Muscular System PDF

11 The Muscular System n Learning Outcomes so T...

11 The Muscular System n Learning Outcomes so These Learning Outcomes correspond by number to this chapter’s sections and indicate what you should be able to do after completing the chapter. ar 11-1 Describe the arrangement of fascicles in the various types of muscles, and explain the resulting functional differences. p. 337 11-2 11-3 muscles more efficient. p. 339 Pe Describe the classes of levers, and explain how they make Predict the actions of a muscle on the basis of its origin and insertion, and explain how muscles interact to produce or oppose movements. p. 339 ht 11-4 Explain how the name of a muscle can help identify its location, appearance, or function. p. 343 11-5 ig Compare and contrast the axial and appendicular muscles. p. 344 11-6 Identify the principal axial muscles of the body, plus their origins, insertions, actions, and innervation. p. 347 yr 11-7 Identify the principal appendicular muscles of the body, plus their origins, insertions, actions, and innervation, and compare the major functional differences between the upper and lower limbs. p. 362 op 11-8 Explain the functional relationship between the muscular system and other body systems, and explain the role of exercise in producing various responses in other body systems. p. 382 C M11_MART6026_11_SE_C11_pp336-388.indd 336 20/10/16 8:10 PM  + CLINICAL CASE Downward-Facing Dog “Breathe and do what you can do,” the a little between classes. By now, three instructor called out to the class in soothing months later, he could stretch his arms tones. Rick concentrated on his yoga overhead and balance on one foot for a few pose. He’d been coming to class with the seconds in Tree Pose. His leg muscles felt encouragement of his nurse practitioner. stronger as he stepped sideways into Warrior “I think yoga could help you move and Pose. His next challenge was to tackle the feel better. Your arthritis medications can most famous yoga pose of all, Downward- only do so much for you. Give yoga the Facing Dog. He thought that he might be old college try. Let’s see you again in three up to trying it. Slow and easy, he told him- months,” she urged. self. What will the nurse practitioner test Rick was impressed with the gentle practice of yoga. The on Rick’s return visit? To find out, turn to the Clinical Case n first week in class his body felt all locked up, like the Tin Man in Wrap-Up on p. 387. 11 The Wizard of Oz. But he stayed with the program and practiced so An Introduction to the Muscular System biceps brachii on the anterior surface of your arm. Other par- ar allel muscles include the rectus abdominis (Figure 11–1b) and In this chapter we describe the gross anatomy of the muscular supinator (Figure 11–1c). system and consider functional relationships between muscles A skeletal muscle fiber can contract until it has shortened Pe and bones of the body. Most skeletal muscle fibers contract at similar rates and shorten to the same degree, but variations in their microscopic and macroscopic organization can dramati- cally affect the power, range, and speed of movement produced when a whole muscle contracts. about 30 percent. The entire parallel muscle shortens by this amount when its fibers contract together, because these fibers are parallel to the long axis of the muscle. Thus, if the muscle is 10 cm (3.9 in.) long and one end is held in place, the other end will move 3 cm when the muscle contracts. The tension devel- oped during this contraction depends on the total number of ht 11-1 Fascicle arrangement is correlated myofibrils the muscle contains. p. 315 with muscle power and range of motion Convergent Muscles Learning Outcome Describe the arrangement of fascicles in ig the various types of muscles, and explain the resulting functional In a convergent muscle, muscle fascicles extending over a broad differences. area come together, or converge, on a common attachment site. Muscle fibers in a skeletal muscle form bundles called fascicles The muscle may pull on a tendon, an aponeurosis, or a slender yr band of collagen fibers known as a raphe (RA-f e; seam). The. (FAS-ih-kulz). p. 293 The muscle fibers in a single fascicle are. parallel, but the arrangement of fascicles in skeletal muscles can muscle fibers typically spread out, like a fan or a broad triangle, vary, as can the relationship between the fascicles and the asso- with a tendon at the apex. Examples include the prominent pec- op ciated tendon. Based on the patterns of fascicle arrangement, toralis muscles of the chest (Figure 11–1d). we can classify skeletal muscles as parallel muscles, convergent A convergent muscle can adapt to different activities muscles, pennate muscles, and circular muscles (Figure 11–1). because the stimulation of different portions of the muscle can change the direction it pulls. However, when the entire muscle C Parallel Muscles contracts, the muscle fibers do not pull as hard on the attach- ment site as would a parallel muscle of the same size. Why? In a parallel muscle, the fascicles are parallel to the long axis The reason is that convergent muscle fibers pull in different of the muscle. Most of the skeletal muscles in the body are directions, rather than all pulling in the same direction as in parallel muscles. Some are flat bands with broad