|NAMES OF SKELETAL MUSCLES
Except for the platysma and the diaphragm, the complete names of all skeletal muscles include the term muscle. Although the full name, such as the biceps brachii muscle, will usually appear in the text, for simplicity only the descriptive name (biceps brachii) will be used in figures and tables.
You need not learn every one of the approximately 700 muscles in the human body, but you will have to become familiar with the most important ones. Fortunately, anatomists assigned names to the muscles that provide clues to their identification. If you can learn to recognize the clues, you will find it easier to remember the names and identify the muscles. The name of a muscle may include information about its fascicle organization, location, relative position, structure, size, shape, origin and insertion, or action.
A muscle name may refer to the orientation of the muscle fibers within a particular skeletal muscle. Rectus means "straight," and rectus muscles are parallel muscles whose fibers generally run along the long axis of the body. Because we have several rectus muscles, the name typically includes a second term that refers to a precise region of the body. For example, the rectus abdominis muscle is located on the abdomen, and the rectus femoris muscle on the thigh. Other directional indicators include transversus and oblique for muscles whose fibers run across or at an oblique angle to the longitudinal axis of the body, respectively.
Table 11-1 includes a useful summary of terms that designate specific regions of the body. They are common as modifiers that help identify individual muscles, as in the case of the rectus muscles. In a few cases, the muscle is such a prominent feature of the region that the regional name alone will identify it. Examples include the temporalis muscle of the head and the brachialis muscle of the arm.
Muscles visible at the body surface are often called externus or superficialis, whereas deeper muscles are termed internus or profundus. Superficial muscles that position or stabilize an organ are extrinsic; muscles located entirely within the extrinsic organ are intrinsic.
Structure, Size, and Shape
Some muscles are named after distinctive structural features. The biceps brachii muscle, for example, has two tendons of origin; the triceps brachii muscle has three; and the quadriceps group, four. Shape is sometimes an important clue to the name of a muscle. For example, the trapezius, deltoid, rhomboideus, and orbicularis muscles look like a trapezoid, a triangle, a rhomboid, and a circle, respectively. Long muscles are called longus (long) or longissimus (longest), and teres muscles are both long and round. Short muscles are called brevis. Large ones are called magnus (big), major (bigger), or maximus (biggest); and small ones are called minor (smaller) or minimus (smallest).
Origin and Insertion
Many names tell you the specific origin and insertion of each muscle. In such cases, the first part of the name indicates the origin, and the second part the insertion. The genioglossus muscle, for example, originates at the chin (geneion) and inserts in the tongue (glossus). Although the names may be long and difficult to pronounce, Table 11-1 and the anatomical terms introduced in Chapter 1 can help you identify and remember them.
Many muscles are named flexor, extensor, retractor, abductor, and so on. These are such common actions that the names almost always include other clues as to the appearance or location of the muscle. For example, the extensor carpi radialis longus muscle is a long muscle along the radial (lateral) border of the forearm. When it contracts, its primary function is extension at the carpus (wrist).
A few muscles are named after the specific movements associated with special occupations or habits. The sartorius muscle is active when you cross your legs. Before sewing machines were invented, a tailor would sit on the floor cross-legged, and the name of this muscle was derived from sartor, the Latin word for "tailor." On the face, the buccinator muscle compresses the cheeks, as when you purse your lips and blow forcefully. Buccinator translates as "trumpet player." Another facial muscle, the risorius muscle, was supposedly named after the mood expressed. The Latin term risor, however, means "laugher"; a more appropriate description for the effect would be "grimace."