Some Characteristics Used for Naming Muscles Help
Introduction Some Characteristics Used for Naming Muscles
In this section, we will examine some of the general characteristics or criteria frequently employed to name major skeletal muscles.
Characteristic #1: Body location. Many muscles are either totally or partially named for their body location. Consider, for example, the tibialis ( tih -bee- AL -is) anterior muscle. From Figure 14.1, you can see that this muscle is named for its location “in front of” (anterior) to the tibia ( TIB -ee-ah) or “shin bone.” The name tibia also means “pipe” or “flute,” apparently from its shape. The tibia (and its associated skeletal muscles) is found not just within humans but also in amphibians, reptiles, birds, and other mammals.
Characteristic #2: Muscle shape. Just as the tibia bone (and hence the tibialis anterior muscle) is partially named for its resemblance to an ancient Roman flute, various skeletal muscles are likewise named for their shapes. Look at the deltoid ( DELL -toyd) muscle (Figure 14.1). This muscle “resembles” (- oid ) a “triangle” ( delt ) in the upper shoulder area.
Characteristic #3: Points of attachment . Remember that each skeletal muscle is attached to a bone by one or more tendons at either end. The origin of a muscle is the least movable tendon or attachment of the muscle. Picture it like a heavy anchor. The origin of the biceps brachii muscle, for instance, is at the bones of the shoulder. The insertion of a muscle, on the other hand, is the more movable tendon or attachment. The insertion of the biceps brachii is made upon the bones in the lower arm.
Within a particular bone–muscle lever system, then, when the muscle contracts and exerts a pulling force, only the insertion end moves. The origin end remains stationary, because it is firmly anchored. During contraction, the insertion end of a muscle moves towards the origin end. In the case of the biceps brachii, when it contracts its lower tendons flex ( FLEKS ) or “bend” the arm at the elbow joint. [ Study suggestion: Put down this book for a moment and flex your own forearm. Try to imagine the lower tendons of your biceps brachii pulling upon their insertion on your forearm bones to raise your lower arm.]
Some muscles are even named for their points of attachment (origin and insertion). A good example is provided by the sternocleidomastoid ( ster -noh- kleye -doh- MASS -toyd) muscle. Figure 14.3 reveals that this muscle attaches to the sternum ( STER -num) or main bone of the “chest” ( stern ). Its tendons also hook onto the clavicle ( KLAV -uh-kul) or collar bone, which is named for its resemblance to a “little key” ( clavicul ) used in ancient times. Finally, the sternocleidomastoid tendons attach to a third place – the mastoid ( MASS -toyd) process of the skull – which literally “resembles” (- oid ) a “little breast” ( mast ).
When the sternocleidomastoid contracts, it nods the head, drawing the chin down upon the chest. [ Study suggestion: From the preceding information, which attachment do you think represents the insertion end of the sternocleidomastoid? – What attachments are the origin end?]
Characteristic #4: Relative size. Some muscles are named for their relative size: that is, how big they are compared to their neighbors. Consider two muscles in the gluteal ( GLOO -tee-al) or “rump” region – the gluteus ( GLOO -tee-us) maximus ( MACKS -ih-mus) and the gluteus minimus ( MIN -ih-mus). [ Study suggestion: Which do you think is the larger muscle, the one with a more “minimum” or more “maximum” size?]
Characteristic #5: Number of muscle “heads.” A muscle head is a major division of a muscle, with one or more tendons attached. In Latin, ceps ( SEPS ) means “head,” while bi- denotes “two.” Biceps ( BUY -seps), therefore, means “two-headed.”
Brachii ( BRAY -kee-eye) stands for “arm.” Hence, the name of the biceps brachii muscle translates exactly to mean a “two-headed” muscle in the upper “arm.” The biceps brachii has two major heads or divisions to it, and is hooked onto bones by two tendons above the muscle, and two below it.
Characteristic #6: Direction of muscle fibers. Several muscles are given Latin names describing the direction of their individual muscle fibers – long, slender, fiber-shaped muscle cells. Consider the rectus ( WRECK -tus) abdominis (ahb- DAHM -ih-nus) muscle. (Review Figure 14.1.) It is located in the front of the abdomen (trunk midsection), and its fibers are oriented in a “straight” (rect), vertical direction.
Characteristic #7: Association with real or mythological characters . Certain muscles are associated with real people, or with people who only existed in myth. A very intriguing example is the sartorius (sar- TOR -ee-us). This muscle oddly means “presence of” (-us) a “tailor” (sartori )! The naming connection is to the way tailors used to sit in ancient times – cross-legged upon the ground (Figure 14.4). The sartorius is actually located along the inner aspect of each thigh. Thus, when it contracts, it flexes (bends) the lower leg, as was done by ancient tailors who used to sit on their bent legs!
Characteristic #8: Major body actions. Some muscles are named for their major body actions. Consider as an example the masseter (mah- SEE -ter) muscle in the lower jaw. Its name comes from Latin for “chewer.” You use the masseter to lift your lower jaw as you chew meat or gum, of course!
Practice problems for these concepts can be found at: The Neuromuscular (Nerve-Muscle) Connection Test