Muscle

Muscle is a contractile form of tissue. It is one of the four major tissue types, the other three being epithelium, connective tissue and nervous tissue. Muscle contraction is used to move parts of the body, as well as to move substances within the body.

Types

There are three general types of muscle:

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

• Cardiac muscle is a specalized kind of muscle found only within the heart.
• Skeletal muscle or "voluntary muscle" is anchored by tendons to bone and is used to effect skeletal movement such as locomotion.
• Smooth muscle or "involuntary muscle" is found within structures such as the intestines, throat and blood vessels.

Cardiac and skeletal muscle are "striated" in that they contain sarcomeres and are packed into highly regular arrangements of bundles; smooth muscle has neither. Striated muscle is often used in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Skeletal muscle is further divided into two subtypes:

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

• Type I, slow oxidative, "slow twitch", or "red" muscle is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color. It can carry more oxygen and sustain aerobic activity.
• Type II, glycolytic, "fast twitch", or "white" muscle is less dense in mitochondria and myoglobin. It can contract more quickly and with a greater amount of force than Type I muscle, but can only sustain short, anaerobic bursts of activity before a build-up of lactic acid in tissue begins to interfere with muscular contraction and causes pain.