VMED 5163 - Sliding Filament Theory

Muscle fibers

Skeletal muscle cells, also known as ___, are striated with many small fibers

Long, striated, cylindrical, multiple peripherally located nuclei

What are the major characteristics of muscle fibers?

Myofibrils

The majority of the sarcoplasm of a muscle cell is filled with what units?

Myofilaments

Myofibrils consist of many ___ of two types

Actin and myosin; myosin are thicker

What are the types of myofilaments? Which of the filament types are thicker?

The basic contractile unit of a muscle cell; from one Z line to the next Z line

What is a sarcomere and where are their boundaries?

Actin; thin

Myofilaments of ___ anchor on the Z line. Are these filaments thick or thin?

Anchors the myosin filaments at their center

Where is the M line located?

Myosin filaments

During the process of muscle contraction, which filaments facilitate movement?

There is an shortening or narrowing of the sarcomere toward the center

What occurs to the sarcomere during contraction?

A band

Which portion of the sarcomere contains both actin and myosin filaments?

Located at the center of the A band and contains only myosin

Where is the H zone located and what does it contain?

I band and H zone

During contraction, which portions of the sarcomere become more narrow or smaller?

Remains unaltered

What happens to the A band during muscle contraction?

The globular head of a myosin molecule

Which structure forms a cross bridge during the process of muscle contraction?

Actin filaments

Globular heads of myosin make contact with what structure during the cross bridge cycle?

Dimer

Myosin proteins within the cross bridge cycle are always present as a ___

Act as myosin ATPase enzyme by splitting ATP to ADP

How do the globular myosin heads act in order to release energy?

Hydrolysis of ATP

Activation of the cross bridge is achieved by

Release of a phosphate group

After the cross bridge is formed, and myosin heads bind to actin filaments, a conformational change is caused by what?

A power stroke

After the phosphate group is released from myosin, what causes filament pulling?

A new molecule of ATP binds to the myosin head

Which step of the cross bridge cycle ends in detachment of the cross bridge?

Cross bridge formation, power stroke, cross bridge detachment, and reactivation of myosin heads

What are the four simple steps of the cross bridge cycle?

ATP

Which molecule is critical during the cross bridge cycle?

Pumping of calcium back into the sarcoplasmic reticulum for muscle relaxation

While ATP serves as an energy source for the cross bridge cycle, what other main function does it have in muscle movement?

Anaerobic respiration, aerobic respiration, and use of phosphate groups donated by phosphocreatine

Through which processes is ATP generated in skeletal muscle?

For very quick production of ATP in situations where anaerobic respiration will not keep up with demand, such as during strenuous exercise

When is ATP generation through phosphocreatine seen?

Transfer of a phosphate group directly onto ADP

Via an enzyme known as creatine kinase, phosphocreatine can assist in ATP generation by which process?