1. The Physiology of Skeletal Muscle Contraction
Muscle Cell Anatomy
Sarcolemma
 Muscle cell membrane
Sarcoplasmic reticulum
 Reservoir of Ca++
 Ions needed for muscle fibers to contract
Mitochondria
 Source of ATP
 Provides energy
for movement
of contraction
Myofibrils
 Made of actin
and myosin
filaments

2. Myofilament Anatomy Each myofibril is made of alternating
rows of actin and
myosin filaments
The actin
myofilaments slide
over the myosin to
shorten the muscle

3. Sliding Filament Theory
Message traveling along
neuron causes release of
acetylcholine.
Acetylcholine diffuses
across neuromuscular
junction and binds to sarcolemma.
Changes permeability allowing stored Ca++ ions in the sarcoplasmic reticulum to flood into the muscle fibers

4. Sliding Filament Theory
Influx of Ca++ ions causes actin fibers slide
along myosin filaments.
Sliding shortens and thickens muscle.

5. What makes the filaments slide along each other?
Myosin made up of bundles of fibers with heads that act as “hands” to pull the actin fibers along the myosin.
Troponin proteins in the actin fibers act like hand holds for the myosin heads to “grab”.
Myosin
Actin

6. How the tropomyosin complex works: