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
