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The ability to maintain a stable internal environment is crucial for survival. This stability requires that the body move. We must, for example, gather food and shelter, make tools and clothing, and defend ourselves. While many systems within the body play a role in movement, the majority of body movements are produced by the skeletal system and the muscular system. We’ve examined the architecture of the skeleton to see how it supports and joints allows movement. Bone and joints can’t move by themselves. They need to be moved by something. The muscular system, which is the mass of skeletal muscles that moves the body’s framework (Figures 10-1), is our subject. The movement of our bodies is one of the most obvious and readily observed “characteristics” of life.

 We contract skeletal muscle when we move, talk, run, walk, or engage in any other activity that is under our “willed” control. The body has more than 600 skeletal muscle. They collectively account for 40% to 50% of our total body weight. Together with the scaffolding provided to the skeleton muscles also influence the shape and contours our bodies. The purposeful movement of the body is ultimately determined by the contraction of muscle cells. The physiology and causes of muscle contraction are discussed in Chapter 11. This chapter will discuss the physiology of muscular contraction. CHAPTER OUTLINE Skeletal muscle structure, 281 Connective tissue components, 272 Muscle actions, 282

 Muscle attachments, 282 Muscles that Move the Hand and Shoulder, 282 Muscles that Move the Hand and Shoulder, 293 Muscles that Move the Upper Arm, 293, 293 and 294 Muscles that Move the Forearm, 294 Muscles to Move the Forearm, 293 Muscles to Move the Shoulder Girdle, 28284 Second-class Lever, 10-1 A general overview of the Body muscula tendon Gastrocnemius Medialis Retus Sartorius Soleus tendon Gastrocnemius L I Figure 10-1 Anterior view. 280 Unit 2 Support & Movement Sternocleidomastoid Seventh cervical verbra Teres minor Triceps brachii Teres major Biceps dorsi Semitendinosus Hamstring group Gastrocnemius Peroneus peroneus brevis Trapezius

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 Internal abdominal oblique Gracilis Iliotibial track Soleus Calcaneal tendon, Achilles tendon Splenius capitis Detoi Figure 10-2 General overview of the body muscles. View from the posterior. Posterior view. How muscles are grouped and related to each other, as well as how they attach to the skeleton, determine the purpose of body movement. Following a discussion on muscle shape and how they attach to and move bone, there is information about specific muscles and their groups. This chapter will conclude with a discussion on posture. SKELETAL MOUSE STRUCTURE CONNECTIVE TISUES COMPONENTS The delicate connective tissue membrane known as the endomysium covers highly specialized skeletal muscles cells (Figure 10-3). The perimysium is a stronger connective tissue envelope that binds together groups of skeletal muscle fibers. The epimysium covers the whole muscle. The epimysium covers the entire muscle and the fibrous structures that connect it to bones or other structures. This ensures that muscles can be securely harnessed to the structures they pull against during contraction. For example, the epimysium and perimysium of a muscular may be continuous with fibrous tissue. This fibrous tissue can extend from the muscle like a tendon. A strong, tough cord that runs along one end with the fibrous endosteum covering a bony bone. The fibrous wrap of a muscle can be a flat, broad sheet of connective tissue known as an aponeurosis. This usually joins with other muscles’ fibrous wrappings. Tendons and aponeuroses are so strong and durable that even injuries severe enough to break bones and tear muscles can’t often cause them to be torn. However, they can be pulled from bones occasionally. Facia is the fibrous connective tissue that surrounds the muscle organ, outside the epimysium, and tendon. Fascia refers to the fibrous connective tissue under the skin that surrounds many deeper organs such as the skeletal muscles or bones. The fascia just below the skin (the hypodermis), is sometimes called superficial fascia. While the fascia surrounding muscles and bones are sometimes called deep fascia, it is also known as deep fascia. Tendon sheaths are tubes-shaped structures made of fibrous connective tissues. They surround certain tendons, particularly those at the wrist and ankle. Tendon sheaths, like bursae have a lining made of synovial membrane. The tendon can move in the tendon sheath easily due to its smooth, moist surface. Anatomy and Structure of the Muscular Systems Chapter 10 281 Figure 10-3. The connective tissue coverings of the muscle organs, the epimysium and perimysium are connected with one another and the tendon. The perimysium