chapter 12 physio

Types of muscle

Skeletal, cardiac, smooth

Muscle function

Movement, force production, heat generation

Skeletal muscle control

Somatic motor neurons

Cardiac and smooth muscle control

Autonomic nervous system, hormones, paracrine signals

Sarcomere

Contractile unit of muscle

Actin

Thin filament

Myosin

Thick filament

What shortens during contraction

Sarcomere

Sliding filament theory

Actin and myosin slide past each other

What blocks myosin binding

Tropomyosin

What exposes binding sites

Ca2+ binds to troponin

Power stroke

Myosin pulls actin when Pi is released

Rigor state

Myosin stuck to actin without ATP

Excitation-contraction coupling

ACh triggers action potential leading to Ca2+ release and contraction

DHP receptor

Voltage sensor in T-tubules

RyR receptor

Releases Ca2+ from sarcoplasmic reticulum

Relaxation

Ca2+ pumped back into SR using ATP

No Ca2+

No contraction

No ATP

No relaxation (rigor)

Phosphocreatine

Fastest source of ATP

Anaerobic metabolism

Fast ATP production, low yield

Aerobic metabolism

Slow ATP production, high yield

Muscle fatigue

Inability to maintain force

Summation

Increased stimulus increases force

Tetanus

Maximal sustained contraction

Motor unit

One neuron and all its muscle fibers

Recruitment

Increasing motor units increases force

Length-tension relationship

Force depends on sarcomere length

Slow-twitch fibers

Fatigue-resistant, oxidative metabolism

Fast glycolytic fibers

Fast contraction, fatigue quickly

Smooth muscle key difference

No troponin

Smooth muscle contraction

Ca2+ binds calmodulin to activate MLCK

MLCK

Phosphorylates myosin to allow contraction

Smooth muscle Ca2+ source

Sarcoplasmic reticulum and extracellular fluid

Cardiac muscle features

Striated, gap junctions, autorhythmic