There are three distinct types of muscle:
skeletal muscle,
cardiac or heart muscle, and
smooth (non-striated) muscle.
Muscles provide strength, balance, posture, movement, and heat for the body to keep warm. There are more than 600 muscles in an adult male human body. A kind of elastic tissue makes up each muscle, which consists of thousands, or tens of thousands, of small muscle fibers. Each fiber comprises many tiny strands called fibrils, impulses from nerve cells control the contraction of each muscle fiber.
Skeletal Skeletal muscle, is a type of
striated muscle, composed of
muscle cells, called
muscle fibers, which are in turn composed of
myofibrils. Myofibrils are composed of
sarcomeres, the basic building blocks of striated muscle tissue. Upon stimulation by an
action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the
sliding filament model of muscle contraction. Within the sarcomere,
actin and
myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped
myosin heads that project toward the actin filaments, and provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style; they swivel toward the center of the sarcomere, detach, and then reattach to the nearest active site of the actin filament. This is called a ratchet-type drive system.
Calcium ions are required for each cycle of the sarcomere. Calcium is released from the
sarcoplasmic reticulum into the
sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin-binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the
sarcoplasmic reticulum. Image: Muscles anterior labeled.png|Skeletal muscles, viewed from the front Image: Muscle posterior labeled.png|Skeletal muscles, viewed from the back
Cardiac Heart muscle is striated muscle but is distinct from skeletal muscle because the
muscle fibers are laterally connected. Furthermore, just as with smooth muscles, their movement is involuntary. Heart muscle is controlled by the
sinus node influenced by the
autonomic nervous system.
Smooth Smooth muscle contraction is regulated by the autonomic
nervous system,
hormones, and local chemical signals, allowing for gradual and sustained contractions. This type of
muscle tissue is also capable of adapting to different levels of stretch and tension, which is important for maintaining proper blood flow and the movement of materials through the
digestive system. == Physiology ==