A&P Chapter 11

extensor hallucis longus and extensor digitorum longus

-The extensor hallucis longus is a thin muscle between and partly deep to the tibialis anterior and extensor digitorum longus muscles -This featherlike muscle is lateral to the tibialis anterior muscle, where it can also be palpated easily

back injuries and heavy lifting

-The four factors associated with increased risk of back injury are amount of force, repetition, posture, and stress applied to the backbone. Poor physical condition, poor posture, lack of exercise, and excessive body weight contribute to the number and severity of sprains and strains. Back pain caused by a muscle strain or ligament sprain will normally heal within a short time and may never cause further problems. However, if ligaments and muscles are weak, discs in the lower back can become weakened and may herniate (rupture) with excessive lifting or a sudden fall, causing considerable pain. -Full flexion at the waist, as in touching your toes, overstretches the erector spinae muscles. Muscles that are overstretched cannot contract effectively. Straightening up from such a position is therefore initiated by the hamstring muscles on the back of the thigh and the gluteus maximus muscles of the buttocks. The erector spinae muscles join in as the degree of flexion decreases. Improperly lifting a heavy weight, however, can strain the erector spinae muscles. The result can be painful muscle spasms, tearing of tendons and ligaments of the lower back, and herniating of intervertebral discs. The lumbar muscles are adapted for maintaining posture, not for lifting. This is why it is important to bend at the knees and use the powerful extensor muscles of the thighs and buttocks while lifting a heavy load.

quadriceps femoris

-The quadriceps femoris muscle is the largest muscle in the body, covering most of the anterior surface and sides of the thigh. -The muscle is actually a composite muscle, usually described as four separate muscles: (1) rectus femoris, on the anterior aspect of the thigh; (2) vastus lateralis, on the lateral aspect of the thigh; (3) vastus medialis, on the medial aspect of the thigh; and (4) vastus intermedius, located deep to the rectus femoris between the vastus lateralis and vastus medialis.

hernia

A hernia is a protrusion of an organ through a structure that normally contains it, which creates a lump that can be seen or felt through the skin's surface.

effort

A lever is acted on at two different points by two different forces: the effort (E), which causes movement, and the load w0708-nu or resistance, which opposes movement. The effort is the force exerted by muscular contraction; the load is typically the weight of the body part that is moved or some resistance that the moving body part is trying to overcome (such as the weight of a book you might be picking up). Motion occurs when the effort applied to the bone at the insertion exceeds the load. Consider the biceps brachii flexing the forearm at the elbow as an object is lifted. When the forearm is raised, the elbow is the fulcrum. The weight of the forearm plus the weight of the object in the hand is the load. The force of contraction of the biceps brachii pulling the forearm up is the effort.

pulled hamstrings

A strain or partial tear of the proximal hamstring muscles is referred to as pulled hamstrings or hamstring strains. Like pulled groins, they are common sports injuries in individuals who run very hard and/or are required to perform quick starts and stops. Sometimes the violent muscular exertion required to perform a feat tears away a part of the tendinous origins of the hamstrings, especially the biceps femoris, from the ischial tuberosity. This is usually accompanied by a contusion (bruising), tearing of some of the muscle fibers, and rupture of blood vessels, producing a hematoma (collection of blood) and sharp pain. Adequate training with good balance between the quadriceps femoris and hamstrings and stretching exercises before running or competing are important in preventing this injury.

urogenital triangle and anal triangle

A transverse line drawn between the ischial tuberosities divides the perineum into an anterior urogenital triangle that contains the external genitals and a posterior anal triangle that contains the anus. The perineal body of the perineum, a muscular intersection anterior to the anus into which several perineal muscles insert (described in Section ). Clinically, the perineum is very important to physicians who care for women during pregnancy and treat disorders related to the female genital tract, urogenital organs, and the anorectal region.

digastric

As a group, the suprahyoid muscles elevate the hyoid bone, floor of the oral cavity, and tongue during deglutition (swallowing). As its name suggests, the digastric muscle has two bellies, anterior and posterior, united by an intermediate tendon that is held in position by a fibrous loop. This muscle elevates the hyoid bone and larynx (voice box) during swallowing and speech. In a reverse muscle action (RMA), when the hyoid is stabilized, the digastric depresses the mandible and is therefore synergistic to the lateral pterygoid in the opening of the mouth.

gravity and the mandible

As just noted, three of the four muscles of mastication close the mandible and only the lateral pterygoid opens the mouth. The force of gravity on the mandible offsets this imbalance. When the masseter, temporalis, and medial pterygoid muscles relax, the mandible drops. Now you know why the mouth of many persons, particularly the elderly, is open while the person is asleep in a chair. In contrast, astronauts in zero gravity must work hard to open their mouths.

femoral triangle

At the junction between the trunk and lower limb is a space called the femoral triangle. The base is formed superiorly by the inguinal ligament, medially by the lateral border of the adductor longus muscle, and laterally by the medial border of the sartorius muscle. The apex is formed by the crossing of the adductor longus by the sartorius muscle. The contents of the femoral triangle, from lateral to medial, are the femoral nerve and its branches, the femoral artery and several of its branches, the femoral vein and its proximal tributaries, and the deep inguinal lymph nodes. The femoral artery is easily accessible within the triangle and is the site for insertion of catheters that may extend into the aorta and ultimately into the coronary vessels of the heart. Such catheters are utilized during cardiac catheterization, coronary angiography, and other procedures involving the heart. Inguinal hernias frequently appear in this area.

Bell's palsy

Bell's palsy, also known as facial paralysis, is a unilateral paralysis of the muscles of facial expression. It is due to damage or disease of the facial (VII) nerve. Possible causes include inflammation of the facial nerve due to an ear infection, ear surgery that damages the facial nerve, or infection by the herpes simplex virus. The paralysis causes the entire side of the face to droop in severe cases. The person cannot wrinkle the forehead, close the eye, or pucker the lips on the affected side. Drooling and difficulty in swallowing also occur. Eighty percent of patients recover completely within a few weeks to a few months. For others, paralysis is permanent. The symptoms of Bell's palsy mimic those of a stroke.

reverse muscle action (RMA)

Certain muscles are also capable of reverse muscle action (RMA). This means that during specific movements of the body the actions are reversed; therefore, the positions of the origin and insertion of a specific muscle are switched.

medial (adductor) compartment of the thigh

Deep fascia (intermuscular septum) separates the muscles of the thigh that act on the femur (thigh bone) and tibia and fibula (leg bones) into medial, anterior, and posterior compartments. Most of the muscles of the medial (adductor) compartment of the thigh have a similar orientation and adduct the femur at the hip joint. (See the adductor magnus, adductor longus, adductor brevis, and pectineus, which are components of the medial compartment, in Exhibit 11.Q.)

Injury of Levator Ani and Urinary Stress Incontinence

During childbirth, the levator ani muscle supports the head of the fetus, and the muscle may be injured during a difficult childbirth or traumatized during an episiotomy (a cut made with surgical scissors to prevent or direct tearing of the perineum during the birth of a baby). The consequence of such injuries may be urinary stress incontinence, that is, the leakage of urine whenever intra-abdominal pressure is increased—for example, during coughing. One way to treat urinary stress incontinence is to strengthen and tighten the muscles that support the pelvic viscera. This is accomplished by Kegel exercises, the alternate contraction and relaxation of muscles of the pelvic floor. To find the correct muscles, the person imagines that she is urinating and then contracts the muscles as if stopping in midstream. The muscles should be held for a count of three, then relaxed for a count of three. This should be done 5-10 times each hour—sitting, standing, and lying down. Kegel exercises are also encouraged during pregnancy to strengthen the muscles for delivery.

rotator (musculotendinous) cuff

Four deep muscles of the shoulder—subscapularis, supraspinatus, infraspinatus, and teres minor—strengthen and stabilize the shoulder joint. These muscles join the scapula to the humerus. Their flat tendons fuse together to form the rotator (musculotendinous) cuff, a nearly complete circle of tendons around the shoulder joint, like the cuff on a shirtsleeve. The supraspinatus muscle is especially subject to wear and tear because of its location between the head of the humerus and acromion of the scapula, which compress its tendon during shoulder movements, especially abduction of the arm. This is further aggravated by poor posture with slouched shoulders.

central tendon

From their various origins, the fibers of the muscular portion converge and insert into the central tendon, a strong aponeurosis located near the center of the muscle. The central tendon fuses with the inferior surface of the pericardium (covering of the heart) and the pleurae (coverings of the lungs).

