Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

©2018 Achieve Test Prep Page 120 of 367 Many muscles are named flexor, extensor, pronator, abductor, etc. Muscles with these common action names usually have other descriptors in their names, such as the extensor carpi radialis longus muscle, which is a long muscle along the radial (lateral) border of the forearm. Its primary function is extension at the carpus (wrist). 11.6 Aging As the body ages, the size and power of muscle tissue declines. As humans age, skeletal muscle fibers become smaller in diameter. This reduction in size reflects primarily a decrease in the number of myofibrils. Skeletal muscles loss elasticity. Fibrous connective tissue increases in skeletal muscle with aging in a process called fibrosis . Location in the Body Regional terms are often used as modifiers that assist in distinguishing individual muscles. At times, a muscle is such a noticeable feature of a body region that a name referring to the region alone will distinguish it. Examples include the temporalis muscle of the head and the brachialis muscle of the arm. Origin and Insertion Some muscle names describe the locations for their origin and insertion. Many times, the beginning 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). The orientation of the muscle fascicles within skeletal muscle may provide the basis for the muscle name. For example, rectus means “straight,” and the rectus muscles are muscles whose fibers commonly run parallel to the long axis of the body. There are 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 found in the abdomen, and the rectus femoris muscle is part of the thigh. Relative Position Muscles closer to the body surface are referred to as externus or superficialis, whereas deeper muscles are referred to as internus or profundus. Some superficial muscles have an additional role which includes positioning or stabilizing an organ; they are called extrinsic muscles. Those muscles located entirely within an organ are intrinsic. Structural Characteristics Some muscles are labeled after distinctive physical features. With two tendons of origin, one of the major muscles of the upper arm is called the biceps brachii muscle; the triceps brachii muscle has three tendons; and the quadriceps group has four. A critical indication to the name of a muscle can be its shape. For example, the trapezius, deltoid, rhomboid, and orbicularis muscles look like a trapezoid, a triangle, a rhombus, and a circle, respectively. Many terms refer to muscle size. Long muscles are often called longus (long) or longissimus (longest). Action