The term muscle refers to individual, discrete organs of the body. However, the structure and actions of tissues are often quite different in detail from the structure and actions of organs.
Shivering is a state in which the muscles of the body are primarily concerned with producing heat. Contraction means the production of tension through the interaction of the muscle tissues
Smooth muscle tissue consists of elongated cellular elements. Striated muscle tissue is composed of fibers. These fibers represent the fusion of many cells into a single functioning fiber. Cardiac muscle tissue is also composed of banded fibers. However, its fibers have a branched character.
The fiber, as a whole, is surrounded by a membrane known as the sarcolemma. The fiber is filled with a type of intracellular fluid called sarcoplasm. Within the sarcoplasm is a tubular system called the sarcoplasmic reticulum that stores calcium, which is necessary for the muscle activation and contraction.
The Sliding Filament Theory involves energy provided by the mitochondria in the form of ATP. With this energy, the myosin bridges swing and draw the actin filaments over the myosin filaments. The length of the striated muscle fiber is thus shortened.
When stimulated to contract by a nervous impulse, a striated muscle fiber contracts totally or not at all.
There are two types of striated muscle fibers-fast (white) and slow (red).
Fast (white): The fast striated muscle fibers can contract rapidly and strongly but only for a short time.
Slow (red): The slow striated muscle fibers tend to contract more slowly but for a sustained duration. The red color of slow striated muscle fibers is because of myoglobin protein.
The endomysium is a meshwork of fibrous connective tissue (FCT) that surrounds each striated muscle fiber individually.
A group of these striated muscle fibers is bound together in a bundle (fascicle) by an FCT envelope known as the perimysium.
The entire muscle is bound within an FCT sheath called the epimysium.
If a tendon is broad and flat rather than cord-like, we call it an aponeurosis
If the striated muscle fibers appear to be attached to one tendon in a featherlike arrangement, the muscle structure is known as pennate. If all of the fibers are on one side of the tendon, the muscle structure is unipennate.
If the fibers are on two sides, the muscle structure is bipennate. If the feather-like arrangement is branched, the muscle structure is multipennate