By R. Stan. State University of New York College of Environmental Science and Forestry.
The control of neuronal excitability is discussed in more detail in Chapter 2 discount 100mg silagra visa. It has been known for many years that stimulation of muscle or cutaneous afferents to one segment of the spinal cord produces a prolonged inhibition of motoneuron activity without any accompanying change in conductance of the motoneuron membrane buy generic silagra 50 mg online, i purchase 100mg silagra with mastercard. Such inhibition is probably generic 100mg silagra fast delivery, therefore, of presynaptic origin and is, in fact, associated with a depolarisation of the afferent nerve terminals and a reduction in release of the excitatory NT. If it is assumed that the amount of NT released from a nerve terminal depends on the amplitude of the potential change induced in it, then if that terminal is already partly depolarised when the impulse arrives there will be a smaller change in potential and it will release less transmitter (Fig. There is no direct evidence for this concept from studies of NT release but electrophysiological experiments at the crustacean neuromuscular junction, which has separate excitatory and inhibitory inputs, show that stimulation of the inhibitory nerve, which released GABA, reduced the EPSP evoked postsynaptically by an excitatory input without directly hyperpolarising (inhibiting) the muscle fibre. Certainly when GABA is applied to various in vivo and in vitro preparations (spinal cord, cuneate nucleus, olfactory cortex) it will produce a depolarisation of afferent nerve terminals that spreads sufficiently to be recorded in their distal axons. Such presynaptic inhibition can last much longer (50±100 ms) than the postsynaptic form (5 ms) and can be a very effective means of cutting off one particular excitatory input without directly reducing the overall response of the neuron. How GABA can produce both presynaptic depolarisation and conventional postsynaptic hyperpolar- isation by the same receptor, since both effects are blocked by the same antagonist, bicuculline, is uncertain (see Chapter 2) although an increased chloride flux appears to be involved in both cases. If nerve terminals are depolarised, rather than hyper- polarised by increased chloride flux, then their resting membrane potential must be different from (greater than) that of the cell body so that when chloride enters and the potential moves towards its equilibrium potential there is a depolarisation instead of a hyperpolarisation. This form of presynaptic inhibition must be distinguished from another means of attenuating NT release, i. This was first shown at peripheral noradrenergic synapses where the amount of noradrenaline released from nerve terminals is reduced by applied exogenous noradrenaline and increased by appropriate (alpha) adrenoceptor antagonists. Thus through presynaptic (alpha) adrenoreceptors, which can be distinguished from classical postsynaptic (alpha) adrenoreceptors by relatively specific agonists and antagonists, neuronal-released noradrenaline is able to inhibit its own further (excessive) release. It is a mechanism for controlling the synaptic concentration of noradrenaline. This inhibition does not necessarily involve any change in membrane potential but the receptors are believed to be linked to and inhibit adenylate cyclase. Whether autoinhibition occurs with all NTs is uncertain but there is strong evidence for it at GABA, dopamine and 5-HT terminals. There is also the interesting possibility that presynaptic inhibition of this form, with or without potential changes, need not be restricted to the effect of the NT on the terminal from which it is released. Numerous studies in which brain slices have been loaded with a labelled NT and its release evoked by high K or direct stimulation show NEUROTRANSMITTER SYSTEMS AND FUNCTION: OVERVIEW 17 Figure 1. A noradrenergic terminal has been shown to possess receptors for a wide range of substances, so-called heteroceptors (see Langer 1981, 1997) and although this may be useful for developing drugs to manipulate noradrenergic transmission it seems unlikely that in vivo all of the receptors could be innervated by appropriate specific synapses or reachable by their NT. They may be pharmacologically responsive but not always physiologically active (see Chapter 4). CONTROL OF SYNAPTIC NT CONCENTRATION Having briefly discussed the presynaptic control of NT release it is necessary to consider how the concentration of a NT is controlled at a synapse so that it remains localised to its site of release (assuming that to be necessary) without its effect becoming too excessive or persistent. Although one neuron can receive hundreds of inputs releasing a number of different NTs, the correct and precise functioning of the nervous system presumably requires that a NT should only be able to act on appropriate receptors at the site of its release. This control is, of course, facilitated to some extent by having different NTs with specific receptors so that even if a NT did wander it could only work where it finds its receptors and was still present in sufficient concentration to meet their affinity requirements. Normally the majority of receptors are also restricted to the immediate synapse. Nevertheless, from release (collection) studies we know that enough NT must diffuse (overflow) to the collecting system, be that a fine probe in vivo or the medium of a perfusion chamber in vitro, to be detected. Thus one must assume that either the concentration gradient from the collecting site back to the active synaptic release site is so steep that the NT can only reach an effective concentration at the latter, or it is not unphysiological for a NT to have an effect distal from its site of release. Released NT, if free to do so, would diffuse away from its site of release at the synapse down its concentration gradient. The structure of the synapse and the narrow gap between pre- and postsynaptic elements reduces this possibility but this means that there must be other mechanisms for removing or destroying the NT so that it, and its effects, do not persist unduly at the synapse but are only obtained by regulated impulse controlled release.
