Motor system part one Flashcards
what is the Definition of a motor unit?
Motor neuron and the muscle fibers it innervates
what are the properties of “Slow (S)” motor units
- Generate small forces
- Fatigue slowly
- Small alpha motor neurons with fine caliber axons
- Innervate a small number muscle fibers
- Recruited first due to high input resistance of neuron
what are the properties of “Fast fatigue-resistant (FR)” motor units
- Intermediate sized alpha motor neurons with medium caliber axons
- Innervate an intermediate number of muscle fibers
- Generate large forces
- Fatigue slowly
- Recruited second
what are the properties of “Fast fatigable (FF)” motor units
- Large alpha motor neurons with thick axons
- Innervate a large number of muscle fibers
- Generate large forces
- Fatigue quickly
- Recruited last
what did the reinnervation experiments suggest?
motor neuron identity governs muscle phenotype
Motor neurons that innervate the hand are located most ______ in the anterior horn of the cervical enlargement of the spinal cord.
Laterally
Motor neurons that innervate the shoulder are located most ______ in the anterior horn of the cervical enlargement of the spinal cord.
medially
Muscle spindles relay ____ information
stretch
gamma motor neurons regulate the length of the ______ during voluntary contraction, this allows the system to maintain sensitivity to
stretch
intrafusal muscle fiber (Muscle spindle)
describe the feedback loop that happens when you pick up an object that is lighter than expected?
muscle overshortens > muscle spindle becomes slack > decreased firing of 1a sensory afferents > decreases firing of alpha motor neuron
describe the feedback loop that happens when you pick up an object that is heavier than expected?
muscle undershortens > muscle spindle is stretched > increased firing of 1a sensory afferents > increases firing of alpha motor neuron
Muscle spindles are a specialized type of
sensory receptor, known as a ________
proprioceptor