holds the muscle fibers together in groups called fascicles. SIZE, SHAPE AND FIBER ARRANGEMENT Skeletal muscles are organs. They are composed mainly of skeletal muscles tissue and important connective tissue components. The size, shape and arrangement of the fibers in skeletal muscles can vary greatly. They can have very small strands like the stapedius muscle in the middle ear or large masses such as those of the thighs. Some skeletal muscles have a broad shape while others are more narrow. Some are tapering and long, while others are shorter and more blunt. Some are triangular and others quadrilateral while some are irregular. Some forms flat sheets while others form bulky masses. Different muscles have different arrangements of fibers. Figure 10-4, A shows that some fibers run parallel to the long axis (Figure 10-4). Some fibers converge to narrow attachments (Figure 10, 4, B), while others are oblique or pennate (Figure 10, 4, C), much like feathers in an oldfashioned plume pen (double-feathered), (Figure, 10-4 D). You can even have curved fibers, such as the sphincters in the face (Figure 10-4 E). Because of their relationship to function, the direction of the fibers that make up a muscle’s structure is important. A muscle that has a bipennate or parallel fiber arrangement can result in a stronger contraction than one with a parallel arrangement. ATTACHMENT OF MOSCLES Most muscles attach to at least one joint. One bone is usually fixed while the other one contracts. The origin and the insertion are both points of attachment. The point of attachment at the origin that doesn’t move when the muscle contracts is called the origin. When contraction happens, the origin bone is the most stationary of the two bones. Figure 10-5, which shows the point at which the muscle contracts, is the insertion. When the muscle shrinks, the insertion bone moves towards the origin bone. If you’re wondering why the bones don’t move together, it is because they are pulled on by the contracting muscles. One of these is usually stabilized by isometric contractions from other muscles, or by features that make it less mobile. We can refer to the terms origin and insert as useful points of reference. Multiple points of origin and insertion can be found in many muscles. These attachment points are essential for muscle actions. Understanding their functional relationships during muscle contraction is key. The functional information provided by the attachment points of the biceps Brachii is shown in Figure 10.5. When contraction occurs, distal insertion of the radius of lower arm causes flexion. However, it is important to realize that origin and movement 282 Unit 2 Support Movement A B C E Figure 10-4 Muscle structure and fiber arrangement. A, Parallel. B, Convergent. C, Pennate. D, Bipennate. E, Sphincter. Figure 10-5 The attachments of a skeletal muscles. The muscle inserts at the skeletal portion that moves when it contracts (insertion) from its origin. 1. Identify the connective tissues membrane that (a) covers individual muscle fibres, (b), surrounds groups skeletal muscle fibers (fascicles), or (c) covers the entire muscle. 2. Name the connective tissue that links a muscle and a bone. 3. Name three different types of fiber arrangement found in skeletal muscles. These points may change depending on the circumstances. You can grab an object and pull it down from above, but you can also pull yourself towards the object. While origin and insertion may be convenient terms, they don’t always give the right information to fully understand muscle action. MUSCLE ACTIONS Skeletal muscle almost always acts in groups, rather than individually. Because of this, most movements are the result of coordinated actions between several muscles. One group of muscles contracts while the others relax. This creates a movement pattern that can be used to classify muscles or groups. Many terms can be used to describe the muscle action in any specific movement pattern. These terms are particularly important and will be discussed in the next paragraphs. Each term suggests a key concept that is crucial to understanding functional muscle patterns such as flexion, extension and abduction. A muscle or group that performs a specific function is called a prime mover or an agonist. A muscle’s “action” or “function”, which is the movement it produces, is called a prime mover. In Figure 10-5, for example, the biceps Brachii is acting as a prime movers during flexion of your forearm. An antagonist is a muscle that contracts in opposition to prime movers (agonists). They relax while the prime mover contracts to produce movement. The simultaneous contraction of a prime moving muscle and its antagonist muscle can result in rigidity or lack of movement. An antagonist may be a misnomer, as muscles work together, not against each other, in normal movement patterns. Antagonists