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Unit Two

Shier-Butler-Lewis: Human Anatomy and Physiology, Ninth Edition

Front Matter

View from the Top

© The McGraw-Hill Companies, 2001

ill. People with MG have

whole-body level, this causes weak and easily fatigued muscles.

MG affect hundreds of thousands of people worldwide, usually women, beginning in their twenties or thirties and men in their sixties and people develop a characteristic flat culty chewing and swallowing due to affected facial and neck muscles. Many ratory musclhe are affected , requ irlng a ventilator to support breathing. MG

threat to health, with a third of patients dying, a third worsening, and only a bcetylchioline. • Removing the thymus gland, immune response.

the damage.

Plasma exchange, which rapidly removes the damaging

This helps people in crisis.

i OO Reconnect to chapter 2, Proteins, page54 Cross-bridge Cycling

The force that shortens the sarcomeres comes from cross-bridges pulling on the thin filaments. A myosin cross-bridge can attach to an actin binding site and bend slightly, pulling on the actin filament. Then the head can release, straighten, combine with another binding site f ther down the actin filament, and pull again (fig. 9.11).


When ni cle fiber synapse can TheTt

Breakdown of ATP puts the myosin cross-bridge in a "cocked" position (fig. 9.12a). When a muscle is stimulated to contract, a cocked cross-bridge attaches to actin (9.12b) and pulls the actin filament toward the center of the sarcomere, shortening the sarcomere and thus shortening the muscle (9.12c). When another ATP binds, the cross-bridge is first released from the actin binding site (9.12d), then breaks down the ATP to return to the cocked position (9.12a). This cross-bridge cycle may repeat over nerve in fiber.

Sec the sarco fiber cea quickly reticulum the cytos this also this step

Strenuous athletic activity may partially or completely tear the calcaneal (Achilles) tendon. This injury occurs

Learn the Ropes and reconnect OO to key concepts found in previous chapters that promote your understanding of new information.

into fascinating Clinical Applications found throughout the chapters. Explore information on related pathology, historical insights, and technological applications of knowledge in anatomy and physiology.


side of the It arises from the of the fibula. Its over the front the surface of the of the of the of the toes by means of a stout tendon that passes behind the lateral malleolus. It everts the foot, assists in plantar flexion, and helps support the arch of the foot (figs. 9.40. and 9.42).

As in the wrist, fascia in various reg ankle thicken to form retinacula. Anteriorly, f extensor retinacula connect the tibia and fibyl? as well as the calcaneus and fascia of the sole. These retinacula form sheaths for tendons crossing the front of the ankle (fig. 9.40).

Posteriorly, on the inside, aflexor retinaculum ru between the medial malleolus and the calcaneus and forms sheaths for tendons passing beneath the foot (fig. 9.41). Peroneal retindcula connect the lateral malleo-lus and the calcaneus, providing sheaths for tendons on the lateral side ofpe ankle (fig. 9.40

Strenuous athletic activity may partially or completely tear the calcaneal (Achilles) tendon. This injury occurs

Cloy sports that involve quick movhments and direo-

The soleus (so'le-us) is a thick, flat muscle located beneath the gastrocnemius, and together these two muscles form the calf of the leg. The soleus arises from the tibia and fibula, and it extends to the heel by way of the calcaneal tendon. It acts with the gastrocnemius to cause plantar flexion of the foot (figs. 9.40 and 9.41). The flexor digitorum longus (

r digitorum longus (flek'sor dij"I-to'rum long'gus) extends from the posterior surface of the tibia to the foot. Its tendon passes along the plantar surface of the foot. There the muscle divides into four parts that at-

-Span Changes energetic and can undertake a great variety of physical activities. At a microscopic level, though, supplies of the molecules that enable muscles to function-myoglobin, ATP, and creatine phosphate-decline. The diameters of some muscle fibers may subtly shrink, as the muscle layers in the walls of veins actually thicken, making the vessels more rigid and less elastic. Very gradually, the muscles become smaller, drier, and capable of less forceful contraction. Connective tissue and adipose cells begin to replace some muscle tissue.

By age 80, effects of aging on the muscular system are much more noticeable. Nearly half the muscle mass present in young adulthood has atrophied, particularly if imme tach to the terminal bones of the four lateral toes. This muscle assists in plantar flexion of the foot, flexion of the four lateral toes, and inversion of the foot (fig. 9.41).


The tibialis posterior (tib"e-a'lis pos-ter'e-or) is the deepest of the muscles on the back of the leg. It connects the fibula and tibia to the ankle bones by means of a tendon that curves under the medial malleolus. This muscle assists in inversion and plantar flexion of the foot (fig. 9.41).

Evertor ent in young adulthood has atrophied, particularly if person is relatively inactive. Aging affects the inter-the muscular and nervous systems. Decline neuron activity leads to muscle atrophy, and diminishing muscular strength slows reflexes.

Exercise can help maintaining a healthy muscular system, even among the oldest of the old. It counters the less effective oxygen delivery that results from the decreased muscle mass that accompanies age. Exercise also maintains the flexibility of blood vessels, which can decrease the likelihood of hypertension developing. However, a physician should be consulted before starting any exercise p Acc cise shoul aerobics— down." ; muscle stra cles. Stre a machine tance. Th important t

There's No Escaping the Fact that aging is a part of life. Because our organs and organ systems are interrelated, aging-related changes in one influence the functioning of others. LifeSpan Changes, found at the ends of several chapters, chart the changes specific to particular organ systems.

c exercise, which the kgsi cnsosptneistciuistfteiscroemfcuowsmecimlgehestnaldgisfatiisnnhgsotuoalrdruebssieingsgi-n after a person is ac-

oxygen utilization b^muscles end p rovide^e ndurance. Perhaps the best "s!de effect" of exercising the muscular system as one grows older is on mood-those who are active report fewer bouts wilh depression.


Expand Your Understanding of medical terminology. Brush up on phonetic pronunciations and definitions of related terms often used in clinical situations.

Chronic disease es that are weak and easily the immune system's attack on junctions so that stimuli are not iilillf^

im?; :om^eeeee■ittitet;aí,i;■f h-t'^oJel°,;ee;eyeeesc c0" tiaac" ml"y !es'o»?|"i3h,Lo,aaofk,loeec;a;oa,pbtt■ny p,,,.

torticOiíiiik(tIt,"CtPkoIl'iaC| tandiUonm which the neck |cacl"a,

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85»/» of pptients, the disease causes on the actin filaments, allowing linkages to myosin cross-bridges and actin (fig. 9.11b).

between and over, as long as ATP is present and nerve cause ACh release at that neuromuscular mnctio

Myosin cross-bridges contain the enzyme ATPase, which catalyzes the breakdown of ATP to ADP and phos-

marizes and relax

Signs of aging in the muscular system begin to appear in one's forties, although a person usually still feels quite tional changes. A torn calcaneal tendon usually re-ruires surgical treatment.

The peroneus (fibularis) longus (p"^-!"^! long'gus) is a long, straplike muscle located on the lateral side of is a long, straplike muscle located on the lateral side ot the leg. It connects the tibia and the fibula to the foot

Shier-Butler-Lewis: Human Anatomy and Physiology, Ninth Edition

Front Matter

View from the Top

© The McGraw-Hill Companies, 2001

Shier-Butler-Lewis: Human Anatomy and Physiology, Ninth Edition

© The McGraw-Hill Companies, 2001

Integumentary System Lymphatic System

Skeletal System Digestive System

Nervous System Respiratory System oxygen for body

Endocrine System Urinary System

Cardiovascular System Reproductive System

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