Gross Anatomy and Functions of Skeletal Muscles

Transcription

1 tat78135_ch09_ indd Page /29/07 12:55:54 AM epg C H A P T E R /Volumes/ve401/MHIA044/mhtat1%0/tat1ch09 9 Gross Anatomy and Functions of Skeletal Muscles Introduction Mannequins are rigid, expressionless, immobile recreations of the human form. They cannot walk or talk. One of the major characteristics of living human beings is our ability to move about. Without muscles, humans would be little more than mannequins. We would not be able to hold this book or turn its pages. We would not be able to blink, so our eyes would dry out. None of these inconveniences would bother us for long because we would not be able to breathe, either. We use our skeletal muscles all the time. Postural muscles are constantly contracting to keep us sitting or standing upright. Respiratory muscles are constantly functioning to keep us breathing, even when we sleep. Communication of any kind requires skeletal muscles, whether we are writing, typing, or speaking. Even silent communication with hand signals or facial expression requires skeletal muscle function. This chapter explains the general principles (p. 228) of the muscular system and describes in detail the head and neck muscles (p. 232), trunk muscles (p. 239), scapular and upper limb muscles (p. 244), and hip and lower limb muscles (p. 253). The chapter concludes with a discussion of bodybuilding (p. 261). Colorized SEM of skeletal muscle. Tools for Success A virtual cadaver dissection experience Audio (MP3) and/or video (MP4) content, available at 227

2 228 Chapter 9 General Principles This chapter is devoted to the description of the major named skeletal muscles. The structure and function of cardiac and smooth muscle are considered in other chapters. Most skeletal muscles extend from one bone to another and cross at least one joint. Muscle contraction causes most body movements by pulling one bone toward another across a movable joint. The action of a muscle is the movement accomplished when it contracts. Some muscles are not attached to bone at both ends. For example, some facial muscles attach to the skin, which moves as the muscles contract. The two points of attachment of each muscle are its origin and insertion (figure 9.1 ). The origin, also called the fixed end or the head, is usually the most stationary end of a muscle. Some muscles have multiple heads; for example, the biceps brachii has two heads and the triceps brachii has three heads. The insertion, also called the mobile end, is usually the end of the muscle undergoing the greatest movement. A muscle can insert on more than one structure. Generally, the origin of a muscle is the proximal or medial end of a muscle, whereas the insertion is the distal or lateral end of a muscle. The part of the muscle between the origin and the insertion is the belly. Muscles are connected to bones and other structures by tendons. Tendons are long, cablelike structures; broad, sheetlike structures called aponeuroses (ap ō-noo-rō sēz, apo, from + neuron, sinew); or short, almost nonexistent structures. Muscles are typically grouped so that the action of one muscle or group of muscles is opposed by that of another muscle or group of muscles. For example, the biceps brachii flexes the elbow and the triceps brachii extends the elbow. A muscle that accomplishes a certain movement, such as flexion, is called the agonist (ag ō-nist, a contest). A muscle acting in opposition to Extension Ulna Radius Origins, fixed ends, or heads of biceps (two heads) brachii on scapula Biceps brachii (belly) Tendon Insertion, or mobile end, of biceps brachii on radial tuberosity Figure 9.1 Flexion Muscle Attachment Scapula Origins, fixed ends, or heads of triceps (three heads) brachii on scapula and humerus Humerus Insertion, or mobile end, of triceps brachii on olecranon process Muscles are attached to bones by tendons. The biceps brachii has two heads, which originate on the scapula. The triceps brachii has three heads, which originate on the scapula and humerus. The biceps brachii inserts onto the radial tuberosity and onto nearby connective tissue. The triceps brachii inserts onto the olecranon process of the ulna. an agonist is called an antagonist (an-tag ō-nist). The biceps brachii is the agonist in elbow flexion, whereas the triceps brachii is the antagonist, which extends the elbow. P R E D I C T 1 The triceps brachii is the agonist for extension of the elbow. What muscle is its antagonist? Muscles also tend to function in groups to accomplish specific movements. For example, the deltoid, biceps brachii, and pectoralis major all help flex the shoulder. Furthermore, many muscles are members of more than one group, depending on the type of movement being considered. For example, the anterior part of the deltoid muscle functions with the flexors of the shoulder, whereas the posterior part functions with the extensors of the shoulder. Members of a group of muscles working together to produce a movement are called synergists (sin er-jistz). For example, the biceps brachii and brachialis are synergists in elbow flexion. Among a group of synergists, if one muscle plays the major role in accomplishing the desired movement, it is the prime mover. The brachialis is the prime mover in flexing the elbow. Fixators are muscles that hold one bone in place relative to the body while a usually more distal bone is moved. Certain trunk muscles are fixators of the scapula. They hold the scapula in place while muscles attached to the scapula contract to move the humerus. 1. Define origin, insertion, and belly of a muscle; tendon and aponeurosis; agonist and antagonist; and synergist, prime mover, and fixator. Nomenclature Muscles are named according to their location, size, shape, orientation of fasciculi, origin and insertion, number of heads, and function. Recognizing the descriptive nature of muscle names makes learning those names much easier. 1. Location. A pectoralis (chest) muscle is located in the chest, a gluteus (buttock) muscle is located in the buttock, and a brachial (arm) muscle is located in the arm. 2. Size. The gluteus maximus (large) is the largest muscle of the buttock, and the gluteus minimus (small) is the smallest. The pectoralis major (larger of two muscles) is larger than the pectoralis minor (smaller of two muscles). A longus (long) muscle is longer than a brevis (short) muscle. 3. Shape. The deltoid (triangular) muscle is triangular, a quadratus (quadrate) muscle is rectangular, and a teres (round) muscle is round. 4. Orientation of fasciculi. A rectus (straight) muscle has muscle fasciculi running straight with the axis of the structure to which the muscle is associated, whereas the fasciculi of an oblique muscle lie oblique to the longitudinal axis of the structure. 5. Origin and insertion. The sternocleidomastoid originates on the sternum and clavicle and inserts onto the mastoid process of the temporal bone. The brachioradialis originates in the arm (brachium) and inserts onto the radius. 6. Number of heads. A biceps ( bi, two + ceps, head) muscle has two heads, and a triceps ( tri, three + ceps, head) muscle has three heads.

