By P. Runak. Sterling College, Vermont.

Thin pads of The Synovial Joints hyaline cartilage develop on the surfaces of the epiphyses that contact the joint cavity famvir 250 mg visa quinolones antiviral. As the joint continues to develop buy 250mg famvir with mastercard hiv infection rate in uganda, a EXPLANATION highly vascular synovial membrane forms on the inside of the The sites of developing synovial joints (freely movable joints) are joint capsule and begins secreting a watery synovial fluid into the discernible at 6 weeks as mesenchyme becomes concentrated in joint cavity famvir 250 mg lowest price acute hiv infection symptoms rash. At this In certain developing synovial joints, the mesenchymal stage, the future joints appear as intervals of less concentrated cells do not migrate away from the center of the joint cavity. As cartilage cells develop within a forming Rather, they give rise to cartilaginous wedges called menisci, as bone, a thin flattened sheet of cells forms around the cartilagi- in the knee joint, or to complete cartilaginous pads called articu- nous model to become the perichondrium. Most synovial joints have formed completely by the end Surrounding the gap, the flattened mesenchymal cells differenti- of the third month. Shortly thereafter, fetal muscle contrac- ate to become the joint capsule. During the early part of the third month of development, the Joint movement enhances the nutrition of the articular carti- mesenchymal cells still remaining within the joint capsule begin to lage and prevents the fusion of connective tissues within migrate toward the epiphyses of the adjacent developing bones. At 12 weeks, the synovial joints are formed and have either (c) a free joint cavity (e. Articulations © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 8 Articulations 207 Extension MOVEMENTS AT SYNOVIAL JOINTS In extension, which is the reverse of flexion, the joint angle is Movements at synovial joints are produced by the contraction of increased (fig. Extension returns a body part to anatomi- skeletal muscles that span the joints and attach to or near the cal position. In an extended joint, the angle between the articu- bones forming the articulation. An exception is the ankle joint, in which levers, the muscles provide the force, and the joints are the fulcra, there is a 90° angle between the foot and leg in anatomical posi- or pivots. Examples of extension are straightening of the elbow or Objective 10 List and discuss the various kinds of knee joints from flexion positions. Hyperextension occurs when movements that are possible at synovial joints. An example of hyperex- Objective 11 Describe the components of a lever and tension is bending the neck to tilt the head backward, as in look- explain the role of synovial joints in lever systems. Objective 12 Compare the structures of first-, second-, and A common injury in runners is patellofemoral stress syndrome, third-class levers. Dur- ing normal knee movement, the patella glides up and down the As previously mentioned,the range of movement at a sy- patellar groove between the femoral condyles. In patellofemoral novial joint is determined by the structure of the individual joint stress syndrome, the patella rubs laterally, causing irritation to the membranes and articular cartilage within the knee joint. The quently experience this condition from prolonged running on the movement at a hinge joint,for example,occurs in only one plane, slope of a road near the curb. Joint movements are broadly classified as angu- Abduction lar and circular. Each of these categories includes specific types of movements,and certain special movements may involve several Abduction is movement of a body part away from the main axis of the specific types. The description of joint movements are in of the body,or away from the midsagittal plane,in a lateral direc- reference to anatomical position (see fig. This term usually applies to the upper and lower extremities but can also apply to the fingers or toes,in which case the line of reference is the longitudinal axis of the limb. An Angular Movements example of abduction is moving the arms sideward,away from the body. Angular movements increase or decrease the joint angle pro- duced by the articulating bones. The four types of angular move- Adduction ments are flexion, extension, abduction, and adduction. Adduction, the opposite of abduction, is movement of a body part toward the main axis of the body (fig. In anatomical Flexion position, the upper and lower extremities have been adducted to- Flexion is movement that decreases the joint angle on an antero- ward the midplane of the body. Flexion of the elbow joint is a forward movement, whereas flexion of the knee is a backward move- Circular Movements ment. In the ankle joint, flexion occurs as the top surface In joints that permit circular movement, a bone with a rounded (dorsum) of the foot is elevated.

