Lct 30-31 - Skeletal Muscle

BIOSCI107

What is the basic structure of skeletal muscle fibres?

Long, cylindrical, multinucleated cells with peripheral nuclei, striated, voluntary control

What is a sarcomere?

The basic contractile unit of muscle, extending from Z disc to Z disc

What is the role of T-tubules and SR in skeletal muscle?

T-tubules conduct APs deep into muscle; SR stores/releases Ca²⁺ for contraction

What does myosin do in muscle contraction?

Binds to actin, hydrolyses ATP, pivots to pull actin filament—causing contraction

What initiates the cross-bridge cycle?

Ca²⁺ binds to troponin, shifting tropomyosin and exposing actin-binding sites

What are the four steps of the cross-bridge cycle?

Formation → Power stroke → Detachment → Reactivation

What is the difference between isotonic and isometric contraction?

Isotonic: muscle shortens; Isometric: muscle length constant, tension changes

What is the length-tension relationship?

Max force at optimal sarcomere length (~2–2.2 µm); too short or too long reduces tension

What happens in excitation-contraction coupling?

AP triggers Ca²⁺ release from SR → binds troponin → cross-bridge cycling starts

What are the 3 main ATP sources for muscle?

Creatine phosphate, Anaerobic glycolysis, Aerobic respiration

How is contraction strength graded in skeletal muscle?

Via frequency of stimulation (summation) and recruitment of more motor units
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