provide control and precision during the contraction of prime movers. Synergists are muscles which contract simultaneously with the prime mover. They assist or complement prime-movers actions, resulting in a more efficient movement. Joint stabilizers are usually the function of fixator muscles. They are often used to maintain balance and posture during contractions of prime movers that act on the joints in the legs and arms. Complex movement patterns mean that muscles can serve multiple functions, including as prime movers, antagonists, synergists or fixators. In flexion, a prime mover may be either an antagonist in extension or a fixator or synergist in other movements. LEVER SYSTEMS A muscle’s central portion, known as the belly, shrinks when it contracts. The amount and type of movement are determined by the resistance or load that is applied, the attachment of tendinous extremities to bone (origin/insertion) and the type of joint involved. Muscles that move one part of a body don’t lie over it in almost all cases. The muscle belly lies in the area that is being moved. Therefore, muscles that move the lower arms lie proximal to them, that is, in their upper arms. Understanding muscle action requires knowledge of lever systems. A lever is a bar that can be turned around a fixed point, called its fulcrum. These levers are made up of bones and joints. An attaching muscle contracts a bone lever and applies a pulling force to it. This causes the insertion bones to move around its joint fulcrum. A lever system, a simple mechanical device, makes it easier to move a weight or another load. The four components of a lever are: (1) a rod or bone (bone), (2) an adjustable pivot (F), around the rod’s movement (joint), (3) a load or resistance to be moved (L), and (4) a force (or pull) that causes movement (muscle contraction). Figure 10-6 illustrates the three types of lever arrangements. All three types of lever arrangements are present in the human body. Anatomy and Function of the Muscular System Chapter 10, 283 Box 10, 1 SPORTS & FITNESS Assessing Muscle Strength Athletic trainers and other healthcare providers are often required for muscle strength assessments in order to evaluate athletic injuries. The optimum angle to pull is a basic principle that governs muscle action in a lever-system. This principle is essential for accurate assessment of muscle strength. The ideal angle of pull for any muscle should be right angles to the long axis bone to which it is attached. The strength of contraction drops dramatically if the angle of pull is not right-angled and becomes more parallel to its long axis. This principle is clearly demonstrated by the brachialis muscle contracting. From the humerus to the ulna, the brachialis runs across the elbow. The elbow is extended in this anatomical position. The angle of pull for the brachialis parallels the long axis (see Figure 10-17 D). This angle makes it very difficult for the brachialis to contract. The muscle’s contraction strength is significantly increased when the elbow is flexed at a right angle. To accurately test the brachialis muscle’s strength, the forearm should always be extended at the elbow. It is possible to accurately assess functional strength by understanding the angle of pull of each muscle. 1. Identify the attachment point of a muscle to bone that: (a. does not move when the muscles contract; (b. moves when the muscles contract). 2. What is the name of a muscle that performs a specific function? 3. What kind of muscles help maintain balance and posture during contractions of muscles that act on the joints of the arms or legs? 4. Name the muscles that are used as joint stabilizers. First-Class Levers. As shown in Figure 10-6 A, the fulcrum of a first-class lever is located between the effort (or pull) and resistance (or load (W), such as in a set or scales, pair of scissors, or child’s seesaw. A first-class lever is shown in action by the head being lifted or tipped backwards on the atlas. The load is in the skull’s facial area. The joint between the atlas and skull is the fulcrum. The pull is produced by the muscles of the back. Firstclass levers in the human body are rare. They are primarily used to provide stability. Second-Class Levers The load is between the fulcrum (or the joint at the point where the pull is applied) and the second-class lever. As an example, the wheelbarrow is frequently used. It is controversial to find second-class levers within the human body. This type of lever is sometimes interpreted by authorities as the lifting of the body on the feet (Figure 10-6 B). The fulcrum is the point at which the toes touch the ground. The load is located at the ankle. The pull is exerted through the Achilles tendon by the gastrocnemius muscles. A second-class lever is one that opens the mouth to resist resistance (depression or compression of the mandible). Third-Class Levers A third-class lever is one that exerts a pull between the fulcrum, resistance or load to move. This type of lever is commonly used by flexing the forearm at an elbow joint (Figure 10-6 C). Third-class levers allow for rapid and extensive movement, and they are the most commonly found in the body. These allow for the insertion of a muscle close to the joint it moves. 