MUSCLE STRUCTURE AND PHYSIOLOGY

J. Rosenbluth, April 2012

MUSCLE• Skeletal muscle fibers

– Contraction mechanism– Excitation-contraction coupling

• Gross properties of skeletal muscle

• Pathology/Clinical examples

Myofibrils

Skeletal muscle band pattern

Double “antiparallel” array of myofilamnts (H.E.Huxley)

Sliding filament model

Myosin filament formation

Low-angle X-ray diffraction of skeletal muscle (meridional pattern)

Decorated F-actin

Antiparallel array of myofilaments

Double hexagonal array (vertebrate skeletal muscle)

Crossbridge position during relaxation (top) vs contraction (bottom)

Cross-bridge Cycle

– Attached

– Released

– Cocked

– Force generating

– Attached

Triads (amphibian)

Skeletal muscle triad (amphibian)

Triad structure

Actin filament with Tr and Tm

Tropomyosin movement

Pennate Muscles

Length-TensionRelationship

Load-Velocity Relationship

Twitch vs Tetanic Tension

Fiber types (cat gastrocnemius)

Twitch contraction times

Skeletal Muscle Fatigue

“Winging”(facio-scapulo-humeral dystrophy)

“Pseudohypertrophy” (Duchenne dystrophy)

Charcot-Marie-Tooth disease

Spinal muscular atrophy