attachments. parallel muscles. (aponeuroses; ap-o-nu-RO-sez) at each end. Others are plump... and cylindrical, with tendons at one or both ends. Such a muscle is spindle shaped, with a central body, also known as Pennate Muscles the belly. For example, the biceps brachii of the arm is a parallel In a pennate muscle (PEN-a t; penna, feather), the fascicles. muscle with a central body (Figure 11–1a). When a parallel form a common angle with the tendon. Because the mus- muscle contracts, it shortens and gets larger in diameter. When cle fibers pull at an angle, contracting pennate muscles do you flex your elbow, you can see the bulge of the contracting not move their tendons as far as parallel muscles do. But 337 M11_MART6026_11_SE_C11_pp336-388.indd 337 20/10/16 8:10 PM  338 UNIT 2 Support and Movement Figure 11–1 Muscle Types Based on Pattern of Fascicle Arrangement. Parallel Muscles Convergent Muscles a Parallel muscle b Parallel muscle c Wrapping d Convergent muscle (Biceps brachii) with tendinous muscle (Pectoralis) bands (Supinator) (Rectus abdominis) Tendon Base of muscle n 11 (h) Fascicle (d) so Cross (g) section Body (a) (belly) (b) Cross section ar (e) (c) (f) Pennate Muscles e Unipennate muscle (Extensor f Bipennate muscle (Rectus femoris) Pe g Multipennate muscle (Deltoid) Circular Muscles h Circular muscle (Orbicularis oris) digitorum) ht Contracted ig Tendons yr Extended tendon Relaxed op Cross section a pennate muscle contains more muscle fibers—and thus (Figure 11–1f). If the tendon branches within a pennate mus- C more myofibrils—than does a parallel muscle of the same cle, the muscle is said to be multipennate. The triangular deltoid size. For this reason, the pennate muscle produces more of the shoulder is multipennate (Figure 11–1g). tension. There are three types of pennate muscles, depending on the arrangement of the fascicles with the tendon. If all the muscle Circular Muscles fascicles are on the same side of the tendon, the pennate muscle In a circular muscle, or sphincter (SFINK-ter), the fascicles are is unipennate. The extensor digitorum, a forearm muscle that concentrically arranged around an opening. When the muscle extends the finger joints, is unipennate (Figure 11–1e). More contracts, the diameter of the opening becomes smaller. Circu- commonly, a pennate muscle has fascicles on both sides of a lar muscles surround body openings or hollow organs and act central tendon. Such a muscle is called bipennate. The rectus as valves in the digestive and urinary tracts. An example is the femoris, a prominent muscle that extends the knee, is bipennate orbicularis oris of the mouth (Figure 11–1h). M11_MART6026_11_SE_C11_pp336-388.indd 338 20/10/16 8:10 PM  Chapter 11 The Muscular System 339 A familiar example of a second-class lever is a loaded Checkpoint wheelbarrow. The load lies between the applied force and the 1. Based on patterns of fascicle arrangement, name the four fulcrum (Figure 11–2b). The weight is the load, and the upward types of skeletal muscle. lift on the handle is the applied force. We can describe the posi- 2. Why does a pennate muscle generate more tension than tions as F–L–AF. In this arrangement, a small force can move does a parallel muscle of the same size? a larger weight because the force is always farther from the 3. Which type of fascicle arrangement would you expect in fulcrum than the load is. That is, the effective force is increased. a muscle guarding the anal opening between the large intestine and the exterior? Notice, however, that when a force moves the handle, the load moves more slowly and covers a shorter distance. In other See the blue Answers tab at the back of the book. words, the effective force is increased at the expense of speed and distance. The body has few second-class levers. Ankle exten- n sion (plantar flexion) by the calf muscles involves a second- 11-2 The use of bones as levers class lever (see Figure 11–2b). 11 increases muscle efficiency so In a third-class lever, such as a pair of tongs, the applied Learning Outcome Describe the classes of levers, and explain force is between the load and the fulcrum (Figure 11–2c). We how they make muscles more efficient. can describe the positions as F–AF–L. Third-class levers are the Skeletal muscles do not work in isolation. For muscles attached most common levers in the body. The effect is the reverse of to the skeleton, the nature and site of their connections deter- that for a second-class lever: Speed and distance traveled are ar mine the force, speed, and range of the movement they produce. increased at the expense of effective force. These characteristics are interdependent, and the relationships Not every muscle is part of a lever system, but the presence of can explain a great deal about the general organization of the levers provides speed and versatility far in excess of what we would muscular and skeletal systems. or direction of movement produced by muscle contraction. Pe Attaching the muscle to a lever can modify the force, speed, A lever is a rigid structure—such as a board, a crowbar, or a bone—that moves on a fixed point called a fulcrum. A lever predict for the body on the basis of muscle physiology alone. Checkpoint 4. Define a lever, and describe the three classes of levers. 