Golfer's Elbow

Golfer's elbow is a condition that can be caused by strain of the flexor muscles, especially the flexor carpi radialis, as a result of repetitive movements such as swinging a golf club. Strain can, however, be caused by many actions. Pianists, violinists, movers, weight lifters, bikers, and those who use computers are among those who may develop pain near the medial epicondyle (medial epicondylitis).

superior extensor retinaculum and inferior extensor retinaculum

In a situation analogous to the wrist, the tendons of the muscles of the anterior compartment are held firmly to the ankle by thickenings of deep fascia called the superior extensor retinaculum (transverse ligament of the ankle) and inferior extensor retinaculum (cruciate ligament of the ankle).

anterior (flexor) compartment

In the arm, the biceps brachii, brachialis, and coracobrachialis muscles compose the anterior (flexor) compartment.

compartments

In the limbs, functionally related skeletal muscles and their associated blood vessels and nerves are grouped together by fascia into regions called compartments.

intrinsic tongue muscles

Intrinsic tongue muscles originate and insert within the tongue. These muscles alter the shape of the tongue rather than moving the entire tongue. The extrinsic and intrinsic muscles of the tongue insert into both lateral halves of the tongue.

iliotibial tract

It is well developed laterally where, together with the tendons of the tensor fasciae latae and gluteus maximus muscles, it forms a structure called the iliotibial tract. The tract inserts into the lateral condyle of the tibia.

superficial inguinal ring

Just superior to the medial end of the inguinal ligament is a triangular slit in the aponeurosis referred to as the superficial inguinal ring, the outer opening of the inguinal canal

anterior and posterior thoracic muscles

Muscles that move the pectoral girdle can be classified into two groups based on their location in the thorax: anterior and posterior thoracic muscles. The anterior thoracic muscles are the subclavius, pectoralis minor, and serratus anterior. The posterior thoracic muscles are the trapezius, levator scapulae, rhomboid major, and rhomboid minor.

extrinsic muscles of the hand

Muscles of the forearm that move the wrist, hand, and digits are many and varied. Those in this group that act on the digits are known as extrinsic muscles of the hand (ex-= outside) because they originate outside the hand and insert within it. As you will see, the names for the muscles that move the wrist, hand, and digits give some indication of their origin, insertion, or action. Based on location and function, the muscles of the forearm are divided into two groups: (1) anterior compartment muscles and (2) posterior compartment muscles.

extrinsic eye muscles

Muscles that move the eyeballs are called extrinsic eye muscles because they originate outside the eyeballs (in the orbit) and insert on the outer surface of the sclera ("white of the eye"). The extrinsic eye muscles are some of the fastest contracting and most precisely controlled skeletal muscles in the body.

anterior compartment of the leg

Muscles that move the foot and toes are located in the leg. The muscles of the leg, like those of the thigh, are divided by deep fascia into three compartments: anterior, lateral, and posterior. The anterior compartment of the leg consists of muscles that dorsiflex the foot.

Impingement Syndrome

One of the most common causes of shoulder pain and dysfunction in athletes is known as impingement syndrome, which is sometimes confused with another common complaint, compartment syndrome. The repetitive movement of the arm over the head that is common in baseball, overhead racquet sports, lifting weights over the head, spiking a volleyball, and swimming puts these athletes at risk. Impingement syndrome may also be caused by a direct blow or stretch injury. Continual pinching of the supraspinatus tendon as a result of overhead motions causes it to become inflamed and results in pain. If movement is continued despite the pain, the tendon may degenerate near the attachment to the humerus and ultimately may tear away from the bone (rotator cuff injury). Treatment consists of resting the injured tendons, strengthening the shoulder through exercise, massage therapy, and surgery if the injury is particularly severe. During surgery, an inflamed bursa may be removed, bone may be trimmed, and/or the coracoacromial ligament may be detached. Torn rotator cuff tendons may be trimmed and then reattached with sutures, anchors, or surgical tacks. These steps make more space, thus relieving pressure and allowing the arm to move freely.

fascicles

Recall from Chapter 10 that the skeletal muscle fibers (cells) within a muscle are arranged in bundles known as fascicles. Within a fascicle, all muscle fibers are parallel to one another. The fascicles, however, may form one of five patterns with respect to the tendons: parallel, fusiform (spindle-shaped, narrow toward the ends and wide in the middle), circular, triangular, or pennate (shaped like a feather)

Rotator Cuff Injury

Rotator cuff injury is a strain or tear in the rotator cuff muscles and is common among baseball pitchers, volleyball players, racquet sports players, and swimmers due to shoulder movements that involve vigorous circumduction. It also occurs as a result of wear and tear, aging, trauma, poor posture, improper lifting, and repetitive motions in certain jobs, such as placing items on a shelf above your head. Most often, there is tearing of the supraspinatus muscle tendon or the rotator cuff. This tendon is especially predisposed to wear and tear because of its location between the head of the humerus and acromion of the scapula, which compresses the tendon during shoulder movements. Poor posture and poor body mechanics also increase compression of the supraspinatus muscle tendon.

muscles of mastication (chewing)

The muscles that move the mandible (lower jawbone) at the temporomandibular joint (TMJ) are known as the muscles of mastication (chewing)

intrinsic muscles of the hand

Several of the muscles discussed in Exhibit 11.N move the digits in various ways and are known as extrinsic muscles of the hand. They produce the powerful but crude movements of the digits. The intrinsic muscles of the hand in the palm produce the weak but intricate and precise movements of the digits that characterize the human hand. The muscles in this group are so named because their origins and insertions are within the hand.

Shin splint syndrome (shin splints)

Shin splint syndrome, or simply shin splints, refers to pain or soreness along the tibia, specifically the medial, distal two-thirds. It may be caused by tendinitis of the anterior compartment muscles, especially the tibialis anterior muscle, inflammation of the periosteum (periostitis) around the tibia, or stress fractures of the tibia. The tendinitis usually occurs when poorly conditioned runners run on hard or banked surfaces with poorly supportive running shoes. The condition may also occur with vigorous activity of the legs following a period of relative inactivity or running in cold weather without proper warmup. The muscles in the anterior compartment (mainly the tibialis anterior) can be strengthened to balance the stronger posterior compartment muscles.

pronator teres and pronator quadratus

Some muscles that move the radius and ulna are involved in pronation and supination at the radioulnar joints. The pronators, as suggested by their names, are the pronator teres and pronator quadratus muscles.

external intercostals

The 11 pairs of external intercostals occupy the superficial layer, and their fibers run in an oblique direction interiorly and anteriorly from the rib above to the rib below. They elevate the ribs during inhalation to help expand the thoracic cavity.

plantar aponeurosis (fascia)

The deep fascia of the foot forms the plantar aponeurosis (fascia) that extends from the calcaneus bone to the phalanges of the toes. The aponeurosis supports the longitudinal arch of the foot and encloses the flexor tendons of the foot.

carpal tunnel syndrome

Structures within the carpal tunnel, especially the median nerve, are vulnerable to compression, and the resulting condition is called carpal tunnel syndrome. Compression of the median nerve leads to sensory changes over the lateral side of the hand and muscle weakness in the thenar eminence. This results in pain, numbness, and tingling of the fingers. The condition may be caused by inflammation of the digital tendon sheaths, fluid retention, excessive exercise, infection, trauma, and/or repetitive activities that involve flexion of the wrist, such as keyboarding, cutting hair, or playing the piano. Treatment may involve the use of nonsteroidal anti-inflammatory drugs (such as ibuprofen or aspirin), wearing a wrist splint, corticosteroid injections, or surgery to cut the flexor retinaculum and release pressure on the median nerve.

lumbricals

The 11 or 12 intermediate (midpalmar) muscles include the lumbricals, palmar interossei, and dorsal interossei. The lumbricals, as their name indicates, are worm-shaped. They originate from and insert into the tendons of other muscles (flexor digitorum profundus and extensor digitorum).

