By G. Kirk. Montreat College. 2018.
Form of muscular dystrophy affecting adults of both Distal muscular dystrophy (DD)—A form of mus- sexes order prednisone 10 mg free shipping, and causing weakness in the eye muscles and cular dystrophy that usually begins in middle age or throat cheap 40 mg prednisone with mastercard. Both DMD and BMD are caused by alterations in causes the muscle cell membrane to lose some of its the gene for the protein called dystrophin buy prednisone 10mg low cost. The genes responsible include leading to DMD prevents the formation of any dys- LGMD2D on chromosome 17 generic 20mg prednisone with mastercard, which codes for the trophin prednisone 10mg free shipping, while that of BMD allows some protein to be alpha-sarcoglycan protein; LGMD2E on chromosome 4, made, accounting for the differences in severity and age which codes for the beta-sarcoglycan protein; LGMD2C of onset between the two conditions. Differences among on chromosome 13, which codes for the gamma-sarco- the other muscular dystrophies in terms of the muscles glycan protein; and LGMD2F on chromosome 5, which involved and the ages of onset are less easily explained. Some cases of A number of genes have been found to cause autosomal recessive LGMD are caused by an alteration LGMD. A majority of the more severe autosomal reces- in a gene, LGMD2A, on chromosome 15, which codes sive types of LGMD with childhood-onset are caused by for a muscle enzyme, calpain 3. The relationship between alterations in the genes responsible for making proteins this alteration and the symptoms of the condition is called sarcoglycans. Alterations in a gene called LGMD2B on chro- proteins that are normally located in the muscle cell mosome 2 that codes for the dysferlin protein, is also membrane along with dystrophin. Loss of these proteins responsible for a minority of autosomal recessive LGMD GALE ENCYCLOPEDIA OF GENETIC DISORDERS 771 cases. Their linkage to alterations in the LGMD2G gene on chromosome 17 any other chromosome or genetic feature is under inves- which codes for a protein, telethonin, is responsible for tigation. The • The gene(s) responsible for DD have not yet been exact role of telethonin is not known. The autosomal dominant LGMD genes merosin, which is made by a gene called laminin. These merosin protein usually lies outside muscle cells and types of LGMD are considered quite rare. When merosin is not produced, the muscle fibers degenerate soon after The genes causing these types of LGMD, their chro- birth. A second gene called integrin is responsible for mosomal location, and the proteins they code for (when CMD in a few individuals but alterations in this gene known) are listed below: are a rare cause of CMD. The gene responsible for • LGMD1A (chromosome 5): myotilin Fukuyama CMD is FCMD and it is responsible for • LGMD1B (chromosome 1): laminin making a protein called fukutin whose function is not clear. The distribution of • COL6A2 (chromosome 21): collagen VI alpha 2 symptoms, age of onset, and progression differ signifi- cantly. Pain is sometimes a symptom of each, usually due • COL6A3 (chromosome 2): collagen VI alpha 3 to the effects of weakness on joint position. The causes of the other muscular dystrophies are not DUCHENNE MUSCULAR DYSTROPHY (DMD) A boy as well understood: with Duchenne muscular dystrophy usually begins to • EDMD is due to a alteration in the gene for a protein show symptoms as a pre-schooler. Most patients walk three to six months later than expected and have difficulty running. Later on, a boy with • Myotonic dystrophy is caused by alterations in a gene DMD will push his hands against his knees to rise to a on chromosome 19 for an enzyme called myotonin pro- standing position, to compensate for leg weakness. About tein kinase that may control the flow of charged parti- the same time, his calves will begin to enlarge, though cles within muscle cells. This gene alteration is called a with fibrous tissue rather than with muscle, and feel firm triple repeat, meaning it contains extra triplets of DNA and rubbery; this condition gives DMD one of its alter- code. It is possible that this alteration affects nearby nate names, pseudohypertrophic muscular dystrophy. He genes as well, and that the widespread symptoms of will widen his stance to maintain balance, and walk with myotonic dystrophy are due to a range of genetic dis- a waddling gait to advance his weakened legs. Contractures (permanent muscle tightening) usually • The gene for OPMD appears to also be altered with a begin by age five or six, most severely in the calf muscles. Nearly all cases of this age often leads to scoliosis (a side-to-side spine cur- FSH are associated with a deletion (missing piece) of vature) and kyphosis (a front-to-back curvature). Researchers are investi- gating the molecular connection of this deletion and The most serious weakness of DMD is weakness of FSH. It is not yet certain whether the deleted material the diaphragm, the sheet of muscles at the top of the contains an active gene or changes the regulation or abdomen that perform the main work of breathing and activity of a nearby FSH gene.
