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Just as the steel beams of a building provide a scaffold to support its weight purchase 60 caps serpina visa, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body buy cheap serpina 60 caps. While some bones only serve as a support for the muscles effective serpina 60caps, others also transmit the forces produced when your muscles contract. For information on the interaction of the skeletal and muscular systems, that is, the musculoskeletal system, seek additional content. For example, your ribs protect your lungs and heart, the bones of your vertebral column (spine) protect your spinal cord, and the bones of your cranium (skull) protect your brain (Figure 6. Some orthopedic problems can be treated with medications, exercises, braces, and other devices, but others may be best treated with surgery (Figure 6. In recent years, orthopedists have even performed prenatal surgery to correct spina bifida, a congenital defect in which the neural canal in the spine of the fetus fails to close completely during embryologic development. Orthopedists commonly treat bone and joint injuries but they also treat other bone conditions including curvature of the spine. Lateral curvatures (scoliosis) can be severe enough to slip under the shoulder blade (scapula) forcing it up as a hump. Spinal curvatures can also be excessive dorsoventrally (kyphosis) causing a hunch back and thoracic compression. These curvatures often appear in preteens as the result of poor posture, abnormal growth, or indeterminate causes. As people age, accumulated spinal column injuries and diseases like osteoporosis can also lead to curvatures of the spine, hence the stooping you sometimes see in the elderly. Some orthopedists sub-specialize in sports medicine, which addresses both simple injuries, such as a sprained ankle, and complex injuries, such as a torn rotator cuff in the shoulder. Mineral Storage, Energy Storage, and Hematopoiesis On a metabolic level, bone tissue performs several critical functions. For one, the bone matrix acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium, and phosphorus. These minerals, incorporated into bone tissue, can be released back into the bloodstream to maintain levels needed to support physiological processes. Calcium ions, for example, are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses. The softer connective tissue that fills the interior of most bone is referred to as bone marrow (Figure 6. Yellow marrow contains adipose tissue; the triglycerides stored in the adipocytes of the tissue can serve as a source of 218 Chapter 6 | Bone Tissue and the Skeletal System energy. Their shapes and their functions are related such that each categorical shape of bone has a distinct function. Long bones are found in the arms (humerus, ulna, radius) and legs (femur, tibia, fibula), as well as in the fingers (metacarpals, phalanges) and toes (metatarsals, phalanges). Short Bones A short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness. The only short bones in the human skeleton are in the carpals of the wrists and the tarsals of the ankles. Examples include the cranial (skull) bones, the scapulae (shoulder blades), the sternum (breastbone), and the ribs. Irregular Bones An irregular bone is one that does not have any easily characterized shape and therefore does not fit any other classification. These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces. Sesamoid Bones A sesamoid bone is a small, round bone that, as the name suggests, is shaped like a sesame seed. These bones form in tendons (the sheaths of tissue that connect bones to muscles) where a great deal of pressure is generated in a joint. Sesamoid bones vary in number and placement from person to person but are typically found in tendons associated with the feet, hands, and knees. Bone Classifications Bone Features Function(s) Examples classification Femur, tibia, fibula, metatarsals, Cylinder-like shape, longer Long Leverage humerus, ulna, radius, than it is wide metacarpals, phalanges Cube-like shape, Provide stability, support, Short approximately equal in while allowing for some Carpals, tarsals length, width, and thickness motion Points of attachment for Sternum, ribs, scapulae, cranial Flat Thin and curved muscles; protectors of bones internal organs Irregular Complex shape Protect internal organs Vertebrae, facial bones Small and round; embedded Protect tendons from Sesamoid Patellae in tendons compressive forces Table 6. Bone is hard and many of its functions depend on This OpenStax book is available for free at http://cnx. Later discussions in this chapter will show that bone is also dynamic in that its shape adjusts to accommodate stresses. Gross Anatomy of Bone The structure of a long bone allows for the best visualization of all of the parts of a bone (Figure 6. The hollow region in the diaphysis is called the medullary cavity, which is filled with yellow marrow. The wider section at each end of the bone is called the epiphysis (plural = epiphyses), which is filled with spongy bone. Each epiphysis meets the diaphysis at the metaphysis, the narrow area that contains the epiphyseal plate (growth plate), a layer of hyaline (transparent) cartilage in a growing bone. When the bone stops growing in early adulthood (approximately 18–21 years), the cartilage is replaced by osseous tissue and the epiphyseal plate becomes an epiphyseal line. The medullary cavity has a delicate membranous lining called the endosteum (end- = “inside”; oste- = “bone”), where bone growth, repair, and remodeling occur. The outer surface of the bone is covered with a fibrous membrane called the periosteum (peri- = “around” or “surrounding”).

