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This is an example of muscular system diseases. This document is useful in studying muscular system diseases.
62 The Body Systems: Clinical and Applied Topics The Muscular System muscular paralysis are usually caused by ner- vous system disorders. These movements will The muscular system includes over 700 skeletal be described further in sections dealing with muscles that are directly or indirectly attached to abnormal nervous system function. the skeleton by tendons or aponeuroses. The mus- cular system produces movement, as the contrac- tions of skeletal muscles pull on the attached SIGNS AND SYMPTOMS bones. Muscular activity does not always result in OF MUSCULAR SYSTEM movement, however; it can also be important in stabilizing skeletal elements and preventing move- DISORDERS ment. Skeletal muscles are also important in Two common symptoms of muscular disorders are guarding entrances or exits of internal passage- pain and weakness in the affected skeletal mus- ways, such as those of the digestive, respiratory, cles. The potential causes of muscle pain include: urinary, or reproductive systems, and in generating heat to maintain our stable body temperatures. 1. Muscle trauma: Examples of traumatic injuries Skeletal muscles contract only under the com- to a skeletal muscle would include a laceration, 7 mand of the nervous system. For this reason, clini- a deep bruise or crushing injury, a muscle tear, cal observation of muscular activity may provide or a damaged tendon. direct information about the muscular system, and 2. Muscle infection: Skeletal muscles may be indirect information about the nervous system. The infected by viruses, as in some forms of myosi- assessment of facial expressions, posture, speech, tis, or colonized by parasitic worms, such as and gait can be an important part of the physical those responsible for trichinosis (p. 64). These examination. Classical signs of muscle disorders infections usually produce pain that is restrict- include the following: ed to the involved muscles. Diffuse muscle pain • Gower’s sign is a distinctive method of stand- may develop in the course of other infectious ing from a sitting or lying position on the floor. diseases, such as influenza or measles. This method is used by children with muscular 3. Related problems with the skeletal system: dystrophy (p. 65). They move from a sitting Muscle pain may result from skeletal problems, position to a standing position by pushing the such as arthritis (p. 59) or a sprained ligament trunk off the floor with the hands and then near the point of muscle origin or insertion. moving the hands to the knees. The hands are 4. Problems with the nervous system: Muscle pain then used as braces to force the body into the may be experienced due to inflammation of standing position. This extra support is neces- sensory neurons or stimulation of pain path- sary because the pelvic muscles are too weak ways in the CNS. to swing the weight of the trunk over the legs. • Ptosis is a drooping of the upper eyelid. It may Muscle strength can be evaluated by applying be seen in myasthenia gravis (p. 66), botulism an opposite force against a specific action. For (p. 65), myotonic dystrophy (p. 65), or following example, the examiner might exert a gentle extend- damage to the cranial nerve (N III) innervating ing force while asking the patient to flex the arm. the levator palpabrae superioris muscle of the Because the muscular and nervous systems are so eyelid. closely interrelated, a single symptom, such as muscle weakness, can have a variety of different • A muscle mass, an abnormal dense region with- causes (Figure A-22). Muscle weakness may also in a muscle, is sometimes seen or felt in a skele- develop as a consequence of a condition that affects tal muscle. A muscle mass may result from torn the entire body, such as anemia or acute starvation. muscle or tendon tissue, a hematoma, or the Figure A-23 (p. 64) provides an overview of deposition of bone around a skeletal muscle, as muscular system disorders. in myositis ossificans. • Abnormal contractions may indicate problems Necrotizing Fasciitis EAP p. 178 with the muscle tissue or its innervation. Muscle spasticity exists when a muscle has excessive Several bacteria produce enzymes such as muscle tone. A muscle spasm is a sudden, hyaluronidase or cysteine protease. Hyaluronidase strong, and painful involuntary contraction. breaks down hyaluronic acid and the proteoglycans • Muscle flaccidity exists when the relaxed skele- (large polysaccharide molecules linked by polypep- tal muscle appears soft and relaxed and its tide chains) that make up the intercellular cement contractions are very weak or absent. between adjacent cells. Cysteine protease breaks down conective tissue proteins. These bacteria are • Muscle atrophy is skeletal muscle deterioration, dangerous because they can spread rapidly by or wasting, due to disuse, immobility, or inter- liquifying the matrix and dissolving the intercellu- ference with the normal muscle innervation. lar cement that holds epithelial cells together. The • Abnormal patterns of muscle movement, such streptococci are one group of bacteria that secrete as tics, choreiform movements, or tremors, and both of these enzymes. Streptococcus A bacteria are The Muscular System 63 Infection Myositis Trichinosis Trauma Inherited disorders Muscular bruise Muscular dystrophies or tear Myotonic dystrophy Primary Muscular System Disorders Probable immune disorders 7 Myasthenia gravis Guillain–Barré syndrome Cardiovascular problems SYMPTOM: MUSCLE WEAKNESS Anemia Heart failure Vascular blockage Metabolic or nutritional problems Electrolyte disturbances (ex.: hypercalcemia, hypocalcemia) Problems with Starvation peripheral nerves Nervous System Trauma Disorders Demyelination disorders Diphtheria Problems with Destruction of Problems at motor pathways motor neurons synaptic knobs in neuromuscular Spinal cord Stroke junctions injuries Polio Multiple Rabies Botulism sclerosis Huntington’s Other neurotoxins Demyelination disease disorders Figure A-22 Potential Causes of Muscle Weakness involved in many human diseases, most notably minor cuts become major open wounds, with interi- “strep throat,” a pharyngeal infection. In most or connective tissues dissolving. There were only 7 cases the immune response is sufficient to contain reported cases, but 5 of the victims died. The and ultimately defeat these bacteria before exten- pathogen responsible was a strain of Streptococcus A sive tissue damage has occurred. that overpowered immune defenses and swiftly However, in 1994 tabloid newspapers had a field invaded and destroyed soft tissues. More over, the day recounting stories of “killer bugs” and “flesh-eat- pathogens eroded their way along the fascial wrap- ing bacteria” that terrorized residents of the city of ping that covers skeletal muscles and other organs. Gloucester, England. The details were horrific— The term for this condition is necrotizing fasciitis. 64 The Body Systems: Clinical and Applied Topics Infection Trauma Myositis Necrotizing fasciitis Hernias Tetanus Compartment syndrome Trichinosis Bruises and tears Fibromyalgia Carpal tunnel syndrome MUSCLE DISORDERS Inherited disorders Tumors Muscular dystrophy Myomas Duchenne’s muscular dystrophy Sarcomas 7 Secondary disorders Nervous system: Immune problems: Botulism Myasthenia gravis Poliomyelitis Cardiovascular system: Metabolic problems: Anemia Hypercalcemia Heart failure Hypocalcemia Figure A-23 Disorders of the Muscular System In some cases the muscle tissue was also destroyed, larvae then migrates through the body tissues to a condition called myositis. reach the muscles, where they complete their early The problem is not restricted to the United development. The migration and subsequent set- Kingdom. Some form of very aggressive infectious tling produce a generalized achiness, muscle and soft tissue invasion occurs roughly 75–150 times joint pain, and swelling in infected tissues. An esti- annually in the U.S. At present it is uncertain mated 1.5 million Americans carry Trichinella whether the recent surge in myositis and necrotizing around in their muscles, and up to 300,000 new faciitis reflects increased awareness of the condition infections occur each year. The mortality rate for or the appearance of a new strain of strep bacteria. people who have symptoms severe enough to require treatment is approximately 1 percent. Trichinosis EAP p. 178 Fibromyalgia and Chronic Trichinosis (trik-i-N«-sis; trichos, hair + nosos, disease) results from infection by a parasitic nema- Fatigue Syndrome EAP p. 178 tode worm, Trichinella spiralis. Symptoms include Fibromyalgia (-algia, pain) is a disorder that has diarrhea, weakness, and muscle pain. The muscu- formally been recognized only since the mid-1980s. lar symptoms are caused by the invasion of skele- Although first described in the early 1800s, the tal muscle tissue by larval worms, which create condition is still somewhat controversial because small pockets within the perimysium and endomy- the reported symptoms cannot be linked to any sium. Muscles of the tongue, eyes, diaphragm, anatomical or physiological abnormalities. chest, and leg are most often affected. However, physicians now recognize a distinctive Larvae are common in the flesh of pigs, horses, pattern of symptoms that warrant consideration as dogs, and other mammals. The larvae are killed a clinical entity. when the meat is cooked; people are most often Fibromyalgia may be the most common muscu- exposed by eating undercooked pork. Once eaten, loskeletal disorder affecting women under 40 years the larvae mature within the intestinal tract, where of age. There may be as many as 6 million cases in they mate and produce eggs. The new generation of the United States today. Symptoms include chronic The Muscular System 65 aches, pain, and stiffness and multiple tender and calcium levels rise to the point that key pro- points at specific, characteristic locations. The four teins denature. The muscle fiber then degenerates. most common tender points are (1) just below the Researchers have recently identified and cloned the kneecap, (2, 3) distal to the medial and lateral epi- gene for