3 tat78135_ch09_ indd Page /28/07 11:38:51 PM epg /Volumes/ve401/MHIA044/mhtat1%0/tat1ch09 Gross Anatomy and Functions of Skeletal Muscles Function. An abductor moves a structure away from the midline, and an adductor moves a structure toward the midline. The masseter (a chewer) is a chewing muscle. to how much weight can be lifted and how high it can be lifted. For example, consider what happens when the child on one end of the seesaw is much larger than the child on the other end. 2. List the criteria used to name muscles, and give an example of each. Class II Lever In a class II lever system, the weight is located between the fulcrum and the pull (see figure 9.2b). An example is a wheelbarrow; the wheel is the fulcrum and the person lifting on the handles provides the pull. The weight, or load, carried in the wheelbarrow is placed between the wheel and the operator. In the body, an example of a class II lever is depression of the mandible (as in opening the mouth; in this case, the whole system, the wheelbarrow and the person lifting it, is upside down). Movements Accomplished by Muscles When muscles contract, the pull (P), or force, of muscle contraction is applied to levers, such as bones, resulting in movement of the levers (figure 9.2). A lever is a rigid shaft capable of turning about a hinge, or pivot point, called a fulcrum (F) and transferring a force applied at one point along the lever to a weight (W), or resistance, placed at another point along the lever. The joints function as fulcrums, the bones function as levers, and the muscles provide the pull to move the levers. Three classes of levers exist based on the relative positions of the levers, weights, fulcrums, and forces. Class III Lever In a class III lever system, the most common type in the body, the pull is located between the fulcrum and the weight (see figure 9.2c). An example is a person using a shovel. The hand placed on the part of the handle closest to the blade provides the pull to lift the weight, such as a shovelful of dirt, and the hand placed near the end of the handle acts as the fulcrum. In the body, the action of the biceps brachii muscle (force) pulling on the radius (lever) to flex the elbow (fulcrum) and elevate the hand (weight) is an example of a class III lever. This type of lever system does not allow as great a weight to be lifted, but the weight can be lifted a greater distance. Class I Lever In a class I lever system, the fulcrum is located between the pull and the weight (see figure 9.2a). A child s seesaw is an example of this type of lever. The children on the seesaw alternate between being the weight and the pull across a fulcrum in the center of the board. The head is an example of this type of lever in the body. The atlanto-occipital joint is the fulcrum, the posterior neck muscles provide the pull depressing the back of the head, and the face, which is elevated, is the weight. With the weight balanced over the fulcrum, only a small amount of pull is required to lift a weight. For example, only a very small shift in weight is needed for one child to lift the other on a seesaw. This system is quite limited, however, as W P 3. Using the terms fulcrum, lever, and force, explain how contraction of a muscle results in movement. Define the three classes of levers, and give an example of each in the body. Muscle Anatomy An overview of the superficial skeletal muscles is presented in figure 9.3. Muscles of the head, neck, trunk, and limbs are described in the following sections. Muscles often can cause more than one action. The discussion of muscle actions is sometimes simplified to emphasize the main actions. Consult the tables for more details. W F F Class III lever Class I lever P W P (a) F W P F Class II lever (c) W Figure 9.2 P P W F (b) F Lever Classes (a) Class I: The fulcrum (F ) is located between the weight (W ) and the pull (P), or force. The pull is directed downward, and the weight, on the opposite side of the fulcrum, is lifted. In the example in the body, the fulcrum extends through several cervical vertebrae. (b) Class II: The weight (W ) is located between the fulcrum (F ) and the pull (P ), or force. The upward pull lifts the weight. The movement of the mandible is easier to compare to a wheelbarrow if the head is considered upside down. (c) Class III: The pull (P ), or force, is located between the fulcrum (F ) and the weight (W ). The upward pull lifts the weight.

4 tat78135_ch09_ indd Page /28/07 11:38:57 PM epg /Volumes/ve401/MHIA044/mhtat1%0/tat1ch09 Chapter Facial muscles Sternocleidomastoid Trapezius Deltoid Pectoralis major Serratus anterior Biceps brachii Rectus abdominis Linea alba External abdominal oblique Brachioradialis Flexors of wrist and fingers Tensor fasciae latae Retinaculum Pectineus Adductor longus Vastus lateralis Rectus femoris Gracilis Vastus intermedius (deep to the rectus femoris and not visible in figure) Sartorius Quadriceps femoris Patella Vastus medialis Tibialis anterior Gastrocnemius Fibularis longus Soleus Fibularis brevis Extensor digitorum longus Retinaculum Figure 9.3 (a) Anterior view General Overview of the Superficial Body Musculature

5 tat78135_ch09_ indd Page /28/07 11:38:59 PM epg /Volumes/ve401/MHIA044/mhtat1%0/tat1ch09 Gross Anatomy and Functions of Skeletal Muscles 231 Sternocleidomastoid Splenius capitis Seventh cervical vertebra Trapezius Infraspinatus Deltoid Teres minor Teres major Triceps brachii Latissimus dorsi External abdominal oblique Extensors of the wrist and fingers Gluteus medius Gluteus maximus Adductor magnus Iliotibial tract Semitendinosus Hamstring muscles Gracilis Biceps femoris Semimembranosus Gastrocnemius Soleus Fibularis longus Fibularis brevis (b) Posterior view Figure 9.3 (continued) Calcaneal tendon (Achilles tendon)

