Neuro: 3.05 - Medial Motor Pathways

Front 1

What are the tracts of the medial motor pathways?

Back 1

- Anterior Corticospinal Tract
- Vestibulospinal Tract
- Reticulospinal Tract
- Tectospinal Tract

Front 2

What is the function of the Lateral Vestibulospinal Tract?

Back 2

- Maintain upright posture and balance
- Excites neurons innervating extensor (anti-gravity) muscles mainly in trunk and lower limbs

Front 3

Where does the Lateral Vestibulospinal Tract arise?

Back 3

Lateral Vestibular Nucleus (Pons)

Front 4

What do the axons of the Lateral Vestibulospinal Tract project to?

Back 4

Ipsilaterally to all levels of spinal cord (trunk and lower limbs)

Front 5

The descending axons of the Lateral Vestibulospinal Tract excite what?

Back 5

Alpha- and gamma- lower motor neurons (LMNs) that innervate extensor muscles of trunk and lower limbs (may be direct or indirect, via interneurons)

Front 6

What modifies the Lateral Vestibulospinal Tract?

Back 6

- Input to lateral vestibular nucleus from cerebellum (floccular and nodular lobes)
- Sensory receptors in utricle, saccule, and semicircular canals via CN VIII

Front 7

What happens if there are lesions to the Vestibular N. or Vestibular Nucleus?

Back 7

Stumbling and/or falling towards the side of the lesion

Front 8

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

Back 8

- 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)

Front 9

What can cause Lateral Medullary Syndrome?

Back 9

Occlusion to vertebral a. or PICA

Front 10

What are the symptoms of Lateral Medullary Syndrome?

Back 10

- 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)

Front 11

What causes the dysphagia (difficulty swallowing), dysarthria (difficult articulation of speech), and decreased gag reflex in the Lateral Medullary Syndrome? Which side?

Back 11

Lesion to nucleus ambiguus - CN XI and X - ipsilateral to lesion

Front 12

What causes loss of pain and temperature from face in the Lateral Medullary Syndrome? Which side

Back 12

Lesion to spinal tract of V - descends ipsilaterally to spinal nucleus of V - ipsilateral to lesion

Front 13

What causes the vertigo, nausea, vomiting, and nystagmus in the Lateral Medullary Syndrome? Which side?

Back 13

Lesion to Vestibular nuclei - ipsilateral to lesion

Front 14

What causes the loss of pain and temperature sensation from body in the Lateral Medullary Syndrome? Which side?

Back 14

Lesion to anterolateral system (spinothalamic tract) which decussates in spinal cord - contralateral to lesion

Front 15

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?

Back 15

- Lateral Medullary Syndrome
- Face - ipsilateral
- Body - contralateral

Front 16

What are the three functions of the Medial Vestibulospinal Tract?

Back 16

- Adjusts head position in response to changes in posture
- Coordinates eye movements with each other
- Coordinates eye movements to compensate for head movements (VOR)

Front 17

Where does the Medial Vestibulospinal Tract arise?

Back 17

Medial Vestibular Nucleus (rostral medulla)

Front 18

What do the axons of the Medial Vestibulospinal Tract project to?

Back 18

- 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

Front 19

The descending axons of the Medial Vestibulospinal Tract inhibit what?

Back 19

Inhibit α-LMNs and γ-LMNs controlling neck and axial muscles

Front 20

What modifies the Medial Vestibulospinal Tract?

Back 20

Sensory information from the medial vestibular nuclei modulates activity of this pathway to adjust head position in response to changes in posture

Front 21

Which clinical conditions/processes can affect the Medial Vestibulospinal Tract?

Back 21

- Internuclear Ophthalmoplegia (INO)
- Vestibulo-ocular Reflex (VOR)
- Doll's Eyes Maneuver

Front 22

What is lesioned in an Internuclear Ophthalmoplegia (INO)?

Back 22

Lesion of the Medial Longitudinal Fasciculus (MLF)

Front 23

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?

Back 23

- 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 *

Front 24

What is the explanation for the symptoms of an Internuclear Ophthalmopolegia (INO)?