284 Unit 2 Support & Movement A B/C Figure 10-6 Lever classes. A, Class I: Force or pull (P), load (L) between F and F; B, Class II (L) load (L), between F and force/pull (P); C Class III (Force or pull) between F and L. Each lever rod is colored yellow. HOW MUSCLES ARE NAMED. The first thing that you notice about the names of the muscles is their mysterious and foreign nature. This is due to the fact that they are largely Latin words (sometimes with Greek roots). It is possible that the names of the same muscle may differ from one reference to the next. The difference can sometimes be explained by the fact that science is constantly changing terms. It takes some time for everyone else to get it. It is not uncommon to use the English or Latin version of a Latin name for muscles. The deltoid muscles can be called either deltoideus (Latin), or deltoid, (Latin-based English). Both names are derived from the same source, but they do not necessarily refer to the same thing. We have tried to stick to the English names in this edition. Latin-based names for muscle are more logical and easier to understand if one knows the reasons behind them. The following features are used to name many of the superficial muscles in Figures 10-1, 10-2: * Location. Location is a key factor in the naming of many muscles. Examples include the brachialis (arm), and gluteus(buttock). The following table lists some of the major muscles, sorted by their location. * Function. * Function is often a part or the name of a muscle. The adductor muscles in the thigh move the leg towards the midline of your body. The following table lists selected muscles, sorted by function. * Shape. * Shape is used to name many muscles. The shoulder’s deltoid (triangular-shaped) muscle is triangular in form. * The direction of the fibers. The orientation of the fibers can be used to name muscles. Straight is the term rectus. The fibers of rectus abdominis muscles run straight up and parallel to one another. * The number of divisions or heads. To name a muscle, the number of heads or divisions (points-of-origine) can be used. Part-cep is a term that refers to a head. The triceps (three), quadriceps (4), and biceps (23) all refer to multiple heads or points of origin. A muscle with two heads, the biceps brachii, is located in the arm. * Points of attachment. To name a muscle, you can use its origin and insertion points. The sternocleidomastoid, for example, has its origin in the sternum and the clavicle. It inserts onto the mastoid process at the temporal bone. * The size of the muscle. A relative size of a muscular can be used to identify it, particularly if it is smaller than other nearby muscles. The gluteus maximus, which is also known as the “buttock”), is the largest muscle in the gluteal (Greek: glautos). There is also a smaller gluteal muscles, gluteus minimus and a mid-sized gluteal muscular, gluteus medius, nearby. Anatomy and Function of the Muscular System Chapter10 285 Table 10-1 Select Muscles Grouped Based on Location. Term Meaning Neck Sternocleidomastoid Shoulder Deltoid Upper Arm Biceps brachii Triceps Brachii Brachioradialis Triceps brachii Forearm Brachioradialis Tibialis anterior Posterior Surface Gastrocnemius Soleus Pelvic Floor Levator ani Coccygeus Name the four main components of any lever system. 2. Identify three types of lever systems in the human body. Give one example. 3. What type of lever system allows for rapid and extended movement, and is the most commonly found in the body’s? 4. Give an example of a particular muscle that you would use each criteria to determine its name. TIPS FOR DETERMINING MUSCLE ACTIONS These structural details can be linked to functional principles which will make your study of muscle more enjoyable and easier than you might think. These are some specific tips for deducing the actions of muscles. 1. Begin by familiarizing yourself with the names, shapes and general locations for the larger muscles using Table 10-1. 2. From your knowledge about the shape and location of the muscle, try to determine which bones the ends of a muscular attach to. Take, for example, a close look at the deltoid muscles in Figures 10-1 through 10. What bones seems it to attach to? See Table 10-10, p. 295 to help you find the answer. 