If the virus replicates early during the course of infection in the lower respiratory tract discount serpina 60 caps visa, this would result in smaller drop- lets with higher viral load and higher infectivity buy serpina 60 caps visa, because specific immunosurveil- lance is still not established buy 60caps serpina mastercard. Transmission of H5N1 from animal to human may occur in a different way by direct (and indirect) contact to infected poultry. Therefore winter epidemics in Europe and North America may be explained by closer contacts and stay in less ventilated rooms. Influenza virus is well adapted: for unknown reasons its ability to survive is best in lower relative humidity and at lower environmental temperatures (Hemmes 1960). Avian influenza (H5N1) might be less adapted to droplet transmission: the incubation period is longer (Chotpitaya- sunondh 2005), theoretically resulting in less simultaneous onset in many persons during an epidemic. Intestinal replication and symptoms precede respiratory mani- festations by up to one week (Apisarnthanarak 2004), allowing onset of specific immune response before spread by infectious droplets can evolve. As a conse- quence, nasopharyngeal replication in avian influenza is less than in human influ- enza (Peiris 2004) but viral replication is prolonged (Beigel 2005). Until now transmission of H5N1 between humans has been rare (Buxton Bridges 2000, Ung- chusak 2005) and rather inefficient. In conclusion, avian influenza virus (H5N1) presumably requires several passages to enable human-to-human transmission and to finally reach an infectivity rate which is effective enough to generate an epidemic or pandemic. Immunology Influenza causes an acute infection of the host and initiates a cascade of immune reactions activating almost all parts of the immune defense system. Innate immunity is an essential prerequisite for the adaptive immune response, firstly, to limit the initial viral replication and antigen load, and secondly, because the antigen-specific lymphocytes of the adaptive immune response are activated by co-stimulatory molecules that are induced on cells of the innate immune system during their interaction with viruses (Figure 3). The adaptive immune response requires some days to be effective but then helps to contain the viral spread, to eradicate the virus, and finally to establish a memory response resulting in a long-lived resistance to re-infection with homologous virus. Cross-protection within a subtype of influenza has only rarely been observed and infections essentially induce no protection across subtypes or between types A and B (Treanor 2005). Influenza infection induces both systemic and local antibody (humoral immunity), as well as cytotoxic T cell responses (cellular immunity), each of which is important in recovery from acute infection and resistance to reinfection. The humoral branch of the immune system comprises B-lymphocytes (left), which after interac- tion with influenza differentiate into antibody-secreting plasma cells. These cells gain effector cell function to either help directly, release cytokines, or mediate cytotoxicity following recognition of antigen (Adapted from Flint 2004). Not shown is the formation of a cellular memory immune response and the various forms of innate immunity induced by influenza. The antigen specificity arises from random rearrangements of genes coding for the hypervariable region of immuno- globulins in the cells, whilst still in the bone marrow. The naïve B cells then enter the circulation and travel via the blood stream and lymphatics through tissue and lymphoid organs. In the lymph nodes, naïve B cells recognize cognate antigen by their surface antibodies, become activated, switch from IgM to IgG production (class-switch), increase their immunoglobulin specificity and affinity, and differen- tiate into plasma cells or memory B cells as the cell continues to divide in the pres- ence of cytokines. While IgA is transported across the mucosal epithelium of the upper airway, where it serves to neutralize and clear viral infection, IgG is primarily responsible for the protection of the lower respiratory tract (Palladino 1995, Rene- gar 2004). The peak in antibody titers are seen between 4-7 weeks after infection, and are followed by a steady decline. This is because neuraminidase cleaves the cellular-receptor sialic acid residues to which the newly formed particles are attached. Similar effects have been proposed for antibodies against M2 protein of influenza A, although in general, antibodies against internal antigens are non- neutralizing, disappear more rapidly and do not appear to play a role in protective immunity. Either mucosal or systemic antibody alone can be protective if present in sufficient con- centrations, and optimal protection occurs when both serum and nasal antibodies are present (Treanor 2005). Antibodies act in immunity against influenza by neu- tralization of the virus or lysis of infected cells via complement or antibody- dependent cellular toxicity. Hosts that survive an acute virus infection and clear the