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49 Cards in this Set
- Front
- Back
What are the tracts of the medial motor pathways? |
- Anterior Corticospinal Tract
- Vestibulospinal Tract - Reticulospinal Tract - Tectospinal Tract |
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What is the function of the Lateral Vestibulospinal Tract?
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- Maintain upright posture and balance
- Excites neurons innervating extensor (anti-gravity) muscles mainly in trunk and lower limbs |
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Where does the Lateral Vestibulospinal Tract arise?
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Lateral Vestibular Nucleus (Pons)
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What do the axons of the Lateral Vestibulospinal Tract project to?
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Ipsilaterally to all levels of spinal cord (trunk and lower limbs)
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The descending axons of the Lateral Vestibulospinal Tract excite what?
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Alpha- and gamma- lower motor neurons (LMNs) that innervate extensor muscles of trunk and lower limbs (may be direct or indirect, via interneurons)
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What modifies the Lateral Vestibulospinal Tract?
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- Input to lateral vestibular nucleus from cerebellum (floccular and nodular lobes)
- Sensory receptors in utricle, saccule, and semicircular canals via CN VIII |
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What happens if there are lesions to the Vestibular N. or Vestibular Nucleus?
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Stumbling and/or falling towards the side of the lesion
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What is this dog using to stay balanced and maintain upright posture? What would happen if one of these pathways was cut on one side
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- Lateral Vestibulospinal Tract is activating the antigravity muscles to maintain posture
- If one side is lesioned, fall to the side of the lesion (because opposite side is unopposed) |
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What can cause Lateral Medullary Syndrome?
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Occlusion to vertebral a. or PICA
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What are the symptoms of Lateral Medullary Syndrome?
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- Dysphagia, dysarthria, decreased gag reflex (ipsilateral)
- Loss of pain and temp from face (ipsilateral) - Vertigo, nausea, vomiting, nystagmus (ipsilateral) - Loss of pain and temp. sensation from body (contralateral) |
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What causes the dysphagia (difficulty swallowing), dysarthria (difficult articulation of speech), and decreased gag reflex in the Lateral Medullary Syndrome? Which side?
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Lesion to nucleus ambiguus - CN XI and X - ipsilateral to lesion
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What causes loss of pain and temperature from face in the Lateral Medullary Syndrome? Which side
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Lesion to spinal tract of V - descends ipsilaterally to spinal nucleus of V - ipsilateral to lesion
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What causes the vertigo, nausea, vomiting, and nystagmus in the Lateral Medullary Syndrome? Which side?
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Lesion to Vestibular nuclei - ipsilateral to lesion
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What causes the loss of pain and temperature sensation from body in the Lateral Medullary Syndrome? Which side?
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Lesion to anterolateral system (spinothalamic tract) which decussates in spinal cord - contralateral to lesion
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If you see a checkerboard pattern of loss of pain and temperature in the face and body, what is the cause? Which side is ipsilatera/contralateral?
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- Lateral Medullary Syndrome
- Face - ipsilateral - Body - contralateral |
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What are the three functions of the Medial Vestibulospinal Tract?
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- Adjusts head position in response to changes in posture
- Coordinates eye movements with each other - Coordinates eye movements to compensate for head movements (VOR) |
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Where does the Medial Vestibulospinal Tract arise?
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Medial Vestibular Nucleus (rostral medulla)
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What do the axons of the Medial Vestibulospinal Tract project to?
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- Project bilaterally (both ipsilateral and contralateral) to ventral horn of the cervical spinal cord and to LMNs associated with the spinal accessory nerve; within the medial longitudinal fasciculus (MLF)
- Project superiorly in the MLF to the nuclei of CNs III, IV, and VI - coordinates eye movements w/ each other and w/ head movements |
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The descending axons of the Medial Vestibulospinal Tract inhibit what?
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Inhibit α-LMNs and γ-LMNs controlling neck and axial muscles
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What modifies the Medial Vestibulospinal Tract?
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Sensory information from the medial vestibular nuclei modulates activity of this pathway to adjust head position in response to changes in posture
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Which clinical conditions/processes can affect the Medial Vestibulospinal Tract?
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- Internuclear Ophthalmoplegia (INO)
- Vestibulo-ocular Reflex (VOR) - Doll's Eyes Maneuver |
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What is lesioned in an Internuclear Ophthalmoplegia (INO)?
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Lesion of the Medial Longitudinal Fasciculus (MLF)
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What are the symptoms of a lesion to the medial longitudinal fasciculus (MLF) on one side, between the nuclei of CN VII and III? Name of this disordre?
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- On attempted horizontal gaze, eye on side of lesion cannot fully adduct (look medially)
- Eye on opposite side of lesion exhibits nystagmus to side eyes are trying to look - Left MLF injury --> left INO (left eye can't adduct / medial rectus not working) * Internuclear Ophthalmoplegia * |
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What is the explanation for the symptoms of an Internuclear Ophthalmopolegia (INO)?
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Input to medial rectus m. is interrupted by interruption of signal between abducens nucleus and contralateral oculomotor nucleus
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What are some potential causes of Internuclear Ophthalmopolegia (INO)?
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- Multiple Sclerosis (loss of myelination)
- Pontine infarcts - Tumor - Trauma |
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What is the purpose of the Vestibulo-Ocular Reflex (VOR)?
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Maintain vision on stationary object while the head or body is moving
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What is the afferent component for the Vestibulo-Ocular Reflex (VOR)? Efferent?