dystrophin; that gene is located on the X condyles of the humerus, and (4) the junction chromosome. Rats with DMD have been cured by between the second rib and the cartilage attaching insertion of this gene into their muscle fibers, a it to the sternum. An additional clinical criterion is technique that may eventually be used to treat that the pains and stiffness cannot be explained by human patients. other mechanisms. Individuals with this condition The inheritance of DMD is sex-linked: Women frequently report chronic fatigue; they feel tired on carrying the defective genes are unaffected, but each awakening and often complain of awakening of their male children will have a 50 percent chance repeatedly during the night. of developing DMD. Now that the specific location of Most of these symptoms could be attributed to the gene has been identified, it is possible to deter- other problems. For example, chronic depression can mine whether or not a woman is carrying the defec- lead to fatigue and poor-quality sleep. As a result, the tive gene. It is also possible to use an innovative pattern of tender points is really the diagnostic key to prenatal test to determine if a fetus has this condi- 7 fibromyalgia. This symptom distinguishes fibromyal- tion. In this procedure, a small sample of fluid is col- gia from chronic fatigue syndrome (CFS). The cur- lected from the membranous sac that surrounds the rent symptoms accepted as a definition of CFS fetus. This fluid contains fetal cells, called amnio- include (1) sudden onset, usually following a viral cytes, that are collected and cultivated in the labora- infection, (2) disabling fatigue, (3) muscle weakness tory. Researchers then insert a gene, called MyoD, and pain, (4) sleep disturbance, (5) fever, and (6) that triggers their differentiation into skeletal muscle enlargement of cervical lymph nodes. fibers. These cells can then be tested not only for the Attempts to link either fibromyalgia or CFS to a signs of muscular dystrophy but for indications of viral infection or to some physical or psychological other inherited muscular disorders. trauma have not been successful, and the cause MYOTONIC DYSTROPHY. Myotonic dystrophy is remains unknown. Treatment is limited to relieving a form of muscular dystrophy that occurs in the symptoms when possible. For example, anti-inflam- united states at an incidence of 13.5 per 100,000 matory medications may help relieve pain, drugs population. Symptoms may develop in infancy, but can be used to promote sleep, and exercise pro- more often develop after puberty. As with other grams may help maintain normal range of motion. forms of muscular dystrophy, adults developing myotonic dystrophy experience a gradual reduction The Muscular Dystrophies in muscle strength and control. Problems with other EAP p. 185 systems, especially cardiovascular and digestive sys- The muscular dystrophies (DIS-tr|-fƒz) are inher- tems, often develop. There is no effective treatment. ited diseases that produce progressive muscle The inheritance of myotonic dystrophy is weakness and deterioration. One of the most com- unusual because children of an individual with mon and best understood conditions is myotonic dystrophy commonly develop more severe Duchenne’s muscular dystrophy (DMD). This symptoms than those of the parent. The increased form of muscular dystrophy appears in childhood, severity of the condition appears to be related to often between the ages of 3 and 7. The condition the presence of multiple copies of a specific gene on generally affects only males. A progressive muscu- chromosome 19. For some reason, the nucleotide lar weakness develops, and the individual usually sequence of that gene gets repeated several times, dies before age 20 because of respiratory paralysis. and the number can increase from generation to Skeletal muscles are primarily affected, although generation. This has been called a “genetic stutter.” for some reason the facial muscles continue to The greater the number of copies, the more severe function normally. In later stages of the disease, the symptoms. It is not known why the stutter the facial muscles and cardiac muscle tissue may develops, nor how the genetic duplication affects also become involved. the severity of the condition. The skeletal muscle fibers in a person with DMD patient are structurally different from those Botulism EAP p. 184 of other individuals. Abnormal membrane perme- Botulinus (bot-≈-LI¯-nus) toxin prevents the release ability, cholesterol content, rates of protein synthe- of ACh at the synaptic terminal. It thus produces a sis, and enzyme composition have been reported. severe and potentially fatal paralysis of skeletal DMD sufferers also lack a protein, called dys- muscles. A case of botulinus poisoning is called trophin, found in normal muscle fibers. It is botulism.1 The toxin is produced by a bacterium, attached to the inner surface of the sarcolemma Clostridium botulinum, that does not need oxygen to near the triads. Although the functions of this pro- grow and reproduce. Because the organism can live tein remain uncertain, dystrophin is suspected to play a role in the regulation of calcium ion chan- 1 This disorder was described 200 years ago by German nels in the sarcolemma. In children with DMD, cal- physicians treating patients poisoned by dining on contami- cium channels remain open for an extended period, nated sausages. Botulus is the Latin word for sausage. 