Myofibrils

Myofibrils are built from what three kinds of proteins

Contractile proteins, regulatory proteins, structural proteins

Z disc

Narrow plate shaped regions of dense protein material separate one sarcomere from the next..

A band

The darker middle part of the sarcomere; extends the entire length of the thick filaments

A band and I band

bands create the striations that can been seen in both myfibrils and in whole skeletal and cardiac muscle fibers

Microfilaments (filaments)

bundles of protein that form myofibril

Troponin

component of thin filament; when calcium ions combine it changes shape. the change move tropomyosin away from myosin binding sites on actin molecules and muscle contraction subsequently begins as myosin bind to actin

tropomyosin

component of thin filament; when skeletal muscle relaxed it covers myosin binding sites on actin molecules, preventing myosin from binding to actin

Contractile proteins

generates force during muscle contraction

I band

lighter, less dense area the contains the rest of the thin filaments but no thick filaments; a z disc passes through the center

thin

made of protein actin; on the actin there is an area known as active sites (will make contact with cross bridges)

thick

made of protein myosin

Actin

main component of the thin filament; each actin has a myosin binding site where myosin head of thick filament binds during muscle contraction

Myosin

main component of thick filaments and functions as a motor protein in all three types of tissue; bind to myosin binding sites on actin molecules of thin filaments during muscle contraction

sarcomeres

myofilaments inside the myofibril do not extend the entire length of a muscle fiber instead they are arranged in compartments

Two contractile proteins

myosin and actin

H zone

narrow region in center of each A band that contains thick filaments but no thin filaments

Regulatory Proteins

proteins that help switch muscle contraction process on and off

2 types

thick and thin

2 types of regulatory proteins

tropomyosin and troponin

M line

Region in the center of H zone that contains protein that hold thick filaments together at center of sarcomere