Skeletal Muscle (2)

Skeletal muscle structure

Skeletal muscle structure

attaches to bone, striated voluntary

Skeletal muscle function

tension generation > muscle contraction > movement

Smooth muscle structure

walls of hollow organs, not striated, involuntary

Smooth muscle function

tension generation > move substances

Cardiac muscle structure

only in heart, striated, involuntary

Cardiac muscle function

tension generation > eject blood from heart

Properties of all muscle tissue

excitability, contractibility, extensibility, elasticity

Sarcomere

smallest contractile unit of a muscle fiber

Myosin

two heads that hinge, ATP binding site

Actin

made of tropomyosin (thread) and troponin (myosin binding site)

Z-disc

attaches thin filaments and myofibrils to one another

Sarcoplasmic reticulum

storage place for Calcium

T-tubule system

runs transverse to myofibrils

Myofibril

densely packed, rodlike

Skeletal muscle excitation process

action potential reaches neuromuscular junction > voltage channels open > push calcium in > ACh releases from vesicles > ACh binds to receptors > ACh breakdown/reuptake

Motor end plate potential (contraction)

action potential goes along sarcolemma and down t-tubules > sarcoplasmic reticulum releases calcium > calcium binds to troponin changing its shape > myosin attaches to binding sites > contraction begins

Low calcium concentration

tropomyosin doesn’t move, blocking binding sites (no contraction)

High calcium concentration

cross bridge formation, generating tension (contraction)

Cross bridge cycle

formation, power stroke, detachment, cocking of myosin head

Power stroke

myosin head pivots & pulls actin toward the center

Rigor mortis

No ATP production, so myosin can’t be detached

Generating more muscle tension

increase frequency, increase number of activated motor units, increase the size of muscle fibers, use muscle at optimal length (80%-120%)