By G. Ketil. Oklahoma State University.

Muscular System © The McGraw−Hill Anatomy purchase voltaren 50 mg visa knox gelatin for arthritis in dogs, Sixth Edition Companies buy voltaren 100mg with amex arthritis in my back symptoms, 2001 240 Unit 4 Support and Movement FIGURE 9. Contrast the following terms: endomysium and epimysium; Objective 7 Distinguish between isotonic and isometric fascia and tendon; aponeurosis and retinaculum. Give some examples of synergistic muscles and Objective 8 Define motor unit and discuss the role of motor state which muscles are antagonistic. Skeletal Muscle Fibers Despite their unusual elongated shape, muscle cells have the SKELETAL MUSCLE FIBERS AND same organelles as other cells: mitochondria, intracellular mem- branes, glycogen granules, and so forth. Unlike most other cells TYPES OF MUSCLE CONTRACTION in the body, however, skeletal muscle fibers are multinucleated Muscle fiber contraction in response to a motor impulse results and striated (fig. In addition, some skeletal muscle fibers from a sliding movement within the myofibrils in which the length may reach lengths of 30 cm (12 in. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 9 Muscular System 241 Sarcolemma Sarcoplasm Myofilaments Myofibrils Striations Nucleus (a) Muscle fiber (b) FIGURE 9. A networkof membranous chan- cle myofibrils are due to the arrangement of these myofilaments. At high magnification, thin dark lines can be seen in the of transverse tubules (T tubules) runs perpendicular to the sar- middle of the I bands. The arrangement coplasmic reticulum and opens to the outside through the sar- of thick and thin filaments between a pair of Z lines forms a re- colemma. Also embedded in the muscle fiber are many threadlike peating structural pattern that serves as the basic subunit of structures called myofibrils (fig. These subunits, from Z line to proximately one micrometer (1µm) in diameter and extend in Z line, are known as sarcomeres (fig. A longitudinal section parallel from one end of the muscle fiber to the other. They are of a myofibril thus presents a side view of successive sarcomeres so densely packed that other organelles—such as mitochondria (fig. Each extend from the edge of one stack of thick myosin filaments to myofibril is composed of even smaller protein filaments, or myo- the edge of the next stack of thick filaments. Thin filaments are about 6 nm in diameter and are appearance because they contain only thin filaments. Thick filaments are about 16 nm in filaments, however, do not end at the edges of the I bands. Because thick and thin filaments overlap at the edges of each A band, the edges of the A band are darker in appear- actin: L. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 242 Unit 4 Support and Movement Sarcolemma Myofibrils Triad of the reticulum: Terminal cisternae A band Transverse tubule I band Sarcoplasmic reticulum Z line Mitochondria Nucleus Waldrop FIGURE 9. The central H zones thus contain only thick filaments on a single row of dark thick myofilaments in this transverse sec- that are not overlapped by thin filaments. There are numerous sarcomeres within each When a muscle is stimulated to contract, it decreases in myofibril that are out of the plane of the section (and out of the length as a result of the shortening of its individual fibers. A better appreciation of the three-dimensional struc- Shortening of the muscle fibers, in turn, is produced by shorten- ture of a myofibril can be obtained by viewing the myofibril in ing of their myofibrils, which occurs as a result of the shorten- transverse section. As the seen that the Z lines are actually disc-shaped (Z stands for sarcomeres shorten in length, however, the A bands do not Zwıschenscheibe, a German word meaning “between disc”), and shorten but instead appear closer together. The I bands—which that the thin filaments that penetrate these Z discs surround the represent the distance between A bands of successive thick filaments in a hexagonal arrangement. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 9 Muscular System 243 Sarcoplasm Skeletal muscle fiber Nucleus I band Sarcolemma H zone (c) A band (a) Z line Actin myofilaments Myofibrils Myosin myofilaments (b) H zone Sarcomere H zone A band I band Myofilaments Z line FIGURE 9. The thin actin filaments composing the I band do not of the elbow, for example, occurs against the force of gravity and shorten, however. Close examination reveals that the length of the weight of the objects being lifted. The tension produced by the thick and thin myofilaments remains constant during muscle the contraction of each muscle fiber separately is insufficient to contraction.

