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83 Cards in this Set
- Front
- Back
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How many cranial nerve nuclei are located in the brainstem
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Nine
Exception: CN 1, 2, (+ XI ?) |
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Alar and Basal Plates: derivatives and location
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- Motor fibers are derived from the BASAL plate and are located more medially
- Sensory fibers address from the ALAR plates and I located more laterally |
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How many nuclei associated with a cranial nerve
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Individual cranial nerve carries more than one modality and therefore have more than one nucleus associated with it.
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Reticular formation: structure and function
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– Integration and modulation info going through the brainstem
Structure – Lateral zone processes afferent information – Medial zone processes Eafford information |
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At which level of the spinal cord are all of the following apparent:
spinothalamic tract red nucleus substantia nigra basis pedunculi |
Midbrain
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At which level of the spinal cord are all of the following apparent:
Spinal trigeminal nucleus Lateral cuneate nucleus Spinal vestibular nucleus Dorsal Motor nucleus of Vegas Hypoglossal nucleus |
Open Medulla
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At which level of the spinal cord are all of the following apparent:
Spinal trigeminal nucleus Nucleus Cuneatus Nucleus Gracialis Hypoglossal nucleus |
Closed medulla
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Which landmark can used for the midbrain and micrographs
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Red nucleus
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Functions of the vestibular system
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– Sensory organ to detect body position and motion
– Equilibrium: balance and postural stability – Motor output: reflexes and controlled motor movements – Vision: control of head and eye motion and stabilization of visual gaze during head/body movement |
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Anatomical structures of the vestibular system
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– Otic capsule
– Membranous labyrinth – Perilymph – Fine connective tissue |
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Otic capsule
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In the petrous part of the temporal bone (bony labyrinth?)
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Components of the membranous labyrinth
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1) 5 vestibular sensory organs:
– 3 semicircular canals – 2 otoliths 2) Auditory cochlea 3) Endolymphatic sac |
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What are the three semicircular canals
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– Superior/anterior
– Posterior – Lateral/horizontal *arranged orthogonally to each other |
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Function of the semicircular canals
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– Detect angular ACCELERATION = head rotation [ each canal sensitive to specific plane]
– Together, specify the DIRECTION and AMPLITUDE of head rotation |
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Perilymph
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Fluid between the membranous and bony labyrinth
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Function of fine connective tissue in vestibular system
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To suspend the membranous from the bony labyrinth
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What is the bony labyrinth
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cavity in the petrous part of the temporal bone that contains the membranous labyrinth
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What are the otolithic organs?
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Urticle
Saccule = to saclike organs between the semicircular canals and the cochlea |
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Function of the otolithic organs?
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Sense body orientation and linear motion
Urticle: horizontal plane Saccule: sagittal plane |
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Composition of Perilymph + drainage
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– Similar to extracellular fluid and CSF
– Low potassium and high sodium content – Ultrafiltrate of CSF or blood – Drains via venules and middle ear mucosa |
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What is the endolymph
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Contained within contiguous open lumen of semicircular canals, urticles and saccules
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Composition of endolymph + production + absorption
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– Unique extracellular fluid
– HIGH potassium and LOW sodium content – Produced by the dark cells of the sensory epithelium – Absorbed by the endolymphatic sac |
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What are the five sensory epithelia
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Cristae of the semicircular canals [3]
Maculae of the utricle and saccule [2] |
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Hair cells function + location
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– Part of sensory epithelium
– Receptor cells for detecting movement of endolymph |
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Types of hair cells
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– Stereocilia [60-100/hair cell]
- Kinocilium [1/hair cell] |
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When neurotransmitter is released by the hair cells
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Glutamate
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What are the supporting cells to the hair cells + importance
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– Microvilli with tight junctions
– Important so that only cilia are exposed to high potassium levels |
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Are there more hair cells in the urticle/saccules or in the ampulla of the semicircular
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urticle/saccules >> Ampula
35 000 vs 8000 |
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How does endolymph motion transform into neuronal signals (at rest and in motion)
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– In the stereocilia there are stretch activated potassium channels
