M2 - Sliding Filament Theory Flashcards
What fills most of the space inside a skeletal muscle fiber?
Myofilaments—actin and myosin.
Why do skeletal muscle fibers have multiple nuclei?
Because many cells fuse together during development.
What is sarcoplasm?
The cytoplasm of a muscle cell; site of metabolic reactions and contains myoglobin and glycogen.
What is the sarcolemma?
The membrane of a muscle cell; regulates entry and exit of materials.
What is the sarcoplasmic reticulum?
Smooth ER in muscle cells; stores and releases calcium ions for muscle contraction.
What does myoglobin do?
It is an iron-containing protein that stores and carries oxygen in muscle cells and gives red meat its color.
What are myofibrils made of?
Myofilaments—thin actin filaments and thick myosin filaments.
What is a sarcomere?
The contractile unit of a muscle cell; repeating subunit of actin and myosin.
What causes the striated appearance of skeletal muscle?
The arrangement of actin and myosin into repeating sarcomeres.
What are troponin and tropomyosin?
Ion-receptor proteins on actin that block myosin-binding sites.
What is the structure of myosin?
A thick filament made of two polypeptide chains with globular heads at the ends.
What happens during muscle contraction?
Actin and myosin filaments slide past each other, shortening the sarcomere and contracting the muscle.
What are the steps of muscle contraction?
Depolarization & calcium ion release → Cross-bridge formation → Sliding of filaments → Sarcomere shortening.
What triggers the release of calcium ions in a muscle cell?
A nerve signal causes the sarcoplasmic reticulum to release calcium ions into the sarcoplasm.
What happens when calcium ions bind to troponin?
Troponin changes shape, moving tropomyosin and exposing myosin-binding sites on actin.
What is a cross-bridge in muscle contraction?
When the myosin head binds to actin.
What does the myosin head do after attaching to actin?
It flexes to pull the actin filament, then uses ATP to detach and reset.
How does ATP play a role in muscle contraction and relaxation?
ATP is required to detach myosin from actin; without it, muscles stay contracted (as in rigor mortis).
What is rigor mortis and why does it occur?
It is the stiffening of the body after death due to lack of ATP, preventing muscle relaxation.
How does calcium control muscle contraction?
Calcium binds to troponin, allowing tropomyosin to move and expose binding sites so myosin can attach.