Functional Divisions Although all parts of the nervous system work in co- ordination generic 5mg prednisone mastercard, portions may be grouped together on the Functionally order prednisone 20mg with amex, the nervous system is divided according to basis of either structure or function cheap prednisone 5 mg. Any tissue or organ that carries out a command from the nerv- ous system is called an effector buy prednisone 5 mg otc, all of Posterior view which are muscles or glands prednisone 5mg overnight delivery. The somatic nervous system is controlled voluntarily (by conscious Brain Cranial nerves will), and all its effectors are skeletal Central muscles (described in Chapter 8). The nervous system involuntary division of the nervous sys- Spinal tem is called the autonomic nervous cord system (ANS), making reference to its automatic activity. It is also called the visceral nervous system because it Peripheral nervous controls smooth muscle, cardiac mus- system cle, and glands, much of which make up the soft body organs, the viscera. The ANS is further subdivided into a sympathetic nervous system and a parasympathetic nervous system based on organization and how each affects specific organs. Although these divisions are help- ful for study purposes, the lines that di- vide the nervous system according to function are not as distinct as those that classify the system structurally. For example, the diaphragm, a skeletal muscle, typically functions in breath- ing without conscious thought. In ad- dition, we have certain rapid reflex responses involving skeletal muscles— drawing the hand away from a hot stove, for example—that do not in- volve the brain. In contrast, people can be trained to consciously control invol- untary functions, such as blood pres- sure, heart rate, and breathing rate, by Figure 9-1 Anatomic divisions of the nervous system. These tiny gaps, called nodes Table 9•1 Functional Divisions of the Nervous System (originally, nodes of Ranvier), are im- CHARACTERISTICS portant in speeding the conduction of nerve impulses. DIVISION CONTROL EFFECTORS SUBDIVISIONS The outermost membranes of the Schwann cells form a thin coating Somatic nervous Voluntary Skeletal muscle None system known as the neurilemma (nu-rih- Autonomic nervous Involuntary Smooth muscle, Sympathetic LEM-mah). This covering is a part of system cardiac muscle, and parasympa- the mechanism by which some periph- and glands thetic systems eral nerves repair themselves when in- jured. Under some circumstances, damaged nerve cell fibers may regen- Checkpoint 9-1 What are the two divisions of the nervous sys- erate by growing into the sleeve tem based on structure? Cells of the brain and the spinal cord are myelinated, not by Schwann cells, but by Checkpoint 9-2 The nervous system can be divided functionally into two divisions based on type of control and effectors. What di- vision is voluntary and controls skeletal muscle, and what division is involuntary and controls involuntary muscles and glands? Dendrites Structure of a Neuron The main portion of each neuron, the cell body, contains Cell body Nucleus the nucleus and other organelles typically found in cells. A distinguishing feature of the neurons, however, are the long, threadlike fibers that extend out from the cell body and carry impulses across the cell (Fig. Axon branch Dendrites are neuron fibers that conduct impulses to the cell body. Most dendrites have a highly branched, Axon treelike appearance (see Fig. In Chapter 11, we describe how the dendrites of the sensory system may be modified to respond to a specific type of stimulus. These im- pulses may be delivered to another neuron, to a muscle, or to a gland. An axon is a single fiber, which may be quite long and which branches at its end. The Myelin Sheath Some axons are covered with a fatty material called myelin that insulates and protects the fiber (see Fig. In the PNS, this covering is pro- Muscle duced by special connective tissue cells called Schwann Figure 9-2 Diagram of a motor neuron. The break in the (shvahn) cells that wrap around the axon like a jelly roll, axon denotes length. The arrows show the direction of the nerve depositing layers of myelin (Fig. ZOOMING IN Is the neuron shown here a sensory complete, small spaces remain between the individual or a motor neuron? Even in the peripheral nerves, however, re- pair is a slow and uncertain process. The fibers and cell bodies of the gray Neuron matter are not covered with myelin. Checkpoint 9-3 The neuron, the functional unit of the nervous Fibers of system, has long fibers extending from the cell body.
