Sample Chapter 10 from the Textbook (35559.0K) - McGraw-Hill

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334 PART 2 Support and Movement Table 10.12 Muscles of the Pelvic Floor and Perineum (see figure 10.19) Muscle Origin Insertion Nerve Action Bulbospongiosus (bul′bō-spŭn′jē-ō′sŭs) Male—central tendon of perineum and median raphe of penis Female—central tendon of perineum Dorsal surface of penis and bulb of penis Pudendal Constricts urethra; erects penis Base of clitoris Pudendal Erects clitoris Coccygeus (kok-si′jē-ŭs; not illustrated) Ischiocavernosus (ish′ē-ō-kav′er-nō′sŭs) Levator ani (lē-vā′tor, le-vā′ter ā′nī ) Ischial spine Coccyx S3 and S4 Elevates and supports pelvic floor Ischial ramus Corpus cavernosum Perineal Compresses base of penis or clitoris Posterior pubis and ischial spine Sacrum and coccyx Fourth sacral Elevates anus; supports pelvic viscera External anal sphincter (ā′năl sfingk′ter) Coccyx Central tendon of perineum Fourth sacral and pudendal Keeps orifice of anal canal closed External urethral sphincter (ū -rē′thrăl sfingk′ter; not illustrated) Pubic ramus Median raphe Pudendal Constricts urethra Transverse perinei (pĕ r′i-nē′ī ) Deep Ischial ramus Median raphe Pudendal Supports pelvic floor Superficial Ischial ramus Central perineal Pudendal Fixes central tendon Median raphe Urethra Ischiocavernosus Bulbospongiosus Central tendon of perineum Deep transverse perineal Superficial transverse perineal Levator ani Vagina Ischial tuberosity Anus External anal sphincter Gluteus maximus Coccyx (a) Male, inferior view (b) Female, inferior view FIGURE 10.19 Muscles of the Pelvic Floor and Perineum (Muscle names are in bold.) 10.4 Upper Limb Muscles Learning Outcomes After reading this section, you should be able to A. Describe the movements of the scapula and list the muscles associated with it. B. Name and locate the muscles acting on the shoulder and arm and explain their movements. C. List and describe the muscles and movements of the forearm, wrist, hand, and fingers. D. Distinguish between extrinsic and intrinsic hand muscles.
CHAPTER 10 Muscular System 335 Table 10.13 Muscles Acting on the Scapula (see figure 10.20) Muscle Origin Insertion Nerve Action Levator scapulae (lē-vā′tor, le-vā′ter skap′ū -lē) Transverse processes of C1–C4 Superior angle of scapula Dorsal scapular Elevates, retracts, and rotates scapula; laterally flexes neck Pectoralis minor (pek′tō-ra′lis) Third to fifth ribs Coracoid process of scapula Medial pectoral Depresses scapula or elevates ribs Rhomboideus (rom-bō-id′ē-ŭs) Major Spinous processes of T1–T4 Medial border of scapula Dorsal scapular Retracts, rotates, and fixes scapula Minor Spinous processes of C6–C7 Medial border of scapula Dorsal scapular Retracts, slightly elevates, rotates, and fixes scapula Serratus anterior (ser-ā′tŭs) Subclavius (sŭb-klā′vē-ŭs) First to eighth or ninth ribs Medial border of scapula Long thoracic Rotates and protracts scapula; elevates ribs First rib Clavicle Subclavian Fixes clavicle or elevates first rib Trapezius (tra-pē′zē-ŭs) External occipital protuberance, ligamentum nuchae, and spinous processes of C7–T12 Clavicle, acromion process, and scapular spine Accessory and cervical plexus Elevates, depresses, retracts, rotates, and fixes scapula; extends neck The major connection of the upper limb to the body is accomplished by muscles (table 10.13; figure 10.20). The muscles of the upper limb include those that move the scapula and those that move the arm, forearm, and hand. Scapular Movements The muscles attaching the scapula to the thorax include the trapezius, levator scapulae (skap′ū-lē), rhomboideus (rom-bō-id′ē-ŭs) major and rhomboideus minor, serratus (sĕr-ā′tŭs) anterior, and pectoralis (pek′tō-ra′lis) minor. These muscles move the scapula, permitting a wide range of movements of the upper limb, or they act as fixators to hold the scapula firmly in position when the arm muscles contract. The superficial muscles that act on the scapula can easily be seen on a living person (see figure 10.5b): The trapezius forms the upper line from each shoulder to the neck, and the origin of the serratus anterior from the first eight or nine ribs can be seen along the lateral thorax. The serratus anterior inserts onto the medial border of the scapula (figure 10.20c). Arm Movements The arm is attached to the thorax by several muscles, including the pectoralis major and the latissimus dorsi (lă-tis′i-mŭs dōr′sī; table 10.14; see figures 10.20b, 10.21, and 10.22). Notice that the pectoralis major is listed in table 10.14 as both a flexor and an extensor. The muscle flexes the extended shoulder and extends the flexed shoulder. Try these movements and notice the position and action of the muscle. The deltoid (deltoideus) muscle (figure 10.21) is also listed in table 10.14 as a flexor and an extensor. The deltoid muscle is like three muscles in one: The anterior fibers flex the shoulder, the lateral fibers abduct the arm, and the posterior fibers extend the shoulder. The deltoid muscle is part of the group of muscles that binds the humerus to the scapula. However, the primary muscles holding the head of the humerus in the glenoid cavity are called the rotator cuff muscles (listed separately in table 10.14) because they form a cuff or cap over the proximal humerus (figure 10.23). A rotator cuff injury involves damage to one or more of these muscles or their tendons, usually the supraspinatus muscle. The muscles moving the arm are involved in flexion, extension, abduction, adduction, rotation, and circumduction (table 10.15). To visualize how these muscle groups work together, imagine that you want to raise your arm so that your hand is high above your head. First, you must abduct your arm from the anatomical position through 90 degrees (to the point at which the hand is level with the shoulder); this involves moving the humerus and is accomplished by the deltoid muscle assisted by the rotator cuff muscles, which hold the head of the humerus tightly in place. In the initial phase of abduction (first 15 degrees), the deltoid is assisted by the supraspinatus. Place your hand on your deltoid, and feel it contract as you abduct 90 degrees. Next, move your arm from 90 degrees to 180 degrees, so that your hand is high above your head; this movement primarily involves rotation of the scapula, which is accomplished by the trapezius and serratus anterior muscles. Feel the inferior angle of your scapula as you abduct your arm to 90 degrees and then rotate to 180 degrees. Do you notice a big difference? Bear in mind that your arm cannot move from 90 degrees to 180 degrees unless the head of the humerus is held tightly in the glenoid cavity by the rotator cuff muscles, especially the supraspinatus. Damage to the supraspinatus muscle can prevent abduction past 90 degrees.
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Page 7 and 8: FUNDaMeNTal Figure Sternocleidomast
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Sample Chapter 10 from the Textbook (35559.0K) - McGraw-Hill

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