Term
| what is the function of the vestibular system |
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Definition
| the vestibular system provides a sense of balance along with information regarding body position; allows rapid compensatory movements in response to both self-induced and externally generated forces |
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Term
| where is the peripheral portion of the vestibular system located |
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Definition
|
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Term
| what is the peripheral vestibular system in the inner ear like? |
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Definition
| a tiny accelerometer/guidance device that continually conveys information concerning motion and head and body position to integrative centers in the CNS |
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Term
| what does the vestibular system constantly work to do? |
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Definition
| keep posture/balance/equilibrium |
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Term
| what 2 functions is the vestibular system a key component in? |
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Definition
| postural reflexes and eye movements |
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Term
| what functions are impaired when the vestibular system is damaged |
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Definition
| balance, sense of orientation in space, control of eye movements when the head is moving |
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Term
| where is much of the circuitry of the vestibular system locate |
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Definition
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Term
| what might vestibular dysfunction indicate |
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Definition
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Term
| what is the main peripheral component of the vestibular system? |
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Definition
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Term
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Definition
| set of inter-connected canals |
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Term
| what do hair cells in the labyrinth do |
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Definition
| transduce physical motion into neural impulses |
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Term
| where is the labyrinth located |
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Definition
| deep within the temporal bone |
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Term
| what does the labyrinth consist of |
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Definition
| 2 otolith organs, 3 semicircular canals |
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Term
| what are the 2 otolith organs |
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Definition
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Term
| what is the function of the sacculus and utricle |
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Definition
| sacculus and utricle are specialized to respond to linear accelerations of the head and static head positions relative to gravity |
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Term
| what is the function of the semicircular cnals |
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Definition
| the semicircular canals are specialized to respond to rotational acceleration of the head |
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Term
| when I'm sleeping at night, what part of the labyrinth detects which way my head is laying? |
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Definition
| utricle and sacculus (static position relative to gravity) |
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Term
| when I'm spinning around, which part of the labyrinth determines where my head is |
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Definition
| semicircular canals (rotational acceleration of the head) |
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Term
| where are hair cells located |
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Definition
| within the utricle, saccule, and ampullae |
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Term
| what are ampullae and where are they |
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Definition
| 3 swellings located at the base of the semicircular canals that contain specialized hair cells |
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Term
| how do hair cells transduce motion into neural impulses? |
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Definition
| The hair cells project tiny stereocilia into endolymph fluid within the labyrinth. The endolymph is moved with head motion. Movement of the endolymph displaces the stereocilia, producing action potentials in CN VIII |
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Term
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Definition
| fluid in the labyrinth that circulates throughout the semicircular canals |
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Term
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Definition
| little hairs projecting out of the specialized hair cells in the labyrinth |
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Term
| in how many degrees of freedom does body movement occur |
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Definition
|
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Term
| what are the 2 types of body movement degrees of freedom? |
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Definition
| translational, rotational |
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Term
| what are translational movements |
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Definition
| linear movements along the X, Y, Z axes |
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Term
| which part of the labyrinth is concerned with translational movements including linear acceleration and static displacement |
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Definition
| otolith organs: utricle and saccule |
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Term
| what are rotational movements |
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Definition
| rotation about the X, Y, Z axes: roll, pitch, yaw |
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Term
| which part of the labyrinth is concerned with rotational movements |
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Definition
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Term
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Definition
| rolling about the x axis, as in doing cartwheels to the side |
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Term
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Definition
| rolling about the y axis, same direction as when you pitch a baseball or do a forward flip |
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Term
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Definition
| spinning around the z axis, straight up and down |
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Term
| what do the otolith organs detect |
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Definition
| translational movements like displacement and linear acceleration |
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Term
| what special sensory epithelium do the utricle and saccule contain |
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Definition
|
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Term
|
Definition
| sensory epithelium in the utricle and saccule that consists of hair cells and supporting cells with an overlying gelatinous layer |
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Term
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Definition
| the fibrous otolithic membrane |
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Term
| what is embedded in the otolithic membrane |