The cranium of an adult buy silagra 50 mg otc, however discount silagra 50mg overnight delivery, has limited resilience and tends to splinter silagra 100 mg low cost. A hard blow to the head fre- quently breaks the bone on the opposite side of the skull in what is Thoracic Region called a contrecoup fracture buy 50mg silagra with mastercard. The sphenoid bone, with its numerous foramina, is the weakest bone of the cranium. It frequently sustains a Developmental Conditions contrecoup fracture as a result of a hard blow to the top of the head. The most frequently fractured bones of the face are the When serious deformities of the chest do occur, they are almost nasal bones and the mandible. Trauma to these bones generally always due to an overgrowth of the ribs. In pigeon breast (pectus results in a simple fracture, which is not usually serious. If the carinatum), the sternum is pushed forward and downward like the nasal septum or cribriform plate of the ethmoid bone is fractured, keel of a boat. In funnel chest (pectus excavatum), the sternum is however, careful treatment is required. If the cribriform plate is pushed posteriorly, causing an anterior concavity in the thorax. The absence of ribs is due to incomplete development of the Whiplash is a common injury to the neck due to a sudden thoracic vertebrae, a condition termed hemivertebrae, and may and forceful displacement of the head (see fig. A whiplash is usually extremely painful rib is attached to the transverse process of the seventh cervical and difficult to treat because of the difficulty in diagnosing the vertebra, and it either has a free anterior portion or is attached to extent of the injury. Pressure of a cervical rib on the brachial The sensory organs within the head are also very prone to plexus may produce a burning, prickling sensation (paresthesia) trauma. The eyes may be injured by sudden bright light, and loud along the ulnar border of the forearm and atrophy of the medial noise can rupture the tympanic membrane of the middle ear. Diseases of the Head and Neck The rapid and complex development of the heart and The head and neck are extremely susceptible to infection, espe- major thoracic vessels accounts for the numerous congenital cially along the mucous membranes lining body openings. Cardiac malformations usually arise from developmen- The cutaneous area of the head most susceptible to infec- tal defects in the heart valves, septa (atrial and/or ventricular), tions extends from the upper lip to the midportion of the scalp. The infection may even spread into the sagittal ve- blood in the left atrium. A ventricular septal defect usually oc- nous sinus, causing venous sinus thrombosis. A boil in the facial curs in the upper portion of the interventricular septum and is region may secondarily cause thrombosis of the facial vein or the generally more serious than an atrial septal defect because of spread of the infection to the sinuses of the skull. Before antibi- the greater fluid pressures in the ventricles and the greater otics, such sinus infections had a mortality rate of 90%. Surface and Regional © The McGraw−Hill Anatomy, Sixth Edition Anatomy Companies, 2001 Chapter 10 Surface and Regional Anatomy 335 Congenital valvular problems are classified as either an in- cian as reference locations for palpation (feeling with firm pres- competence (leakage) or a stenosis (constriction) of valves. Im- sure, percussion tapping with the fingertips), and auscultation (lis- proper closure of a valve permits some backflow of blood, causing tening with a stethoscope). As mentioned earlier, many of the an abnormal sound referred to as a murmur. Murmurs are com- ribs are evident on a thin person, and all but the first, and at mon and generally have no adverse affect on a person’s health. The sternum, clavicles, and The tetralogy of Fallot is a combination of four defects scapulae also provide important bony landmarks in conducting a within the heart of a newborn: (1) a ventricular septal defect, physical examination. The nipples in the male and prepubescent (2) an overriding aorta,(3) pulmonary stenosis,and (4) right female are located at the fourth intercostal spaces. It immediately causes a cyanotic con- of the left nipple in males provides a guide for where to listen for dition (blue baby). The breasts and mam- casionally results in both a left and a right aortic arch. In this mary glands are highly susceptible to infections, cysts, and tu- case, there are generally anomalies of other vessels as well. The superficial position of the breasts allows for effective treatment by way of surgery and radiotherapy if tumors are de- Trauma to the Thorax tected early. The importance of breast self-examination (BSE) (see chapter 21) cannot be overemphasized.