66 The Body Systems: Clinical and Applied Topics quite well in a sealed can or jar, most cases of botu- unknown reasons, women are affected twice as lism are linked to improper canning or storing pro- often as men. Estimates of the incidence of this cedures, followed by failure to cook the food disease in the United States range from 2 to 10 adequately before eating. Canned tuna or beets, cases per 100,000 population. smoked fish, and cold soups have most often been One approach to therapy involves the adminis- involved with cases of botulism. Boiling for a half tration of drugs, such as neostigmine, that are hour destroys both the toxin and the bacteria. termed cholinesterase inhibitors. As their name Symptoms usually begin 12–36 hours after eat- implies, these compounds are enzyme inhibitors; ing a contaminated meal. The initial symptoms are they tie up the active sites at which cholinesterase often disturbances in vision, such as seeing double normally binds ACh. With cholinesterase activity or a painful sensitivity to bright lights. These reduced, the concentration of ACh at the synapse symptoms are followed by other sensory and motor can rise enough to stimulate the surviving receptors problems, including blurred speech and an inabili- and produce muscle contraction. ty to stand or walk. Roughly half of botulism patients experience intense nausea and vomiting. Polio EAP p. 184 7 These symptoms persist for a variable period (days Because skeletal muscles depend on their motor to weeks), followed by a gradual recovery; some neurons for stimulation, disorders that affect the patients are still recovering after a year. nervous system can have an indirect affect on the The major risk of botulinus poisoning is respi- muscular system. The poliovirus is a virus that ratory paralysis and death by suffocation. does not produce clinical symptoms in roughly 95 Treatment is supportive: bed rest, observation, percent of infected individuals. The virus produces and, if necessary, use of a mechanical respirator. variable symptoms in the remaining 5 percent. In severe cases drugs that promote the release of Some individuals develop a nonspecific illness ACh, such as guanidine hydrochloride, may be resembling the flu. A second group of individuals administered. The overall mortality rate in the develop a brief meningitis (p. 74), an inflammation United States is about 10 percent. of the protective membranes surrounding the CNS. In the third group of people, the virus attacks Myasthenia Gravis EAP p. 184 somatic motor neurons in the CNS. Myasthenia gravis (mª-as-TH¬-nƒ-uh GRA-vis) is In this third form of the disease, the individual characterized by a general muscular weakness that develops a fever 7–14 days after infection. The fever is often most pronounced in the muscles of the subsides, but recurs roughly a week later, accom- arms, head, and chest. The first symptom is usual- panied by muscle pain, cramping, and paralysis of ly a weakness of the eye muscles and drooping eye- one or more limbs. Respiratory paralysis may also lids. Facial muscles are often weak as well, and the occur, and the mortality rate for this form of polio individual develops a peculiar smile known as the is 2–5 percent for children and 15–30 percent of “myasthenic snarl.” As the disease progresses, adults. If the individual survives, some degree of pharyngeal weakness leads to problems with chew- recovery usually occurs over a period of up to 6 ing and swallowing, and it becomes difficult to hold months. the head upright. For unknown reasons, the survivors of paralyt- The muscles of the upper chest and upper ic polio may develop progressive muscular weak- extremities are next to be affected. All the volun- ness 20–30 years after the initial infection. This tary muscles of the body may ultimately be postpolio syndrome is characterized by fatigue, involved. Severe myasthenia gravis produces respi- muscle pain, and weakness, and, in some cases, ratory paralysis, with a mortality rate of 5–10 per- muscular atrophy. There is no treatment for this cent. However, the disease does not always condition, although rest seems to help. progress to such a life-threatening stage. For Polio has been almost completely eliminated example, roughly 20 percent of patients experience from the U.S. population due to a successful eye problems with no other symptoms. immunization program. In 1954 there were 18,000 The condition results from a decrease in the new cases in the United States; there were 8 in number of ACh receptors on the motor end plate. 