The Study of Skeletal Muscles

The study of the muscular system is called [1]. For the beginner, it is necessary to become familiar with a number of Latin names that describe the muscles. For example, biceps means two [2] and quadriceps means four of them; pollicis means "of the [3]" and hallucis means "of the [4]"; lattisimus means a muscle is very [5] and minimus means it is relatively [6]. Words that describe the shape of a muscle include teres, meaning [7], and deltoid, meaning [8].

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Functions and Structural Organization of Muscles

A muscle consists not only of muscular tissue, but also fibrous connective tissues, including the [9], which ensheaths the muscle as a whole; [10], which encloses each fascicle and separates them from each other; and [11], which ensheaths each muscle fiber within a fascicle. The [12] separates the muscles from the skin. The 9 grades into a tendon at the end of many muscles, but other muscles have no tendons and are said to show a [13] attachment to a bone. When a muscle contracts, one end of it called the [14] remains relatively stationary, whereas the other end, the [15], usually moves a bone. The middle part between 14 and 15 is called the [16] of a muscle.

Muscles can be classified according to shape, or arrangement of their fascicles. Circular muscles typically act as [17] that regulate openings such as the eyelids, mouth, and anus. In the straplike [18] muscles, the fascicles are all more or less parallel. In a [19] muscle, fascicles converge from either side on a central tendon in a featherlike arrangement. [20] muscles are thick in the middle and tapered at each end.

Muscles do not work in isolation, but in groups. The muscle that is primarily responsible for the action of a joint is called the [21]. A muscle that contributes to this action is a [22] and one resists movement and stabilizes a bone is called a [23]. Many muscles work in [24] pairs on opposite sides of a joint–for example, the biceps brachii and triceps brachii, which flex and extend the elbow, respectively. [25] muscles are located entirely within an area of reference–for example, within the hand, eye, or larynx. [26] muscles act on that region through their tendons but are located outside it–for example, muscles of the forearm that act on the fingers.

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Muscles of the Head and Neck

The subtle facial expressions of humans result from the action of numerous small facial muscles. For example, the "kissing muscle," or [27], encircles the mouth and a similar muscle, the [28], encircles the eye. A smile results from contraction of the [29] major and minor, which insert at the corners of the mouth. The [30] muscles, by contrast, draw the corners of the mouth downward and produces a frown. The [31] elevates your eyebrows and wrinkles your forehead. The main muscle of the cheek, used in blowing and sucking, is the [32].

Other muscles of the head are responsible for the tongue movements used in speech and food manipulation. In the names of these muscles, the root -glossus indicates the tongue and is preceded by a root indicating the origins of these muscles; for example, the [33] muscle originates from the styloid process of the cranium and the [34] muscle originates from the hyoid bone. Two powerful chewing muscles are the [35], which arises from the temporal bone above the ear, and the [36], which arises from the zygomatic arch. These insert at different places on the mandible and elevate it when you bite. There are four muscles that form a suprahyoid group, including the [37] which forms the floor of the mouth and the two-bellied [38] which opens the mouth. When you swallow, the [39] muscle elevates the larynx to prevent choking; this action is felt as the bobbing of the "Adam's apple" during swallowing.

Head movements are produced by muscles that originate on the spine, thoracic cage, and pectoral girdle and insert on the cranium. The major flexors, which make you look downward, are the three scalenes and the ropy [40] muscle of the neck, named for its origins on the breastbone and collarbone and its insertion on the bony mound behind your ear. Extensors of the neck, which make you look upward, include a deep muscle with vertical fascicles, the [41]; a more superficial muscle with oblique fascicles, the [42], nicknamed the "bandage muscle;" and a large triangular muscle of the upper back, the [43].

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Muscles of the Trunk

Inhaling is achieved mainly by a downward excursion of the [44] and contraction of the external [45] muscles, which elevate the ribs. Exhaling is normally a passive process, but deep exhalation can be aided by some of the abdominal muscles. The [46] is a vertical, medial, straplike muscle of the abdomen on each side of the linea alba. The most superficial abdominal muscle lateral to this is the [47]. On the back, most of the superficial muscles that straighten the spine belong to a complex named the [48], which describes this action. Deep to this, muscle 41 above continues inferiorly as the semispinalis [49] in the neck region and semispinalis [50] in the thoracic region. In the lumbar region, the major deep muscle is the [51].

