musculi

Musculi is the Latin plural of musculus, used in anatomical terminology to refer to muscles in general or to groups of muscles. The singular musculus denotes a single muscle, while musculi designates multiple muscles. The term derives from Latin, historically linked to the idea of a “little mouse” moving under the skin, a reference to muscle contractions used in early anatomical descriptions.

Muscle tissue is traditionally classified into three major types: skeletal muscles, which are voluntary and striated and attach to bones; smooth muscles, which are involuntary and found in the walls of hollow organs and vessels; and cardiac muscle, a specialized, striated tissue that forms the heart. Musculi vary in size, location, and function but share a common organization.

Structure and organization: individual muscle fibers (myocytes) are bundled into fascicles and surrounded by connective tissue layers—the endomysium around each fiber, the perimysium around fascicles, and the epimysium around the whole muscle. Tendons or aponeuroses connect muscles to bones or other structures. The neuromuscular system provides motor innervation, and blood vessels supply oxygen and nutrients necessary for contraction and repair.

Physiology: muscle contraction follows the sliding filament mechanism, with actin and myosin cross-bridges powered by ATP and regulated by calcium signaling from the sarcoplasmic reticulum. Contraction is initiated at the neuromuscular junction by acetylcholine. Muscles produce movement, stabilize joints, maintain posture, and generate heat. Fiber types range from slow-twitch oxidative to fast-twitch glycolytic, adapting to training and metabolic demands.

In anatomy, musculi appear in specific groupings and names (for example, musculi intercostales, musculi rotatores) to describe individual muscles and collections.