5. The joint between the occipital bone of the skull and the moves when pressure, called an applied force, is sufficient to ht first cervical vertebra (atlas) is a part of which class of overcome any load that would otherwise oppose or prevent lever? such movement. See the blue Answers tab at the back of the book. In the body, each bone is a lever and each joint is a fulcrum. ig Muscles provide the applied force. The load can vary from the weight of an object held in the hand to the weight of a limb or 11-3 The origins and insertions the weight of the entire body, depending on the situation. The of muscles determine their actions yr important thing about levers is that they can change (1) the Learning Outcome Predict the actions of a muscle on the basis direction of an applied force, (2) the distance and speed of of its origin and insertion, and explain how muscles interact to movement produced by an applied force, and (3) the effective produce or oppose movements. op strength of an applied force. To understand the actions of skeletal muscles, we need to There are three classes of levers. A lever is classified understand where they are connected to the bones that act as according to the relative position of three elements: applied levers and which joints they cross. force, fulcrum, and load. Regardless of the class of lever, all follow the same mechanical principles: A mechanical C advantage occurs when the applied force is farther from Origins and Insertions the fulcrum than the load. A mechanical disadvantage In Chapter 10 we noted that when both ends of a myofibril are occurs when the applied force is closer to the load than the free to move, the ends move toward the center during a con- fulcrum. traction. In the body, the ends of a skeletal muscle are always We find examples of each class of lever in the human attached to other structures that limit their movement. In most body (Figure 11–2). A pry bar or crowbar is an example of a cases one end is fixed in position, and during a contraction the first-class lever. In such a lever, the fulcrum (F) lies between other end moves toward the fixed end. The less movable end is the applied force (AF) and the load (L). We can describe the called the origin of the muscle. The more movable end is called positions as L–F–AF. The body has few first-class levers. One, the insertion of the muscle. The origin is typically proximal involved with extension of the neck and lifting the head, is to the insertion. Almost all skeletal muscles either originate or shown in Figure 11–2a. insert on the skeleton. M11_MART6026_11_SE_C11_pp336-388.indd 339 20/10/16 8:10 PM  340 UNIT 2 Support and Movement Figure 11–2 The Three Classes of Levers. a First-class lever The fulcrum (F) lies between the Splenius capitis and applied force (AF) and the load (L). semispinalis capitis Example: Pry bar L AF Load F Fulcrum AF L n F Applied L 11 force AF so F b Second-class lever ar The load (L) lies between the applied force (AF) and the fulcrum (F). Gastrocnemius Example: Wheelbarrow L AF Pe AF Fulcrum F Load L AF Applied force L ht F F ig c Third-class lever The force (F) is applied between the load (L) and the fulcrum (F). yr Applied force Load AF AF AF L op F Biceps brachii F L Fulcrum L C Example: Tongs F The decision as to which end is the origin and which is muscular system is that you can actually do the movements the insertion is usually based on movement from the anatomi- and think about the muscles involved. As a result, laboratory cal position. As an example, consider the gastrocnemius, a calf activities focusing on muscle actions are often like disorganized muscle that extends from the distal portion of the femur to aerobics classes. the calcaneus. As Figure 11–2b shows, when the gastrocnemius When we cannot easily determine the origins and insertions contracts, it pulls the calcaneus toward the knee. As a result, on the basis of movement from the anatomical position, we have we say that the gastrocnemius has its origin at the femur and other rules to use. If a muscle extends between a broad aponeu- its insertion at the calcaneus. Part of the fun of studying the rosis and a narrow tendon, the aponeurosis is the origin and the M11_MART6026_11_SE_C11_pp336-388.indd 340 20/10/16 8:10 PM  Chapter 11 The Muscular System 341 tendon is the insertion. If several tendons are at one end and just movement. The biceps brachii is an agonist that produces one is at the other, the muscle has multiple origins and a single flexion at the elbow. insertion. However, these simple rules cannot cover every situa- An antagonist is a muscle whose action opposes that of tion. Knowing which end is the origin and which is the insertion a particular agonist. The triceps brachii is an agonist that is ultimately less important than knowing where the two ends extends the elbow. For this reason, it is an antagonist of the attach and what the muscle accomplishes when it contracts. biceps brachii. Likewise, the biceps brachii is an antagonist Most muscles originate at a bone, but some originate at a of the triceps brachii. connective tissue sheath or band. Examples of these sheaths or Agonists and antagonists are functional opposites. If one bands include intermuscular septa (components of the deep fascia produces flexion, the other produces extension. When an ago- that may separate adjacent skeletal muscles), tendinous inscriptions