• In resting conditions, some channels are open and allows some membrane depolarization to occur causing activation of voltage sensitive calcium channels → glutamate release → VIII nerve excitation • Activation occur when stereocilia are pushed towards kinocilium → opening of more stretch sensitive potassium channels → more Ca enters cell → increased impulse frequency • To inhibits, move stereocilia in opposite direction of kinocilium → closing of strech receptors → hyperpolarization |
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What is the ampula
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Swelling at the end of semicircular canals
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Describe the hair cells in the ampulla
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All hair cells in the ampulla orient in the SAME direction, with kinocilium closest to utricle
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What is the cupula
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Acellular, gelatinous mass
– Hinged gate spaning the ampulla lumen – Senses motion of fluid to semicircular canals – Hair cells cilia embedded into cupula – Surrounded by endolymph |
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What is the sensory epithelium of the semicircular canals
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Cristae
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What is a sensory epithelium of the otholithic organs
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Maculae of orticle and saccule
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Describe the otholitic membrane
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acellular gelatinous mass
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What is the otoconia
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Calcium carbonate crystals that sit on top of the oncolytic membrane
– Pressure on the otoconia deflects hair cell cilium – Response to gravitational force – Detects head tilt and acceleration/deceleration |
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During a head turned to the left, what is happening to the firing rates in the left and right ampula
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– Increase firing rate on the left ampula
– Decreased firing rate on the right ampula |
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Striola
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Central curvilinear landmark within the otholithic organs
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Vestibular afferents: neuron cell type
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Bipolar
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Scarpa's ganglion
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aka Vestibular ganglion
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Path of the vestibularcochlear nerve
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int. auditory meatus --> cranial cavity --> enters brainstem at junction of pons and medulla (cebellopontine angle) --> vestibular nuclear complex & cerebellum
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Location of vestibular nuclear complex
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Dorsal pons and the medulla beneath the fourth ventricle
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What are the four vestibular nuclei
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1) lateral vestibular nucleus aka Deiter's nucleus
2) medial vestibular nucleus 3) superior & medial vestibular nuclei 4) inferior vestibular nucleus |
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Role of lateral vestibular nucleus
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Innervates gravity–opposing muscles of LIMBS to maintain POSTURE
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Role of medial vestibular nucleus
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Reflex adjustments of NECK and TRUNK muscles to RESTORE head position after disturbance
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Role of superior and medial vestibular nuclei
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– Eye movements
– This vestibulo-ocular reflux |
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Role of inferior vestibular nucleus
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Integrates multisensory input, and cerebellum to regulate VOR gain (calibration of system)
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Input to lateral vestibular nucleus
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- urticle
- saccule - semicircular canal |
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Pathway of lateral vestibular nucleus (Deiter's nucleus)
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Lateral vestibulospinal tract
– Descends entire spinal cord (mostly in ant. cord) – Uncrossed [ipsilateral] |
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Target of lateral vestibular nucleus
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Ventral horn: at Alpha & Gamma neurons that innervate gravity opposing muscles of limbs
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What senses angular acceleration (head rotation)?
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semicircular canals
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What senses linear head motion?
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urticle and saccules
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In someone falling toward their left, how does the lateral vestibular system respond?
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- innervation of hair cells from left semicirular canals, urticl ena saccule --> vest. ganglion --> CNVIII -- > lat vesticular nucleus
- left lateral vestibular nucleus activated - left lateral vestibular tract activated - uncrossed innervation of spinal cord [IPSILATERAL] - proximal left arm and leg musculature innervated to counter imbalance |
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Function of medial vestibular nucleus
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- influences neck and axial muscles
- stabalizes head in space |
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Input to medial vestibular nucleus
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primarily semicircular canals
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Medial vestibulospinal tract pathway
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- medial vestiulospinal nucleus --> tract
- descends in medial longitudinal fasciculus - bilateral projections to cervical and upper thoracic spinal cord (ipsilateral projections more dense) - motor neurons innervate neck musculature - contralateral projection cross at level of medulla |
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In someone falling toward their left, how does the medial vestibular system respond?