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Unlike meniscal tears 100 mg voltaren fast delivery rheumatoid arthritis in back and neck, which are usually multiplanar and three-dimensional (3D) reconstructions vertical in children buy voltaren 100 mg mastercard rheumatoid arthritis lung cancer, intrameniscal nutrient ves- are considered (Fig. In the context of trauma, CT is sels are horizontal, central, originate from the capsu- optimal for detection of subtle fractures (e. In slipped capital femoral epiphysis, CT demonstrates the physeal irregularity, the degree of inferior and posterior displace- ment of the femoral head, and the retroversion of the con- tralateral femur. In acetabular fractures, 3D reconstruc- tions demonstrate the relationships between fragments better. In infants with hip dislocation who have under- gone reduction and placement of the hips in an abduction spica cast, CT can be used to assess the position of the femoral heads. If a low mAs technique is used, the total ovarian dose can be as low as 112 mrad (1. Two-year-old In adolescents and young adults with undetected hip dys- girl with an abscess plasia, CT with 3D reconstructions demonstrates the con- in the soft tissues of figuration and containment of the femoral head, acetabu- the thigh. Sagittal post-gadolinium lar architecture, and narrowing of the joint space. In the T1-weighted image spine, vertebral abnormalities and fusions between verte- shows enhancement brae or ribs are easily demonstrated with CT. Frontal and posterior oblique 3D surface renderings of the spine of a 3-month-old girl with a severe defect of the bony thorax. The study was performed using a multi-detector CT, without need for sedation. Multiple tarsal ing treatment for developmental dysplasia of the hip coalitions may occur in up to 20% of cases and not (DDH) [31, 32]. Although accuracy for Calvé-Perthes disease, and with femoral ischemia of detecting tarsal coalitions is comparable for CT and MR other etiologies, MR imaging will demonstrate marrow imaging, CT allows easier evaluation of both feet, edema and lack of gadolinium enhancement of the and it is less expensive, and more readily available. MR imaging can also images demonstrate a complete osseous fusion if the depict associated physeal and metaphyseal abnormali- coalition is bony, or irregularity of the articular surfaces of ties and the extent of marrow involvement [36, 37]. In more advanced disease, MR imaging shows the con- tainment of the femoral head and the congruity of the MR Imaging articular surfaces. MR imaging is crucial for evaluating spinal os- MR imaging is the modality of choice for assessing spinal teomyelitis, by depicting epidural abscess and extension abnormalities. In infants, MR imaging evaluates abnor- of the infection into the paraspinal soft tissues. It is also malities of vertebral segmentation, and the location of the very useful in pelvic osteomyelitis, where bony geometry conus medullaris (normally at L2 level, more caudal if the is complex and soft tissue involvement is often the most cord is tethered). In older children, MRI is optimal for important component of the infection; and in patients evaluating protrusion or herniation of the discs, spinal who do not respond after 48 hours of antibiotic therapy stenosis, and nerve root compression. MR mors involving the epidural and subarachnoid spaces are imaging is useful in osteomyelitis involving the physis, best demonstrated with gadolinium-enhanced imaging. MR imaging respond to standard therapeutic measures, MR imaging of osteomyelitis should always include gadolinium en- depicts the position of the femoral head before and af- hancement to ascertain whether the infected volume con- ter reduction and detects obstacles to reduction (pulv- tains drainable pus. Septic arthritis and femoral head ischemia in an 11-year-old boy who had osteomyelitis of the ischium. Tibial torsion is determined by the angle between a physeal widening and sometimes transphyseal bridging. External tibial torsion determined by tients in whom impaired sensation and continued motion physical examination is normally 4° at birth, and 14° at result in repeated physeal damage. A 3D fat-suppressed spoiled gradient-recalled Sonography is the main study in infants younger than 6 echo sequence provides most, if not all, of the informa- months with a question of hip dysplasia because it al- tion required to assess growth arrest [52, 53]. It depicts: the injuries have a similar MR imaging appearance in chil- hypoechoic cartilages of the proximal femoral epiphysis dren and adults. In Coventry, T1-weighted images also depict skip lesions and metas- England, screening of more than 14 000 newborns de- tases or multifocal disease in the contralateral extremity tected a 6% incidence of sonographic abnormalities. In children it is particularly important to evaluate these, nearly 80% were normal by 4 weeks and 90% by extension of tumor into the epiphysis, which occurs in 8 weeks. In the United States, however, hip sonog- Cross-sectional Measurements raphy is usually performed when the physical examina- tion is abnormal or when there are risk factors; Glenoid version is the angle between the main axis of the these include a positive family history, breech delivery, scapula and the glenoid. Femoral anteversion is de- oligohydramnios and conditions sometimes caused by termined by obtaining slices from the femoral head to the uterine crowding, such as torticollis, clubfoot, or lesser trochanter, and slices through the distal femoral metatarsus adductus.

