other. | vertical and perpendicular to each other |
| Anterior semicircular duct on one side is _________ to posterior semicircular duct on the other side. Anterior duct of one side forms a __________________ with posterior duct of the other side. | parallel; functional pair |
| Horizontal ducts of two sides form a . . . | functional pair |
| Hair cells in the two ducts of a functional pair are ____________ polarized. The two ducts respond in ___________ ways to head movements which affect them. | oppositely polarized; opposite ways |
| Neurons in the vestibular nuclei act as what? | comparator units |
| Neurons in the vestibular nuclei act as comparator units. What do they interpret? | Interpret head rotation on basis of relative discharge rates of left and right semicircular canals. |
| Primary sensory (afferent) vestibular neurons are _______ neurons. Their cell bodies form _________, located within the internal acoustic meatus. | bipolar neurons, their cell bodies form vestibular ganglions |
| The peripheral processes (dendrites) of the primary sensory (afferent) vestibular neurons innervate what? | Hair cells of maculae and cristae ampullares. |
| The central processes of the primary sensory (afferent) sensory vestibular neurons form what? | The Vestibular part of CN VIII --> enters brainstem at lateral end of the pontomedullary junction (pontocerebellar angle) |
| Most of their central processes (axons) terminate in what? | Vestibular Nuclei (superior, inferior, lateral, and medial) |
| Where are the vestibular nuclei located? | Vestibular nuclei located in posterolateral part of upper medulla and lower pons, immediately underneath floor of 4th ventricle. |
| A few central processes (axons) travel directly to cerebellum via what? Where do these central processes terminate? | juxtarestiform body (primary vesitibulocerebellar fibers); terminate in cortex of flocculo-nodular lobe and fastigial nucleus (most medial of cerebellar nuclei) |
| Fibers that originate from vestibular nuclei terminate in 3 main areas of the CNS. Name them. | 1. spinal cord 2. cerebellum 3. nuclei of ocular motion |
| The lateral vestibulospinal tract consists of axons that orginate mostly from what? | lateral vestibular nucleus |
| How does the lateral vestibulospinal tract descend? | ipsilaterally, in anterior funiculus of spinal cord. |
| What does the lateral vestibulospinal tract do? | Exerts excitatory influence on motor neurons that innervate paravertebral and limb extensor muscles. |
| The medial vestibulospinal tract consists of what? | axons that originate primarily from medial vestibular nucleus (some fibers also originate from lateral and inferior vestibular nuclei) |
| How does the medial vestibulospinal tract descend? | The medial vestibulospinal tract descends bilaterally in the anterior funiculus of the spinal cord as part of the medial longitudinal fasciculus (MLF) |
| Where does the medial vestibulospinal tract project to? | only to cervical spinal cord segments --> controls neck muscles. Plays a role in stabilizing head position. |
| The Vestibular ganglion and the vestibular nuclei send fibers to the cerebellum (vestibulocerebellum) vis what? | restiform body. Primary vestibulocerebellar fibers are sent by the vestibular ganglion; secondary vestibulocerebellar fibers are sent by vestibular nuclei. |
| Cerebellum sends fibers to vestibular nuclei vis what? | restiform body |
| Vestibular nuclei send fibers to motor nuclei of CN's III, IV, and VI via what? These connections are important how? | MLF; these connections are important in controlling eye movements in response to changes in head position. |
| Perception of motion and spatial orientation arise through convergence of information from what 3 systems at what level? | vestibular, visual, and somatosensory systems at thalmocortical levels. |
| Vestibular nuclei project __________ to thalamus (ventral posterolateral nucleus and posterior nuclei) | bilaterally |
| Thalamic neurons project to two cortical areas located where? | at the inferior end of the primary somatosensory cortex (areas 3a and 2v) |
| What is nystagmus? What phase it is named for? | Nystagmus is a conjugate type of eye movement with a slow phase and fast phase; named after fast phase. <a type of vestibular dysfunction> |
| What is vertigo? | Perception of body motion, when no real motion is occuring; accompanied w/ vomiting, nausea, light-headedness and fainting. |
| benign paroxysmal positional vertigo | brief episodes of vertigo coinciding with changes in body postition; triggered by bending over, ect. |
| What is the hypothesized pathology of benign paroxysmal positional vertigo? | Posterior semicircular duct abnormalities seem to be implicated |
| What, theoretically, happens to the posterior semicircular duct? | otoconial crystals from uticular macula separate from otolithic membrane and become lodged in cupula of crista ampullaries of posterior semicircular duct (cupulolithiasis) |
| What, then, causes the abnormal cupula deflections? | Increased density of cupula causes abnormal cupula deflections when head changes position relative to gravity. |
| Describe the characteristics/symptoms of Meniere's Disease. | recurrent episodes of vertigo accompanied by hearing loss, tinnitis (ringing in the ears), nystagmus, nausea, and vomiting. |
| What is Meniere's Disease probably cause by? | Meniere's Disease is probably caused by an imbalance between production and reabsorption of endolymph --> excessive amt of endolymph and distention of membranous labyrinth (endolymph hydrops) |
| What is the first course of treatment for Meniere's Disease? | diuretic and salt-restricted diet |
| What are second treatment options for Meniere's Disease? | implantation of shunt to drain excess of endolymph into CSF; delivery of vestibulotoxic drug (gentimicin) into perilymph to cause permanent loss of vestibular function on affected side, vestibular nerve section. |
Created by:
Lisa1585