BIOL 1201 Chapter : More Bio
Document Summary
Skeletal muscles are composed of bundles of muscle fibers or cells. Each cell in turn contains many myofibrils or contractile units. Myofibrilas are composed of two types of filaments: thin filaments which are actin molecules and tropomyosin molecules (regulatory protein) and thick filaments which are bundles of myosin molecules. For muscle contraction to take place, the myosin head binds to actin and causes shape change in myosin and shortens myofibril. Atp causes myosin and actin to unbind and reset myosin head. Tropomyosin, troponin, and ca++ regulate the binding of the myosin to the actin. Ca++ binds to troponin and exposes the sites. When you get tired, muscles stop working due to lack of atp and build up of metabolites lactic acid and k+ ions. Lactic acid changed the ph in myofibrils interfering with the ca++ ion binding properly to tropomyosin. When there is no atp in a muscle it cannot be moved, neither contracted nor relaxed.