internal intercostals

The 11 pairs of internal intercostals occupy the intermediate layer of the intercostal spaces. The fibers of these muscles run at right angles to the external intercostals, in an oblique direction interiorly and posteriorly from the inferior border of the rib above to the superior border of the rib below. They draw adjacent ribs together during forced exhalation to help decrease the size of the thoracic cavity.

abductor digiti minimi

The abductor digiti minimi is a short, wide muscle and is the most superficial of the hypothenar muscles. It is a powerful muscle that plays an important role in grasping an object with outspread fingers.

abductor digiti minimi

The abductor digiti minimi, which lies along the lateral border of the sole and is comparable to the same muscle in the hand, abducts the little toe.

abductor pollicis brevis

The abductor pollicis brevis is a thin, short, relatively broad superficial muscle on the lateral side of the thenar eminence.

actions

The actions of a muscle are the main movements that occur when the muscle contracts. In our spring example, this would be the closing of the door.

superior oblique

The actions of the oblique muscles cannot be deduced from their names. The superior oblique muscle originates posteriorly near the tendinous ring, then passes anteriorly superior to the medial rectus muscle, and ends in a round tendon. The tendon extends through a pulleylike loop of fibrocartilaginous tissue called the trochlea (= pulley) on the anterior and medial part of the roof of the orbit. Finally, the tendon turns and inserts on the posterolateral aspect of the eyeball. Accordingly, the superior oblique muscle moves the eyeballs inferiorly and laterally.

adductor hallucis

The adductor hallucis, which has an oblique and transverse head like the adductor pollicis in the hand, adducts the great toe.

adductor pollicis

The adductor pollicis is fan-shaped and has two heads (oblique and transverse) separated by a gap through which the radial artery passes.

anconeus

The anconeus is a small muscle located on the lateral part of the posterior aspect of the elbow that assists the triceps brachii in extending the forearm at the elbow joint.

anterior (flexor) compartment muscles

The anterior (flexor) compartment muscles of the forearm originate on the humerus; typically insert on the carpals, metacarpals, and phalanges; and function primarily as flexors. The bellies of these muscles form the bulk of the forearm. One of the muscles in the superficial anterior compartment, the palmaris longus muscle, is missing in about 10% of individuals (usually in the left forearm) and is commonly used for tendon repair.

deep anterior compartment

The deep anterior compartment muscles are arranged in the following order from lateral to medial: flexor pollicis longus (the only flexor of the distal phalanx of the thumb) and flexor digitorum profundus (ends in four tendons that insert into the distal phalanges of the fingers).

flexor pollicis longus and flexor digitorum profundus

The deep anterior compartment muscles are arranged in the following order from lateral to medial: flexor pollicis longus (the only flexor of the distal phalanx of the thumb) and flexor digitorum profundus (ends in four tendons that insert into the distal phalanges of the fingers).

tendinous intersections

The anterior surface of the muscle is interrupted by three transverse fibrous bands of tissue called tendinous intersections, believed to be remnants of septa that separated myotomes during embryological development. There are usually three tendinous intersections, one at the level of the umbilicus, one near the xiphoid process, and one midway between the other two. A fourth intersection is sometimes found below the level of the umbilicus. These tendinous intersections are fused with the anterior wall of the rectus sheath but have no connections to the posterior abdominal wall. Muscular persons may possess easily demonstrated intersections as the result of exercise and the ensuing hypertrophy of the rectus muscle. Hypertrophy of the muscle tissue, of course, has no effect on the connective tissue of the intersections. Body builders focus on the development of the "six-pack" effect of the abdomen. Small percentages of the population have a variant of the intersections and are able to develop an "eight-pack."

anterior triangle

The anterior triangle is bordered superiorly by the mandible, medially by the cervical midline, and laterally by the anterior border of the sternocleidomastoid muscle. It has its apex at the sternum. The anterior triangle is subdivided into three paired triangles: submandibular, carotid, and muscular. An unpaired submental triangle is formed by the upper part of the combined right and left anterior triangles. The anterior triangle contains submental, submandibular, and deep cervical lymph nodes; the submandibular salivary gland and a portion of the parotid salivary gland; the facial artery and vein; carotid arteries and internal jugular vein; the thyroid gland and infrahyoid muscles; and the following cranial nerves: glossopharyngeal (IX), vagus (X), accessory (XI), and hypoglossal (XII).

splenius

The bandagelike splenius muscles are attached to the sides and back of the neck.

biceps brachii

The biceps brachii is the large muscle located on the anterior surface of the arm. As indicated by its name, it has two heads of origin (long and short), both from the scapula. The muscle spans both the shoulder and elbow joints. In addition to its role in flexing the forearm at the elbow joint, it also supinates the forearm at the radioulnar joints and flexes the arm at the shoulder joint.

brachialis

The brachialis is deep to the biceps brachii muscle. It is the most powerful flexor of the forearm at the elbow joint. For this reason, it is the "workhorse" of the elbow flexors.

brachioradialis

The brachioradialis flexes the forearm at the elbow joint, especially when a quick movement is required or when a weight is lifted slowly during flexion of the forearm.

buccinator

The buccinator muscle forms the major muscular portion of the cheek. The duct of the parotid gland (a salivary gland) passes through the buccinator muscle to reach the oral cavity. The buccinator muscle is so named because it compresses the cheeks (bucc- = cheek) during blowing—for example, when a musician plays a brass instrument such as a trumpet. It functions in whistling, blowing, and sucking and assists in chewing.

carpal tunnel

The carpal tunnel is a narrow passageway formed anteriorly by the flexor retinaculum and posteriorly by the carpal bones. Through this tunnel pass the median nerve, the most superficial structure, and the long flexor tendons for the digits.

quadriceps tendon

The common tendon for the four muscles, known as the quadriceps tendon, inserts into the patella.

coracobrachialis

The coracobrachialis is an elongated, narrow muscle in the arm.

compressor urethrae, sphincter urethrovaginalis, and external urethral sphincter

The deep muscles of the female perineum are the compressor urethrae, sphincter urethrovaginalis, and external urethral sphincter

deep transverse perineal and external urethral sphincter

The deep muscles of the male perineum are the deep transverse perineal and external urethral sphincter

popliteus

The deep muscles of the posterior compartment are the popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus. The popliteus is a triangular muscle that forms the floor of the popliteal fossa.

abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis

The deep posterior compartment muscles are arranged in the following order from lateral to medial: abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.

deep posterior compartment

The deep posterior compartment muscles are arranged in the following order from lateral to medial: abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.

aortic hiatus

The diaphragm has three major openings through which various structures pass between the thorax and abdomen. These structures include the aorta, along with the thoracic duct and azygous vein, which pass through the aortic hiatus

diaphragm

The dome-shaped diaphragm is the most important muscle that powers breathing. It also separates the thoracic and abdominal cavities. The diaphragm has a convex superior surface that forms the floor of the thoracic cavity and a concave, inferior surface that forms the roof of the abdominal cavity

dorsal interossei

The dorsal interossei are the most posterior of this series of muscles. Both sets of interossei muscles are located between the metacarpals and are important in abduction, adduction, flexion, and extension of the fingers, and in movements in skilled activities such as writing, typing, and playing a piano.

erector spinae

The erector spinae is the largest muscle mass of the back, forming a prominent bulge on either side of the vertebral column. It is the chief extensor of the vertebral column. It is also important in controlling flexion, lateral flexion, and rotation of the vertebral column and in maintaining the lumbar curve. As noted above, it consists of three groups: iliocostalis (laterally placed), longissimus (intermediately placed), and spinalis (medially placed). These groups, in turn, consist of a series of overlapping muscles, and the muscles within the groups are named according to the regions of the body with which they are associated.

extensor retinaculum

The extensor retinaculum is located over the dorsal surface of the carpal bones. The extensor tendons of the wrist and digits pass deep to it.

external anal sphincter

The external anal sphincter closely adheres to the skin around the margin of the anus and keeps the anal canal and anus closed except during defecation.

external oblique

The external oblique is the superficial muscle. Its fascicles extend inferiorly and medially.

fibularis (peroneus) tertius

The fibularis (peroneus) tertius muscle is part of the extensor digitorum longus, with which it shares a common origin.

