Before muscle contraction can take place, tropomyosin must be removed from the active site on actin, so that myosin heads can attach. Calcium ions are responsible for attaching to troponin, which will then pull tropomyosin away from the active sites. These calcium ions are stored in the sarcoplasmic reticulum until an action potential stimulates their release.

T-tubules serve to conduct the action potential to the interior of the muscle fiber, allowing for coordinated contraction of sarcomeres throughout the fiber. The sarcolemma is simply the cell membrane of the muscle fiber. Myosin is the filament responsible for binding actin, but does not directly interact with calcium.

Bone tissue is formed by four bone cell types. Osteogenic cells are the progenitor stem cells that differentiate into osteoblasts. Osteoblasts are responsible for creating bone matrix by depositing hydroxyapatite crystal. They will eventually become encapsulated by the bone matrix, and differentiate into osteocytes. Osteocytes are primarily involved in communication and nutrient transfer within the bond matrix. Osteoclasts perform the opposite action osteoblasts and resorb the bone matrix. This process increases mineral concentrations in the blood.

Muscle cells are considered quiescent, and are incapable of mitosis. Instead, muscle mass will increase by hypertrophy (cell growth without division). In the event of damage, muscle satellite cells will differentiate into new myocytes, but the mature myocytes will not divide.

Only skeletal muscle and cardiac muscle contain organized sarcomeres, leading to their striated appearance. Smooth muscle does not contain sarcomeres and does not appear striated. Instead, actin and myosin align in multiple directions, allowing non-linear contraction in smooth muscle. Smooth muscle and cardiac muscle are generally uninucleated, but skeletal muscle cells contain numerous nuclei.

There are three main divisions of muscle tissue. Of these three, only skeletal muscle can be consciously controlled. Smooth muscle and cardiac muscle are under the control of the autonomic nervous system.

Skeletal muscle is used in locomotion and conscious actions, such as eye movements or forced respiration. Smooth muscle is used in vasodilation and vasoconstriction, and surrounds most organs in the body. Smooth muscle is responsible for unconscious diaphragm contractions, stomach contractions, and other visceral activity. Cardiac muscle is only found in the heart and is capable of independent, spontaneous contraction without nervous intervention.

The hydrostatic skeleton is a fluid-filled coelom surrounded by but not made chiefly of muscles in soft bodied, aquatic organisms such as echinoderms.

White fibers have less myoglobin than red fibers. White fibers have less mitochondria than red fibers. White fibers fatigue more quickly than red fibers. 

White fibers primarily use anaerobic respiration (red primarily uses aerobic). Remember that red fibers are active over long periods of sustained stress, while white fibers are more explosive. Red fibers require oxygen from respiration and myoglobin to maintain activity.

When acetylcholine binds to its receptors at the neuromuscular junction, it stimulates an initial influx of sodium ions that cause a localized depolarization of the muscle cell. This depolarization causes voltage-gated calcium channels to open within the T-tubules, carrying the signal into the cell interior. Proteins in the wall of the T-tubules directly interact with the internal sarcoplasmic reticulum, stimulating the organelle to release intracellular calcium. This release liberates myosin-binding sites on actin, allowing contraction to occur.

Sodium ions, potassium ions, and chloride ions play important roles in maintaining membrane potential at the neuromuscular junction, but the T-tubules rely heavily on calcium to interact with the sarcoplasmic reticulum.

Since the triceps and biceps produce opposing motions in the arm, they can be considered antagonists of one another. An antagonist will stretch, while the agonist contracts, and vice versa. Extensors, such as the triceps brachii, will act as antagonists of flexors, such as the biceps brachii.

A synergist assists the agonist by stabilizing the origin bone.