Autonomic Nervous © The McGraw−Hill Anatomy cheap 250 mg famvir zovirax antiviral, Sixth Edition Coordination System Companies buy cheap famvir 250 mg on line hiv infection eye, 2001 Chapter 13 Autonomic Nervous System 449 Hypothalamus Pituitary gland (hypophysis) (a) Waldrop Dorsomedial nucleus Paraventricular nucleus Posterior nucleus Anterior nucleus Ventromedial nucleus Preoptic area Mammillary body Supraoptic nucleus Tuber cinereum Optic chiasma Median eminence Anterior pituitary Posterior pituitary (adenohypophysis) (neurohypophysis) (b) FIGURE 13 cheap 250mg famvir hiv transmission statistics uk. The hypothalamus is also where the body’s thermostat is gyrus of the cerebral cortex, the hypothalamus, the fornix (a fiber located. Experimental cooling of the preoptic-anterior hypothal- tract), the hippocampus, and the amygdaloid nucleus amus causes shivering (a somatic response) and nonshivering (fig. These structures, which were derived early in the thermogenesis (a sympathetic response). Experimental heating of course of vertebrate evolution, were once called the rhinen- this hypothalamic area results in hyperventilation (stimulated by cephalon (ri'nen-sefa˘-lon) or “smell brain,” because of their impor- somatic motor nerves), vasodilation, salivation, and sweat gland tance in the central processing of olfactory information. In primates, these structures are autonomic nervous system The coordination of sympathetic and parasympathetic re- centers involved in such basic emotional drives as anger, fear, flexes by the medulla oblongata is thus integrated with the con- sex, and hunger, and in short-term memory. Complex circuits trol of somatic and endocrine responses by the hypothalamus. This confirms that impulses The limbic system is a group of fiber tracts and nuclei that form from the cerebellum to the medulla oblongata influence activity a ring (limbus) around the brain stem. In addition, the frontal and temporal lobes of the cerebral cortex influence lower brain areas as part of their in- limbic: L. Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 450 Unit 5 Integration and Coordination Corpus callosum Cingulate gyrus Fornix Thalamic nucleus Mammilothalamic Septal area tract Preoptic area Mammillary body Olfactory bulb Olfactory tract Hippocampus Hypothalamus Amygdaloid nucleus Cortex of Cortex of right hemisphere left hemisphere Waldrop FIGURE 13. Gage, was tamping gunpowder into a hole in a rock with a metal rod, when the gunpowder suddenly exploded. The rod—3 feet, 7 inches long and Autonomic Dysreflexia 1 1/4 inches thick—was driven through his left eye and through his brain, finally emerging through the back of his skull. Autonomic dysreflexia, a serious condition producing rapid ele- After a few minutes of convulsions, Gage got up, rode a horse three-quarters of a mile into town, and walked up a long flight of vations in blood pressure that can lead to stroke (cerebrovascular stairs to see a doctor. He recovered well, with no noticeable sensory accident), occurs in 85% of people with quadriplegia and others or motor deficits. His associates, however, noted striking personality with spinal cord lesions above the sixth thoracic level. Before the accident Gage was a responsible, capable, and the spinal cord first produce the symptoms of spinal shock, char- financially prudent man. Afterward, he was much less inhibited so- cially, engaging, for example, in gross profanity (which he had never acterized by the loss of both skeletal muscle and autonomic re- done previously). Eventually, Gage was fired from his job, and his old friends exaggerated state; the skeletal muscles may become spastic be- remarked that he was “no longer Gage. Patients in Knowledge Check this state have difficulty emptying their urinary bladders and 13. Describe the role of the medulla oblongata in the regula- must often be catheterized. Noxious stimuli, such as overdistension of the urinary blad- der, can result in reflex activation of the sympathetic nerves 14. Describe the role of the hypothalamus in the regulation of below the spinal cord lesion. This produces goose bumps, cold the autonomic nervous system and endocrine system. The rise in blood pressure re- What structures are involved in this response? Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Chapter 13 Autonomic Nervous System 451 longata. In response to this sensory input, the medulla oblongata directs a reflex slowing of the heart and vasodilation. Because de- Clinical Case Study Answer scending impulses are blocked by the spinal lesion, however, the The syndrome of organophosphate toxicity consists of symptoms of dan- skin above the lesion is warm and moist (because of vasodilation gerously enhanced parasympathetic activity. Death may result from suf- and sweat gland secretion), whereas it is cold below the level of focation if the victim is unable to clear his airway secretions. You ask about his health in general and learn he has lost 15 pounds in the last year, and he has a long-standing cough that he can’t seem to get rid of. You also no- tice his left eyelid droops, and his left pupil is constricted. He’s surprised when you order a chest X-ray to most likely cause of the indicated lung 3.

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