groin pull

The five major muscles of the inner thigh function to move the legs medially. This muscle group is important in activities such as sprinting, hurdling, and horseback riding. A rupture or tear of one or more of these muscles can cause a groin pull. Groin pulls most often occur during sprinting or twisting, or from kicking a solid, perhaps stationary object. Symptoms of a groin pull may be sudden or may not surface until the day after the injury; they include sharp pain in the inguinal region, swelling, bruising, or inability to contract the muscles. As with most strain injuries, treatment involves PRICE therapy, which stands for protection, rest, ice, compression, and elevation. After the injured part is protected from further damage, ice should be applied immediately, and the injured part should be elevated and rested. An elastic bandage should be applied, if possible, to compress the injured tissue.

belly (body)

The fleshy portion of the muscle between the tendons is called the belly (body), the coiled middle portion of the spring in our example.

flexor digiti minimi brevis

The flexor digiti minimi brevis muscle is also short and wide and is lateral to the abductor digiti minimi muscle.

flexor digiti minimi brevis

The flexor digiti minimi brevis, which lies superficial to the metatarsal of the little toe and is comparable to the same muscle in the hand, flexes the little toe.

flexor digitorum brevis

The flexor digitorum brevis, which lies in the middle of the sole, flexes toes II-V at the interphalangeal and metatarsophalangeal joints.

flexor digitorum longus and flexor hallucis longus

The flexor digitorum longus is smaller than the flexor hallucis longus, even though the former flexes four toes and the latter flexes only the great toe at the interphalangeal joint.

flexor digitorum superficialis

The flexor digitorum superficialis muscle is deep to the other three muscles and is the largest superficial muscle in the forearm.

flexor pollicis brevis

The flexor pollicis brevis is a short, wide muscle that is medial to the abductor pollicis brevis muscle.

flexor retinaculum

The flexor retinaculum is located over the palmar surface of the carpal bones. The long flexor tendons of the digits and wrist and the median nerve pass deep to the flexor retinaculum.

dorsal interossei

The fourth layer is the deepest and consists of two muscle groups. The dorsal interossei are four muscles that abduct toes II-IV, flex the proximal phalanges, and extend the distal phalanges.

gastrocnemius

The gastrocnemius is the most superficial muscle and forms the prominence of the calf.

geniohyoid

The geniohyoid muscle elevates and draws the hyoid bone anteriorly to shorten the floor of the oral cavity and to widen the throat to receive food that is being swallowed. It also depresses the mandible.

gluteus medius

The gluteus medius is mostly deep to the gluteus maximus and is a powerful abductor of the femur at the hip joint. It is a common site for intramuscular injection.

gluteus minimus

The gluteus minimus is the smallest of the gluteal muscles and lies deep to the gluteus medius.

gracilis

The gracilis, the other muscle in the medial compartment, is a long, straplike muscle on the medial aspect of the thigh and knee. This muscle not only adducts the thigh, but also medially rotates the thigh and flexes the leg at the knee joint. For this reason, it is discussed here.

iliocostalis cervicis, iliocostalis thoracis, and iliocostalis lumborum

The iliocostalis group consists of three muscles: the iliocostalis cervicis (cervical region), iliocostalis thoracis (thoracic region), and iliocostalis lumborum (lumbar region).

iliocostalis group

The iliocostalis group consists of three muscles: the iliocostalis cervicis (cervical region), iliocostalis thoracis (thoracic region), and iliocostalis lumborum (lumbar region).

inguinal ligament

The inferior free border of the external oblique aponeurosis forms the inguinal ligament, which runs from the anterior superior iliac spine to the pubic tubercle

inferior oblique

The inferior oblique muscle originates on the maxilla at the anteromedial aspect of the floor of the orbit. It then passes posteriorly and laterally and inserts on the posterolateral aspect of the eyeball. Because of this arrangement, the inferior oblique muscle moves the eyeballs superiorly and laterally.

omohyoid, sternohyoid, and thyrohyoid

The infrahyoid muscles are sometimes called "strap" muscles because of their ribbonlike appearance. Most of the infrahyoid muscles depress the hyoid bone and some move the larynx during swallowing and speech. The omohyoid muscle, like the digastric muscle, is composed of two bellies connected by an intermediate tendon. In this case, however, the two bellies are referred to as superior and inferior, rather than anterior and posterior. Together, the omohyoid, sternohyoid, and thyrohyoid muscles depress the hyoid bone.

infraspinatus

The infraspinatus is a triangular muscle, also named for its location in the infraspinous fossa of the scapula.

inguinal canal

The inguinal canal contains the spermatic cord and ilioinguinal nerve in males, and the round ligament of the uterus and ilioinguinal nerve in females.

inguinal hernia

The inguinal region is a weak area in the abdominal wall. It is often the site of an inguinal hernia, a rupture or separation of a portion of the inguinal area of the abdominal wall resulting in the protrusion of a part of the small intestine. A hernia is much more common in males than in females because the inguinal canals in males are larger to accommodate the spermatic cord and ilioinguinal nerve. Treatment of hernias most often involves surgery. The organ that protrudes is "tucked" back into the abdominal cavity and the defect in the abdominal muscles is repaired. In addition, a mesh is often applied to reinforce the area of weakness.

internal oblique

The internal oblique is the intermediate flat muscle. Its fascicles extend at right angles to those of the external oblique.

dorsal muscles of the foot

The intrinsic muscles of the foot are divided into two groups: dorsal muscles of the foot and plantar muscles of the foot.

(1) thenar, (2) hypothenar, and (3) intermediate

The intrinsic muscles of the hand are divided into three groups: (1) thenar, (2) hypothenar, and (3) intermediate. The thenar muscles include the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and adductor pollicis (acts on the thumb but is not in the thenar eminence).

fibularis (peroneus) longus and fibularis (peroneus) brevis

The lateral (fibular) compartment of the leg contains two muscles that plantar flex and evert the foot: the fibularis (peroneus) longus and fibularis (peroneus) brevis.

lateral (fibular) compartment of the leg

The lateral (fibular) compartment of the leg contains two muscles that plantar flex and evert the foot: the fibularis (peroneus) longus and fibularis (peroneus) brevis.

levator scapulae

The levator scapulae is a narrow, elongated muscle in the posterior portion of the neck. It is deep to the sternocleidomastoid and trapezius muscles. As its name suggests, one of its actions is to elevate the scapula

longissimus capitis, longissimus cervicis, and longissimus thoracis

The longissimus group resembles a herringbone and consists of three muscles: the longissimus capitis (head region), longissimus cervicis (cervical region), and longissimus thoracis (thoracic region).

longissimus group

The longissimus group resembles a herringbone and consists of three muscles: the longissimus capitis (head region), longissimus cervicis (cervical region), and longissimus thoracis (thoracic region).

iliopsoas

The majority of muscles that move the femur (thigh bone) originate on the pelvic girdle and insert on the femur. The psoas major and iliacus muscles share a common insertion (lesser trochanter of femur) and are collectively known as the iliopsoas muscle.

psoas major and iliacus

The majority of muscles that move the femur (thigh bone) originate on the pelvic girdle and insert on the femur. The psoas major and iliacus muscles share a common insertion (lesser trochanter of femur) and are collectively known as the iliopsoas muscle.

lateral pterygoid

The medial and lateral pterygoid muscles assist in mastication by moving the mandible from side to side to help grind food. Additionally, the lateral pterygoid muscles protract (protrude) the mandible. The masseter muscle has been removed in Figure 11.6 to illustrate the deeper pterygoid muscles; the masseter can be seen in Figure 11.4c. Note the enormous bulk of the temporalis and masseter muscles compared to the smaller mass of the two pterygoid muscles.

multifidus

The multifidus muscle in this group, as its name implies, is segmented into several bundles. It extends and laterally flexes the vertebral column. This muscle is large and thick in the lumbar region and is important in maintaining the lumbar curve.

intrinsic muscles of the foot

The muscles in this exhibit are termed intrinsic muscles of the foot because they originate and insert within the foot. The muscles of the hand are specialized for precise and intricate movements, but those of the foot are limited to support and locomotion.