1976, and none since 1994. The World Health Before the remaining receptors can be stimulated Organization now reports that polio has been erad- enough to trigger a strong contraction, the ACh icated from the entire Western Hemisphere. molecules are destroyed by cholinesterase. As a Unfortunately, many parents refuse to immunize result, muscular weakness develops. their children against the poliovirus, because they The primary cause of myasthenia gravis assume that the disease has been “conquered.” appears to be a malfunction of the immune system. Failure to immunize is a mistake because (1) there Roughly 70 percent of the individuals with myas- is still no cure for polio, (2) the virus remains in the thenia gravis have an abnormal thymus, an organ environment in many areas of the world, and (3) up involved with the maintenance of normal immune to 38 percent of children ages 1–4 have not been function. In myasthenia gravis, the immune immunized. A major epidemic could therefore response attacks the ACh receptors of the motor develop very quickly if the virus were brought into end plate as if they were foreign proteins. For the United States from another part of the world. The Muscular System 67 abdominal organs slide into the thoracic cavity, Hernias EAP p. 204 most often through the esophageal hiatus, the When the abdominal muscles contract forcefully, opening used by the esophagus. The severity of the pressure in the abdominopelvic cavity can increase condition will depend on the location and size of dramatically, and those pressures are applied to the herniated organ(s). Hiatal hernias are actually internal organs. If the individual exhales at the same very common, and most go unnoticed. Radiologists time, the pressure is relieved, because the see them in about 30 percent of individuals whose diaphragm can move upward as the lungs collapse. upper gastrointestinal tracts are examined with But during vigorous isometric exercises or when lift- barium contrast techniques. When clinical compli- ing a weight while holding one’s breath, pressure in cations develop, they usually occur because the abdominopelvic cavity can rise to 106 kg/cm2 abdominal organs that have pushed into the tho- (1500 lb/in.2), roughly 100 times normal pressures. racic cavity are exerting pressure on structures or Pressures this high can cause a variety of problems, organs there. As is the case with inguinal hernias, among them the development of a hernia. a diaphragmatic hernia may result from congenital A hernia develops when a visceral organ pro- factors or from an injury that weakens or tears the trudes abnormally through an opening in a muscu- diaphragmatic muscle. lar wall or partition. There are many types of 7 hernias; we will consider only inguinal (groin) her- Sports Injuries EAP p. 208 nias and diaphragmatic hernias here. Late in the development of the male, the testes Sports injuries affect amateurs and professionals descend into the scrotum by passing through the alike. A 5-year study of college football players abdominal wall at the inguinal canals. In the adult indicated that 73.5 percent experienced mild male, the spermatic ducts and associated blood injuries, 21.5 percent moderate injuries, and 11.6 vessels penetrate the abdominal musculature at percent severe injuries during their playing the inguinal canals on their way to the abdominal careers. Contact sports are not the only activities reproductive organs. In an inguinal hernia, the that show a significant injury rate; a study of 1650 inguinal canal enlarges, and the abdominal con- joggers running at least 27 miles per week reported tents such as a portion of the intestine (or more 1819 injuries in a single year. rarely the bladder) are forced into the inguinal Muscles and bones respond to increased use canal (Figure A-24). If the herniated structures by enlarging and strengthening. Poorly conditioned become trapped or twisted within the inguinal sac, individuals are therefore more likely to subject surgery may be required to prevent serious compli- their bones and muscles to intolerable stresses cations. Inguinal hernias are not always caused by than are people in good condition. Training is also unusually high abdominal pressures. Injuries to important in minimizing the use of antagonistic the abdomen, or inherited weakness or distensibili- muscle groups and keeping joint movements within ty of the canal, may have the same effect. the intended ranges of motion. Planned warm-up The esophagus and major blood vessels pass exercises before athletic events stimulate circula- through an opening in the diaphragm, the muscle tion, improve muscular performance and control, that separates the thoracic and abdominopelvic and help prevent injuries to muscles, joints, and cavities. In a diaphragmatic hernia, also called a ligaments. Stretching exercises stimulate muscle hiatal hernia (hª-£-tal; hiatus, a gap or opening), circulation and help keep ligaments and joint cap- sules supple. Such conditioning extends the range of motion and prevents sprains and strains when sudden loads are applied. Dietary planning can also be important in pre- venting injuries to muscles during endurance events, such as marathon running. Emphasis has often been placed on the importance of carbohy- Inguinal drates, leading to the practice of “carbohydrate External canal abdominal loading” before a marathon. But while