3. Next, identify which bone moves when a muscle contracts. The bone that is moved by a muscle’s contraction, is the insertion bone. The bone that is relatively still is the origin bone. You can often tell which bone is the insertion bone simply by moving one bone after another. Sometimes, one bone can function as the insert bone. While not all muscle attachments can easily be deduced like those of the deltoid or rote memory, it is possible to learn them all more quickly by using this deduction method. 4. Apply the principle that a muscle’s insertion moves towards its origin to deduce its actions. Compare your results with the text. As in steps 2/3, the method of deduction is meant to be a guide only and not a complete solution for determining muscle actions. 5. In order to determine which muscle performs a particular action (rather than which action a given muscles produces in step 4, you need to infer the insertion bone, which is the bone that moves during the action). The origin and body of the muscle will be located on one or more bones towards which the insertion moves, often a bone or multiple bones proximal or proximal the insertion bone. Combine these findings about origin and movement with your knowledge of the names and locations of the muscles to determine the source of the action. If you want to identify the prime mover behind the action of raising your upper arms straight up to the sides, then you can infer that the muscle inserts onto the humerus. This is because it is the bone that moves. It is likely to move toward the shoulder, which is the clavicle or scapula. You know that the deltoid muscles fulfills these conditions so you can conclude that it is the one that raises the upper arms in the sideways direction. Important Skeletal Muscles The main skeletal muscles are listed and grouped in the following tables and figures.When you begin to study the muscles of your body, the first thing that you notice is how mysterious and foreign the names are. This is due to the fact that they are primarily Latin words (sometimes with Greek roots). It is possible that the names of the same muscle may differ from one reference to the next. The difference can sometimes be explained by the fact that science is constantly changing terms. It takes some time for everyone else to get it. It is not uncommon to use the English or Latin version of a Latin name for muscles. The deltoid muscles can be called either deltoideus (Latin), or deltoid, (Latin-based English). Both names are derived from the same source, but they do not necessarily refer to the same thing. We have tried to stick to the English names in this edition. Latin-based names for muscle are more logical and easier to understand if one knows the reasons behind them. The following features are used to name many of the superficial muscles in Figures 10-1, 10-2: * Location. Location is a key factor in the naming of many muscles. Examples include the brachialis (arm), and gluteus(buttock). The following table lists some of the major muscles, sorted by their location. * Function. * Function is often a part or the name of a muscle. The adductor muscles in the thigh move the leg towards the midline of your body. The following table lists selected muscles, arranged according to their function. * Shape. * Shape is used to name many muscles. The shoulder’s deltoid (triangular-shaped) muscle is triangular in form. * The direction of the fibers. The orientation of the fibers can be used to name muscles. Straight is the term rectus. The fibers of rectus abdominis muscles run straight up and parallel to one another. * The number of divisions or heads. To name a muscle, the number of heads or divisions (points-of-origine) can be used. Part-cep is a term that refers to a head. The triceps (three), quadriceps (4), and biceps (23) all refer to multiple heads or points of origin. A muscle with two heads, the biceps brachii, is located in the arm. * Points of attachment. To name a muscle, you can use its origin and insertion points. The sternocleidomastoid, for example, has its origin in the sternum and the clavicle. It inserts onto the mastoid process at the temporal bone. * The size of the muscle. A relative size of a muscular can be used to identify it, particularly if it is smaller than other nearby muscles. The gluteus maximus, which is also known as the “buttock” region’s largest muscle, is an example. There is also a smaller gluteal muscles, gluteus minimus and a mid-sized gluteal muscular, gluteus medius, nearby. Anatomy and Function of the Muscular System Chapter10 285 Table 10-1 Select Muscles Grouped Based on Location. Term Meaning Neck Sternocleidomastoid Shoulder Deltoid Upper Arm Biceps brachii Triceps Brachii Brachialis Brachioradialis Triceps brachii Triceps Brachialis Brachialis Brachioradialis Triceps brachii Leg Anterior Surface Tibialis Soleus Gastrocnemius Soleus Name the four main components of any lever system. 2. Identify three types of lever systems in the human body. Give one example. 