anterior (extensor) compartment of the thigh

The muscles of the anterior (extensor) compartment of the thigh extend the leg (and flex the thigh). This compartment contains the quadriceps femoris and sartorius muscles.

posterior (flexor) compartment of the thigh

The muscles of the posterior (flexor) compartment of the thigh flex the leg (and extend the thigh). This compartment is composed of three muscles collectively called the hamstrings: (1) biceps femoris, (2) semitendinosus, and (3) semimembranosus. The hamstrings are so named because their tendons are long and stringlike in the popliteal area. Because the hamstrings span two joints (hip and knee), they are both extensors of the thigh and flexors of the leg.

mylohyoid

The mylohyoid muscle elevates the hyoid bone and helps press the tongue against the roof of the oral cavity during swallowing to move food from the oral cavity into the throat.

occipitofrontalis

The occipitofrontalis is an unusual muscle in this group because it is made up of two parts: an anterior part called the frontal belly (frontalis), which is superficial to the frontal bone, and a posterior part called the occipital belly (occipitalis), which is superficial to the occipital bone. The two muscular portions are held together by a strong aponeurosis (sheetlike tendon), the epicranial aponeurosis, also called the galea aponeurotica, that covers the superior and lateral surfaces of the skull.

opponens digiti minimi

The opponens digiti minimi muscle is triangular and deep to the other two hypothenar muscles.

opponens pollicis

The opponens pollicis is a small, triangular muscle that is deep to the flexor pollicis brevis and abductor pollicis brevis muscles.

palmar interossei

The palmar interossei are the smallest and more anterior of the interossei muscles.

pectoralis minor

The pectoralis minor is a thin, flat, triangular muscle that is deep to the pectoralis major. Besides its role in movements of the scapula, the pectoralis minor muscle assists in forced inhalation.

piriformis, obturator internus, obturator externus, superior gemellus, inferior gemellus, and quadratus femoris

The piriformis, obturator internus, obturator externus, superior gemellus, inferior gemellus, and quadratus femoris muscles are all deep to the gluteus maximus muscle and function as lateral rotators of the femur at the hip joint.

abductor hallucis

The plantar muscles are arranged in four layers. The most superficial layer, called the first layer, consists of three muscles. The abductor hallucis, which lies along the medial border of the sole and is comparable to the abductor pollicis brevis in the hand, abducts the great toe at the metatarsophalangeal joint.

plantaris

The plantaris is a small muscle that may be absent; conversely, sometimes there are two of them in each leg. It runs obliquely between the gastrocnemius and soleus muscles.

popliteal fossa

The popliteal fossa is a diamond-shaped space on the posterior aspect of the knee bordered laterally by the tendons of the biceps femoris muscle and medially by the tendons of the semitendinosus and semimembranosus muscles.

posterior (extensor) compartment muscles

The posterior (extensor) compartment muscles of the forearm originate on the humerus, insert on the metacarpals and phalanges, and function as extensors. Within each compartment, the muscles are grouped as superficial or deep.

posterior compartment of the leg

The posterior compartment of the leg consists of muscles in superficial and deep groups.

posterior triangle

The posterior triangle is bordered inferiorly by the clavicle, anteriorly by the posterior border of the sternocleidomastoid muscle, and posteriorly by the anterior border of the trapezius muscle. The posterior triangle is subdivided into two triangles, occipital and supraclavicular (omoclavicular), by the inferior belly of the omohyoid muscle. The posterior triangle contains part of the subclavian artery, external jugular vein, cervical lymph nodes, brachial plexus, and the accessory (XI) nerve.

scapular muscles

The remaining seven muscles, the scapular muscles, arise from the scapula

rotatores

The rotatores muscles of this group are short and are found along the entire length of the vertebral column. These small muscles contribute little to vertebral movement but play important roles in monitoring the position of the vertebral column and providing proprioceptive feedback to the stronger vertebral muscles.

sartorius

The sartorius is a long, narrow muscle that forms a band across the thigh from the ilium of the hip bone to the medial side of the tibia. The various movements it produces (flexion of the leg at the knee joint and flexion, abduction, and lateral rotation at the hip joint) help effect the cross-legged sitting position in which the heel of one limb is placed on the knee of the opposite limb. Its name means tailor's muscle; it was so called because tailors often assume a cross-legged sitting position. (Because the major action of the sartorius muscle is to move the thigh rather than the leg, it could have been included in Exhibit 11.Q.)

quadratus plantae and lumbricals

The second layer consists of the quadratus plantae, a rectangular muscle that arises by two heads and flexes toes II-V at the metatarsophalangeal joints, and the lumbricals, four small muscles that are similar to the lumbricals in the hands. They flex the proximal phalanges and extend the distal phalanges of toes II-V.

semispinalis capitis, semispinalis cervicis (cervical region), and semispinalis thoracis

The semispinalis muscles in this group are also named according to the region of the body with which they are associated: semispinalis capitis (head region), semispinalis cervicis (cervical region), and semispinalis thoracis (thoracic region). These muscles extend the vertebral column and rotate the head.

soleus

The soleus, which lies deep to the gastrocnemius, is broad and flat. It derives its name from its resemblance to a flat fish (sole).

spinalis capitis, spinalis cervicis, and spinalis thoracis

The spinalis group also consists of three muscles: the spinalis capitis, spinalis cervicis, and spinalis thoracis.

spinalis group

The spinalis group also consists of three muscles: the spinalis capitis, spinalis cervicis, and spinalis thoracis.

subscapularis

The subscapularis is a large triangular muscle that fills the subscapular fossa of the scapula and forms a small part in the apex of the posterior wall of the axilla.

flexor carpi radialis, palmaris longus, and flexor carpi ulnaris

The superficial anterior compartment muscles are arranged in the following order from lateral to medial: flexor carpi radialis, palmaris longus, and flexor carpi ulnaris (the ulnar nerve and artery are just lateral to the tendon of this muscle at the wrist).

superficial anterior compartment

The superficial anterior compartment muscles are arranged in the following order from lateral to medial: flexor carpi radialis, palmaris longus, and flexor carpi ulnaris (the ulnar nerve and artery are just lateral to the tendon of this muscle at the wrist).

calcaneal (Achilles) tendon

The superficial muscles share a common tendon of insertion, the calcaneal (Achilles) tendon, the strongest tendon of the body. It inserts into the calcaneal bone of the ankle. The superficial and most of the deep muscles plantar flex the foot at the ankle joint. The superficial muscles of the posterior compartment are the gastrocnemius, soleus, and plantaris—the so-called calf muscles. The large size of these muscles is directly related to the characteristic upright stance of humans.

extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris

The superficial posterior compartment muscles are arranged in the following order from lateral to medial: extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum (occupies most of the posterior surface of the forearm and divides into four tendons that insert into the middle and distal phalanges of the fingers), extensor digiti minimi (a slender muscle usually connected to the extensor digitorum), and extensor carpi ulnaris.

superficial posterior compartment

The superficial posterior compartment muscles are arranged in the following order from lateral to medial: extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum (occupies most of the posterior surface of the forearm and divides into four tendons that insert into the middle and distal phalanges of the fingers), extensor digiti minimi (a slender muscle usually connected to the extensor digitorum), and extensor carpi ulnaris.

supinator

The supinator of the forearm is aptly named the supinator muscle. You use the powerful action of the supinator when you twist a corkscrew or turn a screw with a screwdriver.

supraspinatus

The supraspinatus, a rounded muscle named for its location in the supraspinous fossa of the scapula, lies deep to the trapezius.

patellar ligament

The tendon continues below the patella as the patellar ligament, which attaches to the tibial tuberosity. The quadriceps femoris muscle is the great extensor muscle of the leg.

retinacula

The tendons of the muscles of the forearm that attach to the wrist or continue into the hand, along with blood vessels and nerves, are held close to bones by strong fasciae. The tendons are also surrounded by tendon sheaths. At the wrist, the deep fascia is thickened into fibrous bands called retinacula (retinacul = holdfast).

tensor fasciae latae

The tensor fasciae latae muscle is located on the lateral surface of the thigh. The fascia lata is a layer of deep fascia, composed of dense connective tissue, that encircles the entire thigh.

