ike many things in life, individual muscles aren't appreciated until we see what happens whan trey cfo rot work. For children with Hfoebius syndroms, abserce of tre sixth and seventh cranial reives, whch cany impulses from tre brain to the musclas of tre rase, taads to an l re first signs or Utoebius syndrome are typcally difficulty sixk-ing, excessive drooling, and sometimes crossed eyes. The chid has difficulty swallowing ard chokes easily, cannot move the tongue well, and s very sensitive to brght light because he or she cannot squint or blink or even avert the eyas. Specal bottles and feeding tubes can help the from attertior to thi that woud erabe her was l years od, Chelsey had two and cardiac, as described in chapter 5 (pages 160-161). This chapter focuses on the skeletal muscles, which are usually attached to bones and are under conscious control.

Structure of a Skeletal

A skeletal muscle is an organ of the muscular system. It is composed primarily of skeletal muscle tissue, nervous tissue, blood, and connective tissues.

Connective Tissue Coverings n individual skeletal muscle is separated from adjacent muscte^nd held in position by layers of dense connective tissue called fascia (fash'e-ah). This connective tissue surrounds each muscle and may project beyond the end of its muscle fibers to form a cordlike tendon. Fibers in a tendon intertwine with those in the periosteum of a bone, attaching the muscle to the bone. In other cases, the connective tissues associated with a muscle form broad, fibrous sheets called aponeuroses (ap"o-nu-ro'sez), which may attach to the coverings of adjacent muscles (figs. 9.1 and 9.2).

A tendon, or the connective tissue sheath of a tendon (tenosynovium), may become painfully inflamed and swollen following an injury or the repeated stress of ath-' letic activity. These conditions are called tendinitis and monly affected are those associated with the joint capsules of the shoulder, elbow, hip, and knee, and those involved with moving the wrist, hand, thigh, and foot.

The layer of connective tissue that closely surrounds a skeletal muscle is called the epimysium. Another layer of connective tissue, called the perimysium, extends inward from the epimysium and separates the muscle tissue into small sections. These sections contain bundles of skeletal muscle fibers called fascicles (fasciculi). Each muscle fiber within a fascicle (fasciculus) lies d endomysium (figs. 9.2 and 9.3). Layers of

rniiscl. elk

Explain how the locations of skeletal muscles help produce movements and how muscles interact.

Identity and locate the major skeletal muscles ot each body region and describe the action of each muscle.

tetan- stiff: tetan of muscl. lit voluntar-, of one's that can by from mouth, supplying the missing "smile apparatus." Gradually, she ac quired the subte, and not-so-subte, muscular movements of the moutl yourosters to undergo

Chelsey irspired

Reinforce Your Mastery of chapter content by answering the review questions found at the end of major sections of the narrative.

with the sarcolemma and thus contain extracellular fluid. Each transverse tubule lies between two enlarged portions of the sarcoplasmic reticulum called cisternae, and these three structures form a triad near the region where the actin and myosin filaments overlap (fig. 9.7).

Although muscle fibers and the connective tissues associated with them are flexible, they can tear if overstretched. This type of injury is common in athletes and is called a muscte stran. The seriousness of the injury depends on the degree of damage the tissues sustain. In a mild strain, only a few muscle fibers are injured, the fascia remains intact, and little function is lost. In a severe strain, many muscle fibers as well as fascia tear, and muscle function may be lost completely. A severe strain is very painful and is accompanied by discoloration and swelling of tissues due to ruptured blood vessels. Surgery may be required to reconnect the sep-

Actin, myosin, troponin, and tropomyosin are abundant in muscle cells. Scarcer proteins are also vital to muscle function. This is the case for a rod-shaped muscle protein called dystrophin. It accounts for only 0.002% of total muscle protein in skeletal muscle, but its absence causes the devastating inherited disorder Duchenne muscular dystrophy, a disease that usually affects boys. Dystrophin binds to the inside face of muscle cell membranes, supporting them against the powerful force of contraction. Without even these minute amounts of dystrophin, muscle cells burst and die. Other forms of muscular dystrophy result from abnormalities of other proteins to which dystrophin attaches.

skeletal muscle.

Describe the general structure of a skeletal muscle fit Explain why skeletal muscle fibers appear striated. Explain the physical relationship between the

Skeletal Muscle Contraction

A muscle fiber contraction is a complex interaction of several cellular and chemical constituents. The final result is a movement within the myofibrils in which the filaments of actin and myosin slide past one another, shortening the sarcomeres. When this happens, the mus-

The Sliding Filament Theory

The sarcomere is considered the functional unit of skeletal muscles. This is because contraction of an entire skeletal muscle can be described in terms of the shortening of sarcomeres within it. According to the sliding filament theory, when sarcomeres shorten, the thick and thin filaments do not themselves change length. Rather, they just slide past one another, with the thin filaments m ward the center of the sarcomere from both ends. As this occurs, the H zones and thelbaadsgSfnarrower, the regions of overlap wjdan, 'TOothe Z lines move closer to-gether.shoWen'ifigThe sarcomere (fig. 9.8).

^ Neuromuscular Junction

Each skeletal muscle fiber is connected to an extension (a nerve axon) of a motor neuron (mo'tor nu'ron) that passes outward from the brain or spinal cord. Normally a skeletal muscle fiber contracts only upon stimulation by

The site where the axon and muscle fiber meet is called a neuromuscular junction (myoneural junction). There, the muscle fiber membrane is specialized to form a motor end plate, where nuclei and mitochondria are abundant and the sarcolemma is extensively folded (fig. 9.9).

Unit Two

Watch for Signs directing you to exciting animations found in the Online Essential Study Partner.

Processes come alive and help you navigate through complex concepts.

There Are No Boundaries when it comes to illustrations, photographs, and tables. The art is designed and placed to help you visualize structures and processes, to clarify complex ideas, to represent how structures relate to each other, to summarize sections of the narrative, and to present pertinent data.

In September 1 985, two teenage tourists from Hong Kong went to the emergency room at Montreal Children's Hospital complaining of extreme nausea and weakness. Although doctors released them when they could not identify a cause of the symptoms, the girls returned that night — far sicker. Now they were becoming paralyzed and had difficulty breathing. This time, physicians recognized

Botulism occurs when the bacterium Clostridium botu-linum grows in an anaerobic (oxygen-poor) environment, such as in a can of food. The bacteria produce a toxin that prevents the release of acetylcholine from nerve terminals. Symptoms include nausea, vomiting, and diarrhea, headache, dizziness, and blurred or double vision, and finally, weakness, hoarseness, and difficulty swallow-

ing and, eventually, breathing. Fortunately, physicians can administer an antitoxin substance that binds to and inactivates botulinum toxin in the bloodstream, stemming further symptoms, although not correcting damage already

Prompt treatment saved the touring teens, and astute medical detective work led to a restaurant in Vancouver where they and thirty-four others had eaten roast beef sandwiches. The bread had been coated with a garlic-butter spread. The garlic was bottled with soybean oil and should have been refrigerated. It was not. With bacteria that the garlic had picked up in the soil where it grew, and eight months sitting outside of the refrigerator, conditions were just right for C. botuiinum to produce its deadly

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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