Her excellent cooperation generic 50 mg silagra visa, patience buy silagra 50mg with amex, and good-natured repar- their many helpful suggestions and comments silagra 100mg on-line. My colleagues in the tee with the author were key elements in completing the ﬁnal draft in Department of Neurosurgery at UMMC (Drs discount 50 mg silagra free shipping. Mandybur) and in This sixth edition would not have been possible without the inter- the Department of Neurology at UMMC (especially Drs. Corbett est and support of the publisher, Lippincott Williams & Wilkins. Betty Sun (Acquisitions Editor), to fered valuable input on a range of clinical issues. Lancon (Neurosurgery) for his signiﬁcant contri- (Editorial Assistant), Ms. Joe Scott (Marketing Manager) for their encourage- as co-author of Chapter 9 and his careful review of all new clinical in- ment, continuing interest, and conﬁdence in this project. Amanda eration has given me the opportunity to make the improvements seen Ellis, B. I am indebted to the following individuals for their careful review Last, but certainly not least, I would like to express a special thanks of previous editions of the book: Drs. Dietrichs, in progress, carefully reviewed all changes in the text and all ques- J. The goal is not Abooks are becoming available to students and instruc- only to show external and internal structure per se but also tors, it is appropriate to brieﬂy outline the approach used in to demonstrate that the relationship between brain anatomy this volume. Most books are the result of 1) the philosophic and MRI/CT, the blood supply to speciﬁc areas of the CNS approach of the author/instructor to the subject matter and and the arrangement of pathways located therein, the neu- 2) students’ needs as expressed through their suggestions roactive substances associated with pathways, and examples and opinions. The present atlas is no exception, and as a re- of clinical deﬁcits are inseparable components of the learn- sult, several factors have guided its further development. An effort has been made to provide a for- These include an appreciation of what enhances learning in mat that is dynamic and ﬂexible—one that makes the learn- the laboratory and classroom, the inherent value of corre- ing experience an interesting and rewarding exercise. The goal is to make considering that approximately 50% of what goes wrong in- it obvious to the user that structure and function in the CNS side the skull, producing neurological deﬁcits, is vascular- are integrated elements and not separate entities. To emphasize the value of this information, the dis- Most neuroanatomic atlases approach the study of the tribution pattern of blood vessels is correlated with external CNS from fundamentally similar viewpoints. These atlases spinal cord and brain anatomy (Chapter 2) and with inter- present brain anatomy followed by illustrations of stained nal structures such as tracts and nuclei (Chapter 5), re- sections, in one or more planes. Although variations on this viewed in each pathway drawing (Chapter 7), and shown in theme exist, the basic approach is similar. This approach atlases do not make a concerted effort to correlate vascular has several advantages: 1) the vascular pattern is immediately patterns with external or internal brain structures. Also, related to the structures just learned, 2) vascular patterns most atlases include little or no information on neurotrans- are shown in the sections of the atlas in which they belong, mitters and do not integrate clinical examples and informa- 3) the reader cannot proceed from one part of the atlas to tion with the study of functional systems. Following a brief period The ability to diagnose a neurologically compromised pa- devoted to the study of CNS morphology, a signiﬁcant por- tient is speciﬁcally related to a thorough understanding of tion of many courses is spent learning functional systems. This pathway structure, function, blood supply, and the rela- learning experience may take place in the laboratory because tionships of this pathway to adjacent structures. To this end it is here that the student deals with images of representative Chapter 7 provides a series of semidiagrammatic illustrations levels of the entire neuraxis. Each ﬁgure shows 1) been made to provide the student with a comprehensive and in- the trajectory of ﬁbers that comprise the entire pathway; 2) tegrated guide—one that correlates, 1) external brain anatomy the laterality of ﬁbers comprising the pathway, this being an with MRI and blood supply; 2) meninges and ventricles with extremely important concept in diagnosis; 3) the positions examples of meningeal, ventricular, and brain hemorrhage; and somatotopy of ﬁbers comprising each pathway at repre- 3) internal brain anatomy with MRI, blood supply, the orga- sentative levels; 4) a review of the blood supply to the en- nization of tracts and nuclei and selected clinical examples; 4) tire pathway; 5) important neurotransmitters associated summaries of clinically relevant pathways with neurotrans- with ﬁbers of the pathway; and 6) examples of deﬁcits seen mitters, numerous clinical correlations, and the essential con- following lesions of the pathway at various levels through- cept of laterality; and 5) includes a large variety of images such out the neuraxis. This chapter is designed to be used by itself as angiogram, computed tomography (CT), magnetic reso- or integrated with other sections of the atlas; it is designed to nance imaging (MRI), magnetic resonance angiography provide the reader with the structural and clinical essentials (MRA), and magnetic resonance venography (MRV). Introduction and Reader’s Guide 3 The advent and common use of imaging methods (MRI, The Brain and Related Structures in CT MRA, and MRV) mandates that such images become an inte- STRUCTURE/FLUID/SPACE GREY SCALE gral part of the educational process when teaching and/or Bone, acute blood Very white learning clinically applicable neuroscience. To this end, this Enhanced tumor Very white book contains about 175 MRI and CT images and 12 MRA and Subacute blood Light grey MRV. All of these images are directly correlated with external Muscle Light grey brain anatomy such as gyri and sulci, internal structures in- Grey matter Light grey cluding pathways and nuclei, cranial nerves and adjacent struc- White matter Medium grey tures, or they demonstrate examples of hemorrhages related Cerebrospinal ﬂuid Medium grey to black to the meninges and ventricles or the parenchyma of the brain.