teres major

The teres major is a thick, flattened muscle inferior to the teres minor that also helps form part of the posterior wall of the axilla.

teres minor

The teres minor is a cylindrical, elongated muscle, often inseparable from the infraspinatus, which lies along its superior border.

thenar eminence

The thenar muscles plus the adductor pollicis form the thenar eminence, the lateral rounded contour on the palm that is also called the ball of the thumb.

pubococcygeus, puborectalis, and iliococcygeus

The three components of the levator ani muscle are the pubococcygeus, puborectalis, and iliococcygeus.

levator ani

The three components of the levator ani muscle are the pubococcygeus, puborectalis, and iliococcygeus. The levator ani is the largest and most important muscle of the pelvic floor. It supports the pelvic viscera and resists the inferior thrust that accompanies increases in intra-abdominal pressure during functions such as forced exhalation, coughing, vomiting, urination, and defecation. The muscle also functions as a sphincter at the anorectal junction, urethra, and vagina.

hypothenar eminence

The three hypothenar muscles act on the little finger and form the hypothenar eminence, the medial rounded contour on the palm that is also called the ball of the little finger. The hypothenar muscles are the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi.

plantar interossei

The three plantar interossei abduct toes III-V, flex the proximal phalanges, and extend the distal phalanges. The interossei of the feet are similar to those of the hand. However, their actions are relative to the midline of the second digit rather than the third digit as in the hand.

tibialis posterior

The tibialis posterior is the deepest muscle in the posterior compartment. It lies between the flexor digitorum longus and flexor hallucis longus muscles.

extrinsic tongue muscles

The tongue is divided into lateral halves by a median fibrous septum. The septum extends throughout the length of the tongue. Inferiorly, the septum attaches to the hyoid bone. Muscles of the tongue are of two principal types: extrinsic and intrinsic. Extrinsic tongue muscles originate outside the tongue and insert into it. They move the entire tongue in various directions, such as anteriorly, posteriorly, and laterally.

transversospinales

The transversospinales are so named because their fibers run from the transverse processes to the spinous processes of the vertebrae.

transversus abdominis

The transversus abdominis is the deep muscle, with most of its fascicles directed transversely around the abdominal wall. Together, the external oblique, internal oblique, and transversus abdominis form three layers of muscle around the abdomen. In each layer, the muscle fascicles extend in a different direction. This is a structural arrangement that affords considerable protection to the abdominal viscera, especially when the muscles have good tone.

trapezius

The trapezius is a large, flat, triangular sheet of muscle extending from the skull and vertebral column medially to the pectoral girdle laterally. It is the most superficial back muscle and covers the posterior neck region and superior portion of the trunk. The two trapezius muscles form a trapezoid (diamond-shaped quadrangle)—hence its name.

triceps brachii

The triceps brachii is the large muscle located on the posterior surface of the arm. It is the more powerful of the extensors of the forearm at the elbow joint. As its name implies, it has three heads of origin, one from the scapula (long head) and two from the humerus (lateral and medial heads). The long head crosses the shoulder joint; the other heads do not.

posterior (extensor) compartment

The triceps brachii muscle forms the posterior (extensor) compartment.

splenius capitis and splenius cervicis

The two muscles in this group are named on the basis of their superior attachments (insertions): splenius capitis (head region) and splenius cervicis (cervical region). They extend the head and laterally flex and rotate the head.

gluteus maximus

There are three gluteal muscles: gluteus maximus, gluteus medius, and gluteus minimus. The gluteus maximus is the largest and heaviest of the three muscles and is one of the largest muscles in the body. It is the chief extensor of the femur. In its reverse muscle action (RMA), it is a powerful extensor of the torso at the hip joint.

extensor hallucis brevis and the extensor digitorum brevis

There are two dorsal muscles, the extensor hallucis brevis and the extensor digitorum brevis. The latter is a four-part muscle deep to the tendons of the extensor digitorum longus muscle, which extends toes II-V at the metatarsophalangeal joints.

flexor hallucis brevis

Three muscles compose the third layer. The flexor hallucis brevis, which lies adjacent to the plantar surface of the metatarsal of the great toe and is comparable to the same muscle in the hand, flexes the great toe.

adductor longus, adductor brevis, and adductor magnus

Three muscles on the medial aspect of the thigh are the adductor longus, adductor brevis, and adductor magnus. They originate on the pubic bone and insert on the femur. These three muscles adduct the thigh and are unique in their ability to both medially and laterally rotate the thigh. When the foot is on the ground, these muscles medially rotate the thigh, but when the foot is off the ground, they are lateral rotators of the thigh. This results from their oblique orientation, from an anterior origin to a posterior insertion. In addition, the adductor longus flexes the thigh and the adductor magnus extends the thigh. The pectineus muscle also adducts and flexes the femur at the hip joint.

superior and inferior recti, and lateral and medial recti

Three pairs of extrinsic eye muscles control movements of the eyeballs: (1) superior and inferior recti, (2) lateral and medial recti, and (3) superior and inferior obliques. The four recti muscles (superior, inferior, lateral, and medial) arise from a tendinous ring in the orbit and insert into the sclera of the eye. As their names imply, the superior and inferior recti move the eyeballs superiorly and inferiorly; the lateral and medial recti move the eyeballs laterally and medially, respectively.

levator palpebrae superioris

Unlike the recti and oblique muscles, the levator palpebrae superioris does not move the eyeballs, since its tendon passes the eyeball and inserts into the upper eyelid. Rather, it raises the upper eyelids, that is, opens the eyes. It is therefore an antagonist to the orbicularis oculi, which closes the eyes.

genioglossus, styloglossus, hyoglossus, palatoglossus

When you study the extrinsic tongue muscles, you will notice that all of their names end in glossus, meaning tongue. You will also notice that the actions of the muscles are obvious, considering the positions of the mandible, styloid process, hyoid bone, and soft palate, which serve as origins for these muscles. For example, the genioglossus (origin: the mandible) pulls the tongue downward and forward, the styloglossus (origin: the styloid process) pulls the tongue upward and backward, the hyoglossus (origin: the hyoid bone) pulls the tongue downward and flattens it, and the palatoglossus (origin: the soft palate) raises the back portion of the tongue.

tibialis anterior

Within the anterior compartment, the tibialis anterior is a long, thick muscle against the lateral surface of the tibia, where it is easy to palpate (feel).

scalene group

Within the scalene group (Figure 11.19c), the anterior scalene muscle is anterior to the middle scalene muscle, the middle scalene muscle is intermediate in placement and is the longest and largest of the scalene muscles, and the posterior scalene muscle is posterior to the middle scalene muscle and is the smallest of the scalene muscles. These muscles flex, laterally flex, and rotate the head and assist in deep inhalation.

interspinales and intertransversarii

Within the segmental muscle group, the interspinales and intertransversarii muscles unite the spinous and transverse processes of consecutive vertebrae. They function primarily in stabilizing the vertebral column during its movements, and providing proprioceptive feedback.

caval opening (foramen for the vena cava)

and the inferior vena cava, which passes through the caval opening (foramen for the vena cava). In a condition called a hiatus hernia, the stomach protrudes superiorly through the esophageal hiatus.

depression

inferior movement of the scapula, as in pulling down on a rope attached to a pulley.

elevation

superior movement of the scapula, such as shrugging the shoulders or lifting a weight over the head.

esophageal hiatus

the esophagus with accompanying vagus (X) nerves, which pass through the esophageal hiatus

prime mover (agonist) and antagonist

-Movements often are the result of several skeletal muscles acting as a group. Most skeletal muscles are arranged in opposing (antagonistic) pairs at joints—that is, flexors-extensors, abductors-adductors, and so on. Within opposing pairs, one muscle, called the prime mover or agonist (= leader), contracts to cause an action while the other muscle, the antagonist (anti- = against), stretches and yields to the effects of the prime mover. In the process of flexing the forearm at the elbow, for instance, the biceps brachii is the prime mover, and the triceps brachii is the antagonist. The antagonist and prime mover are usually located on opposite sides of the bone or joint, as is the case in this example. -With an opposing pair of muscles, the roles of the prime mover and antagonist can switch for different movements. For example, while extending the forearm at the elbow against resistance (i.e., lowering the load shown in Figure 11.2c), the triceps brachii becomes the prime mover, and the biceps brachii is the antagonist. If a prime mover and its antagonist contract at the same time with equal force, there will be no movement.

