Skeletal muscle nomenclature is primarily rooted in Latin and Greek, serving as anatomical shorthand. This system allows medical professionals and students to quickly deduce a muscle’s characteristics. Understanding this naming system reveals a muscle’s likely location, size, shape, fiber orientation, function, and attachment points.
Using Location and Position for Muscle Names
Many skeletal muscles are named for the specific bone, body region, or relative position they occupy. Terms identifying a bone, such as temporalis (near the temporal bone) or frontalis (over the frontal bone), indicate the muscle’s general area. Names can also reference a broader body region, such as the pectoralis muscles in the chest or the brachii muscles in the arm.
Positional prefixes and suffixes offer detailed locational context relative to other structures. For instance, anterior and posterior indicate a muscle is toward the front or back of the body. Other directional terms include superficial (closer to the surface), deep (farther from the surface), or intercostal (situated between the ribs). The tibialis anterior, for example, is located on the front of the tibia bone.
How Physical Structure Determines Muscle Names (Shape, Size, and Fiber Direction)
The physical characteristics of a muscle contribute to its name. Muscle size is a common descriptor, using terms like maximus (largest), medius (medium), minimus (smallest), longus (long), and brevis (short). The gluteus maximus, gluteus medius, and gluteus minimus muscles are named this way to distinguish them based on their relative size in that region.
Muscle shape frequently lends itself to a geometric or familiar object name. The deltoid muscle, covering the shoulder, is named because its shape resembles the Greek letter delta, which is a triangle. The trapezius muscle is named for its trapezoidal shape, while orbicularis muscles, such as those around the eye or mouth, are circular. Other shape-based names include rhomboid for a parallelogram shape and latissimus for a wide, broad muscle.
The arrangement and angle of the muscle fibers influence the anatomical name. Muscles with fibers that run straight, or parallel to the midline, are labeled rectus, as seen in the rectus abdominis. If the fibers run perpendicular to the midline, the term transversus is used, such as with the transversus abdominis. Fibers that run at a slanted or diagonal angle are designated as oblique, naming the external and internal oblique muscles of the abdomen.
Naming Muscles by Their Function and Connecting Points
A muscle’s name can directly indicate the action or movement it produces. This functional naming convention employs terms like Flexor (to bend a joint) and Extensor (to straighten a joint). Similarly, an Abductor moves a limb away from the midline, while an Adductor moves it toward the midline.
Other action-based names include Levator (which lifts or elevates a structure) and Depressor (which lowers or depresses a structure). For example, the levator scapulae is a muscle that elevates the scapula, or shoulder blade. This descriptive approach means that simply knowing the muscle’s name provides a clear picture of its primary role.
Some muscles are named based on the number of tendons of origin, or “heads,” they possess. The prefix bi- means two, so the biceps brachii muscle has two points of origin on the scapula. The triceps brachii, located on the back of the arm, has three heads, indicated by the prefix tri-. The large muscle group on the front of the thigh, the quadriceps femoris, is named using the prefix quadri-, signifying its four distinct heads of origin.
Muscle names can specify the muscle’s attachment points, noting the origin (the stationary attachment) and the insertion (the movable attachment). In this convention, the origin is always named before the insertion. The sternocleidomastoid muscle, a prominent neck muscle, is an excellent example of this method. Its name is a compound of its origins on the sterno (sternum) and cleido (clavicle), and its insertion on the mastoid process of the skull.