Flashcards in Motor Systems Deck (8)
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)
Define motor unit.
all the muscle fibers innervated by a LMN (motor neurons of brainstem and spinal cord)
Define size principle.
LMNs are recruited in order of size and force
S units --- (add)--- FR units ---- (add) --- FF units
Define upper motor neuron.
corticospinal and corticobulbar neurons
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
Describe the components/functions of the 4-major "control systems" of the spinal cord LMNs
Reflex and pattern generators in the spinal cord
-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?
-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
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