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- Afferent: neck proprioceptors and CN VIII
- Efferent: Medial Vestibulospinal Tract to abducens nucleus and via MLF to oculomotor nucleus |
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What happens if the Vestibulo-Ocular Reflex (VOR) is normal?
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If brainstem vestibular connections are intact, head movements result in conjugate eye movements that are equal and opposite to the side of the head movement
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If your Vestibulo-Ocular Reflex (VOR) is abnormal, what does this mean?
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- Eye movement goes with the head movement
- Brainstem dysfunction - Medial Vestibulospinal Tract is not intact |
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What is the Doll's Eye Maneuver used for? What must you rule out before doing it?
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- For brainstem evaluation in a comatose patient
- Cervical spinal injury must be ruled out before attempting this maneuver!!! |
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What do you do in the Doll's Eye Maneuver?
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- Turn head in one direction should cause eyes to turn in opposite direction
- Indicates pathways connecting vestibular nuclei in medulla to extraocular nuclei in pons and midbrain are functioning and brainstem is intact - Absence of response indicates brainstem dysfunction (interruption of MLF) |
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What is the function of the Corticotectal Tract and the Tectospinal Tract?
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- Facilitate reflexive turning movements of eyes and head
- Also facilitate upward gaze - Helps you move your eyes and head to something that caught your attention (e.g., pitcher sees baseball player trying to steal base and turns to look at him) |
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Where do the Corticotectal fibers arise? Project to?
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- Retina
- Visual cortex - Inferior parietal lobes - Project to Superior Colliculus |
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Where do the Tectospinal fibers arise? Project to?
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- Superior Colliculus
- Decussate in dorsal tegmentum - Terminate in contrlateral cervical spinal cord (CN XI nucleus - SCM) - Other fibers project to the pontine paramedian reticular formation (PRRF) and then via the medial longitudinal fasciculus (MLF) to control extraocular muscles for upward gaze |
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Which clinical concern affects the Corticotectal Tract and Tectospinal Tract?
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Parinaud's Syndrome / Dorsal Midbrain Syndrome / Collicular Syndrome
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What is lesioned in Parinaud's Syndrome / Dorsal Midbrain Syndrome / Collicular Syndrome?
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- Superior Colliculus or Posterior Commissure of Midbrain
- Leads to a lesion of the Corticotectal Tract / Tectospinal Tract (control movements of eye, head, and upward gaze) |
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What are the implications of a lesion to the superior colliculus or posterior commissure of the midbrain?
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- Impaired vertical / upward gaze
- Large, irregular pupils w/ light-near dissociation (pupils do not constrict w/ light but do constrict w/ accommodation) - Eyelid abnormalities (retraction or ptosis) - Convergence - retraction nystagmus (attempted upward gaze --> eyes oscillate between convergence and retraction) |
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If a patient can not gaze upward, what is this a sign of?
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- Parinaud's Syndrome / Dorsal Midbrain Syndrome / Collicular Syndrome
- Superior Colliculus or Posterior Commissure of Midbrain lesion - Leads to a lesion of the Corticotectal Tract / Tectospinal Tract (control movements of eye, head, and upward gaze) |
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What are some common causes of Parinaud's Syndrome / Dorsal Midbrain Syndrome / Collicular Syndrome?
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- Hydrocephalus resulting from aqueductal stenosis
- Pineal gland tumors |
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What is the reticular formation composed of?
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Scattered groups of neuron cell bodies and fibers that extend throughout the brain
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What are the functions of the Reticulospinal Tracts?
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- Help maintain upright posture by influencing voluntary and reflexive movements
- Inhibit (LRST) or exciting (MRST) motor neurons innervating axial musculature - Convey autonomic information from higher levels to influence respiration, circulation, sweating, shivering, pupil dilation, and sphincter muscles of GI and urinary tracts |
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What is the other name for the Lateral Reticulospinal Tract? Function?
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- Medullary Reticulospinal Tract
- M for Medulla = Mellows = Inhibits extensor spinal reflex actively by inhibiting spinal motor neurons (Also, ascending fibers project to intralaminar and thalamic nuclei to play a role in arousal and sleep) |
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What is the other name for the Medial Reticulospinal Tract? Function?
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- Pontine Reticulospinal Tract
- P for Pontine = Pump up! = Excites spinal motor neurons that innervate axial muscles and leg extensors |
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What is the pathway of the Lateral (Medullary) Reticulospinal Tract (LRST)?
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- Axons (crossed and uncrossed) descend bilaterally through lateral funiculus to all spinal cord levels
- Also, ascending fibers of LRST project to intralaminar and and thalamic nuclei (arousal and sleep) |
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What is the pathway of the Medial (Pontine) Reticulospinal Tract (LRST)?
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Axons descend ipsilaterally in the anterior funiculus to all spinal cord levels
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Which clinical condition affects the Medial and Lateral Reticulospinal Tracts?
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Decerebrate Posturing / Decerebrate Rigidity
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What are the symptoms of Decerebrate Posturing / Decerebrate Rigidity?
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- Increased muscle tone
- Extension of upper and lower limbs with arms adducted and medially rotated - Arched back - Feet extended - Toes curled |
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What is the explanation for the symptoms of Decerebrate Posturing / Decerebrate Rigidity?
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- Transection of brain between superior and inferior colliculi in midbrain
- Removes excitatory cortical input to INHIBITORY LRST (medulla) - Ascending input to MRST (pons) is still intact - Facilitory influence of MRST is now unopposed by inhibitory influence of LRST - Leads to facilitation of extensor motor neurons |
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What is Locked-In Syndrome?
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Patient is aware and awake but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in body except for eyes
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