nist contracts to produce a particular movement, the corre- that join muscle fibers to form long muscles such as the rectus sponding antagonist is stretched, but it usually does not relax n abdominis, the interosseous membranes of the forearm or leg, and completely. Instead, it contracts eccentrically, with just enough 11 the fibrous sheet that spans the obturator foramen of the pelvis. tension to control the speed of the movement and ensure its so smoothness. p. 318 Actions You may find it easiest to learn about muscles in agonist– When a muscle contracts, it produces a specific action, or antagonist pairs (flexors–extensors, abductors–adductors) that movement. As introduced in Chapter 9, when a muscle moves act at a specific joint. This method highlights the functions of ar a portion of the skeleton, that movement may involve flex- the muscles involved, and it can help organize the information ion, extension, adduction, abduction, protraction, retraction, into a logical framework. The tables in this chapter are arranged elevation, depression, rotation, circumduction, pronation, to support such an approach. Pe supination, inversion, eversion, lateral flexion, opposition, or reposition. (Before proceeding, you may want to review the discussions of planes of motion and Spotlight Figure 9–2 and Figures 9–3 to 9–5.) pp. 272–276 We can describe actions in two ways, one focused on the When a synergist (syn-, together + ergon, work) contracts, it helps a larger agonist work efficiently. Synergists may provide additional pull near the insertion or may stabilize the point of origin. Their importance in assisting a particular movement may change as the movement progresses. In many cases, they bone and one on the joint. The first way describes actions in are most useful at the start, when the agonist is stretched and ht terms of the bone or region affected. For example, we say a unable to develop maximum tension. For example, the latis- muscle such as the biceps brachii performs “flexion of the fore- simus dorsi is a large trunk muscle that extends, adducts, and arm.” However, specialists such as kinesiologists and physical medially rotates the arm at the shoulder joint. A much smaller therapists increasingly use the second way, which identifies the ig muscle, the teres (TER-ez) major, assists in starting such move-. joint involved. In this approach, we say the action of the biceps ments when the shoulder joint is at full flexion. brachii is “flexion at (or of) the elbow.” Examples of muscle A fixator is a synergist that assists an agonist by prevent- action are presented in Spotlight Figure 11–3. yr ing movement at another joint, thereby stabilizing the In complex movements, muscles commonly work in groups origin of the agonist. Recall that the biceps brachii is an rather than individually. Their cooperation improves the effi- agonist that produces flexion at the elbow. It has two ten- ciency of a particular movement. For example, large muscles of op dons that originate on the scapula and one that inserts on the limbs produce flexion or extension over an extended range the radius. During flexion, the trapezius and rhomboid of motion. These muscles cannot produce powerful movements act as fixators by stabilizing and preventing the movement at full extension due to the positions of the articulating bones, of the scapula. but they are usually paired with one or more smaller muscles C that provide assistance until the larger muscle can perform at maximum efficiency. At the start of the movement, the smaller Checkpoint muscle produces maximum tension, while the larger muscle produces minimum tension. The importance of the smaller 6. The gracilis attaches to the anterior surface of the tibia at one end, and to the pubis and ischium of the pelvis at the “assistant” decreases as the movement proceeds and the effec- other. When the muscle contracts, flexion occurs at the hip. tiveness of the primary muscle increases. Which attachment point is considered the muscle’s origin? To describe how muscles work together, we can use the 7. Muscle A abducts the humerus, and muscle B adducts following four functional types: agonist, antagonist, synergist, the humerus. What is the relationship between these two and fixator. muscles? An agonist, or prime mover, is a muscle whose con- 8. Define the term synergist as it relates to muscle action. traction is mostly responsible for producing a particular See the blue Answers tab at the back of the book. > Go to > Study Area > Menu > Animations & Videos > ™ > Origins, Insertions, Actions, Innervations M11_MART6026_11_SE_C11_pp336-388.indd 341 20/10/16 8:10 PM  SPOTLIGHT > Figure 11–3 Go to > Study Area > Muscle Action ™ > Group Muscle Actions and Joints The action produced by a muscle at any one joint is largely dependent upon the structure of the joint and the location of the insertion of the muscle relative to the axis of movement at the joint. The direction, or geometric paths, of the action produced by a muscle—called lines Abduction and Adduction of action—is often represented by an arrow (or more At joints that permit adduction and abduction, muscles whose than one arrow in fan-shaped muscles). lines of action cross the medial side of a joint are adductors of that joint, and muscles whose lines of action cross the Flexion and Extension lateral