virus are in general immune to infections by the same virus. Nevertheless, acute infections caused by influenza virus occur repeatedly, despite active immune clearance. This is because influenza displays a structural plasticity as it can tolerate many amino acid substitutions in its structural proteins without losing its infectivity. These changes are the reason for the annual epidemic spread of influenza and require new vaccines to be formulated before each annual epidemic. In contrast, antigenic shift is a major change in the surface protein of a virion, as genes encoding completely new surface proteins arise after recombination or reassortment of genomes or genome segments. In contrast, antigenic shift can only occur under certain circumstances, is relatively rare and the likely reason for pandemics. The cellular immune response Dendritic cells have been shown to play a central role in initiating and driving T lymphocyte responses. They are a sparsely distributed, migratory group of bone- marrow derived leukocytes that are specialized for the uptake, transport, processing and presentation of antigens to T cells (Figure 3). The basic paradigm is that lung- resident dendritic cells acquire antigen from the invading pathogen, become acti- vated, and subsequently travel to the local draining lymph nodes (Legge & Braciale 2003). The newly activated T cells acquire effector cell functions and migrate 104 Pathogenesis and Immunology to the site of infection in the lung where they mediate their antiviral activities (Fig- ure 3). Following recovery from an infection, a state of immunological memory ensues in which the individual is better able to control a subsequent infection with the same pathogen (Ahmed & Gray 1996). Memory is maintained by antigen-specific T cells that persist at increased frequencies, have reduced requirements for co-stimulatory signals in comparison to naïve T cells, and respond quickly to antigenic re- stimulation (Woodland & Scott 2005). Th cells can be further sub- divided into at least Th1 and Th2 cells, based on the type of cytokines they produce.

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Because there is one of each pathway on either side of the spinal cord generic serpina 60caps online, they are not likely to interact order 60caps serpina otc. If none of the other subtests suggest particular deficits with the pathways safe serpina 60caps, the deficit is likely to be in the cortex where conscious perception is based. The mental status exam contains subtests that assess other functions that are primarily localized to the parietal cortex, such as stereognosis and graphesthesia. A final subtest of sensory perception that concentrates on the sense of proprioception is known as the Romberg test. Without visual feedback that the body is in a vertical orientation relative to the surrounding environment, the patient must rely on the proprioceptive stimuli of joint and muscle position, as well as information from the inner ear, to maintain balance. This test can indicate deficits in dorsal column pathway proprioception, as well as problems with proprioceptive projections to the cerebellum through the spinocerebellar tract. Touching a specialized caliper to the surface of the skin will measure the distance between two points that are perceived as distinct stimuli versus a single stimulus. The patient keeps their eyes closed while the examiner switches between using both points of the caliper or just one. Why is the distance between the caliper points closer on the fingertips as opposed to the palm of the hand? Muscle Strength and Voluntary Movement The skeletomotor system is largely based on the simple, two-cell projection from the precentral gyrus of the frontal lobe to the skeletal muscles. These fibers travel through the deep white matter of the cerebrum, then through the midbrain and pons, into the medulla where most of them decussate, and finally through the spinal cord white matter in the lateral (crossed fibers) or anterior (uncrossed fibers) columns. Movement disorders may be the result of changes to the muscle tissue, such as scarring, and these possibilities need to be ruled out before testing function. Along with this inspection, muscle tone is assessed by moving the muscles through a passive range of motion. If muscle tone is present, muscle strength is tested by having the patient contract muscles against resistance. The examiner will ask the patient to lift the arm, for example, while the examiner is pushing down on it. Lateral differences in strength—being able to push against resistance with the right arm but not the left—would indicate a deficit in one corticospinal tract versus the other. An overall loss of strength, without laterality, could indicate a global problem with the motor system. While keeping the eyes closed, if the patient unconsciously allows one or the other arm to slowly relax, toward the pronated position, this could indicate a failure of the motor system to maintain the supinated position. Reflexes Reflexes combine the spinal sensory and motor components with a sensory input that