64) compare skeletal, smooth, and cardiac muscles as to their body location, microscopic anatomy, regulation of contraction, speed of contraction, and rhythmicity. 65) what is the effect of aging on skeletal muscles? 66) discuss the role of the myosin heads in sliding filament theory.

The answers are as follows:
64. SKELETAL MUSCLES
Body location: it is usually attached to the bone or to the skin.
Microscopic anatomy: it is made up of very long, cylindrical multinucleated cells which are striated.
Regulation of contraction: the nervous system controls the voluntary contraction of the skeletal muscles.
Speed of contraction: the speed of contraction ranges from slow to fast.
Rhythmicity: the skeletal muscle is arrhythmic.
SMOOTH MUSCLES
Body location: found in the wall of hollow visceral organs [not including those of the heart].
Microscopic anatomy: made up of single fusiform, uninucleated cells that are without striation.
Regulation of contraction: smooth muscles undergo involuntary contractions which are controlled by the nervous system and hormones.
Speed of contraction: very slow. it is the slowest of the three muscles.
Rhythmicity: rhythmic.
CARDIAC MUSCLES
Body location: located in the wall of the heart.
Microscopic anatomy: it is composed of branching chains of cells, that are uninucleated; they are striated and posses intercalated discs.
Regulation of contraction: Undergo involuntary contractions, which are controlled by nervous system, heart pacemarker and hormones.
Speed of contraction: slow.
Rhythmicity: rhythmic.

65. Aging brings about gradual loss in muscle functions. As one grows older, there are usually age related alterations in the skeletal muscle functions. The factors that affect the rate of muscle loss are sex and level of muscle activity. Loss of muscle mass also occurs as one grows older.

66. The sliding filament theory states that, during contraction the thin filaments slide past the thick filaments and the sacomere shortens.
During contraction, the myosin head attaches to the myosin binding site on the actin filament. Using energy from ATP, the myosin head move toward the center of the sacomere, attaching and detaching several times. As a result of this, the thin actin filament is pulled toward the center of the sacomere. This leads to the shorten of the muscle cells.