side of a joint are abductors of that joint. n At joints that permit flexion and extension, muscles whose lines of action cross the anterior side of a joint are flexors LATERAL MEDIAL of that joint, and muscles whose lines of action cross the so posterior side of a joint are Abductor extensors of that joint. The gluteus medius Hip joint ANTERIOR POSTERIOR and minimus cross the lateral side of ar the hip joint. So Flexor Extensor they are abductors Adductor of the hip joint. The biceps brachii The triceps brachii The adductor crosses on the crosses on the magnus crosses anterior side of the elbow joint. So it is a flexor of the elbow joint. FLEXION posterior side of the elbow joint. So Pe it is an extensor of the elbow joint. on the medial side of the hip joint. So it is an adductor of the hip joint. ABDUCTION ht Elbow joint ADDUCTION ig EXTENSION yr Medial and Lateral Rotation At joints that permit rotation, op movement or turning of the body Shoulder joint part occurs around its axis. The shoulder joint is a ball-and-socket joint that permits rotation. The POSTERIOR ANTERIOR subscapularis has lines of action C that cross the anterior aspect of the shoulder joint. When the Lateral rotator Medial rotator subscapularis contracts it The teres minor crosses The subscapularis produces medial rotation at the the posterior side of the crosses on the anterior joint. The teres minor has lines of shoulder joint. When it side of the shoulder joint. action that cross the posterior contracts, it rotates the When it contracts, it aspect of the shoulder joint. When shoulder laterally. rotates the shoulder the teres minor contracts, it medially. produces lateral rotation at the shoulder. Scapula Humerus 342 M11_MART6026_11_SE_C11_pp336-388.indd 342 20/10/16 8:10 PM  Chapter 11 The Muscular System 343 11-4 Descriptive terms are used name of a muscle may include descriptive information about its region of the body; position, direction, and fascicle arrange- to name skeletal muscles ment; structural characteristics; and action. Table 11–1 includes Learning Outcome Explain how the name of a muscle can help identify its location, appearance, or function. a useful summary of muscle terminology. The human body has approximately 700 muscles. You do not need to learn every one of their names, but you will have to Region of the Body become familiar with many of them. Fortunately, the names Regional terms are most common as modifiers that help iden- anatomists assigned to the muscles include descriptive terms tify individual muscles. In a few cases, a muscle is such a promi- that can help you remember the names and identify the mus- nent feature of a body region that a name referring to the region cles. When you are faced with a new muscle name, it is help- alone will identify it. Examples include the temporalis of the ful to first identify the descriptive portions of the name. The head and the brachialis (bra-ke-A-lis) of the arm (Figure 11–4a). n.. 11 so Table 11–1 Muscle Terminology Terms Indicating Specific Terms Indicating Position, Direction, Terms Indicating Structural Regions of the Body or Fascicle Arrangement Characteristics of the Muscle Terms Indicating Actions ar Abdominal (abdomen) Anterior (front) NATURE OF ORIGIN GENERAL Ancon (elbow) External (on the outside) Biceps (two heads) Abductor (movement away) Auricular (ear) Extrinsic (outside the structure) Triceps (three heads) Adductor (movement toward) Brachial (arm) Capitis (head) Carpi (wrist) Cervicis (neck) Inferior (below) Pe Internal (away from the surface) Intrinsic (within the structure) Lateral (on the side) Quadriceps (four heads) SHAPE Deltoid (triangle) Depressor (lowering movement) Extensor (straightening movement) Flexor (bending movement) Levator (raising movement) Coccygeal (coccyx) Medial (middle) Orbicularis (circle) Pronator (turning into prone position) ht Costal (rib) Oblique (slanting) Pectinate (comblike) Supinator (turning into supine position) Cutaneous (skin) Posterior (back) Piriformis (pear shaped) Tensor (tensing movement) Femoris (thigh) Profundus (deep) Platysma (flat plate) ig Glossal (tongue) Rectus (straight) Pyramidal (pyramid) SPECIFIC Hallux (great toe) Superficial (toward the surface) Rhomboid (parallelogram) Buccinator (trumpeter) Ilium (groin) Superior (toward the head) Serratus (serrated) Risorius (laugher) yr Inguinal (groin) Transverse (crosswise) Splenius (bandage) Sartorius (like a tailor) Lumbar (lumbar region) Teres (round and long) Nasalis (nose) Trapezius (trapezoid) op Nuchal (back of neck) Ocular (eye) OTHER STRIKING FEATURES Oris (mouth) Alba (white) Palpebra (eyelid) Brevis (short) Pollex (thumb) Gracilis (slender) C Popliteal (posterior to knee) Latae (wide) Psoas (loin) Latissimus (widest) Radial (forearm) Longissimus (longest) Scapular (scapula) Longus (long) Temporal (temple) Magnus (large) Thoracic (thorax) Major (larger) Tibial (tibia; shin) Maximus (largest) Ulnar (ulna) Minimus (smallest) Minor (smaller) Vastus (great) M11_MART6026_11_SE_C11_pp336-388.indd 343 20/10/16 8:10 PM  344 UNIT 2 Support and Movement Figure 11–4 An Overview of the Major Skeletal Muscles. Axial Muscles Appendicular Muscles Frontal belly of occipitofrontalis Trapezius Temporoparietalis (reflected) Clavicle Temporalis Deltoid Sternum Sternocleidomastoid Pectoralis major n Latissimus dorsi 11 