6 232 Head and Neck Muscles The muscles of the head and neck involved in facial expression, mastication (chewing), movement of the tongue, and movement of the head and neck are emphasized in this chapter. Other head and neck muscles are considered in later chapters movement of the Chapter 9 eye and hearing in chapter 14, speech in chapter 20, and swallowing in chapter 21. Facial Expression The skeletal muscles of facial expression ( table 9.1 and figure 9.4 ) are cutaneous muscles, which attach to and move the skin. Many Table 9.1* Muscles of Facial Expression (See Figures 9.4 and 9.5) Muscle Origin Insertion Nerve Action Auricularis (aw-rik ū-lăr is) Aponeurosis over head Ear Facial Move ear superiorly, posteriorly, muscles and mastoid process and anteriorly Buccinator (buk sĭ-nā tōr) Mandible and maxilla Orbicularis oris at Facial Retracts angle of mouth; angle of mouth flattens cheek Corrugator supercilii Nasal bridge and Skin of eyebrow Facial Depresses medial portion of eyebrow; (kōr ŭ gā ter, soo per-sil ē-ī) orbicularis oculi draws eyebrows together, as in frowning Depressor anguli oris Lower border of Skin of lip near Facial Depresses angle of mouth, (dē-pres ŏr ang gū-līōr is) mandible angle of mouth as in frowning Depressor labii inferioris Lower border of Skin of lower lip and Facial Depresses lower lip, as in frowning (dē-pres ŏr lā bē-ī in-fēr ē-ōr-is) mandible orbicularis oris Levator anguli oris Maxilla Skin at angle of mouth Facial Elevates angle of mouth, as in smiling (lē-vā tor, le-vē ter ang gū-līōr is) and orbicularis oris Levator labii superioris (lē-vā tor, Maxilla Skin and orbicularis Facial Elevates upper lip, as in sneering le-vā ter lā bē-ī sū-pēr ē-ōr-is) oris of upper lip Levator labii superioris alaeque Maxilla Ala at nose and Facial Elevates lateral side of nostril nasi (lē-vā tor, le-vā ter lā bē-ī upper lip and upper lip sū-pēr ē-ōr-is ă-lak ā nā zī) Levator palpebrae superioris Lesser wing of Skin of eyelid Oculomotor Elevates upper eyelid (lē-vā tor, le-vā ter pal-pē brē sphenoid sū-pēr ē-ōr-is) (not illustrated) Mentalis (men-tā lis) Mandible Skin of chin Facial Elevates and wrinkles skin over chin; protrudes lower lip, as in pouting Nasalis (nā ză-lis) Maxilla Bridge and ala of nose Facial Dilates nostril Occipitofrontalis Occipital bone Skin of eyebrow Facial Moves scalp; elevates eyebrows (ok-sip i-tō-frŭn tā lis) and nose Orbicularis oculi Maxilla and frontal bones Circles orbit and Facial Closes eyelids (ōr-bik ū-lā ris ok ū-lī) inserts near origin Orbicularis oris Nasal septum, maxilla, Fascia and other Facial Closes lips (ōr-bik ū-lā ris ōr is) and mandible muscles of lips Platysma (plă-tiz mă) Fascia of deltoid and Skin over inferior Facial Depresses lower lip; wrinkles skin of pectoralis major border of mandible neck and upper chest Procerus (prō-sē rŭs) Bridge of nose Frontalis Facial Creates horizontal wrinkles between eyes, as in frowning Risorius (ri-sōr ē-ŭs) Platysma and Orbicularis oris and skin Facial Abducts angle of mouth, as in smiling masseter fascia at corner of mouth Zygomaticus major Zygomatic bone Angle of mouth Facial Elevates and abducts upper lip, (zī gō-mat i-kŭs) as in smiling Zygomaticus minor Zygomatic bone Orbicularis oris of Facial Elevates and abducts upper lip, (zī gō-mat i-kŭs) upper lip as in smiling *The tables in this chapter are to be used as references. As you study the muscular system, first locate the muscle on the figure, and then find its description in the corresponding table

7 tat78135_ch09_ indd Page /28/07 11:39:01 PM epg /Volumes/ve401/MHIA044/mhtat1%0/tat1ch09 Gross Anatomy and Functions of Skeletal Muscles 233 Epicranial aponeurosis (galea) Occipitofrontalis (frontal portion) Orbicularis oculi Temporalis Corrugator supercilii Occipitofrontalis (occipital portion) Procerus Auricularis muscles Levator labii superioris alaeque nasi Levator labii superioris Zygomaticus minor Masseter Zygomaticus major Splenius capitis Levator anguli oris Levator scapulae Orbicularis oris Sternocleidomastoid Mentalis Trapezius Depressor labii inferioris Scalene muscles Depressor anguli oris Risorius (cut) (a) Lateral view Buccinator Platysma (cut) Corrugator supercilii Occipitofrontalis (frontal portion) Temporalis Orbicularis oculi Procerus Nasalis Orbicularis oculi (palpebral portion) Zygomaticus minor and major (cut) Levator labii superioris alaegue nasi Levator labii superioris Zygomaticus minor Levator anguli oris (cut) Zygomaticus major Masseter Levator anguli oris Buccinator Risorius Orbicularis oris Depressor anguli oris Mentalis Depressor labii inferioris Platysma (b) Anterior view Figure 9.4 Muscle of the Head and Neck