3. What type of lever system allows for rapid and extended movement, and is the most commonly found in the body’s? 4. Give an example of a particular muscle that you would use each criteria to determine its name. TIPS FOR DETERMINING MUSCLE ACTIONS These structural details can be linked to functional principles which will make your study of muscle more enjoyable and easier than you might think. These are some specific tips for deducing the actions of muscles. 1. Begin by familiarizing yourself with the names, shapes and general locations for the larger muscles using Table 10-1. 2. From your knowledge about the shape and location of the muscle, try to determine which bones the ends of a muscular attach to. Take, for example, a close look at the deltoid muscles in Figures 10-1 through 10. What bones seems it to attach? See Table 10-10, p. 295 to help you find the answer. 3. Next, identify which bone moves when a muscle contracts. The bone that is moved by a muscle’s contraction, is the insertion bone. The bone that is relatively still is the origin bone. You can often tell which bone is the insertion bone simply by moving one bone after another. Sometimes, one bone can function as the insert bone. While not all muscle attachments can easily be deduced like those of the deltoid however, it is possible to learn them all more quickly by using this deduction method rather than relying solely on rote memory. 4. Apply the principle that a muscle’s insertion moves towards its origin to deduce its actions. Compare your results with the text. As in steps 2/3, the method of deduction is meant to be a guide only and not a complete solution for determining muscle actions. 5. In order to determine which muscle performs a particular action (instead determining which action a given muscles produces, as shown in step 4), you need to infer the insertion bone (bone that is in motion during the action). The origin and body of the muscle will be located on one or more bones towards which the insertion moves, often a bone or multiple bones proximal or proximal the insertion bone. Combine these findings about origin and movement with your knowledge of the names and locations of the muscles to determine the source of the action. If you want to identify the prime mover behind the action of raising your upper arms straight up to the sides, then you can infer that the muscle inserts onto the humerus. This is because it is the bone that moves. It is likely to move toward the shoulder, which is the clavicle or scapula. You know that the deltoid muscles fulfills these conditions so you can conclude that it is the one that raises the upper arms in the sideways direction. Important Skeletal Muscles The major skeletal muscles are listed and grouped. They are illustrated in the following tables and figures. Begin your study by reviewing the important superficial muscles286. Table 10-2 Select Muscles Grouped according to Function. Extensor Carpi Radialis, Longus, and Brevis. Flexor carpi radioalis. Gluteus medius. Evertors Peroneus longus. Pectoralis major. Invertor Tibialis anterior. Figures 10-1. These figures illustrate specific muscles or important groups of muscles. The tables 10-3 through 10-15 provide basic information about many muscles. Each table contains a description of a specific group of muscles that moves one part of your body. Each muscle is listed with the actions it performs. However, a single muscle can rarely perform a particular action. Muscles work in groups and act as prime movers, antagonists, fixators, synergists, and synergists to create movements. FACIAL EXPRESSION MUSCLES The facial expression muscles (Table 10-3) are distinctive in that at least one point of attachment to the deep layers or the neck of the skin is where they attach. These muscles can be contracted (Figure 10-7) to produce a variety facial expressions. The occipitofrontalis (ahk-SIP-it-o-front-AL-is), or epicranius, is in reality two muscles. The forehead (frontal bone) is covered by one portion, while the other covers the back of the skull. These two parts of the muscle, known as the bellies, are connected by connective tissue aponeurosis, which covers the top part of the skull. The occipitofrontalis’ frontal section raises eyebrows and horizontally wrinkles forehead skin. Corrugator supercilii, (COR-uGATor su-perSIL-i), ties the eyebrows together and creates vertical wrinkles (frowning). The orbicularis supercilii (or-BICu-LAR-us OKu-li), encircles the eye and closes it (blinking), while the buccinator and orbicularis oris, (BUK-siNA-tor), pucker the mouth (kissing), and press the cheeks and lips against the teeth. The major zygomaticus (ZIGO-MAT-ikus) draws the corner of your mouth upward (laughing). Anatomy of the Muscular System Chapter10 287 Table 10-3 Muscles for Facial Expression and Mastication Nerve Supply Muscles for Facial Expression Occipitofrontalis lateral portion Occipital nerve V