strabismus

-Strabismus (strabismos = squinting) is a condition in which the two eyeballs are not properly aligned. This can be hereditary or it can be due to birth injuries, poor attachments of the muscles, problems with the brain's control center, or localized disease. Strabismus can be constant or intermittent. In strabismus, each eye sends an image to a different area of the brain and because the brain usually ignores the messages sent by one of the eyes, the ignored eye becomes weaker; hence "lazy eye," or amblyopia, develops. External strabismus results when a lesion in the oculomotor (III) nerve causes the eyeball to move laterally when at rest, and results in an inability to move the eyeball medially and inferiorly. A lesion in the abducens (VI) nerve results in internal strabismus, a condition in which the eyeball moves medially when at rest and cannot move laterally. -Treatment options for strabismus depend on the specific type of problem and include surgery, visual therapy (retraining the brain's control center), and orthoptics (eye muscle training to straighten the eyes).

orbicularis oculi

Among the noteworthy muscles in this group are those surrounding the orifices (openings) of the head such as the eyes, nose, and mouth. These muscles function as sphincters, which close the orifices, and dilators, which dilate or open the orifices. For example, the orbicularis oculi muscle closes the eye, and the levator palpebrae superioris muscle opens it

deltoid

Among the scapular muscles, the deltoid is a thick, powerful shoulder muscle that covers the shoulder joint and forms the rounded contour of the shoulder. This muscle is a frequent site of intramuscular injections. As you study the deltoid, note that its fascicles originate from three different points and that each group of fascicles moves the humerus differently.

intramuscular (IM) injection

An intramuscular (IM) injection penetrates the skin and subcutaneous layer to enter the muscle itself. Intramuscular injections are preferred when prompt absorption is desired, when larger doses than can be given subcutaneously are indicated, or when the drug is too irritating to give subcutaneously. The common sites for intramuscular injections include the gluteus medius muscle of the buttock, lateral side of the thigh in the midportion of the vastus lateralis muscle, and the deltoid muscle of the shoulder. Muscles in these areas, especially the gluteal muscles in the buttock, are fairly thick, and absorption is promoted by their extensive blood supply. To avoid injury, intramuscular injections are given deep within the muscle, away from major nerves and blood vessels. Intramuscular injections have a faster speed of delivery than oral medications but are slower than intravenous infusions.

spenalis capitis, semispinalis capitis, splenius capitis, and longissimus capitis

Bilateral contraction of the spenalis capitis, semispinalis capitis, splenius capitis, and longissimus capitis muscles extends the head. However, when these same muscles contract unilaterally, their actions are quite different, involving primarily rotation of the head.

dysphagia

Dysphagia (dys- = abnormal; -phagia = to eat) is a clinical term for difficulty in swallowing. Some individuals are unable to swallow while others have difficulty swallowing liquids, foods, or saliva. Causes include nervous system disorders that weaken or damage muscles of deglutition (stroke, Parkinson's disease, cerebral palsy); infections; cancer of the head, neck, or esophagus; and injuries to the head, neck, or chest.

sternal head and clavicular head

Each SCM consists of two bellies; they are more evident near the anterior attachments. The separation of the two bellies is variable and thus more evident in some persons than in others. The two bellies insert as the sternal head and the clavicular head of the SCM. The bellies also function differently; muscular spasm in the two bellies causes somewhat different symptoms.

superficial transverse perineal, the bulbospongiosus, and the ischiocavernosus

The muscles of the superficial layer are the superficial transverse perineal, the bulbospongiosus, and the ischiocavernosus

mechanical disadvantage

If, instead, the load is farther from the fulcrum and the effort is applied closer to the fulcrum, then a relatively large effort is required to move a small load (but at greater speed). This is called a mechanical disadvantage. Compare chewing something hard (the load) with your front teeth and the teeth in the back of your mouth. It is much easier to crush the hard food item with the back teeth because they are closer to the fulcrum (the jaw or temporomandibular joint) than are the front teeth. Here is one more example you can try. Straighten out a paper clip. Now get a pair of scissors and try to cut the paper clip with the tip of the scissors (mechanical disadvantage) versus near the pivot point of the scissors (mechanical advantage).

ischiococcygeus

In addition to assisting the levator ani, the ischiococcygeus pulls the coccyx anteriorly after it has been pushed posteriorly during defecation or childbirth.

sternothyroid

In addition, the sternothyroid muscle depresses the thyroid cartilage (Adam's apple) of the larynx to produce low sounds; the RMA of the thyrohyoid muscle elevates the thyroid cartilage to produce high sounds.

lever

In producing movement, bones act as levers, and joints function as the fulcrums of these levers. A lever is a rigid structure that can move around a fixed point called a fulcrum

compartment

In the limbs, a compartment is a group of skeletal muscles, their associated blood vessels, and associated nerves, all of which have a common function. In the upper limbs, for example, flexor compartment muscles are anterior, and extensor compartment muscles are posterior.

masseter, temporalis, and medial pterygoid

Of the four pairs of muscles involved in mastication, three are powerful closers of the jaw and account for the strength of the bite: masseter, temporalis, and medial pterygoid. Of these, the masseter is the strongest muscle of mastication.

axial muscles

Of the nine muscles that cross the shoulder joint, all except the pectoralis major and latissimus dorsi originate on the scapula (shoulder blade). The pectoralis major and latissimus dorsi thus are called axial muscles, because they originate on the axial skeleton.

pectoralis major

Of the two axial muscles that move the humerus (arm bone), the pectoralis major is a large, thick, fan-shaped muscle that covers the superior part of the thorax and forms the anterior fold of the thorax. It has two origins: a smaller clavicular head and a larger sternocostal head.

intercostals

Other muscles involved in breathing, called intercostals, span the intercostal spaces, the spaces between ribs. These muscles are arranged in three layers, only two of which are discussed here.

fixators

Some muscles in a group also act as fixators, stabilizing the origin of the prime mover so that the prime mover can act more efficiently. Fixators steady the proximal end of a limb while movements occur at the distal end. For example, the scapula is a freely movable bone that serves as the origin for several muscles that move the arm. When the arm muscles contract, the scapula must be held steady. In abduction of the arm, the deltoid muscle serves as the prime mover, and fixators (pectoralis minor, trapezius, subclavius, serratus anterior muscles, and others) hold the scapula firmly against the back of the chest. The insertion of the deltoid muscle pulls on the humerus to abduct the arm. Under different conditions—that is, for different movements—and at different times, many muscles may act as prime movers, antagonists, synergists, or fixators.

synergists

Sometimes a prime mover crosses other joints before it reaches the joint at which its primary action occurs. The biceps brachii, for example, spans both the shoulder and elbow joints, with primary action on the forearm. To prevent unwanted movements at intermediate joints or to otherwise aid the movement of the prime mover, muscles called synergists (syn- = together; -ergon = work) contract and stabilize the intermediate joints. As an example, muscles that flex the fingers (prime movers) cross the intercarpal and radiocarpal joints (intermediate joints). If movement at these intermediate joints were unrestrained, you would not be able to flex your fingers without flexing the wrist at the same time. Synergistic contraction of the wrist extensor muscles stabilizes the wrist joint and prevents unwanted movement, while the flexor muscles of the fingers contract to bring about the primary action, efficient flexion of the fingers. Synergists are usually located close to the prime mover.

rectus sheaths

The aponeuroses (sheathlike tendons) of the external oblique, internal oblique, and transversus abdominis muscles form the rectus sheaths, which enclose the rectus abdominis muscles.

third-class levers

The effort is between the fulcrum and the load in third-class levers. (Think FEL.) These levers operate like a pair of forceps and are the most common levers in the body. Third-class levers always produce a mechanical disadvantage because the effort is always closer to the fulcrum than the load. In the body, this arrangement favors speed and range of motion over force. The elbow joint, the biceps brachii muscle, and the bones of the arm and forearm are one example of a third-class lever. As we have seen, in flexing the forearm at the elbow, the elbow joint is the fulcrum w0705-nu, the contraction of the biceps brachii muscle provides the effort (E) and the weight of the hand and forearm is the load w0708-nu.

