Motor systems Flashcards by Dave Ed

In the cortex, explain the somatotopic organization. (arm, leg, and face)

Leg medial
Face lateral
Hand in-b/w

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What cells does Polio affect?

Kills anterior horn cells (CST)

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What is Post-Polio Syndrome?

Gradual weakening–when Polio pts have nl loss of ant horn cells, it has more of a dramatic effect because there ant horn cells may be innervating several thousand m. fibers instead of just a few hundred (like a nl person)

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What are the names of the 3 major types of motor units?

S-unit (slow) (is also fatigue-resistant)
FR-unit (fast fatigue-resistant)
FF-unit (fast fatigable)

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Rank the 3 types of motor units from most force to least force.

FF, FR, S

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Rank the 3 types of motor units from most to least mito/caps.

S, FR, FF

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What types and color of m. fibers are involved in each of the 3 motor units?

S: I (red)
FR: IIa (white)
FF: IIb (white)

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Rank the 3 types of motor units from fastest twitch speed to slowest twitch speed.

FF, FR, S

FF and FR both considered “fast,” S considered “slow”

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Where would you find LMNs?

Brainstem and sc

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In the sc, explain the LMN column somatotopic organization. Medial? Lateral? Dorsal? Ventral?

Medial: Axial/trunk (proximal)
Lateral: Distal limb
Dorsal: flexors
Ventral: extensors

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What NT do LMNs typically use? Which receptors are sensitive to them?

- Nicotinic receptors

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What is a motor unit?

All m. fibers innervated by 1 anterior horn cell AKA 1 LMN

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Explain the “size principle” of LMN recruitment.

LMNs are recruited in order of size and force (added, not replaced):

S-units
FR-units
FF-units

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What are examples of UMNs?

Corticospinal and corticobulbar neurons

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Where would you look for the descending tract of the lateral CST in the sc?

Lateral funiculus

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What are the 4 centers of motor control for LMNs?

Reflex and pattern generators in the sc
Descending pw’s
Cortical centers
Basal ganglia and cerebellum

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What is the function of the vestibulospinal tract?

(descending pw)

- Postural adjustments/head movements

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What is the function of the reticulospinal tract?

(descending pw)

- Locomotion and postural control

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What is the function of the tectospinal tract?

(descending pw)

- Reflexive turning of head to visual/auditory stimuli

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What is the function of the rubrospinal tract? (not important)

(descending pw)

- Unknown significance in humans

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What is the function of the basal ganglia/cerebellum in controlling spinal LMNs?

Selection/adjusting movements

Does the CST have multiple origins or a single origin? What about terminations?

Multiple origins and multiple terminations

About what percentage of CST input comes from the primary motor cortex?
About what percentage of CST is made up of Betz cells?

50%

Besides primary motor cortex, what other cortical regions contribute to CST input?

Adjacent frontal motor areas

- Parietal areas

Where is the sensorimotor cortex?

Both sides of the central sulcus

Which part of the internal capsule does the CST pass thru?

Posterior limb

What are the 2 major places that the CST projects to? | Where do the CST indirect/direct collaterals project to?

- Spinal cord and brainstem | - Collaterals (direct and indirect) to basal ganglia, thalamus, reticular formation, sensory nuclei

What percentage of lateral CST decussates to end up in contralateral side?

90%

What are the parts of the lateral CST that don't decussate, and how much of the CST do they make up?

- 8% is anterior CST | - 2% remains as uncrossed CST (unclear why)

Which structures will the anterior CST end up innervating?

Midline structures

L = legs. A = arms. T = trunk Before decussating, what is the order of the arm/trunk/leg somatotopic organization in the CST, from medial to lateral? What about after decussation?

- ATL | - ATL (rotates to stay in same order)

What type of motor function does the CST provide?

Fine

What is the general shape of the structure of neuronal arrangement in the cortex? Are different body parts separated or mixed together?

Radial columns | - Mixed

The corticospinal tract originates/passes thru which of the following? a) Premotor, supplementary motor cortex b) Primary motor cortex c) Brainstem

A only or [A and B]

The reticulospinal tract originates/passes thru which of the following? a) Premotor, supplementary motor cortex b) Primary motor cortex c) Brainstem

[B and C]

The rubrospinal tract originates and passes thru at which of the following? a) Premotor, supplementary motor cortex b) Primary motor cortex c) Brainstem

The vestibulospinal tract originates and passes thru which of the following? a) Premotor, supplementary motor cortex b) Primary motor cortex c) Brainstem

[A and B and C]

If a man can bench 200 lbs, what would happen if he his cerebellum atrophied?

Could still bench 200 lbs, just wouldn't be as coordinated

Lesioning which of the following would cause weakness? (there is more than 1 answer) - LMN - UPN - Cerebellum - Association Cortex - Basal Ganglia -

LMN and UMN

Where do UMNs for CN motor nuclei descend, relative to the CST?

Anterior to it

What are the 3 major parts of the corticonuclear (corticobulbar) tract?

- Motor neurons of CNs - Sensory relay nuclei - Reticular formation

UMNs for CN nuclei may end on ___________, but but most end on interneurons of the _________________.

- Motor neurons | - Reticular formation

Which CN's receive NO direct corticobulbar innervation?

III, IV, VI (no innervation directly to them but to chunks of reticular formation that coordinates those movements in length-appropriate manner)

What part of the internal capsule do the corticobulbar fibers run through?

Genu

The upper part of the face has __-lateral innervation from the facial n., the lower part of the face has __-lateral innervation from the facial n.

bilateral | unilateral (contralateral)

If facial weakness only effects lower part of face, it’s a(n) ________ injury. If it effects both upper and lower sides of face, it’s an _______ injury known as _________.

- UMN | - LMN; Bell's palsy

Wtf are corticobulbar tracts?

Arise from the lateral aspect of the primary motor cortex. Receive the same inputs as the corticospinal tracts. The fibres converge and pass through the internal capsule to the brainstem. The neurons terminate on the motor nuclei of the CNs. Here, they synapse with LMNs, which carry the motor signals to the muscles of the face and neck.

What part of the RF is closely associated w/extra-ocular mm?

PPRF (paramedian pontine reticular formation)

What cortical center "decides" that a movement is needed?

Association cortex

What cortical center is involved w/planning and learning complex movements?

Supplementary motor area

What cortical center "plans" for a movement to occur?

Pre-motor cortex

What cortical center is the origin of "commands" to motor neurons?

Motor cortex