8 234 Chapter 9 Frontal portion of occipitofrontalis Levator palpebrae superioris Zygomaticus major Levator anguli oris Mentalis Frontal portion of occipitofrontalis Zygomaticus minor Zygomaticus major Risorius (a) (b) Procerus Orbicularis oculi Nasalis Depressor anguli oris Corrugator supercilii Levator labii superioris alaeque nasi Levator labii superioris Depressor labii inferioris Nasalis Orbicularis oris Buccinator Platysma (c) Figure 9.5 Surface Anatomy, Muscles of Facial Expression (d) animals have cutaneous muscles over the trunk that allow the skin to twitch to remove irritants, such as insects. In humans, cutaneous muscles are confined primarily to the face and neck. Facial expressions resulting from contraction of these muscles are used for nonverbal communication ( figure 9.5 ). Several muscles act on the skin around the eyes and eyebrows. The occipitofrontalis (ok-sip i-tō-frŭn-tă lis) raises the eyebrows and furrows the skin of the forehead. The orbicularis oculi (ōr-bik ū-lā ris ok ū-lī, circular structure of the eye) closes the eyelids and causes crow's-feet wrinkles in the skin at the lateral corners of the eyes. The levator palpebrae (le-vā ter palpē brē, lifter of the eyelid) superioris raises the upper lids. A droopy eyelid on one side, called ptosis (tō sis), usually indicates that the nerve to the levator palpebrae superioris, or the part of the brain controlling that nerve, has been damaged. The corrugator supercilii (kōr ŭ-gā ter, kōr ŭ-gā tōr soo per-sil ē-ī, wrinkle above the eyelid) draws the eyebrows inferiorly and medially, producing vertical corrugations (furrows) in the skin between the eyes. Several muscles function in moving the lips and the skin surrounding the mouth (see figures 9.4 and 9.5 ). The orbicularis oris (ōr-bik ū-lā ris ōr is, circular structure of the mouth) closes the mouth and the buccinator (buk si-nā-tōr, trumpeter) flattens the cheek. They are called the kissing muscles because they pucker the lips. Smiling is accomplished by the zygomaticus (zī gōmat i-kŭs) major and minor, the levator anguli (ang gū-lī) oris, and the risorius (rī-sōr ē-ŭs, laughter). Sneering is accomplished by the levator labii (lā bē-ī, lip) superioris and frowning or pouting by the depressor anguli oris, the depressor labii inferioris, and the mentalis (men-tā lis, chin). If the mentalis muscles are well developed on each side of the chin, a chin dimple, where the skin is tightly attached to the underlying bone or other connective tissue, may appear between the two muscles. 4. What are cutaneous muscles? How are they used for communication? 5. What causes a dimple on the chin? P R E D I C T 2 Harry Wolf, a notorious flirt, on seeing Sally Gorgeous, raises his eyebrows, winks, whistles, and smiles. Name the facial muscles he uses to carry out this communication. Sally, thoroughly displeased with this exhibition, frowns and flares her nostrils in disgust. What muscles does she use (see table 9.1 )? Movement of the Mandible Movement of the mandible is complex and is accomplished by the muscles of mastication and the hyoid muscles. Mastication is chewing. The muscles of mastication are the temporalis (tem pŏrā lis), masseter (mă-sē ter, chewer), lateral pterygoid (ter ĭgoydz, wing-shaped) and medial pterygoid muscles ( table 9.2 and figure 9.6 ). The temporalis and masseter muscles are powerful elevators of the mandible; they close the mouth to crush food between the teeth. Clench your teeth and feel the temporalis on the side of the head and the masseter on the side of the cheek. The medial and lateral pterygoids cause lateral and medial excursion of the mandible, moving it from side to side.

9 tat78135_ch09_ indd Page /28/07 11:39:05 PM epg /Volumes/ve401/MHIA044/mhtat1%0/tat1ch09 Gross Anatomy and Functions of Skeletal Muscles 235 Table 9.2 Muscles of Mastication (See Figure 9.6) Muscle Origin Insertion Nerve Action Temporalis (tem-po -ra lis) Temporal fossa Anterior portion of mandibular ramus and coronoid process Mandibular division of trigeminal Elevates and retracts mandible; involved in excursion Masseter (ma se-ter) Zygomatic arch Lateral side of mandibular ramus Mandibular division of trigeminal Elevates and protracts mandible; involved in excursion Pterygoids (ter i-goydz) Lateral Lateral side of lateral pterygoid plate and greater wing of sphenoid Condylar process of mandible and articular disk Mandibular division of trigeminal Protracts and depresses mandible; involved in excursion Medial Medial side of lateral pterygoid plate and tuberosity of maxilla Medial surface of mandible Mandibular division of trigeminal Protracts and elevates mandible; involved in excursion Epicranial aponeurosis (galea) Occipitofrontalis (frontal portion) Temporalis fascia Temporalis Temporalis tendon Temporalis Zygomatic arch (cut) Zygomatic arch Orbicularis oris Orbicularis oris Buccinator Buccinator Masseter Masseter (cut) (b) Lateral view (a) Lateral view Sphenoid bone Temporalis tendon (cut) Lateral pterygoid Lateral pterygoid plate Temporal bone Superior head Inferior head Medial pterygoid plate Articular disk Head of mandible Lateral pterygoid Medial pterygoid Medial pterygoid Buccinator (c) Lateral view Figure 9.6 (d) Posterior view Muscles of Mastication (a) Temporalis is exposed. (b) Masseter and zygomatic arch are cut away to expose the temporalis. (c) Masseter and temporalis muscles are removed, and the zygomatic arch and part of the mandible are cut away to reveal the deeper muscles. (d) Frontal section of the head, showing the pterygoid muscles.

10 236 Chapter 9 Table 9.3 Hyoid Muscles (See Figure 9.7) Muscle Origin Insertion Nerve Action Suprahyoid Muscles Digastric (dī-gas trik) Geniohyoid (jĕ-nī-ō-hī oyd) (not illustrated) Mylohyoid (mī lō-hī oyd) Stylohyoid (stī-lō-hī oyd) Mastoid process (posterior belly) Mental protuberance of mandible Body of mandible Styloid process Mandible near midline (anterior belly) Body of hyoid Hyoid Hyoid Posterior belly facial; anterior belly mandibular division of trigeminal Fibers of C1 and C2 with hypoglossal Mandibular division of trigeminal Facial Depresses and retracts mandible; elevates hyoid Protracts hyoid; depresses mandible Elevates floor of mouth and tongue; depresses mandible when hyoid is fixed Elevates hyoid Infrahyoid Muscles Omohyoid (ō-mō-hī oyd) Sternohyoid (ster nō-hī oyd) Sternothyroid (ster nō-thī royd) Thyrohyoid (thī-rō-hī oyd) Superior border of scapula Manubrium and first costal cartilage Manubrium and first or second costal cartilage Thyroid cartilage Hyoid Hyoid Thyroid cartilage Hyoid Upper cervical through ansa cervicalis Upper cervical through ansa cervicalis Upper cervical through ansa cervicalis Upper cervical, passing with hypoglossal Depresses hyoid; fixes hyoid in mandibular depression Depresses hyoid; fixes hyoid in mandibular depression Depresses larynx; fixes hyoid in mandibular depression Depresses hyoid and elevates thyroid cartilage of larynx; fixes hyoid in mandibular depression The hyoid muscles attach to the hyoid bone ( table 9.3 and figure 9.7 ). The suprahyoid muscles are superior to the hyoid, whereas the infrahyoid muscles are inferior to it. Slight mandibular depression involves relaxation of the mandibular elevators and the pull of gravity. The digastric (two bellies) muscles are the most important muscles for opening the mouth. The hyoid muscles also move the hyoid or hold it in place. Along with other muscles, the hyoid muscle are involved with swallowing and movement of the larynx. To observe this movement, place your hand on your larynx (Adam s apple) and swallow. 6. Name the muscles primarily responsible for opening and closing the mandible and for lateral and medial excursion of the mandible. Mylohyoid Stylohyoid Hyoid bone Digastric (anterior belly) Digastric (posterior belly) Omohyoid (superior belly) Thyroid cartilage Sternohyoid Cricothyroid Sternocleidomastoid Trapezius Omohyoid (inferior belly) Thyrohyoid Thyroid gland Clavicle Sternothyroid Sternum Figure 9.7 Hyoid Muscles Anterior superficial view