directly generates a motor response. A deep tendon reflex is commonly known as a stretch reflex, and is elicited by a strong tap to a tendon, such as in the knee-jerk reflex. A superficial reflex is elicited through gentle stimulation of the skin and causes contraction of the associated muscles. For the arm, the common reflexes to test are of the biceps, brachioradialis, triceps, and flexors for the digits. For the leg, the knee-jerk reflex of the quadriceps is common, as is the ankle reflex for the gastrocnemius and soleus. The muscle is quickly stretched, resulting in activation of the muscle spindle that sends a signal into the spinal cord through the dorsal root. The fiber synapses directly on the ventral horn motor neuron that activates the muscle, causing contraction. If a muscle is stretched, it reflexively contracts to return the muscle to compensate for the change in length. The most common superficial reflex in the neurological exam is the plantar reflex that tests for the Babinski sign on the basis of the extension or flexion of the toes at the plantar surface of the foot. The plantar reflex is commonly tested in newborn infants to establish the presence of neuromuscular function. To elicit this reflex, an examiner brushes a stimulus, usually the examiner’s fingertip, along the plantar surface of the infant’s foot. An infant would present a positive Babinski sign, meaning the foot dorsiflexes and the toes extend and splay out. As a person learns to walk, the plantar reflex changes to cause curling of the toes and a moderate plantar flexion. If superficial stimulation of the sole of the foot caused extension of the foot, keeping one’s balance would be harder. The descending input of the corticospinal tract modifies the response of the plantar reflex, meaning that a negative Babinski sign is the expected response in testing the reflex. Other superficial reflexes are not commonly tested, though a series of abdominal reflexes can target function in the lower thoracic spinal segments. Testing reflexes of the trunk is not commonly performed in the neurological exam, but if findings suggest a problem with the thoracic segments of the spinal cord, a series of superficial reflexes of the abdomen can localize function to those segments. If contraction is not observed when the skin lateral to the umbilicus (belly button) is stimulated, what level of the spinal cord may be damaged? Comparison of Upper and Lower Motor Neuron Damage Many of the tests of motor function can indicate differences that will address whether damage to the motor system is in the upper or lower motor neurons. The clasp-knife response occurs when the patient initially resists movement, but then releases, and the joint will quickly flex like a pocket knife closing. Forceful trauma to the trunk may cause ribs or vertebrae to fracture, and debris can crush or section through part of the spinal cord. The full section of a spinal cord would result in paraplegia, or loss of voluntary motor control of the lower body, as well as loss of sensations from that point down. The ascending tracts in the spinal cord are segregated between the dorsal column and spinothalamic pathways. This means that the sensory deficits will be based on the particular sensory information each pathway conveys.

Two extrinsic ligaments trusted serpina 60 caps, the tibial collateral ligament on the medial side and the fibular collateral ligament on the lateral side quality serpina 60caps, serve to resist hyperextension or rotation of the extended knee joint buy serpina 60caps online. Two intracapsular ligaments, the anterior cruciate ligament and posterior cruciate ligament, span between the tibia and the inner aspects of the femoral condyles. The anterior cruciate ligament resists hyperextension of the knee, while the posterior cruciate ligament prevents anterior sliding of the femur, thus supporting the knee when it is flexed and weight bearing. The medial and lateral menisci, located between the femoral and tibial condyles, are articular discs that provide padding and improve the fit between the bones. It consists of the articulation between the talus bone and the medial malleolus of the tibia, the distal end of the tibia, and the lateral malleolus of the fibula. Gliding motions at the subtalar and intertarsal joints of the foot allow for inversion/eversion of the foot. The ankle joint is supported on the medial side by the deltoid ligament, which prevents side- to-side motions of the talus at the talocrural joint and resists excessive eversion of the foot. The lateral ankle is supported by the anterior and posterior talofibular ligaments and the calcaneofibular ligament. An inversion ankle sprain, a common injury, will result in injury to one or more of these lateral ankle ligaments. In the skull, the bones develop either directly from mesenchyme through the process of intramembranous ossification, or indirectly through endochondral ossification, which initially forms a hyaline cartilage model of the future bone, which is later converted into bone. In both cases, the mesenchyme between the