Cranial nervous VII Cranial neuro VII Cranial neural nerve VII Cranial brain nerve VII Cranial root VII Cranial, or masticatory, nerves. A, Lateral view. B, Anterior View. MUSCLE OF MATICATION (MASS-ti-KA–shun) The muscles responsible for chewing are shown in Figure 10.7. These strong muscles (see Table 10-3) can either raise or retract the mandible (masseter and mas-SE–ter, and temporalis and tempo-RAL–is), or protrude it while causing sideways movements (pterygoids and TER-i­goids). The pull of gravity opens the mandible when mastication is performed. The buccinator muscles hold food between the teeth while the mandible moves upwards and downwards, as well as from side to side. MUSCLES THAT MOVE HEAD – The head movement is controlled by the paired muscles to either side of your neck (Figure 10-8). The Table 10-4 table lists the functions and points of attachment of key muscles within this group. When both sternocleidomastoid (STERno-KLI-do-MAS-toyd) muscles (Figure 10-7) contract at the same time, the head is flexed on the thorax–hence the name “prayer muscle.” If only one muscle contracts, the head and face are turned to the opposite side. The broad semispinaliscapitis (sem’e-spi-NAL) muscles help to bend the head laterally and extends the head. The splenius capsitis (SPLEY-ne-usKAP-i-tis), together with the other muscles, act as strong extensors. They return the head to its upright position after flexion. Contraction of one muscle results in tilting towards the opposite side and rotation. Figure 10-8 does not show the bandlike longissimus capsitis muscles (lon-JISi-mus KAPi-tis). They extend from the neck vertebrae to either the mastoid process or temporal bone and cause the head to move together. The contracting muscle will rotate the head towards the contracting side by contracting one more. 288 Unit 2 Support & Movement Semispinalis Capitis Sternocleidomastoid Trapius Ligamentum Nuchae S L I Table 10-4 Muscles that Move the Head Muscle Origin Insertion Nerve Supply Sternocleidomastoid Splenius capsitis Longissimus Capitis Sternum Clavicle Vertebrae (transverse process of the upper six thoracic and articular process of the lower four cervical nerves) Bend the head and rotates toward the contracting side. The posterior view shows the muscles of the neck, and the back. Rectus Abdominis External abdominal Oblique Rectus Absdominis (covered with sheath). Inguinal ligament Linea Alba Transversus abdominis Internal abdominal Oblique S R I A B TRUNK MUSCLE MUSCLES OF the THORAX. The thorax muscles are crucial for respiration (discussed at Chapter 24). In Figure 10-9, and Table 10-5, you can see that the internal intercostal (INKOS-tal), muscles attach to the spine at different locations and have different fiber orientations. The result is that the external intercostals contract, elevating the ribs. However, the internal intercostals reduce the ribs. This is important for the breathing process. The dome-shaped diaphragm, (DI-afram), flattens during inspiration. This increases the size and volume the thoracic cavity. Air is able to enter the lungs as a result. MUSCLES OF ABDOMINAL WHELL The muscles of the anterior abdominal wall and lateral abdominal walls (Figure 10-10, Table 10-6) are arranged in three levels. Each layer has fibers that run in different directions. This is similar to the pattern of layers in a plywood sheet. This creates a strong “girdle”, which is made of muscle and covers the abdominal cavity and all its internal organs. Anatomy of the Muscular System Chapter 10. 289 1. What does the term origin and insertion mean? 2. The facial expression muscle responsible for facial expressions has two parts: one that covers the forehead and one that covers the back of your skull. 3. Which muscle group is responsible for chewing movements? 4. What is the action and function of the sternocleidomastoid muscles? External intercostals Intercostal central tendon of dialyphrum Diaphragm 1 3 4 5 6 7 9 10 10 S R I Table 10-5 Thorax Muscles Origin Insertion Function Nerve Supply Internal intercostals Diaphragm Rib; lower border; forward fibers; Rib; inner surface; backward fibers Lower circumference of the thorax (of the rib cage) Rib; upper border of ribs below origin Rib; Rib; Rib; thorax muscles of the thorax. Anterior view. You will notice the relationship between internal and external intercostal muscle groups and the placement of diaphragm. Figure 10-10 The trunk and abdominal muscles. A, Anterior view showing superficial muscle. B, Anterior view showing more muscles. The anterolateral (side), abdominal walls have three layers of muscle. These are the outermost, or external, oblique, middle, and inner layers. The rectus abdominalis is a band-shaped or strapshaped muscle that runs along the midline of your abdomen, from the pubis to the thorax. The rectus abdominalis protects the abdominal viscera and flexes