11 Gross Anatomy and Functions of Skeletal Muscles 237 Table 9.4 Tongue Muscles (See Figure 9.8) Muscle Origin Insertion Nerve Action Intrinsic Muscles Longitudinal, transverse, and vertical (not illustrated) Within tongue Within tongue Hypoglossal Change tongue shape Extrinsic Muscles Genioglossus (jĕ nī-ō-glos ŭs) Mental protuberance of mandible Tongue Hypoglossal Depresses and protrudes tongue Hyoglossus (hī ō-glos ŭs) Hyoid Side of tongue Hypoglossal Retracts and depresses side of tongue Styloglossus (stī lō-glos ŭs) Styloid process of temporal bone Tongue (lateral and inferior) Hypoglossal Retracts tongue Palatoglossus (pal-ă-tō-glos ŭs) Soft palate Tongue Pharyngeal plexus Elevates posterior tongue Styloid process Palatoglossus Tongue Frenulum Stylohyoid Genioglossus Styloglossus Hyoglossus Mandible Geniohyoid Hyoid bone Figure 9.8 Tongue Muscles As seen from the right side. Lateral view Tongue Movements The tongue is very important in mastication and speech: (1) It moves food around in the mouth; (2) with the buccinator (see figure 9.6 a ), it holds food in place while the teeth grind it; (3) it pushes food up to the palate and back toward the pharynx to initiate swallowing; and (4) it changes shape to modify sound during speech. The tongue consists of intrinsic and extrinsic muscles ( table 9.4 and figure 9.8 ). The intrinsic muscles are entirely within the tongue and are named for their fiber orientation. They are involved in changing the shape of the tongue. The extrinsic muscles are outside of the tongue but attached to it. They are named for their origin and insertion. The extrinsic muscles move the tongue about as a unit and also help change its shape. Tongue Rolling Everyone can change the shape of the tongue, but not everyone can roll the tongue into the shape of a tube. This ability apparently is partially controlled genetically, but other factors are involved. In some cases, one of a pair of identical twins can roll the tongue but the other twin cannot. It is not known exactly what tongue muscles are involved in tongue rolling, and no anatomical differences are reported between tongue rollers and nonrollers. 7. Define the intrinsic and extrinsic tongue muscles and describe the movements they produce.

12 238 Chapter 9 Table 9.5 Muscles Moving the Head and Neck (See Figures 9.4a, 9.9, and 9.10) Muscle Origin Insertion Nerve Action Levator scapulae (lē-vā tor, le-vā ter skap ū-lē) Transverse processes of C1 C4 Superior angle of scapula Dorsal scapular laterally flexes neck; elevates, retracts, and rotates scapula Scalene (skā lēn) muscles C2 C6 First and second ribs Cervical and brachial plexuses Flex, laterally flex, and rotate neck Semispinalis capitis (sem ē-spī-nā lis ka pĭ-tis) C4 T6 Occipital bone Dorsal rami of cervical nerves Extends and rotates head Splenius capitis (splē nē-ŭs ka pĭ-tis) C4 T6 Superior nuchal line and mastoid process Dorsal rami of cervical nerves Extends, rotates, and laterally flexes head Splenius cervicis (splē nē-ŭs ser-vī sis) Spinous processes of C3 C5 Transverse processes of C1 C3 Dorsal rami of cervical nerves Rotates and extends neck Sternocleidomastoid (ster nō-klī dō-mas toyd) Manubrium and medial clavicle Mastoid process and superior nuchal line Accessory (cranial nerve XI) One contracting alone: rotates. flexes, and laterally flexes head and neck Both contracting together: flex neck and extend head Trapezius (tra-pē zē-ŭs) Occipital protuberance, nuchal ligament, spinous processes of C7 T12 Clavicle, acromion process, and scapular spine Accessory (cranial nerve XI) Extends and laterally flexes head and neck Semispinalis capitis Splenius capitis Sternocleidomastoid Trapezius Seventh cervical vertebra Figure 9.9 Posterior view Superficial Neck Muscles Splenius cervicis (Levator scapulae) Head and Neck Movements The head and neck are moved by posterior, lateral, and anterior neck muscles ( table 9.5 ). The trapezius (tra-pē zē-ŭs) and splenius capitis (splē nē-ŭs ka pĭ-tis) on the posterior neck are the major superficial muscles extending the head and neck ( figure 9.9 ). The lateral neck muscles are involved with rotation, flexion, and lateral flexion of the head and neck (see figure 9.4 a ). The sternocleidomastoid (ster nō-klī dō-mas toyd) muscle is the prime mover of the lateral muscle group. Contraction of only one sternocleidomastoid muscle causes rotation and lateral flexion of the head, as occurs with an upward sideways glance. Contraction of both sternocleidomastoids results in flexion of the neck or extension of the head, depending on what other neck muscles are doing. Deep neck muscle are located along the vertebral column. The deep posterior neck muscles ( figure 9.10 ) extend, rotate, and laterally flex the head and neck, whereas the deep anterior neck muscles (not illustrated) flex the head.