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- innervation of hair cells from left semicirular canals, urticl ena saccule --> vest. ganglion --> CNVIII -- > left MEDIAL vesticular nucleus
- left medial vesticular nucleus activated - activation of medial vestibulocpinal tract (decending MLF bilateral) - innervates cervial motor neurons - neck muscles respond to keep head erect |
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Function of the superior and medial vestibular nuclei
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Reflex to stabilize visual image in response to head turn
(Vestibulo-ocular reflex VOR) |
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Input to superior and medial vestibular nuclei
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Semicircular canals
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Pathways from superior and medial vestibular nuclei in VOR
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3 neuron arc
1) bipolar neuron's 2) medial and superior vestibular nuclei 3) Motor neuron's in the abducens nucleus and the oculomotor nuclei that innervate oculomotor muscles |
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Which muscles are innervated by horizontal VOR
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Lateral recti [L&R]
Medial recti [L&R] |
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Projections to medial rectus originate from
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Midbrain at oculomotor nucleus
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Projections to lateral rectus originate from
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Pons at abducens nucleus
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Describe VOR to medial rectus
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Semicircular canals --> Scarpa's ganglion --> medial vestiular nucleus (rostra medulla --> synapse --> aducens nucleus (pons) --> synapse --> MLF --> cross over --> oculomotor nucleus (midbrain) --> synapse --> innervate medial rectus
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Describe VOR to medial rectus
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Semicirular canals --> Scarpa's ganglion --> medial vestiular nucleus (rostra medulla --> synapse --> aducens nucleus (pons) --> synapse --> abducens nerve --> innervate lateral rectus
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Explain why there are 4 synapses happening in the abducens nucleus
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At the abducens nuclei, activation of the left nucleus will cause inhibition of right and thus only left lat rectus + right medial rectus will be activated in a given movement
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What is in charge of adjusting VOR and control of gain
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Inferior vestibular nucleus
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Function of Inferior vestibular nucleus
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Eye + Vestibular vestibular system --> cerebellum --> Purkinje cells --> are they them same? --> if not system recalibrate to compensate
- direct connection of where your body is moving, and a visual represeantion of what happening - detects slippage between visual and vestibular input |
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Define : Nystagmus
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Rhythmic alteration of slow (VOR) and fast (saccades) eye movements during VOR
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Pathological vs physiological nystagmus
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- saccades happen normally during normal eye movement (they are generally not perfectly smooth motions)
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Caloric testing for nystagmus
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- inject warm fluid into ear canal
- induce fluid movement on one side through semicircular - percieved by CNS as head movement ---> cause nystgmus |
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Causes of dizziness and balance disorders
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– Often difficult to diagnose
– Maybe due to vestibular dysfunction – Non-vestibular causes: fluctuations in blood pressure, Visual system problems, peripheral neuropathies |
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Benign paroxysmal positional vertigo (BPPV)
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- small part of oticonia breaks off
- can get stuck in ampulla of semicircular canals - sense gravity in linera motion - mismatch between right and left |
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Meniere's disease
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– A.k.a. endolymphatic hydrops
–problem getting rid of endolymph but you keep making it - increase in pressure of endolymph |
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Vesticular neuritis
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– Viral infection of the vestibulo-cochlear nerve or facial nerve
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Perilymph fistula
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- hole in the oval or round windows of the cochlea
- lumens are contiguous, so in case of leak you wlil get decrease in pressure of endolymph |
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Ototoxicity
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- hair cells very metabolically active and sensitive to toxins
- particularly sensitive to aminoglycoside Ab - can damage or kill hair cells |
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Mal de Debarquement
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- adjust to being on boat
- come back to land - vestibular system cannot undergo necessary plasticity to readjust to life on land - can last for days or can be permanent |
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Aging, dizziness and balance
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- common deficit of aging are problem with audition, dizziness and stability
- usually problem with hair cells dying - also get problems with visual system |
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Characteristics of bilateral vestibular dysfunction
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- could be caused by toxicity (aminoglycosides)
- slow onset of loss of vestibular function - instability of eyes with head movements - instability when walking in dark (w/o visual input) |
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Characteristics of unilateral vestibular dysfunction
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- severe acute symptoms
- extreme diziness, nausea and vomitting - deviation towards side of lesion when walking - abnormal nystagmus - displaced otoconia |
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Characteristics of vestibular compensation
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- gradual recovery from unilateral lesions
- learning induced changes to central circuits - vestibular inputs ignored in favor of vision and proprioception |
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Some common causes of dizziness due to mismatch bw vestibular and visual inputs
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- rotation induced dizziness
- false visual motion (optic ilusion) - motion sickness - alcohol |