Serratus anterior so Biceps brachii Rectus abdominis Triceps brachii External oblique Brachialis ar Pronator teres Brachioradialis Extensor carpi radialis longus Linea alba Pe Extensor carpi radialis brevis Palmaris longus Flexor carpi radialis Flexor digitorum superficialis ht Flexor retinaculum Flexor carpi ulnaris Gluteus medius Tensor fasciae latae ig Iliopsoas Pectineus yr Adductor longus Iliotibial tract Gracilis Sartorius op Patella Rectus femoris Vastus lateralis Vastus medialis Tibia Gastrocnemius Fibularis longus C Tibialis anterior Soleus Extensor digitorum longus Superior extensor retinaculum Lateral malleolus of fibula Inferior extensor retinaculum Medial malleolus of tibia a Anterior view ATLAS: Plates 1a; 39a–d M11_MART6026_11_SE_C11_pp336-388.indd 344 20/10/16 8:10 PM  Chapter 11 The Muscular System 345 Figure 11–4 An Overview of the Major Skeletal Muscles. (continued) Axial Muscles Appendicular Muscles Occipital belly of occipitofrontalis Sternocleidomastoid Trapezius Deltoid Infraspinatus n Teres minor Teres major 11 External oblique so Rhomboid major Triceps brachii (long head) Triceps brachii (lateral head) ar Latissimus dorsi Brachioradialis Extensor carpi radialis longus Pe Anconeus Flexor carpi ulnaris Extensor digitorum Extensor carpi ulnaris Gluteus medius Tensor fasciae latae ht Gluteus maximus Adductor magnus ig Semitendinosus Semimembranosus Iliotibial tract yr Gracilis Biceps femoris Sartorius op Plantaris Gastrocnemius Soleus C Calcaneal tendon Calcaneus b Posterior view ATLAS: Plates 1b; 40a,b M11_MART6026_11_SE_C11_pp336-388.indd 345 20/10/16 8:11 PM  346 UNIT 2 Support and Movement Position, Direction, or Fascicle Arrangement other clues as to the appearance or location of the muscle. For example, the extensor carpi radialis longus is a long muscle along Muscles visible at the body surface are often called externus or the radial (lateral) border of the forearm. When it contracts, its superficialis. Deeper muscles are termed internus or profundus. primary function is extension at the carpus (wrist). Superficial muscles that position or stabilize an organ are called A few muscles are named after the specific movements extrinsic. Muscles located entirely within an organ are intrinsic. associated with special occupations or habits. The buccinator Muscle names may be directional indicators. For exam- (BUK-si-na-tor) on the face compresses the cheeks—when, for. ple, transversus and oblique indicate muscles that run across example, you purse your lips and blow forcefully. Buccinator (transversus) or at a slanting (oblique) angle to the longitudi- translates as “trumpeter.” Another facial muscle, the risorius nal axis of the body. (ri-SOR-e-us), was supposedly named after the mood expressed:. A muscle name may refer to the orientation of the muscle fas- The Latin word risor means “one who laughs.” However, a more cicles within a particular skeletal muscle. Rectus means “straight,” n appropriate description for the effect would be “a grimace.” The 11 and most rectus muscles have fascicles that run along the longitudi- sartorius (sar-TOR-e-us), the longest in the body, is active when. nal axis of the muscle. Because we have several rectus muscles, the so you cross your legs. Before sewing machines were invented, name typically includes a second term that refers to a precise region a tailor would sit on the floor cross-legged. The name of this of the body. For example, the rectus abdominis of the abdomen is an muscle was derived from sartor, the Latin word for “tailor.” axial muscle that has straight fascicles that run along its long axis. However, in the case of the rectus femoris, rectus refers to “straight ar muscle of the thigh” and not to its fascicles (which are bipennate). Checkpoint 9. Identify the kinds of descriptive information used to Structural Characteristics name skeletal muscles. 10. What does the name flexor carpi radialis longus tell you Some muscles are named after distinctive structural features, such as multiple tendons, shape, and size. Origin and Insertion The biceps brachii, for example, is named after its origin. It has Pe about this muscle? See the blue Answers tab at the back of the book. 11-5 Axial muscles position the axial two tendons of origin (bi-, two + caput, head). Similarly, the skeleton, and appendicular muscles ht triceps brachii has three, and the quadriceps femoris has four. Many muscle names include terms for body places that tell support and move the appendicular you the specific origin and insertion of each muscle. In such skeleton cases, the first part of the name indicates the origin, the second ig Learning Outcome Compare and contrast the axial and part the insertion. The genioglossus, for example, originates at appendicular muscles. the chin (geneion) and inserts in the tongue (glossus). The names The separation of the skeletal system into axial and appen- may be long and difficult to pronounce, but Table 11–1 and yr dicular divisions serves as a useful guideline for subdividing the anatomical terms introduced in Chapter 1 can help you the muscular system: identify and remember them. pp. 10–14 The axial muscles arise on the axial skeleton. This category op Shape and Size includes approximately 60 percent of the skeletal muscles Shape is sometimes an important clue to the name of a mus- in the