Occasionally the ventricular septal defect is so huge that the ventricles form a single cavity buy cheap prednisone 5 mg on line, giving a trilocular heart prednisone 10mg discount. Congenital pulmonary stenosis may affect the trunk of the pulmonary artery buy 20 mg prednisone with visa, its valve or the infundibulum of the right ventricle generic prednisone 20mg on line. If stenosis occurs in conjunction with a septal defect discount prednisone 10mg otc, the compensatory hypertrophy of the right ventricle (developed to force blood through the pulmonary obstruc- tion) develops a sufﬁciently high pressure to shunt blood through the defect into the left heart; this mixing of the deoxygenated right heart blood with the oxygenated left-sided blood results in the child being cyanosed at birth. This results from unequal division of the truncus arteriosus by the spinal septum, resulting in a stenosed pul- monary trunk and a wide aorta which overrides the oriﬁces of both the ven- tricles. The displaced septum is unable to close the interventricular septum, which results in a ventricular septal defect. Cyanosis results from the shunting of large amounts of unsaturated blood from the right ventricle through the ventricular septal defect into the left ventricle and also directly into the aorta. If left uncorrected, it causes progressive work hypertrophy of the left heart and pulmonary hypertension. There may be an extensive obstruction of the aorta from the left subclavian artery to the ductus, which is widely patent and maintains the circulation to the 42 The Thorax lower parts of the body; often there are multiple other defects and fre- quently infants so afﬂicted die at an early age. More commonly there is a short segment involved in the region of the ligamentum arteriosum or still patent ductus. In these cases, circulation to the lower limb is maintained via collateral arteries around the scapula anastomosing with the intercostal arteries, and via the link-up between the internal thoracic and inferior epi- gastric arteries. Clinically, this circulation may be manifest by enlarged vessels being palpable around the scapular margins; radiologically, dilatation of the engorged intercostal arteries results in notching of the inferior borders of the ribs. Abnormal development of the primitive aortic arches may result in the aortic arch being on the right or actually being double. An abnormal right subclavian artery may arise from the dorsal aorta and pass behind the oesophagus—a rare cause of difﬁculty in swallowing (dysphagia lusoria). Rarely, the division of the truncus into aorta and pulmonary artery is incomplete, leaving an aorta–pulmonary window, the most unusual congeni- tal ﬁstula between the two sides of the heart. The superior mediastinum This is bounded in front by the manubrium sterni and behind the ﬁrst four thoracic vertebrae (Fig. Above, it is in direct continuity with the root of the neck and below it is continuous with the three compartments of the inferior mediastinum. Its principal contents are: the great vessels, trachea, oesophagus, thymus—mainly replaced by fatty tissue in the adult, thoracic duct, vagi, left recurrent laryngeal nerve and the phrenic nerves (Fig. The arch of the aorta is directed anteroposteriorly, its three great branches, the brachiocephalic, left carotid and left subclavian arteries, ascend to the thoracic inlet, the ﬁrst two forming a V around the trachea. The brachio- cephalic veins lie in front of the arteries, the left running almost horizontally across the superior mediastinum and the right vertically downwards; the two unite to form the superior vena cava. Posteriorly lies the trachea with the oesophagus immediately behind it lying against the vertebral column. The oesophagus The oesophagus, which is 10in (25cm) long, extends from the level of the lower border of the cricoid cartilage at the level of the 6th cervical vertebra to the cardiac oriﬁce of the stomach (Fig. Course and relations Cervical In the neck it commences in the median plane and deviates slightly to the left as it approaches the thoracic inlet. The trachea and the thyroid gland are its immediate anterior relations, the 6th and 7th cervical vertebrae and pre- The mediastinum 43 Fig. On the left side it is also related to the subclavian artery and the terminal part of the thoracic duct (Fig. Thoracic The thoracic part traverses ﬁrst the superior and then the posterior medi- astinum. From being somewhat over to the left, it returns to the midline at T5 then passes downwards, forwards and to the left to reach the oesophageal opening in the diaphragm (T10). For convenience, the rela- tions of this part are given in sequence from above downwards. Anteriorly, it is crossed by the trachea, the left bronchus (which 44 The Thorax constricts it), the pericardium (separating it from the left atrium) and the diaphragm. Posteriorly lie the thoracic vertebrae, the thoracic duct, the azygos vein and its tributaries and, near the diaphragm, the descending aorta. On the left side it is related to the left subclavian artery, the terminal part of the aortic arch, the left recurrent laryngeal nerve, the thoracic duct and the left pleura. In the posterior mediastinum it relates to the descending thoracic aorta before this passes posteriorly to the oesophagus above the diaphragm.