Back 24

Input to medial rectus m. is interrupted by interruption of signal between abducens nucleus and contralateral oculomotor nucleus

Front 25

What are some potential causes of Internuclear Ophthalmopolegia (INO)?

Back 25

- Multiple Sclerosis (loss of myelination)
- Pontine infarcts
- Tumor
- Trauma

Front 26

What is the purpose of the Vestibulo-Ocular Reflex (VOR)?

Back 26

Maintain vision on stationary object while the head or body is moving

Front 27

What is the afferent component for the Vestibulo-Ocular Reflex (VOR)? Efferent?

Back 27

- Afferent: neck proprioceptors and CN VIII
- Efferent: Medial Vestibulospinal Tract to abducens nucleus and via MLF to oculomotor nucleus

Front 28

What happens if the Vestibulo-Ocular Reflex (VOR) is normal?

Back 28

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

Front 29

If your Vestibulo-Ocular Reflex (VOR) is abnormal, what does this mean?

Back 29

- Eye movement goes with the head movement
- Brainstem dysfunction
- Medial Vestibulospinal Tract is not intact

Front 30

What is the Doll's Eye Maneuver used for? What must you rule out before doing it?

Back 30

- For brainstem evaluation in a comatose patient
- Cervical spinal injury must be ruled out before attempting this maneuver!!!

Front 31

What do you do in the Doll's Eye Maneuver?

Back 31

- 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)

Front 32

What is the function of the Corticotectal Tract and the Tectospinal Tract?

Back 32

- 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)

Front 33

Where do the Corticotectal fibers arise? Project to?

Back 33

- Retina
- Visual cortex
- Inferior parietal lobes
- Project to Superior Colliculus

Front 34

Where do the Tectospinal fibers arise? Project to?

Back 34

- 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

Front 35

Which clinical concern affects the Corticotectal Tract and Tectospinal Tract?

Back 35

Parinaud's Syndrome / Dorsal Midbrain Syndrome / Collicular Syndrome

Front 36

What is lesioned in Parinaud's Syndrome / Dorsal Midbrain Syndrome / Collicular Syndrome?

Back 36

- 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)

Front 37

What are the implications of a lesion to the superior colliculus or posterior commissure of the midbrain?

Back 37

- 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)

Front 38

If a patient can not gaze upward, what is this a sign of?

Back 38

- 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)

Front 39

What are some common causes of Parinaud's Syndrome / Dorsal Midbrain Syndrome / Collicular Syndrome?

Back 39

- Hydrocephalus resulting from aqueductal stenosis
- Pineal gland tumors

Front 40

What is the reticular formation composed of?

Back 40

Scattered groups of neuron cell bodies and fibers that extend throughout the brain

Front 41

What are the functions of the Reticulospinal Tracts?

Back 41

- 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

Front 42

What is the other name for the Lateral Reticulospinal Tract? Function?

Back 42

- 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)

Front 43

What is the other name for the Medial Reticulospinal Tract? Function?

Back 43

- Pontine Reticulospinal Tract
- P for Pontine = Pump up! = Excites spinal motor neurons that innervate axial muscles and leg extensors

Front 44

What is the pathway of the Lateral (Medullary) Reticulospinal Tract (LRST)?

Back 44

- 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)

Front 45

What is the pathway of the Medial (Pontine) Reticulospinal Tract (LRST)?

Back 45

Axons descend ipsilaterally in the anterior funiculus to all spinal cord levels

Front 46

Which clinical condition affects the Medial and Lateral Reticulospinal Tracts?

Back 46

Decerebrate Posturing / Decerebrate Rigidity

Front 47

What are the symptoms of Decerebrate Posturing / Decerebrate Rigidity?

Back 47

- Increased muscle tone
- Extension of upper and lower limbs with arms adducted and medially rotated
- Arched back
- Feet extended
- Toes curled

Front 48

What is the explanation for the symptoms of Decerebrate Posturing / Decerebrate Rigidity?

Back 48

- 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

Front 49

What is Locked-In Syndrome?

Back 49

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