A&P lab test 4 cont

1. Describe the organization of skeletal muscle at the tissue level.

-skeletal muscle is surrounded by epimysium and contains many fascicles. -Fascicles are surrounded by perimysium and contain many muscle fibers. - muscle fibers are surrounded by endomysium and contain many myofibrils - myofibrils are surrounded by sarcoplasmic reticulum and consist of sarcomeres -sarcomeres contain thick and thin filaments

A-band

a dark band of a sacromere that contains thick filaments with an overlap of thin (blue with an overlap of red)

thin filaments

actin - lighter (RED) The main component of the thin filaments is a protein called actin. Actin molecules join together forming chains twisted into a helix configuration. These molecules are very important to the contraction mechanism of muscles because each actin molecule has a single "myosin-binding site" (not illustrated above). The other two protein molecules that form the thin filaments are called troponin and tropomyosin. The molecules of tropomyosin cover the myosin-binding sites on the actin molecules when the muscle fibres are relaxed. Myosin and actin form the main contractile elements of muscles. This is because it is the binding of the thick filaments to the thin filaments - and in particular the positions of these points of attachment - that controls the state of contraction/relaxation of the muscle of which they are apart.

m-line

center of sarcomere. connects the thick filaments to each other

H- zone

includes only thick filaments

I-band

light band- contains only thin filaments

Z-line

mark the boundary between adjacent sarcomeres

2. Identify the structural components of a sarcomere

meeting of thick and thin filaments and are the smallest units of muscle fiber responsible for muscle contraction.

thick filaments

myosin - darker (BLUE) Thick filaments are formed from a protein called myosin which has important properties of elasticity and contractibility. The shape of the myosin molecules has the apperance of two "hockey sticks" or "golf clubs" twisted together. This is illustrated in the diagram above - indicating the two parts of the myosin molecule referred to in Advanced Textbooks about Muscles These are the myosin tail, and the myosin heads, or "crossbridges"

zone of overlap

where the thin and thick filaments overlap each other