13 Gross Anatomy and Functions of Skeletal Muscles 239 Torticollis Torticollis (to r-ti-kol is, twisted neck), or wry neck, is an abnormal twisting or bending of the neck. It can be caused by damage to the sternocleidomastoid muscle, resulting in fibrous tissue formation and contracture of the muscle. Damage to an infant s neck muscles because of interuterine positioning or a difficult birth may cause torticollis. In most cases, the sternocleidomastoid fibrosis resolves spontaneously. Spasmodic torticollis can occur in adults and may have many causes. It is characterized by intermittent contraction of neck muscles, especially the sternocleidomastoid and trapezius, resulting in rotation, flexion, and extension of the neck and elevation of the shoulder. 8. Name the major movements of the head caused by contraction of the trapezius, splenius capitis, and sternocleidomastoid muscles. 9. What movements of the head and neck are produced by the lateral and deep neck muscles? P R E D I C T 3 The parallel ridges or grain on the surface of muscles in muscle drawings represent muscle fasciculi (bundles). Shortening of the right sternocleidomastoid muscle rotates the head in which direction? Trunk Muscles Back Muscles The muscles that extend, laterally flex, and rotate the vertebral column are divided into superficial and deep groups ( table 9.6 and see figure 9.10 ). The superficial muscles are collectively called the erector spinae (spī nē), which literally means the muscles that make the spine erect. The erector spine consists of three subgroups: the iliocostalis (il ē-ō-kos-tā lis), the longissimus (longis i-mŭs), and the spinalis (sp-ī-nā lis). The longissimus group accounts for most of the muscle mass in the lower back. In general, the muscles of the erector spinae extend from the vertebrae to the ribs or from rib to rib, whereas the muscles of the deep group attach between the transverse and spinous processes of individual vertebra. 10. List the actions of the group of back muscles that attaches to the vertebrae or ribs (or both). What is the name of the superficial group? Back Pain Low back pain can result from poor posture, from being overweight, or from having a poor fitness level. A few changes may help: sitting and standing up straight; using a low-back support when sitting; losing weight; exercising, especially the back and abdominal muscles; and sleeping on your side on a firm mattress. Sleeping on your side all night, however, may be difficult because most people change position over 40 times during the night. Abdominal Wall Muscles Muscles of the abdominal wall ( table 9.7 and figure 9.11 ) flex, laterally flex, and rotate the vertebral column. Contraction of the abdominal muscles when the vertebral column is fixed decreases the volume of the abdominal cavity and the thoracic cavity and can aid in such functions as forced expiration, vomiting, defecation, urination, and childbirth. The crossing pattern of the abdominal muscles creates a strong anterior wall, which holds in and protects the abdominal viscera. In a relatively muscular person with little fat, a vertical indentation extends from the xiphoid process of the sternum through the navel to the pubis. This tendinous area of the abdominal wall, called the linea alba (lin ē-ă al bă, white line), consists of white connective tissue rather than muscle. On each side of the linea alba is a rectus abdominis (rek tŭs ab-dom i-nis, rectus, straight) muscle, which flexes the vertebral column. Tendinous intersections cross the rectus abdominis at three or more locations, causing the abdominal wall of a well-muscled lean person to appear segmented. The linea semilunaris (sem-ē-loo-nar is, a crescent- or half-moon-shaped line) is a slight groove in the abdominal wall running parallel to the lateral edge of each rectus abdominis muscle. Lateral to each rectus abdominis is three layers of muscle. From superficial to deep, these muscles are the external abdominal oblique, internal abdominal oblique, and transversus abdominis (trans-ver sŭs ab-dom i-nis) muscles. The fasciculi of these three muscle layers are oriented in different directions to one another. When these muscles contract, they flex, laterally flex, and rotate the vertebral column or compress the abdominal contents. The lateral abdominal wall muscles connect to the linea alba by broad, thin tendons called aponeuroses. These aponeuroses pass anterior and posterior to the rectus abdominis, enveloping it in connective tissue collectively called the rectus sheath (see figure 9.11b ). 11. List the muscles of the anterior abdominal wall. What are their functions? 12. Define linea alba, tendinous intersection, linea semilunaris, and rectus sheath.

14 240 Chapter 9 Splenius capitis (cut) Third cervical vertebra Scalene muscles Deep back muscles Diaphragm Quadratus lumborum Semispinalis capitis Levator scapulae (cut) Longissimus Iliocostalis Longissimus Spinalis Longissimus Iliocostalis Iliocostalis Erector spinae muscles Transversus abdominis Figure 9.10 Deep Neck and Back Muscles On the right, the erector spinae group of muscles is shown. On the left, these muscles are removed to reveal the deeper back muscles. Posterior view Table 9.6 Muscles of the Back (See Figure 9.10) Muscle Origin Insertion Nerve Action Erector spinae (ē-rek tŏ r, ē-rek tōr spī nē; divides into three columns) Iliocostalis (il ē-ō-kos-tā lis) Sacrum, ilium, and angles of ribs Angles of ribs and transverse processes of vertebrae Cervical, thoracic, and lumbar spinal nerves Extends, laterally flexes, and rotates vertebral column; maintains posture Longissimus (lon-gis i-mŭs) Sacrum, transverse processes of lumbar, thoracic, and lower cervical vertebrae Transverse processes of vertebrae, angles of ribs, and mastoid process Cervical, thoracic, and lumbar spinal nerves Extends head, neck, and vertebral column; maintains posture Spinalis (spī-nā lis) Spinous processes of T11 L2 and C7 Spinous processes of upper thoracic vertebrae and axis Cervical and thoracic, spinal nerves Extends neck and vertebral column; maintains posture Deep back muscles Spinous and transverse processes of each vertebrae Next superior spinous or transverse process, ribs, and occipital bone Spinal nerves Extends back and neck, laterally flexes and rotates vertebral column Quadratus lumborum (kwah-drā tŭs lŭm-bōr ŭm) Iliac crest and lower lumbar vertebrae Twelfth rib and transverse processes of upper four lumbar vertebrae Twelfth thoracic and upper lumbar spinal nerves One acting alone: laterally flexes vertebral column and depresses twelfth rib Both contracting together: extend vertebral column