body. They position the head and vertebral column; move the rib cage, which assists the movements that make. cle. For example, the trapezius (tra-PE-ze-us), deltoid, rhomboid. breathing possible; and form the pelvic floor.. (ROM-boyd), and orbicularis (or-bik-u-LA-ris) look like a trap-. C ezoid, a triangle (like the Greek letter delta, ∆), a rhomboid, The appendicular muscles stabilize or move structures of and a circle, respectively. the appendicular skeleton. Forty percent of skeletal muscles Many terms refer to muscle size. Long muscles are called are appendicular muscles, including those that move and longus (long) or longissimus (longest). Teres muscles are both support the pectoral (shoulder) and pelvic girdles and the long and round. Short muscles are called brevis. Large ones are upper and lower limbs. called magnus (big), major (bigger), or maximus (biggest). Figure 11–4 provides an overview of the major axial and Small ones are called minor (smaller) or minimus (smallest). appendicular muscles of the human body. These are superficial muscles, which tend to be rather large. The superficial muscles Action cover deeper, smaller muscles that we cannot see unless the over- Many muscles are named flexor, extensor, pronator, abductor, lying muscles are removed, or reflected—that is, cut and pulled out adductor, and rotator (see Spotlight Figure 11–3). These are of the way. Later figures that show deep muscles in specific regions such common actions that the names almost always include will indicate whether superficial muscles have been reflected. M11_MART6026_11_SE_C11_pp336-388.indd 346 20/10/16 8:11 PM  Chapter 11 The Muscular System 347 Next we study examples of both muscular divisions. Pay but they share a common developmental origin with the attention to patterns of origin, insertion, and action. In the oblique and rectus muscles of the trunk. figures in this chapter, you will find that some bony and carti- The Muscles of the Pelvic Floor. These muscles extend laginous landmarks are labeled to provide orientation. between the sacrum and pelvic girdle. This group forms The tables that follow also contain information about the. the perineum (per-ih-NE-um), a region anterior to the innervation of the individual muscles. Innervation is the distribu- sacrum and coccyx between the inner thighs. tion of nerves to a region or organ. The tables indicate the nerves that control each muscle. Many of the muscles of the head and neck Muscles of the Head and Neck are innervated by cranial nerves, which originate at the brain and pass through the foramina of the skull. In addition, spinal nerves We can divide the muscles of the head and neck into several are connected to the spinal cord and pass through the intervertebral functional groups. The muscles of facial expression, the muscles of n foramina. For example, spinal nerve L1 passes between vertebrae L1 mastication (chewing), the muscles of the tongue, and the muscles and L2. Spinal nerves may form a complex network called a plexus of the pharynx originate on the skull or hyoid bone. 11 Muscles involved with sight and hearing also are based on so after exiting the spinal cord. One branch of this network may con- tain axons from several spinal nerves. Many tables identify the spi- the skull. Here, we will consider the extrinsic eye muscles—those nal nerves involved as well as the names of their specific branches. associated with movements of the eye. In Chapter 17 we discuss the intrinsic eye muscles, which control the diameter of the pupil and the shape of the lens, and the tiny skeletal muscles ar Checkpoint associated with the auditory ossicles. 11. Describe the location and general functions of axial Among the muscles of the anterior neck, the extrinsic muscles muscles. of the larynx adjust the position of the hyoid bone and larynx. 12. Describe the location and general functions of appendicular muscles. See the blue Answers tab at the back of the book. 11-6 Axial muscles are muscles Pe We examine the intrinsic laryngeal muscles, including those of the vocal cords, in Chapter 23. Muscles of Facial Expression The muscles of facial expression originate on the surface of the of the head and neck, vertebral column, skull (Figure 11–5). At their insertions, the fibers of the epimysium ht trunk, and pelvic floor are woven into those of the superficial fascia and the dermis of the Learning Outcome Identify the principal axial muscles of the skin. For this reason, when these muscles contract, the skin moves. body, plus their origins, insertions, actions, and innervation. The largest group of facial muscles is associated with the ig The axial muscles fall into logical groups on the basis of loca- mouth. The orbicularis oris constricts the opening, and other tion, function, or both. The groups do not always have distinct muscles move the lips or the corners of the mouth. The buccinator anatomical boundaries. For example, a function such as exten- has two functions related to eating (in addition to its importance yr sion of the vertebral column involves muscles along its entire to musicians). During chewing, it cooperates with the mastica- length and movement at each of the intervertebral joints. We tory muscles by moving food back across the teeth from the will discuss the axial muscles in four groups: vestibule, the space inside