first-class levers

The fulcrum is between the effort and the load in first-class levers. (Think EFL.) Scissors and seesaws are examples of first-class levers. A first-class lever can produce either a mechanical advantage or a mechanical disadvantage depending on whether the effort or the load is closer to the fulcrum. (Think of an adult and a child on a seesaw.) As we have seen in the preceding examples, if the effort (child) is farther from the fulcrum than the load (adult), a heavy load can be moved, but not very far or fast. If the effort is closer to the fulcrum than the load, only a lighter load can be moved, but it moves far and fast. There are few first-class levers in the body. One example is the lever formed by the head resting on the vertebral column. When the head is raised, the contraction of the posterior neck muscles provides the effort (E), the joint between the atlas and the occipital bone (atlanto-occipital joint) forms the fulcrum w0705-nu, and the weight of the anterior portion of the skull is the load w0708-nu.

sternocleidomastoid (SCM)

The head is attached to the vertebral column at the atlanto-occipital joints formed by the atlas and occipital bone. Balance and movement of the head on the vertebral column involves the action of several neck muscles. For example, acting together (bilaterally), contraction of the two sternocleidomastoid (SCM) muscles flexes the cervical portion of the vertebral column and flexes the head. Acting singly (unilaterally), each sternocleidomastoid muscle laterally flexes and rotates the head.

latissimus dorsi

The latissimus dorsi is a broad, triangular muscle located on the inferior part of the back that forms most of the posterior wall of the axilla. The reverse muscle action (RMA) of the latissimus dorsi enables the vertebral column and torso to be elevated, as in doing a pullup. It is commonly called the "swimmer's muscle" because its many actions are used while swimming; consequently, many competitive swimmers have well-developed "lats."

second-class levers

The load is between the fulcrum and the effort in second-class levers. (Think ELF.) Second-class levers operate like a wheelbarrow. They always produce a mechanical advantage because the load is always closer to the fulcrum than the effort. This arrangement sacrifices speed and range of motion for force; this type of lever produces the most force. This class of lever is uncommon in the human body. An example is standing up on your toes. The fulcrum w0705-nu is the ball of the foot. The load w0708-nu is the weight of the body. The effort (E) is the contraction of the muscles of the calf, which raise the heel off the ground.

pelvic diaphragm

The muscles of the pelvic floor are the levator ani and ischiococcygeus. Along with the fascia covering their internal and external surfaces, these muscles are referred to as the pelvic diaphragm, which stretches from the pubis anteriorly to the coccyx posteriorly, and from one lateral wall of the pelvis to the other. This arrangement gives the pelvic diaphragm the appearance of a funnel suspended from its attachments. The pelvic diaphragm separates the pelvic cavity above from the perineum below. The anal canal and urethra pierce the pelvic diaphragm in both sexes, and the vagina also goes through it in females.

superficial and deep

The muscles of the perineum are arranged in two layers: superficial and deep.

benefits of stretching

The overall goal of stretching is to achieve normal range of motion of joints and mobility of soft tissues surrounding the joints. For most individuals, the best stretching routine involves static stretching, that is, slow sustained stretching that holds a muscle in a lengthened position. The muscles should be stretched to the point of slight discomfort (not pain) and held for about 30 seconds. Stretching should be done after warming up to increase the range of motion most effectively. 1. Improved physical performance. A flexible joint has the ability to move through a greater range of motion, which improves performance. 2. Decreased risk of injury. Stretching decreases resistance in various soft tissues so there is less likelihood of exceeding maximum tissue extensibility during an activity (i.e., injuring the soft tissues). 3. Reduced muscle soreness. Stretching can reduce some of the muscle soreness that results after exercise. 4. Improved posture. Poor posture results from improper position of various parts of the body and the effects of gravity over a number of years. Stretching can help realign soft tissues to improve and maintain good posture.

perineum

The perineum is the region of the trunk inferior to the pelvic diaphragm. It is a diamond-shaped area that extends from the pubic symphysis anteriorly, to the coccyx posteriorly, and to the ischial tuberosities laterally.

peripheral muscular portion

The peripheral muscular portion of the diaphragm originates on the xiphoid process of the sternum, the inferior six ribs and their costal cartilages, and the lumbar vertebrae and their intervertebral discs and the twelfth rib

rectus abdominis

The rectus abdominis muscle is a long muscle that extends the entire length of the anterior abdominal wall, originating at the pubic crest and pubic symphysis and inserting on the cartilages of ribs 5-7 and the xiphoid process of the sternum.

mechanical advantage

The relative distance between the fulcrum and load and the point at which the effort is applied determine whether a given lever operates at a mechanical advantage or a mechanical disadvantage. For example, if the load is closer to the fulcrum and the effort farther from the fulcrum, then only a relatively small effort is required to move a large load over a small distance. This is called a mechanical advantage.

rhomboid major and rhomboid minor

The rhomboid major and rhomboid minor lie deep to the trapezius and are not always distinct from each other. They appear as parallel bands that pass inferiorly and laterally from the vertebrae to the scapula. Their names are based on their shape—that is, a rhomboid (an oblique parallelogram). The rhomboid major is about two times wider than the rhomboid minor. Both muscles are used when forcibly lowering the raised upper limbs, as in driving a stake with a sledgehammer.

serratus anterior

The serratus anterior is a large, flat, fan-shaped muscle between the ribs and scapula. It is so named because of the saw-toothed appearance of its origins on the ribs.

linea alba

The sheaths meet at the midline to form the linea alba (= white line), a tough, fibrous band that extends from the xiphoid process of the sternum to the pubic symphysis. In the latter stages of pregnancy, the linea alba stretches to increase the distance between the rectus abdominis muscles.

stylohyoid

The stylohyoid muscle elevates and draws the hyoid bone posteriorly, thus elongating the floor of the oral cavity during swallowing.

subclavius

The subclavius is a small, cylindrical muscle under the clavicle that extends from the clavicle to the first rib. It steadies the clavicle during movements of the pectoral girdle.

suprahyoid muscles and infrahyoid muscles

Two groups of muscles are associated with the anterior aspect of the neck: (1) the suprahyoid muscles, so called because they are located superior to the hyoid bone, and (2) the infrahyoid muscles, named for their position inferior to the hyoid bone. Both groups of muscles stabilize the hyoid bone, allowing it to serve as a firm base on which the tongue can move.

origin and insertion

When a skeletal muscle contracts, it moves one of the articulating. The two articulating bones usually do not move equally in response to contraction. One bone remains stationary or near its original position, either because other muscles stabilize that bone by contracting and pulling it in the opposite direction or because its structure makes it less movable. Ordinarily, the attachment of a muscle's tendon to the stationary bone is called the origin; the attachment of the muscle's other tendon to the movable bone is called the insertion. A good analogy is a spring on a door. In this example, the part of the spring attached to the frame is the origin; the part attached to the door represents the insertion. A useful rule of thumb is that the origin is usually proximal and the insertion distal; the insertion is usually pulled toward the origin.

intubation during anesthesia

When general anesthesia is administered during surgery, a total relaxation of the muscles results. Once the various types of drugs for anesthesia have been given (especially the paralytic agents), the patient's airway must be protected and the lungs ventilated because the muscles involved with respiration are among those paralyzed. Paralysis of the genioglossus muscle causes the tongue to fall posteriorly, which may obstruct the airway to the lungs. To avoid this, the mandible is either manually thrust forward and held in place (known as the "sniffing position"), or a tube is inserted from the lips through the laryngopharynx (inferior portion of the throat) into the trachea (endotracheal intubation). People can also be intubated nasally (through the nose).

upward rotation

movement of the inferior angle of the scapula laterally so that the glenoid cavity is moved upward. This movement is required to move the humerus past the horizontal, as in raising the arms in a "jumping jack."

downward rotation

movement of the inferior angle of the scapula medially so that the glenoid cavity is moved downward. This movement is seen when a gymnast on parallel bars supports the weight of the body on the hands.

abduction (protraction)

movement of the scapula laterally and anteriorly, as in doing a "push-up" or punching.

adduction (retraction)

movement of the scapula medially and posteriorly, as in pulling the oars in a rowboat.