15 Gross Anatomy and Functions of Skeletal Muscles 241 Pectoralis major Latissimus dorsi Serratus anterior Rectus abdominis (covered by sheath) Linea alba Linea semilunaris Umbilicus External abdominal oblique Iliac crest Inguinal ligament Rectus abdominis (sheath removed) External abdominal oblique Internal abdominal oblique Transversus abdominis Tendinous intersection Inguinal canal (a) Anterior view Linea semilunaris Linea alba Rectus abdominis Skin Fat External abdominal oblique Internal abdominal oblique (b) Superior view Transversus abdominis Transversalis fascia Parietal peritoneum Figure 9.11 Anterior Abdominal Wall Muscles (a) Windows in the side reveal the various muscle layers. (b) Cross section superior to the umbilicus. Table 9.7 Muscles of the Abdominal Wall (See Figure 9.11) Muscle Origin Insertion Nerve Action Anterior Rectus abdominis (rek tŭs ab-dom i-nis) External abdominal oblique Internal abdominal oblique Transversus abdominis (trans-ver sŭs ab-dom i-nis) Pubic crest and symphysis pubis Fifth to twelfth ribs Iliac crest, inguinal ligament, and lumbar fascia Seventh to twelfth costal cartilages, lumbar fascia, iliac crest, and inguinal ligament Xiphoid process and inferior ribs Iliac crest, inguinal ligament, and rectus sheath Tenth to twelfth ribs and rectus sheath Xiphoid process, linea alba, and pubic tubercle Branches of lower thoracic Branches of lower thoracic Lower thoracic Lower thoracic Flexes vertebral column; compresses abdomen Flexes and rotates vertebral column; compresses abdomen; depresses thorax Flexes and rotates vertebral column; compresses abdomen; depresses thorax Compresses abdomen

16 tat78135_ch09_ indd Page /28/07 11:39:17 PM epg /Volumes/ve401/MHIA044/mhtat1%0/tat1ch09 Chapter Median raphe Urethra Ischiocavernosus Bulbospongiosus Central tendon of perineum Deep transverse perineal Superficial transverse perineal Levator ani Vagina Ischial tuberosity Anus External anal sphincter Gluteus maximus Coccyx (a) Male, inferior view Figure 9.12 (b) Female, inferior view Muscles of the Pelvic Floor and Perineum Table 9.8 Muscles of the Pelvic Floor and Perineum (See Figure 9.12) Muscle Origin Insertion Nerve Action Bulbospongiosus (bul bo -spu n je -o su s) Male central tendon of perineum and median raphe of penis Dorsal surface of penis and bulb of penis Pudendal Constricts urethra; erects penis Female central tendon of perineum Base of clitoris Pudendal Erects clitoris Coccygeus (kok-si je -u s) (not illustrated) Ischial spine Coccyx S3 and S4 Elevates and supports pelvic floor Ischiocavernosus (ish e -o -kav er-no su s) Ischial ramus Corpus cavernosum Perineal Compresses base of penis or clitoris Levator ani (le -va tor, le-va ter a nı ) Posterior pubis and ischial spine Sacrum and coccyx Fourth sacral Elevates anus; supports pelvic viscera External anal sphincter (a na l sfingk ter) Coccyx Central tendon of perineum Fourth sacral and pudenda Keeps orifice of anal canal closed External urethral sphincter (u -re thra l sfingk ter) (not illustrated) Pubic ramus Median raphe Pudendal Constricts urethra Deep Ischial ramus Median raphe Pudendal Supports pelvic floor Superficial Ischial ramus Central perineal Pudendal Fixes central tendon Transverse perinei (pe r i-ne ı ) Pelvic Floor and Perineum The pelvis is a ring of bone (see chapter 7) with an inferior opening that is closed by a muscular wall, the pelvic floor, through which the anus and the urogenital openings penetrate (table 9.8 and figure 9.12). Most of the pelvic floor is formed by the coccygeus (kok-si jē-ŭs) muscle and the levator ani (a nī) muscle, referred to jointly as the pelvic diaphragm. The area inferior to the pelvic floor is the perineum (per i-nē ŭm), which is somewhat diamond-shaped. The anterior half of the diamond is the urogenital triangle, and the posterior half is the anal triangle (see chapter 24). The urogenital triangle contains the external urethral sphincter, which allows voluntary control of urination, and the external anal sphincter, which allows voluntary control of defecation. During pregnancy or delivery, the muscles of the pelvic diaphragm and perineum may be stretched or torn, changing the position of the urinary bladder and urethra. As a result, stress urinary incontinence may develop, in which coughing or physical exertion can cause dribbling of urine. 13. What openings penetrate the pelvic floor muscles? Name the area inferior to the pelvic floor.

17 Gross Anatomy and Functions of Skeletal Muscles 243 Third cervical vertebra First thoracic vertebra Anterior scalene Middle scalene Posterior scalene Sternum External intercostals External intercostals 2 1 Internal intercostals 3 4 Diaphragm Central tendon Sternal part Costal part Lumbar part consisting of right and left crura Inferior vena cava Esophagus Aorta Internal intercostals (a) Anterior view (b) Lateral view Figure 9.13 Muscles of the Thorax Table 9.9 Muscles of the Thorax (See Figure 9.13) Muscle Origin Insertion Nerve Action Diaphragm Interior of ribs, sternum, Central tendon of Phrenic Inspiration; depresses and lumbar vertebrae diaphragm floor of thorax Intercostalis (in ter-kos-ta lis) External Inferior margin of each rib Superior border Intercostal Inspiration; elevates ribs of next rib below Internal Superior margin of each rib Inferior border Intercostal Expiration; depresses ribs of next rib above Scalene Transverse processes of C2 C6 First and second rib Cervical and Elevates first and second rib (skā-lēn) muscles brachial plexuses Thoracic Muscles The muscles of the thorax are involved mainly in the process of breathing ( table 9.9 and figure 9.13 ). Contraction and relaxation of these muscle results in changes in thoracic volume, which results in the movement of air into and out of the lungs (see chapter 20). The dome-shaped diaphragm (dī ă-fram, a partition wall) causes the major change in thoracic volume during quiet breathing. When it contracts, the top of the diaphragm moves inferiorly, causing the volume of the thoracic cavity to increase. If the diaphragm or the