the cheeks. In infants, the buccinator op provides suction for suckling at the breast. The Muscles of the Head and Neck. This group includes muscles Smaller groups of muscles control movements of the eye- that move the face, tongue, and larynx. They are responsible brows and eyelids, the scalp, the nose, and the external ear. for verbal and nonverbal communication—laughing, talking, The epicranium (ep-i-KRA-ne-um; epi-, on + kranion, skull), or.. frowning, smiling, whistling, and so on. You also use these scalp, contains the temporoparietalis and the occipitofron- C muscles while eating—especially in sucking and chewing—and talis (ok-sip-ih-to-fron-TAL-is), which has a frontal belly and an. even while looking for food, as some of them control your eye occipital belly. The two bellies are separated by the epicranial movements. This group does not include muscles of the neck aponeurosis, a thick, collagenous sheet. that are involved with movements of the vertebral column. The platysma (pla-TIZ-muh; platys, flat) covers the anterior The Muscles of the Vertebral Column. This group includes numer- surface of the neck. This muscle extends from the base of the neck ous flexors, extensors, and rotators of the vertebral column. to the periosteum of the mandible and the fascia at the corner of the The Oblique and Rectus Muscles. This group forms the mus- mouth. One of the effects of aging is the loss of muscle tone in the cular walls of the trunk between the first thoracic vertebra platysma, resulting in a looseness of the skin of the anterior throat. and the pelvis. In the thoracic area the ribs separate these Now take another look at Figure 11–5 with Table 11–2, muscles, but over the abdominal surface the muscles form which summarizes the muscles of facial expression by region. broad muscular sheets. The neck also has oblique and rec- Focus on identifying the location and function of each of the tus muscles. They do not form a complete muscular wall, major muscles named in this discussion. M11_MART6026_11_SE_C11_pp336-388.indd 347 20/10/16 8:11 PM  348 UNIT 2 Support and Movement Figure 11–5 Muscles of Facial Expression. ATLAS: Plate 3a–d Epicranial aponeurosis Temporoparietalis (cut and reflected) Frontal belly of occipitofrontalis Procerus Temporalis Orbicularis oculi n Nasalis 11 Occipital belly of Levator labii superioris occipitofrontalis so Zygomaticus minor Masseter Levator anguli oris Buccinator ar Zygomaticus major Sternocleidomastoid Mentalis (cut) Orbicularis oris Trapezius Depressor labii inferioris Depressor anguli oris Omohyoid Platysma (cut and reflected) Pe Epicranial aponeurosis a Lateral view ht Frontal belly of occipitofrontalis Temporoparietalis (cut and reflected) Corrugator supercilii ig Temporalis Temporalis (temporoparietalis removed) Orbicularis oculi Procerus yr Nasalis Levator labii superioris Zygomaticus minor Levator anguli oris op Zygomaticus major Orbicularis oris Masseter Risorius Buccinator Platysma Depressor anguli oris Depressor labii inferioris C Mentalis (cut) Sternal head of sternocleidomastoid Thyroid cartilage of the larynx Clavicular head of sternocleidomastoid Trapezius Clavicle Platysmae (cut and reflected) b Anterior view ? Given its name, what does the levator anguli oris do? M11_MART6026_11_SE_C11_pp336-388.indd 348 20/10/16 8:11 PM  Chapter 11 The Muscular System 349 Table 11–2 Muscles of Facial Expression (Figure 11–5) Region and Muscle Origin Insertion Action Innervation MOUTH Buccinator Alveolar process of maxilla Blends into fibers of Compresses cheeks Facial nerve (VII)* and alveolar part of the mandible orbicularis oris Depressor labii inferioris Mandible between the Skin of lower lip Depresses lower lip Facial nerve (VII) anterior midline and the mental foramen Levator labii superioris Inferior margin of orbit, Orbicularis oris Elevates upper lip Facial nerve (VII) superior to the infra-orbital foramen Levator anguli oris Maxilla below the infra- Corner of mouth Elevates corner of mouth Facial nerve (VII) n orbital foramen Mentalis Incisive fossa of mandible Skin of chin Elevates and protrudes Facial nerve (VII) 11 lower lip so Orbicularis oris Maxilla and mandible Lips Compresses, purses lips Facial nerve (VII) Risorius Fascia surrounding parotid Angle of mouth Draws corner of mouth to Facial nerve (VII) salivary gland the side Depressor anguli oris Anterolateral surface of Skin at angle of mouth Depresses corner of mouth Facial nerve (VII) ar mandibular body Zygomaticus major Zygomatic bone near Angle of mouth Retracts and elevates corner Facial nerve (VII) zygomaticomaxillary suture of mouth Zygomaticus minor Zygomatic bone posterior to Upper lip Retracts and elevates Facial nerve (VII) EYE Corrugator supercilii Levator palpebrae zygomaticotemporal suture Orbital rim of frontal bone near nasal suture Tendinous band around optic Pe Eyebrow Upper eyelid upper lip Pulls skin inferiorly and anteriorly; wrinkles brow Elevates upper eyelid Facial nerve (VII) Oculomotor nerve (III)** superioris (Figure 11–6a,b) foramen ht Orbicularis oculi Medial margin of orbit Skin around eyelids Closes eye Facial nerve (VII) NOSE Procerus Nasal bones and lateral nasal Aponeurosis at bridge of Moves nose, changes Facial nerve (VII) cartilages nose and skin of forehead position and shape of nostrils ig Nasalis Maxilla and nasal cartilages