operating oblique Inguinal within aerobic limits, muscles also utilize amino hernia acids extensively, so an adequate diet must include External both carbohydrates and proteins. inguinal Improved playing conditions, equipment, and ring Herniated intestine regulations also play a role in reducing the inci- Spermatic dence of sports injuries. Jogging shoes, ankle or cord knee braces, helmets, and body padding are exam- ples of equipment that can be effective. The sub- stantial penalties now earned for personal fouls in contact sports have reduced the numbers of neck and knee injuries. Several injuries common to those engaged in Figure A-24 An Inguinal Hernia active sports may also affect nonathletes, although 68 The Body Systems: Clinical and Applied Topics the primary causes may differ. A partial listing of activity-related conditions includes the following: Carpal Tunnel Syndrome EAP p. 211 Tenosynovitis is the inflammation of a tendon • Bone bruise: Bleeding within the periosteum of sheath. Carpal tunnel syndrome results from a bone tenosynovitis of the tendon sheath surrounding the • Bursitis: Inflammation of the bursae around flexor tendons of the palm. The inflammation leads one or more joints to compression of the median nerve, a mixed (sen- • Muscle cramps: Prolonged, involuntary, and sory and motor) nerve that innervates the palm. painful muscular contractions Symptoms include pain, especially on palmar flex- ion, a tingling sensation or numbness on the palm, • Sprains: Tears or breaks in ligaments or tendons and weakness in the abductor pollicis. This condi- • Strains: Tears in muscles tion is fairly common and often strikes those • Stress fractures: Cracks or breaks in bones engaged in repetitive hand movements, such as subjected to repeated stresses or trauma typing, working at a computer keyboard, or playing the piano. Treatment involves administration of • Tendinitis: Inflammation of the connective tis- anti-inflammatory drugs such as aspirin, injection sue surrounding a tendon of anti-inflammatory agents, such as glucocorti- Many of these conditions have been discussed in coids (steroid hormones produced by the adrenal previous chapters. cortex), and use of splints to prevent wrist flexion Finally, many sports injuries would be prevent- and stabilize the region. ed if people who engage in regular exercise used Carpal tunnel syndrome is an example of a common sense and recognized their personal limi- cumulative trauma disorder, or overuse syndrome. tations. It can be argued that some athletic events, These disorders are caused by repetitive move- such as the ultramarathon, place such excessive ments of the arms, hands, and fingers. These mus- stresses on the cardiovascular, muscular, respira- culoskeletal problems now account for over 50 tory, and urinary systems that they cannot be rec- percent of all work-related injuries in the United ommended, even for athletes in peak condition. States. CRITICAL-THINKING QUESTIONS c. increase the force and strength of muscle contractions 3-1. A patient experiencing a severe hyper- kalemia could have the following related problems: CeCe answers this question correctly but becomes immediately concerned about this effect on a select a. a below-normal potassium ion concentration group of skeletal muscles. What is CeCe concerned of the interstitial fluid about? b. a more-negative membrane potential of 3-3. Tom broke his right leg in a football game. nerves and muscles After six weeks in a cast, the cast is finally c. unresponsive skeletal muscles and cardiac removed, and when he takes his first few steps, he arrest loses his balance and falls. What is the most likely d. muscle weakness and increased strength of explanation? twitch contractions a. the bone fracture is not completely healed e. all of the above b. the right leg muscles have atrophied due to 3-2. Making hospital rounds, Dr. R., an anes- disuse thesiologist, meets with a first-semester anatomy c. Tom has an undiagnosed neuromuscular and physiology student named CeCe who is sched- disorder uled for surgery the next day. Having just finished 3-4. Samples of muscle tissue are taken from a the unit on skeletal muscles and the nervous sys- champion tennis player and a nonathlete of the tem, CeCe is eager to learn about the anesthesia same age and gender. Both samples are subjected that will be used during the surgery. Dr. R. to enzyme analysis. How would you expect the two explains he will be using a drug, succinyl choline, samples to differ? that competes with acetylcholine and blocks the action of this neurotransmitter at the neuromuscu- 3-5. Calvin steps into a pothole and twists his lar junction. What effect will this have on CeCe’s ankle. He is in a great deal of pain and cannot stand. skeletal muscles? In the hospital, the examining physician notes that Calvin can plantar flex and dorsiflex the foot, but he a. produce paralysis of all the skeletal muscles cannot perform inversion without extreme pain. b. cause tetany of the skeletal muscles Which muscle has probably been injured? The Muscular System 69 NOTES
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