Term
| Describe the decussation of the corticospinal tract: |
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Definition
90% crosses at the decussation of the pyramids- this is the lateral tract
10% remains uncrossed to the spinal level- this is the anterior tract |
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Term
| What muscles are handled by the lateral corticospinal tract? |
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Definition
Distal muscles, fingers, toes, fine articulations
FLEXORS more than extensors |
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Term
| What muscles are handled by the anterior corticospinal tract? |
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Definition
| Trunk muscles, bilaterally innervated so that a lesion of one side of the tract has minimal/imperceptible manifestations |
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Term
| What characterizes a lower motor neuron lesion? |
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Definition
| Muscle weakness, fasciculations, atrophy, fibrillations, decreased reflexes, decreased tone |
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Term
| What characterizes an upper motor neuron lesion? |
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Definition
| Muscle weakness, increased tone, hyperreflexia (spasticity), Babinski's Sign, Hoffmann's Sign, posturing |
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Term
| What is important to remember about ACUTE upper motor neuron lesions? |
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Definition
| Initially they can present with flaccid paralysis (like lower motor neuron) but after one week this develops into spasticity- seen in spinal shock |
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Term
| What is innervated by the corticonuclear (corticobulbar) tract? |
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Definition
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Term
| What is unique about the innervation of the cranial nerves by the corticonuclear tract, and what are the exceptions? |
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Definition
Innervation is bilateral, except for:
Facial Nuc- LOWER FACE is contralateral
Hypoglossal Nuc- GENIOGLOSSUS is contralateral
Nuc Ambiguus- SOFT PALATE AND UVULA are contralateral
Spinal Accessory- SCM and TRAP are ipsilateral |
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Term
| If there is a stroke in the genu of the internal capsule on one side, what do we see? |
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Definition
In this UPPER MOTOR NEURON lesion:
-the upper face and forehead is spared
but the patient can't smile on the OPPOSITE side because there will be lower facial paralysis |
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Term
| What happens if there is a stroke in the midbrain at the level of the occulomotor nucleus on one side? |
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Definition
| Should be ok because innervation to the occulomotor nucleus is bilateral from each corticonuclear tract |
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Term
| What happens to the tongue if the corticonuclear tract is damaged on the RIGHT side? |
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Definition
Tongue deviates OPPOSITE
(Unlike if the nerve or nucleus is damaged, in which case tongue deviates same side) |
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Term
| Where does the corticonuclear tract cross? |
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Definition
| I tricked you- it doesn't "cross" in the traditional sense- most everything is innervated bilaterally, except for 4 things |
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Term
| Where does the rubrospinal tract originate, and where does it cross? |
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Definition
Red Nucleus- crosses right away at the Ventral Tegmental Decussation
-inputs from the cortex and cerebellum |
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Term
| What tract does the rubrospinal tract descend close to? |
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Definition
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Term
| What is innervated by the Rubrospinal tract? What types of muscles are handled mostly by this tract? |
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Definition
Only cervical levels are innervated by this tract- upper extremity
This tract is FLEXOR BIASED and influences mostly flexor tone |
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Term
| What does the rubrospinal tract travel with in the spinal cord? |
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Definition
| In the lateral funiculus with the Lateral Corticospinal Tract |
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Term
| Where does the reticulospinal tract cross? |
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Definition
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Term
| What two tracts are flexor biased? |
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Definition
| Corticospinal and Rubrospinal |
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Term
| What are the two divisions of the reticulospinal tract? |
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Definition
Pontine reticulospinal (medial)
Medullary reticulospinal (lateral) |
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Term
| Describe the course and innervation of the pontine (medial) reticulospinal tract: |
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Definition
Descends uncrossed to facilitate EXTENSOR tone
-high level of spontanteous activity, with input from the deep cerebellar and vestibular nuclei
ALWAYS ACTIVE |
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Term
| Describe the course and innervation of the medullary (lateral) reticulospinal tract: |
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Definition
Descends uncrossed to INHIBIT EXTENSOR TONE
-ANTAGONIZES PONTINE(MEDIAL)RETICULOSPINAL TRACT
-inputs from cerebral cortex, red nucleus, and spinoreticular tract |
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Term
| Why do painful stimuli influence muscle tone via the reticulospinal tracts? |
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Definition
| Both (medial and lateral) receive inputs from the spinoreticular tract, so painful stimuli influences muscle tone |
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Term
| What are the two descending vestibulospinal tracts? |
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Definition
Lateral vestibulospinal tract- all levels of the cord EXTENSORS
Medial vestibulospinal tract- cervical and upper thoracic levels, neck muscles |
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Term
| What is the function of the lateral vestibulospinal tract? |
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Definition
| Balance- keeps you from falling over |
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Term
| What is the function of the medial vestibulospinal tract? |
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Definition
| Head position- keeps eyes level |
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Term
| Where do the vestibulospinal tracts cross? |
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Definition
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Term
| Where does the medial vestibulospinal tract travel? |
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Definition
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Term
| Where does the tectospinal tract cross? |
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Definition
| Dorsal Tegmental Decussation |
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Term
| Where does the tectospinal tract originate? |
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Definition
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Term
| Where does the tectospinal tract run? |
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Definition
| Very close to the MLF, down the brainstem and into the spinal cord |
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Term
| What does the tectospinal tract do? |
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Definition
Helps with visual direction/head orientation toward a visual or auditory stimuli