We recently simpliﬁed this experiment by limiting movements to only one direction purchase 5 mg prednisone overnight delivery. Because the movement was always in the same direction purchase prednisone 40mg with visa, the pattern of forces on that movement depended exclusively on this cue purchase prednisone 5mg otc. We trained subjects (n = 3) extensively on this task effective 10 mg prednisone, providing them with more than 3000 trials order 40mg prednisone with amex, spread over 3 days. Remarkably, in catch trials we consistently found no evidence of after- effects (Figure 11. However, with longer training44 or with explicit instruction about the nature of the forces,45 it is possible to associate color with force ﬁelds. The remarkable difﬁculty in learning this apparently simple task leads to the prediction that the activity ﬁelds of the bases are typically only weakly modulated by the color of the target. To measure generalization, subjects are trained with an input x1 and are then tested with a new input x2. The ﬁrst problem with this approach is that it requires an experimentally naïve set of participants to be trained in each pairing of x1 and x2. As a result, behavioral experiments are often limited to training and testing with one or two pairs of inputs, and conclusions are in terms of qualitative statements regarding the shape of the bases (wide or narrow). The second problem is that in motor control, we have to consider coordinate systems. Generalization depends not only on the distance between training and test locations, but also on the coordinate system in which that space is measured. For example, a force that is experienced at a given location may be generalized in terms of torques on the joints or forces on the hand. These two coordinates predict different patterns of generalization in terms of the position of the hand. The third problem is that the bases that are inferred from one generalization experiment might not be consistent with those that are inferred in another. In other words, adaptation to one force ﬁeld might result in a pattern of generalization that is inconsistent with the pattern observed in adaptation to another ﬁeld. It would indeed be remarkable if behavioral data from a wide variety of force adaptation experiments suggested a consistent shape to the bases. If this were the case, then one could argue that one has estimated the basic motor primitives with which internal models are computed. Finally, even if we are lucky enough to solve all of these problems, we would still have the problem of interpretation: we would hope that the bases that are inferred by this abstract model not only explain behavior, but also are interpretable in terms of the neurophysiology of the motor system. To approach the ﬁrst two questions — being limited to naïve subjects and needing to consider coordinate systems — we have been developing a new mathematical method to estimate the shape of the bases from the trial-to-trial variations in per- formance. That is, the preferred force vector associated with a basis is likely to change most for those bases that are most active. This means that if error on one movement effects behavior on the next movement in a different direction, then some of the bases must be reasonably active during both of these movements. That is because they must be active in the ﬁrst movement to be inﬂuenced by the error and active in the second movement in order to have an inﬂuence on behavior. Thus, generalization of error from one movement to the next can tell us whether the bases are wide enough to encompass both the movements, or, alternatively, whether they are so narrow that they cannot span the gap. The generalization function depends on how the tuning curves encode movements, and one can acquire critical information regarding gen- eralization from the trial-to-trial variations in behavior. Copyright © 2005 CRC Press LLC The importance of this idea is that it suggests that it is not necessary to train in one set and then test in another in order to estimate generalization. From the movement-to-movement changes in performance, one can estimate how error in one movement affected the subsequent movement as a function of the distance of the two movements in the state space (for example, angular distance in the directions of the two movements). Begin with the assumption that the internal model is composed of a linear combination of an unknown set of bases (Equation 11. These bases encode the state of the arm (velocity only in the current case, because we limit movement to a small spatial workspace). Assume that the purpose of learning is to minimize the difference between the expected force in a movement and the actual force, and that adaptation is through gradient descent that results in modiﬁcation of the preferred force vector associated with each basis. The idea was to represent adaptation with basis functions as a hidden-state dynamical system. Once that system was expressed math- ematically, ﬁtting it to the data would provide an estimate of the generalization function.
8 of 10 - Review by G. Kirk
Votes: 47 votes
Total customer reviews: 47