BSC 215 Lecture Notes - Lecture 23: Rhomboid Major Muscle, Temporal Muscle, Myocyte
11 Jun 2018
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Names of Skeletal Muscles
Skeletal muscles are often named after the following characteristics:
• Number of origins: Biceps, triceps, and quadriceps indicate two, three, and four
origins, respectively.
• Location of origin or insertion: The sternocleidomastoid names the sternum
(sterno) and clavicle (cleido) as its origins and the mastoid process of the
temporal bone as its insertion.
• Location: In addition to its origin or insertion, a muscle name may indicate a
nearby bone or body region. For example, the temporalis muscle covers the
temporal bone.
• Shape: The deltoid (triangular), trapezius (trapezoid), serratus (saw‐toothed), and
rhomboideus major (rhomboid) muscles have names that describe their shapes.
• Direction of muscle fibers: The terms rectus (parallel), transverse (perpendicular),
and oblique (at an angle) in muscle names refer to the direction of the muscle
fibers with respect to the midline of the body.
• Size: Maximus (largest), minimus (smallest), longus (longest), and brevis
(shortest) are common suffixes added to muscle names.
• Action: Terms such as flexor (flex the arm), extensor (extend the arm), abductor
(move the arm laterally away from the torso), and adductor (return the arm to the
torso) are added as prefixes to muscle names to indicate the kind of movement
generated by the muscle.
Muscle Size and Arrangement of Muscle Fascicles
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Document Summary
The size of a muscle influences its capabilities. When a muscle fiber (muscle cell) contracts, it can shorten to nearly half its relaxed length. The longer a muscle fiber, the greater range of movement it can generate. In contrast, an increase in the number of muscle fibers increases the strength of the contraction. Muscle fibers are grouped into fascicles, which in turn are grouped to form a muscle. The size (length) and number of fascicles determine the strength and range of movement of a muscle. Common fascicle patterns include the following: parallel fascicles have their long axes parallel to each other. Parallel fascicles can be flat or straplike, or they can bulge at their bellies and be spindle shaped or fusiform: circular fascicles are arranged in concentric rings. Muscles with this pattern form sphincter muscles that control the opening and closing of orifices: pennate fascicles are short and attach obliquely to a long tendon that extends across the entire muscle.