developing bones differentiates into fibrous connective tissue that will unite the skull bones at suture joints. In the limbs, mesenchyme accumulations within the growing limb bud will become a hyaline cartilage model for each of the limb bones. Mesenchyme cells at the margins of the interzone will give rise to the articular capsule, while cell death at the center forms the space that will become the joint cavity of the future synovial joint. The hyaline cartilage model of each limb bone will eventually be converted into bone via the process of endochondral ossification. However, hyaline cartilage will remain, covering the ends of the adult bone as the articular cartilage. The growing bones of child have an Synovial joints are places where bones articulate with each epiphyseal plate that forms a synchondrosis between the other inside of a joint cavity. Being less dense than bone, joints are the ball-and-socket joint (shoulder joint), hinge the area of epiphyseal cartilage is seen on this radiograph as joint (knee), pivot joint (atlantoaxial joint, between C1 and the dark epiphyseal gaps located near the ends of the long C2 vertebrae of the neck), condyloid joint (radiocarpal joint bones, including the radius, ulna, metacarpal, and phalanx of the wrist), saddle joint (first carpometacarpal joint, bones. Which of the bones in this image do not show an between the trapezium carpal bone and the first metacarpal epiphyseal plate (epiphyseal gap)? Which system of the body to maintain stable contact between the bones in all knee malfunctions in rheumatoid arthritis and what does this positions. What ligament supports the knee when flexed and the anterior motions involve increasing or decreasing the angle of the cruciate ligament becomes tight when the knee comes into foot at the ankle? Which ligament of the knee keeps the tibia from is the initial movement of the mandible during opening and sliding too far forward in relation to the femur and which how much mouth opening does this produce? What is a possible consequence following a fracture of the femoral neck within the capsule of the hip joint? Which motion moves the bottom of the foot away from inversion/eversion of the foot the midline of the body? Describe the characteristic structures found at all Describe and give an example for each functional type of synovial joints. The periodontal ligaments are made of collagen fibers for you to cross your arms together in front of your chest. Describe the two types of cartilaginous joints and give extended, weight-bearing knee receives a very strong blow examples of each. Smooth muscle is concerned with various involuntary movements, such as having one’s hair stand on end when cold or frightened, or moving food through the digestive system. All three muscle tissues have some properties in common; they all exhibit a quality called excitability as their plasma membranes can change their electrical states (from polarized to depolarized) and send an electrical wave called an action potential along the entire length of the membrane. While the nervous system can influence the excitability of cardiac and smooth muscle to some degree, skeletal muscle completely depends on signaling from the nervous system to work properly. On the other hand, both cardiac muscle and smooth muscle can respond to other stimuli, such as hormones and local stimuli. This occurs in striated muscle (skeletal and cardiac) after specific binding sites on the actin have been exposed in ++ response to the interaction between calcium ions (Ca ) and proteins (troponin and tropomyosin) that “shield” the actin- ++ ++ binding sites. Ca also is required for the contraction of smooth muscle, although its role is different: here Ca activates enzymes, which in turn activate myosin heads. A muscle can return to its original length when relaxed due to a quality of muscle tissue called elasticity. Differences among the three muscle types include the microscopic organization of their contractile proteins—actin and myosin. The actin and myosin proteins are arranged very regularly in the cytoplasm of individual muscle cells (referred to as fibers) in both skeletal muscle and cardiac muscle, which creates a pattern, or stripes, called striations. Cardiac muscle fibers each have one to two nuclei and are physically and electrically connected to each other so that the entire heart contracts as one unit (called a syncytium). Because the actin and myosin are not arranged in such regular fashion in smooth muscle, the cytoplasm of a smooth muscle fiber (which has only a single nucleus) has a uniform, nonstriated appearance (resulting in the name smooth muscle). Smooth muscle in the walls of arteries is a critical component that regulates blood pressure necessary to push blood through the circulatory system; and smooth muscle in the skin, visceral organs, and internal passageways is essential for moving all materials through the body. Skeletal muscles act not only to produce movement but also to stop movement, such as resisting gravity to maintain posture.

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