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Definition
| tiny crystals of calcium carbonate called otoconia |
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Term
| what is the function of otoconia |
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Definition
| otoconia cause the otolithic membrane to be heavier than surrounding structures so that when the head moves, a shearing motion occurs between the otolithic membrane and the macula, displacing hair cells and generating action potentials in CN VIII |
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Term
| which otolith organ responds to movements of the head in the horizontal plane such as sideways head motions and rapid lateral displacements |
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Definition
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Term
| what is at the base of each of the 3 semicircular canals? |
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Definition
|
|
Term
| what is inside each ampulla |
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Definition
| sensory epithelium (crista) and the hair cells |
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Term
| what do the hair cells in the ampulla project into |
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Definition
| gelatinous mass called the cupula, surrounded by endolymph |
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Term
| what is the result of movement on the endolymph and cupula |
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Definition
| movement of the endolymph, distortion of the cupula |
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Term
| what happens when the head turns in the plane of one of the semicircular canals? |
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Definition
| the inertia of the endolymph produces a force across the cupula, distending it away from from the direction of the head movement and ultimately depolarizing the hair cells, resulting in increased neuronal activity in CN VIII |
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Term
| what is the coordination in function of the semicircular canals? |
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Definition
| each semicircular canal works in concert with a partner on the opposite side of the head |
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Term
| what are the 3 pairings of semicircular canals? |
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Definition
| the 2 horizontal canals form a pair; the right anterior and left posterior canals form a pair; the right posteiror and left anterior canals form a pair |
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|
Term
| compare the direction of deformation of the cupula for the 2 partners |
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Definition
| head rotation deforms the cupula in opposing directions for the two partners, resulting in opposite changes in firing rates |
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Term
| how does the CNS know when my head is still |
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Definition
| the semicircular canals fire the same on each side |
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Term
| what are central vestibular pathways |
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Definition
| important pathways that control eye, head, and postural reflexes |
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Term
| what type of neurons are the sensory neurons of CN VIII |
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Definition
|
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Term
| where do the cell bodies of CN VIII reside |
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Definition
|
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Term
| what do the distal processes of sensory neurons of CN VIII innervate? |
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Definition
| semicircular canals, otolith organs |
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Term
| what do the central processes of the sensory neurons of CN VIII project to |
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Definition
| vestibular nuclei in the brainstem |
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Term
| to where do the vestibular nuclei project |
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Definition
| cranial nerve nuclei that control eye movements; spinal cord; thalamus; cerebellum |
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Term
| where are the vestibular nuclei located |
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Definition
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Term
| what is the function of the vestibular ocular reflex |
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Definition
| permits eye movements that counter head movements; allows eyes to stay fixed when head is turned |
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Term
| if you turn your head to the left while focusing on an object in front of you, in what direction will your eyes reflexively move? |
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Definition
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Term
| what is the first step in activating the vestibular ocular reflex when your head turns to the left? |
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Definition
| activity in the left semicircular canal detects leftward rotation and excites neurons in the left vestibular nucleus |
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Term
| which part of the vestibular nucleus is stimulated by neurons from the semicircular canal when you turn your head |
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Definition
| medial vestibular nucleus |
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Term
| what happens after the medial vestibular nucleus is stimulated in head rotation? |
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Definition
| excitatory fibers from the medial vestibular nucleus cross to innervate the contralateral abducens nucleus |
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Term
| what happens after the contralateral abducens nucleus is stimulated by the medial vestibular nucleus in head rotaiton? |
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Definition
| 2 outputs project from the abducens nucleus |
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Term
| what 2 outputs project form the abducens nucleus following its stimulation in head rotation? |
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Definition
| excitatory fibers contract the lateral rectus of the ipsilateral eye; excitatory projections cross the midline and ascend via the medial longitudinal fasciculus to the left oculomotor nucleus, contracting the left medial rectus |
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Term
| what are the steps of the vestibulo-ocular reflex when you turn your head to the left |
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Definition
| 1. The left semicirucular canal increases its firing rate to the vestibular nucleus. 2. Projections from the medial vestibular nucleus cross to innervate the contralateral (right) abducens nucleus. 3a. Excitatory fibers from the right abducens nucleus contract the lateral rectus of the right eye. 3b. Excitatory projections from the right abducens nucleus cross the midline and ascend via the medial longitudinal fascuiculs to the left oculomotor nuclues to contract hte left medial rectus |
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Term
| what inhibitory responses occur during the vestibulo-ocular reflex when turning your head to the left? |
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Definition
| inhibitory projections from the medial vestibular nucleus to the left abducens nucles decreases activity of the left lateral rectus; inhibitory fibers project to the oculomotor nucleus and cause the riht medial rectus to relax |
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Term
| what is the response of excitatory inputs from the semicircular canal on only one side |
