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Flashcards in Motor Systems Deck (8)
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1

Contrast or compare an S-unit, FR-unit and FF-unit and the 3 types of fibers.

S unit- small MN, type I muscle fiber, red fibbers, ++++ mitchondria, ++++ capillaries

FR unit- type IIa fibers, white fibers, +++ mitochondria, +++ capillaries

FF-unit- Large MN, type IIb fibers, white fibers, ++ mitochondria, ++ capillaries

Type I (red fibers, slow twitch, small force, resistant fatigue)
Type IIa (white fibers, fast twitch, moderate force, resistant fatigue)
Type IIb (white fibers, fast twitch, large force, fatigable)

2

Define motor unit.

all the muscle fibers innervated by a LMN (motor neurons of brainstem and spinal cord)

3

Define size principle.

LMNs are recruited in order of size and force

S units --- (add)--- FR units ---- (add) --- FF units

4

Define upper motor neuron.

corticospinal and corticobulbar neurons

5

Describe the organization of LMNs into "groups"

Arranged into columns:

Medially placed- axial (trunk) muscles
Laterally placed -distal limb mubscles
Dorsally placed- flexor muscles
Ventrally placed- extensor muscles

6

Describe the components/functions of the 4-major "control systems" of the spinal cord LMNs

Reflex and pattern generators in the spinal cord

Descending pathways:
-Corticospinal tract (lateral) – all excitatory (glutamate is the transmitter)
-Vestibulospinal tract – postural adjustments/head movements
-Reticulospinal tract – locomotion and postural control
-Tectospinal tract – reflex turning of head to visual/auditory stimuli
-(Rubrospinal tract) – significance in humans?

Cortical centers:
-Association cortex – “decide” that a movement is needed
-Supplementary motor area – planning/learning complex movements
-Premotor cortex – devise a “plan” for the movement
-Motor cortex – origin of “commands” to motor neurons

Basal ganglia and cerebellum – selection/adjusting movements

7

Describe the Lateral CST (the origins of its components, location within the internal capsule, and terminations

CST – multiple origins and terminations

CST has ~ 1 million fibers
-Primary motor cortex – only 50% of CST
(Betz cells – concentrated here, but only 3% of CST)
-Adjacent Frontal motor and Parietal areas contribute the rest of the CST fibers
(Sensorimotor cortex – both sides of the central sulcus)

CST projects to:
-spinal cord and brainstem
-collaterals (direct and indirect) to basal ganglia, thalamus, reticular formation, sensory nuclei

CST passes through posterior limb of internal capsule

8

Describe the corticobulbar tract (its locations within the internal capsule, pattern of terminations and CN motor nuclei it does and doesn't innervate)

Descend anterior to corticospinal tract

Corticobulbar (corticonuclear) tract
-Motor neurons of cranial nerves
-Sensory relay nuclei
-Reticular formation

May end on motor neurons, most end on interneurons of the reticular formation

Oculomotor, trochlear and abducens nuclei receive no direct corticobulbar innervation (test question!)