This tract is less about muscle tone |
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Term
| If you see the thalamus in a coronal slice, what part of the internal capsule are you looking at? |
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Definition
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Term
| What is a pure motor stroke? |
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Definition
A stroke that takes out just the posterior limb of the internal capsule- no somatosensory deficits (not near VPM, VPL)
***If the stroke is higher, there will be motor AND sensory loss*** |
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Term
| What tract innervates alpha motor neurons that control distal muscles and delicate, precise movements? |
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Definition
| Corticospinal tract (lateral) |
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Term
| What happens to the neurons in the spinal cord with a corticospinal tract lesion? (UMN) |
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Definition
Lose alpha motor neuron control and drive to the inhibitory interneurons (which inhibit alpha motor neurons)
Loss of inhibition= alpha motor neurons more likely to fire |
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Term
| Why does an upper motor neuron lesion cause spasticity |
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Definition
| Loss of inhibition of alpha motor neurons by interneurons, but reticulospinal tract and vestibulospinal tract are still innervating/activating alpha motor neurons |
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Term
| When testing muscles for spasticity in an upper motor neuron (CST) lesion, what do we find? |
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Definition
Spasticity is velocity dependent
Testing slowly shows normal tone
Testing quickly there is a stress response to stretch and joints/muscles become stiff |
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Term
| What is the difference between spasticity and rigidity? |
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Definition
Spasticity is velocity dependent
Rigidity is velocity INDEPENDENT- stiff all the time- think basal nuclei |
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Term
| What happens in a lesion of the thalamus, internal capsule, or cortex ABOVE the red nucleus? |
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Definition
Loss of corticospinal descending control, but the rubrospinal, reticulospinal, and vestibulospinal tracts are ok-
DECORTICATE POSTURING |
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Term
| What is decorticate posturing and why does it happen? |
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Definition
Loss of CST control, but the rubrospinal tract is causing a flexor bias on the upper limbs so it dominates and the arms are flexed inward
Reticulospinal tract is causing an unopposed extensor bias on the lower limb, so the legs are extended |
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Term
| What is the posture called where the arms are flexed and the legs are extended? |
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Definition
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Term
| What happens if there is a lesion below the red nucleus, etc. in the lower brainstem? |
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Definition
Loss of corticospinal tract control and rubrospinal tract
Reticular formation/reticulospinal tract dominates with EXTENSOR BIAS of all 4 limbs
DECEREBRATE POSTURING |
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Term
| What is decerebrate posturing? |
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Definition
| With no opposition from the corticospinal and rubrospinal tracts, the reticulospinal tract dominates with EXTENSOR BIAS on all 4 limbs- the patient is completely extended |
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Term
| What 3 elements compose the "motor cortex"? |
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Definition
| M1, Supplementary motor area, premotor area |
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Term
| What motor function gets lost in a stroke of the Anterior Cerebral Artery? |
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Definition
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Term
| What motor function gets lost in a stroke of the Middle Cerebral Artery? |
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Definition
| Face, Upper Extremities, and Trunk |
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Term
| What do we see in lesions of M1 (primary motor cortex)? |
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Definition
Weakness and apraxia, but not paralysis
-hard to hold a pencil |
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Term
| What do we see in lesions of the premotor area? |
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Definition
| No paralysis, but slow complex limb movements- no facilitation of the M1 neurons- crappy planning and initiation |
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Term
| What effect does the premotor area have on the M1 primary motor cortex neurons? |
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Definition
| The PMA gets M1 neurons closer to threshold |
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Term
| What do we see in lesions of the supplemental motor area? |
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Definition
| Motor apraxia, but not paralysis- |
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Term
| What is the main role of the premotor area? |
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Definition
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Term
| What is the main role of the supplemental motor area? |
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Definition
| Organizing- for movement of an entire limb |
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Term
| What two parts of the brain are required for translating strategy into action? |
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Definition
| Premotor area and supplemental motor area |
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Term
| What is the role of the posterior parietal area? |
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Definition
Motivation or intent- active during motor acts
"I see a pencil, I grab the pencil"
Bigger Picture |
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Term
| What do we see in a lesion of the posterior parietal area? |
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Definition
| CONTRALATERAL HEMINEGLECT |
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Term
| What regions of the thalamus make feedback reciprocal connections to the motor cortex? |
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Definition
| Ventrolateral and ventral anterior nuclei |
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Term
| Which of the Rexed lamina carry lower motor neuron innervation to skeletal muscle? |
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Definition
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Term
| What is the Babinski sign? |
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Definition
Normally, stimulation of the bottom of the foot causes toes to curl
A positive Babinski sign is when they fan out and extend
UPPER MOTOR NEURON- CST DAMAGE |
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Term
| What are the signs and symptoms of spinal shock, and why is it tricky? |
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Definition
Flaccid paralysis, and muscle stretch reflexes are not hyperactive right away but become so
The only sure thing is a positive Babinski sign right away |
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Term
| What happens if you damage the anterior horn of the spinal cord at that level? |
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Definition
| Lower motor neuron lesion- loss of a myotome |
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Term
| What happens below the level of damage to the anterior horn of the spinal cord? |
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Definition
| IPSILATERAL Upper Motor Neuron Signs -killing the tract |
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