18 244 Chapter 9 phrenic nerve supplying it is severely damaged, the amount of air moving into and out of the lungs may be so small that the individual is likely to die without the aid of an artificial respirator. Muscles associated with the ribs change thoracic volume by moving the ribs. The external intercostals (in ter-kos tŭlz, between ribs) increase thoracic volume by elevating the ribs during inspiration, whereas the internal intercostals decrease thoracic volume by depressing the ribs during forced expiration. When the vertebrae are fixed in position by neck muscles, the scalene (skā lēn) muscles elevate the first two ribs. This movement is important when taking a deep breath. When the ribs are fixed in position by the intercostals, the scalenes can cause flexion, lateral flexion, and rotation of the neck (see table 9.5 ). Thus, the ends of a muscle can cause different movements. 14. Describe how the diaphragm, intercostals, and scalenes change thoracic volume. Scapular and Upper Limb Muscles Scapular Movements Trunk muscles form the major connections of the scapula to the body ( table 9.10 and figure 9.14 ). Remember that the scapula is attached to the rest of the skeleton only by the clavicle (see chapter 7). The muscles attaching the scapula to thorax are the trapezius (tra-pē zē-ŭs, a four-side figure with no sides parallel), levator scapulae (lē-vā tor skap ū-lē, lifter of the scapula), rhomboideus (rom-bō-id ē-ŭs, rhomboid-shaped, an oblique parallelogram with unequal sides) major and minor, serratus (ser-ā tŭs, serrated, referring to its appearance on the thorax) anterior, and pectoralis (pek tō-ra lis, chest) m i n or. These muscles move the scapula, permitting a wide range of movements of the upper limb, or act as fixators to hold the scapula firmly in position when the arm muscles contract. The trapezius forms the upper line from each shoulder to the neck, and the origin of the serratus anterior from the first eight or nine ribs can be seen along the lateral thorax. The serratus anterior inserts onto the medial border of the scapula (see figure 9.14c ). 15. Name seven muscles that attach the scapula to the trunk. As a group, what is the function of these muscles? Table 9.10 Muscles Acting on the Scapula (See Figure 9.14) Muscle Origin Insertion Nerve Action Levator scapulae Transverse processes of Superior angle of scapula Dorsal scapular Elevates, retracts, and rotates (lē-vā tor, le-vā ter skap ū-lē) C1 C4 scapula; laterally flexes neck Pectoralis minor (pek tō-ra lis) Third to fifth ribs Coracoid process of scapula Medial pectoral Depresses scapula or elevates ribs Rhomboideus (rom-bō-id ē-ŭs) Major Spinous processes of T1 T4 Medial border of scapula Dorsal scapular Retracts, rotates, and fixes scapula Minor Spinous processes of C6 C7 Medial border of scapula Dorsal scapular Retracts, slightly elevates, rotates, and fixes scapula Serratus anterior First to eighth or ninth ribs Medial border of scapula Long thoracic Rotates and protracts scapula; (ser-ā tūs) elevates ribs Trapezius (tra-pē zē-ŭs) External occipital protuberance, Clavicle, acromion process, Accessory and Elevates, depresses, retracts, ligamentum nuchae, and and scapular spine cervical plexus rotates, and fixes scapula; spinous processes of C7 T12 extends neck

19 tat78135_ch09_ indd Page /28/07 11:39:20 PM epg /Volumes/ve401/MHIA044/mhtat1%0/tat1ch09 Levator scapulae Trapezius Rhomboideus minor Seventh cervical vertebra Rhomboideus major (a) Posterior view Pectoralis major (cut) Coracoid process Supraspinatus tendon Pectoralis minor (cut) Subscapularis Subscapularis Three of four rotator cuff muscles Teres minor Pectoralis major (cut) Teres major (cut) Biceps brachii Pectoralis minor Latissimus dorsi Latissimus dorsi (cut) External abdominal oblique Serratus anterior Ribs (b) Anterior view Scapula Serratus anterior Humerus Figure 9.14 Muscles Acting on the Scapula (a) The trapezius is removed on the right to reveal the deeper muscles. (b) The pectoralis major is removed on both sides. The pectoralis minor is also removed on the right side. (c) The serratus anterior. (c) Lateral view 245

20 246 Chapter 9 Table 9.11 Muscles Acting on the Arm (See Figures ) Muscle Origin Insertion Nerve Action Coracobrachialis Coracoid process Midshaft of humerus Musculocutaneous Adducts arm and flexes shoulder (kōr ă-kō-brā-kē-ā lis) of scapula Deltoid (del toyd) Clavicle, acromion process, Deltoid tuberosity Axillary Flexes and extends shoulder; abducts and scapular spine and medially and laterally rotates arm Latissimus dorsi Spinous processes of Medial crest of Thoracodorsal Adducts and medially rotates arm; (lă-tis i-mŭs dōr sī) T7 L5; sacrum and iliac intertubercular groove extends shoulder crest; inferior angle of scapula in some people Pectoralis major Clavicle, sternum, superior Lateral crest of Medial and lateral Flexes shoulder; adducts and (pek tō-rā lis) six costal cartilages, and intertubercular groove pectoral medially rotates arm; extends external abdominal shoulder from flexed position oblique aponeurosis Teres major Lateral border of Medial crest of Lower subscapular Extends shoulder; adducts and (ter ēz, tēr-ēz) scapula intertubercular groove C5 and C6 medially rotates arm Rotator Cuff Infraspinatus Infraspinous fossa Greater tubercle Suprascapular Laterally rotates arm; (in-fră-spī-nā tŭs) of scapula of humerus C5 and C6 holds head of humerus in place Subscapularis Subscapular fossa Lesser tubercle Upper and lower Medially rotates arm; holds (sŭb-skap-ū-lā ris) of humerus subscapular head of humerus in place C5 and C6 Supraspinatus Supraspinous fossa Greater tubercle Suprascapular Abducts arm; holds head of humerus (soo-pră-spī-nā tŭs) of humerus C5 and C6 in place Teres minor Lateral border of scapula Greater tubercle Axillary C5 and C6 Laterally rotates and adducts arm; (ter ēz, tēr-ēz) of humerus holds head of humerus in place Arm Movements The muscles moving the arm are involved in flexion, extension, abduction, adduction, rotation, and circumduction ( table 9.11 ). Muscles moving the arm have their origins on the trunk and scapula and insert on the arm. The trunk muscles moving the arm are the pectoralis major ( figure 9.15 ) and the latissimus dorsi (lă-tis i-mŭs dōr sī, wide back) muscles ( figure 9.16 ). Notice that the pectoralis major muscle is listed in table 9.11 as both a flexor and an extensor of the shoulder. It flexes the extended shoulder and extends the flexed shoulder. Try these movements and notice the position and action of the muscle. Deltoid (cut) Deltoid Pectoralis major Coracobrachialis Biceps brachii Serratus anterior Figure 9.15 Anterior Muscles Attaching the Upper Limb to the Body