your spine. The MUSCLES OF BACK The head and limb movements are facilitated by the muscles of the back. These muscles will be discussed in detail elsewhere in this chapter. We will now focus on the deeper muscles of the back. The deep back muscles allow us to move the vertebral column and help us bend. They also stabilize our trunk to ensure a stable posture. Because the load is trying bend the back, these muscles get a lot of work. Figure 10-11 shows the erector Spinae group, which is made up of several long, thin muscles that run all the way down our backs. These muscles stretch (straighten, pull back), flex the back laterally, and rotate the vertebral columns a bit. There are many other back muscles that go deeper than the erector spunae muscles. For example, the interspinales or multifides group connect one vertebra to another. They also help to extend and flex the back and neck. The important deep back muscles are summarized in Table 10-7 and Figure 11-11. The reinforced muscular floor protects the pelvic cavity’s outlet. The 290 Unit 2 Support & Movement Table 10-6 Muscles in the Abdominal Wall Muscle Source Insertion Function Nerve Supply External Oblique Internal Oblique Pelvis (iliac Crest and pubis by inguinal Ligament) Pelvis, (lower six) Pelvis, Lumbodorsal Fascia Pelvis (pubic bone, symphysis pubis), Iliolumbar and iliac ligaments; Linea alba through an aponeurosis Ribsym by way of inguinal crest and pubis and pubis by inguinal crest and pubis by inguinal crest) Linea alba (iliac and pubis by inguinal crest) Linea (iliac and pubis by inguinal crest and pubis by inguinal crest and pubis and pubis by inguinal crest and pubis and pubis by inguinal crest and pubis by inguinal crest and pubis via inguinal aponeurosisis (lower three) Abdominal muscles act as antagonists to diaphragm by contracting and relaxing, and vice versa. Flexes trunk; depresses last six ribs. Last five intercostal nervouss; iliohypogastric or ilioinguinal. Lumbar Anatomy: The Muscular System Chapter 10 291 R L I Figure 10-11. Muscles of back. View from the posterior showing the deeper muscles in the back. perineum (per-i-NE-um). The anal canal and urethra, as well as the vagina in females, pass through the floor. Most of the pelvic floor is made up by the levator ani, coccygeus and scapula muscles. They are like hammocks that stretch across the pelvic cavity. The outlet is shaped like a diamond and can be divided by drawing a line from one side to the other between the ischial tubesities. The urogenital triangular is located anteriorly (above), extending to the Symphysis Pubis. The anal triangle lies posterior (behind) and ends at the coccyx. Figure 10-12 shows that the urogenital triangular structures include the bulbospongiosus and ischiocavernosus muscles, which are associated with the penis (male) or the vagina (female). The control of urine flow is achieved by the constriction of muscles known as sphincter urinarae. These muscles encircle both the urethra and are responsible for controlling its movement. The anal triangle is used to access the anal canal. The canal’s terminal section is enclosed by the external anal, which regulates bowel movements. The function, origin, and innervation important muscles in the pelvic floor can be found in Table 10-8. The coc292 Unit 2, Support and Movement Table 10-7-8 Muscles of Pelvic Floor Muscles Origin Insertion Nerve Supply Levator ani Coccyx Perineum and bulb penis Coccyx Perineum and Bulbospongiosus Female Deep transverse occipital/mastoid processes of verbrae Spinal nerves Spinal Nerves Cervical nerves Spinal nervouss Spinal Nerves Table 10-8 Muscles from the Pelvic canal Close anal canal UPPER LIMB MOSCLES These muscles are located in the upper limb and include those that act on the pectoral girdle, shoulder, and arm muscles. MUSCLES ACTING ON THE SHOULDER GIRDL Attachment of the upper extremity and torso can be achieved by muscles with an anterior (chest) placement or a posterior (back, neck). The six muscles that run from the axial bone to the shoulder (Figure 10-9 and Figure 10-13) are responsible for “attaching” the upper extremity of the body to the body. They also allow for extensive movement (Scapula, clavicle). You can move the clavicle forward and back, as well as elevate and depress it. You can do more with your scapula. The smaller pectoralis minor muscle, located on the anterior chest wall, is under the larger pectoralis main muscle. It “fixes” the scapula against its thorax, and raises the ribs when forced inspiration is required. The serratus anterior (pronounced “ser-RAY”-an anterior chest wall muscle) helps to hold the scapula against its thorax to prevent it from “winging”. It is also a strong abductor and useful for pushing or punching. Anatomy of the Muscular System Chapter 10, 293 Urogenital triangle Anal Triangle Ischiocavernosus SCAP-yoolle Deep transverse