It is joints of the foot and hand and in bursae purchase silagra 100 mg line, particularly the usually limited to the IP joints of the hand buy silagra 50mg on line. Clinically olecranon bursa 50mg silagra sale, where they may be associated with un- the joints are acutely inflamed; marginal erosions are derlying erosion of the olecranon purchase silagra 100mg online. Characteristically, the prominent and are superimposed on the standard radi- bones maintain a normal density without evidence of os- ographic features of osteoarthritis. Erosions are often teoporosis and the joint space is often well maintained more pronounced at the PIP joints. Calcium Pyrophosphate Dihydrate Crystal Deposition Disease Diabetic Osteoarthropathy Chondrocalcinosis is the presence of intra-articular cal- Diabetic osteoarthropathy is confined almost exclusive- cium-containing salts within hyaline cartilage and fi- ly to the ankle and foot. Calcium within the fibrocartilage is char- teries of the foot is a frequent and important clue to the acteristically somewhat irregular, as seen in the menis- presence of underlying diabetes but may not always be ci of the knee or the triangular fibrocartilage of the evident. The articular surface is composed of hyaline car- or metatarsals are particularly common manifestations tilage and, when calcified, appears as a fine, linear ra- of diabetic neuropathic joints. Often such fractures or diodensity closely paralleling the bony margins of the dislocations are incidental findings on radiographs ob- joint. Less PD) crystals in the joint cartilage and periarticular tissues Peripheral Arthritis 147 occurs in elderly persons and usually is manifested in the Suggested Readings sixth and seventh decades by the radiographic demon- 1. Aliabadi P, Nikpoor N, Alparslan L (2003) Imaging of neuro- stration of calcifications in the fibrocartilage and hyaline pathic arthropathy. Semin Musculoskelet Radiol 7(3):217-225 cartilage of the knees and wrists. Bennett DL (2004) Spondyloarthropathies: ankylosing are asymptomatic, but in others intermittent acute attacks spondylitis and psoriatic arthritis. Radiol Clin North Am of arthritic pain is associated with a joint effusion. The 42(1):121-134 correct diagnosis is established by the identification of 3. Bohndorf K, Imhof H, Pope TL (2001) Musculoskeletal Imaging: A concise multimodality approach. Radiol Clin North Am 42(1):151-168 The joints most commonly involved are the knee, the 5. Semin radiocarpal joints of the wrist, the MCP joints of the Musculoskelet Radiol 7(2):155-159 hand, the shoulder, and the hip. Radiol Clin North Am 42(1):11-41 cur in this disorder, termed pyrophosphate arthropathy, 7. Klecker RJ, Weissman BN (2003) Imaging features of psoriat- resemble osteoarthritis, with joint-space narrowing, bone ic arthritis and Reiter’s syndrome. Semin Musculoskelet sclerorsis, osteophytes, and subchondral cyst formation. Radiol 7(2):115-126 The unusual distribution of these findings and the pres- 8. Radiol ence of chondrocalcinosis allow a specific diagnosis to Clin North Am 42(1):169-184 be made. Steinbach LS (2004) Calcium pyrophosphate dihydrate and calcium hydroxyapatite crystal deposition diseases: imaging second and third MCP joints, is characteristic of this dis- perspectives. Radiol Clin North Am 42(1):89-107 IDKD 2005 Special Aspects of Musculoskeletal Imaging in Children* D. Sebag2 1 Division of Pediatric Radiology, Massachusetts General Hospital; Department of Radiology, Harvard Medical School, Boston, MA, USA 2 Department of Pediatric Radiology, Hôpital Robert Debré; Faculté de Médecine Lariboisière-Saint-Louis, Université Paris, France The Changing Skeleton of the Child juries before ten years of age. A femoral fracture heals in one week in In children, the skeleton undergoes multiple changes with the newborn, four weeks in the 5-year-old, eight weeks in age. These age-related transformations determine the pat- the 10-year-old, three months in the adolescent, and more terns of injury or disease and their imaging findings. The unossified epiphysis can sepa- Normal Age-Related Variants and Related rate from the smooth metaphysis and, on radiographs, an Diseases apparent dislocation of the hip and shoulder can actually be a separation. The physis or growth plate, initially a flat Radiographs disk between epiphysis and metaphysis, becomes progres- sively undulated after puberty and ultimately closes. The Normal variants are often bilateral, but reassuring symmetry pattern of physeal injuries is thus more complex in older is not always present.
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