Skeletal Muscle Physiology Flashcards
(14 cards)
What is the structure of skeletal muscle from large to small?
Whole muscle → fascicles → muscle fibers (cells) → myofibrils → sarcomeres → myofilaments (actin & myosin).
What happens at the neuromuscular junction?
Motor neuron releases ACh, which binds to receptors on the muscle fiber, causing Na+ influx and an action potential.
What is the neuromuscular junction (NMJ)?
The synapse between a motor neuron and a muscle fiber where ACh is released to trigger muscle contraction.
How is calcium released in a muscle fiber?
The action potential travels into T-tubules, triggering Ca2+ release from the sarcoplasmic reticulum.
What is the sliding filament mechanism?
Myosin heads bind actin, pull it via a power stroke, then detach and reset using ATP — shortening the sarcomere.
What is cross-bridge cycling?
Myosin binds actin, performs a power stroke, detaches when ATP binds, hydrolyzes ATP to reset, and repeats.
How does calcium removal lead to relaxation?
Ca²⁺ is pumped back into the SR, troponin returns to its original shape, tropomyosin blocks binding sites, and contraction stops.
How does calcium cause muscle contraction?
Ca2+ binds troponin, moving tropomyosin to expose actin binding sites for myosin.
How does muscle relaxation occur?
Ca2+ is pumped back into the sarcoplasmic reticulum, troponin returns to its resting state, and tropomyosin blocks binding sites.
What is a muscle twitch?
A single contraction-relaxation cycle in a muscle fiber in response to one action potential.
What is motor unit recruitment?
The activation of additional motor units to increase the strength of contraction.
What is summation?
When a second stimulus occurs before a muscle fully relaxes, causing stronger contraction.
What is tetanus in muscle contraction?
A sustained, maximal contraction from high-frequency stimulation.
How does muscle length affect twitch force?
Maximum force is generated at optimal overlap between actin and myosin; too short or too stretched = weaker force.