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Definition
| eye movements toward the opposite side |
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|
Term
| turning the head to the left produces reflexive eye mvoement in what direction |
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Definition
|
|
Term
| what projections to where are requried for posture adjustments of the head and body |
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Definition
| descending projections from vestibular nuclei to the spinal cord |
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|
Term
| are postural reflexes fast or slow |
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Definition
|
|
Term
| what happens when I trip forward |
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Definition
| the semicircular canals are activated and projects info to the medial vestibular nucleus in the medulla. From there, I send bilateral projections into the spinal cord through the medial vestibulospinal tract. The medial vestibulospinal tracts synapse on areas of the gray matter that control axial/postural muscles to maintain balance |
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|
Term
| how does the medial vestibulospinal tract affect head position |
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Definition
| the medial vestibulospinal tract activates neck muscles and reflexively regulates head position by pulling the head up during a fall |
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Term
| what is the vestibulocervical reflex t |
|
Definition
| the activation of neck muscles by the medial vestibulospinal tract during a fall |
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|
Term
| what happens following extension of the neck during a fall |
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Definition
| extension of the neck can stimulate other reflexes such as forelimb extension to help stabilize body during a fall |
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|
Term
| where do inputs from the otolith organs primarily project |
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Definition
| lateral vestibular nucleus |
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|
Term
| what pathway do axons from the lateral vestibular nucleus form? |
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Definition
| lateral vestibulospinal tract |
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|
Term
| where do axons from the lateral vestibular nucleus that form the lateral vestibulospinal tract synapse? |
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Definition
| on LMNs that innervate axial and proximal limb muscles ipsilaterally |
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|
Term
| what is the function of the lateral vestibulospinal tract |
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Definition
| This pathway mediates balance and maintains upright posture by exciting extensor motor neuron muscle pools and inhibiting flexor motor neuron muscle pools |
|
|
Term
| where is the lateral vestibular nucleus |
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Definition
|
|
Term
| where is the medial vestibular nucleus |
|
Definition
|
|
Term
| which tract helsp straigthen you out when you start to lean too far to one dside? |
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Definition
| lateral vestibuospinal tract |
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|
Term
| what are symptoms of patients with vestibular damage? |
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Definition
| diminished postural stability, gait alterations, difficulty balancing |
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Term
| what 3 things are required for normal balance |
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Definition
| vision, vestibular function, proprioception |
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|
Term
| to where do the superior and lateral vestibular nuclei project |
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Definition
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Term
| to where does the thalamus relay information from the superior and lateral vestibular nuclei |
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Definition
| specific cortical areas involved in the perception of body orientation; lateral and superior vestibular nuclei project positional information to the sensory cortex for integration with other proprioceptive-type input |
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|
Term
| what can testing the vestibular system by observing eye movements give you information about? |
|
Definition
| integrity of the brainstem |
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|
Term
| why do reflexive eye movements not occur when the head is not rotatin |
|
Definition
| output from both vestibular nerves is equal |
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|
Term
| when the head is rotated in the horizontal plane, how does output from vestibular nerves on each side of the head change |
|
Definition
| ipsilateral vestibular afferents increase while contralateral vestibular afferents decrease their firing rates |
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|
Term
| what does the net difference in firing rates of vestiblar afferents do to eye movements as the head turns when you aren't trying to look at one spot while you turn your head |
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Definition
| leads to a slow movement of the eyes to counter the head motion followed by a fast saccadic motion to reset the eyes |
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|
Term
| what is physiological nystagmus |
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Definition
| the normal slow movement of the eyes that counters head motion followed by a fast saccadic eye motion to reset the eyes that occurs when you turn your head to look in a different directoin |
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|
Term
| is physiological nystagmus normal |
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Definition
|
|
Term
| is pathologic nystagmus normal |
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Definition
|
|
Term
| hen does pathologic nystagmus occur |
|
Definition
| pathologic nystagmus can occur if there is unilateral damage to the vestibular system |
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|
Term
| what happens in pathologic nystagmus |
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Definition
| the damaged side of the vestibular system fails to spontaneously fire, producing an unphysiological difference in firing rates between the two sides and causing nystagmus without accompanying head movements |
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|
Term
| how to test vestibular system |
|
Definition
|
|
Term
| if you irrigate one ear with cold water, what happens |
|
Definition
| irrigating with cold water leads to eye movement because convection currents in the canal mimic rotary head movements away from the irrigated ear. You'll see slow eye movement toward the irrigated ear and fast movement away |
|
|
Term
| what does cold water in the ear do to endolymph movment |
|
Definition
|
|
Term
| what is the vestibular response to cold water in the ear |
|
Definition
| decreased signals from that side, makes CNS think you're turning your head away from the irrigated ear |
|
|
Term
| does the examiner detect the fast eye movement or the slow eye movement |
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Definition
|
|
Term
| what is the response of warm water irrigation in an ear |
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Definition
| warm water induces slow eye movement away the irrigated ear and a fast saccade toward the irrigated ear. |
|
|
Term
| what is the COWS mnemonic |
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Definition
| cold opposite, warm same: for cold irrigation, saccade is away. For warm irrigation, saccade is toward the irrigation |
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