Because humans have an upright posture, our viscera are supported largely by muscles of the pelvic floor. The area between the thighs, called the [52], is divided into two triangles–the [53] triangle anteriorly and the [54] triangle posteriorly. In the superficial layer of pelvic floor muscles, the [55] wraps around the bulb of the penis in males and encloses the vagina in females. In the middle muscle layer, the external [56] sphincter and external [57] sphincter control the elimination of urine and feces, respectively. The deep layer of pelvic muscles includes the coccygeus and the [58]. The latter is named for the fact that it elevates the anus during defecation.

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Muscles Acting on the Upper Extremity

The "boxer's muscle" that thrusts your arm forward when you punch or throw something is called the [59]; it extends from the first nine ribs to the medial border of the scapula. The large [60] muscle of the upper back has three groups of fascicles that can tilt, retract, or depress the scapula in addition to extending the neck, as mentioned above at 43. The [61] major and minor extend from the vertebrae to the scapula and retract the scapula.

The thick superficial muscle of the mammary region, called the [62], flexes the shoulder and adducts the humerus. The broad [63] muscle of the lower back produces strong downward movements of the humerus, as in hammering or swimming. The thick, triangular [64] muscle caps the shoulder and abducts the humerus; injections are often given here. On the dorsal side of the scapula, the [65] muscle is named for the fact that it occupies the space superior to the spine and the [66] muscle for the fact that it occupies most of the scapular surface inferior to the spine. The anterior surface of the scapula is occupied by the [67]. The tendons of these three muscles and the teres minor form the [68], a common site of injuries in certain athletes.

The elbow is flexed by two synergistic muscles, the superficial [69] and deeper [70]. Their antagonist is the three-headed [71] on the posterior side of the humerus. Another synergist of elbow flexion is the [72], but its belly lies in the forearm beside the radius. Supination of the forearm is achieved, unsurprisingly, by the supinator muscle, but pronation is achieved by two muscles–the [73] near the elbow and [74] near the wrist.

The fingers are controlled mostly by muscles in the forearm, many of whose tendons pass under a braceletlike [75] on the anterior side of the wrist and [76] on the posterior side. These bands of connective tissue prevent the tendons from bowing up when the muscles contract. Two flexors of the wrist have tendons that stand out prominently just proximal to the palm of your hand–the lateral tendon belongs to the [77] and the medial tendon belongs to the [78]. The four tendons visible on the back of your hand belong to a single muscle that extends the fingers and is appropriately named the [79]. The "anatomical snuffbox," a little pit on the back of the hand at the base of the thumb, is bordered laterally side by the tendon of the [80], a muscle that draws the thumb away from the palm into a "hitchhiking" position, and medially by tendons of the [81] longus and brevis, two tendons that straighten the knuckles of the thumb.

The fleshy pad of the palm at the base of the thumb is the [82] eminence. The web between the thumb and palm is formed by the [83] muscle, which, as its name implies, is an antagonist of 80. Its action, and hence its name, can be inferred quite easily from its location, as is true of many of the muscles we are considering here. In the midpalmar region, there are four dorsal and three palmar [84] between the metacarpal bones and a deeper set of four wormlike [85] muscles that flex the first knuckle of each digit except the thumb.

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Muscles Acting on the Lower Extremity

The broad anterosuperior surface of the pelvis is occupied by the [86] muscle, which together with the psoas major flexes the waist, as in taking a bow. When you are walking, the backswing of your stride results from the action of the [87] muscle of the buttock. Another muscle with a similar name, the [88], shifts your body weight slightly to the left when you raise your right foot, or vice versa. The large muscle of the anterior thigh is the [89]. It has four heads–the [90] lateralis, medialis, and intermedius and the [91] femoris. The medial compartment of the thigh includes the [92] longus, brevis, and magnus (all three named for the same action of the thigh); the long [93], named for its slender shape; and the [94], named for its comblike shape. Muscles of the back of the thigh (the posterior compartment) are called the hamstrings. Their tendons border the pit of the knee (popliteal fossa)–the [95] tendon on the lateral side and the [96] and [97] tendons on the medial side.

Below the knee on the anterior side of the leg, the [98] lies along the lateral side of the tibia; it dorsiflects the foot. The [99] longus extends the great toe and the [100] longus extends the other toes. The superficial muscles of the posterior compartment include the large two-headed [101] and the deeper [102], which together form the triceps surae and insert on the heel by way of the [103] tendon. They produce strong plantar flexion, as in jumping to make a basketball shot. Among the deep muscles are the [104], which flexes the great toe; the [105], which flexes the other toes; and the [106], which unlocks the knee so it can flex. On the plantar aspect of the foot, the most superficial muscle is the [107] brevis, a synergist of 105.

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