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In addition to being a sents pulmonary venous pressure 50 mg voltaren with amex arthritis in dogs aspirin, which order voltaren 50 mg on line arthritis in neck with bone spurs, in turn, reflects potent vasoconstrictor, AII has other important actions in left atrial pressure. Metabolism of vasoactive hor- atrial pressures have a profound effect on gas exchange, and mones by the pulmonary circulation appears to be rather pulmonary wedge pressure provides an indirect measure of selective. Other prostaglandins, such as PGA1 and PGA2, pass through the lungs unaltered. Norepinephrine is inactivated, PULMONARY VASCULAR RESISTANCE but epinephrine, histamine, and arginine vasopressin (AVP) pass through the pulmonary circulation unchanged. With The right ventricle pumps mixed venous blood through the acute lung injury (e. When a vessel is occluded, Pulmonary embolism is clearly one of the more important blood flow stops and perfusion to pulmonary capillaries disorders affecting the pulmonary circulation. The inci- ceases, and the ventilation-perfusion ratio in that lung unit dence of pulmonary embolism exceeds 500,000 per year becomes very high because ventilation is wasted. Pulmonary sult, there is a significant increase in physiological dead embolism is often misdiagnosed and, if improperly diag- space. Besides the direct mechanical effects of vessel oc- nosed, the mortality rate can exceed 30%. These vasoactive mediators also cause endothe- through the right heart and into the pulmonary circulation, lial damage that leads to edema and atelectasis. If the pul- where it lodges in one or more branches of the pulmonary monary embolus is large and occludes a major pulmonary artery. Although most pulmonary emboli originate from vessel, an additional complication occurs in the lung thrombosis in the leg veins, they can originate from the up- parenchyma distal to the site of the occlusion. A thrombus is the major source of lung tissue becomes anoxic because it does not receive pulmonary emboli; however, air bubbles introduced dur- oxygen (either from airways or from the bronchial circula- ing intravenous injections, hemodialysis, or the placement tion). Oxygen deprivation leads to necrosis of lung of central catheters can also cause emboli. The parenchyma will of pulmonary emboli include fat emboli (a result of multi- subsequently contract and form a permanent scar. If the embolism is severe enough, a tors that potentially contribute to the genesis of venous decreased arterial PO2, decreased PCO2, and increased pH thrombosis: (1) hypercoagulability (e. The major screening test for pulmonary embolism tithrombin III, malignancies, the use of oral contraceptives, is the perfusion scan, which involves the injection of ag- the presence of lupus anticoagulant); (2) endothelial dam- gregates of human serum albumin labeled with a radionu- age (e. Several risk factors for proximately 10 to 50 m wide) travel through the right side thrombi include immobilization (e. Only lung areas receiving blood tremity after a fracture), congestive heart failure, obesity, flow will manifest an uptake of the tracer; the nonperfused underlying carcinoma, and chronic venous insufficiency. When a thrombus migrates into the pulmonary circula- The aggregates fragment and are removed from the lungs tion and lodges in pulmonary vessels, several pathophysi- in about a day. These responses are very different from those of the blood flow (5 L/min) as in the systemic circulation, where systemic circulation, where an increase in perfusion pres- the pressure gradient is almost 100 mm Hg. Two local mechanisms in vascular resistance (R) is equal to the pressure gradient ( P) the pulmonary circulation are responsible (Fig. The divided by blood flow () (see Chapter 12): first mechanism is known as capillary recruitment. Under ˙ normal conditions, some capillaries are partially or com- R P/Q (1) pletely closed in the top part of the lungs because of the Pulmonary vascular resistance is extremely low; about low perfusion pressure. As blood flow increases, the pres- one-tenth that of systemic vascular resistance. The differ- sure rises and these collapsed vessels are opened, lowering ence in resistances is a result, in part, of the enormous num- overall resistance. This process of opening capillaries is the ber of small pulmonary resistance vessels that are dilated. The fall in pulmonary vascular resistance with increased With Increased Cardiac Output cardiac output has two beneficial effects. It opposes the Another unique feature of the pulmonary circulation is the tendency of blood velocity to speed up with increased flow ability to decrease resistance when pulmonary arterial pres- rate, maintaining adequate time for pulmonary capillary sure rises, as seen with an increase in cardiac output. It pressure rises, there is a marked decrease in pulmonary vas- also results in an increase in capillary surface area, which 340 PART V RESPIRATORY PHYSIOLOGY FIGURE 20.

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