INTEGRATED BASIC SCIENCES PreTest® Self-Assessment and Review pot

INTEGRATED BASIC SCIENCES PreTest® Self-Assessment and Review NOTICE Medicine is an ever-changing science As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy are required The editor and the publisher of this work have checked with sources believed to be reliable in their efforts to provide information that is complete and generally in accord with the standards accepted at the time of publication However, in view of the possibility of human error or changes in medical sciences, neither the editor nor the publisher nor any other party who has been involved in the preparation or publication of this work warrants that the information contained herein is in every respect accurate or complete, and they are not responsible for any errors or omissions or for the results obtained from use of such information Readers are encouraged to confirm the information contained herein with other sources For example and in particular, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this book is accurate and that changes have not been made in the reccommended dose or in the contraindications for administration This recommendation is particular importance in connection with new or infrequently used drugs INTEGRATED BASIC SCIENCES PreTest® Self-Assessment and Review EDITOR Earl J Brown, MD Associate Professor Department of Pathology East Tennessee State University Johnson City, Tennessee McGRAW-HILL Health Professions Division New York St Louis San Francisco Auckland Bogotá Caracas Lisbon London Madrid Mexico City Milan Montreal New Delhi San Juan Singapore Sydney Tokyo Toronto Copyright © 1999 by The McGraw-Hill Companies, Inc All rights reserved Manufactured in the United States of America Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher 0-07-143558-1 The material in this eBook also appears in the print version of this title: 0-07-052551-X All trademarks are trademarks of their respective owners Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in an editorial fashion only, and to the benefit of the trademark owner, with no intention of infringement of the trademark Where such designations appear in this book, they have been printed with initial caps McGraw-Hill eBooks are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs For more information, please contact George Hoare, Special Sales, at george_hoare@mcgraw-hill.com or (212) 904-4069 TERMS OF USE This is a copyrighted work and The McGraw-Hill Companies, Inc (“McGraw-Hill”) and its licensors reserve all rights in and to the work Use of this work is subject to these terms Except as permitted under the Copyright Act of 1976 and the right to store and retrieve one copy of the work, you may not decompile, disassemble, reverse engineer, reproduce, modify, create derivative works based upon, transmit, distribute, disseminate, sell, publish or sublicense the work or any part of it without McGraw-Hill’s prior consent You may use the work for your own noncommercial and personal use; any other use of the work is strictly prohibited Your right to use the work may be terminated if you fail to comply with these terms THE WORK IS PROVIDED “AS IS” McGRAW-HILL AND ITS LICENSORS MAKE NO GUARANTEES OR WARRANTIES AS TO THE ACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK, INCLUDING ANY INFORMATION THAT CAN BE ACCESSED THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANY WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE McGraw-Hill and its licensors not warrant or guarantee that the functions contained in the work will meet your requirements or that its operation will be uninterrupted or error free Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for any inaccuracy, error or omission, regardless of cause, in the work or for any damages resulting therefrom McGraw-Hill has no responsibility for the content of any information accessed through the work Under no circumstances shall McGraw-Hill and/or its licensors be liable for any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any of them has been advised of the possibility of such damages This limitation of liability shall apply to any claim or cause whatsoever whether such claim or cause arises in contract, tort or otherwise DOI: 10.1036/0071435581 For more information about this title, click here CONTENTS Introduction Acknowledgments CHAPTER CHAPTER CHAPTER CHAPTER CHAPTER HEMATOLOGY Questions Answers, Explanations, and References CARDIOVASCULAR Questions Answers, Explanations, and References vii ix 1 29 73 74 102 RESPIRATORY Questions Answers, Explanations, and References 151 HEAD AND NECK Questions Answers, Explanations, and References 219 GASTROINTESTINAL Questions Answers, Explanations, and References 279 152 177 220 242 280 305 v Copyright © 1999 by The McGraw-Hill Companies, Inc Click here for Terms of Use vi CHAPTER CHAPTER CHAPTER CONTENTS GU/BREAST Questions Answers, Explanations, and References 353 ENDOCRINE Questions Answers, Explanations, and References 437 MUSCULOSKELETAL AND NEUROPATHOLOGY Questions Answers, Explanations, and References Bibliography 354 385 438 461 497 498 528 577 INTRODUCTION One of the current trends in medical education is to integrate material between the basic science courses of the first two years of medical school and to integrate material between the basic science courses and the clinical departments Medical students often feel submerged by the flood of information during medical school and attempts to integrate this material are often met with much frustration The basic premise for this book is to help in the integration of material between the basic science courses of medical school The questions in this book are grouped in sets of three questions around a clinical scenario The organization of each of these three question sets is as follows: the first question in each group covers anatomy illustrated by the clinical scenario [either gross anatomy, microscopic anatomy (histology), or developmental anatomy (embryology)]; the second question in each group covers the normal functioning that is illustrated by the clinical scenario (either biochemistry, physiology, or immunology), and the third question of each set covers the abnormal functions involving the clinical case (namely pathology, pharmacology, or microbiology) The questions in each PreTest® Self-Assessment and Review book parallel the format and degree of difficulty of the questions found in the United States Medical Licensing Examinations (USMLE) Each question is accompanied by an answer, a paragraph explanation, and a specific page reference to an appropriate textbook or journal article A bibliography listing sources can be found following the last chapter of this text An effective way to use this PreTest® is to read a clinical scenario and answer the set of three questions that are associated with that clinical case You should allow yourself about one minute to answer each question in the set As you proceed, indicate your answer beside each question By following this suggestion, you approximate the time limits imposed by the Step After you finish going through the questions in each set, spend as much time as you need verifying your answers and carefully reading the explanations provided Pay special attention to the explanations for the questions you answered incorrectly — but read every explanation The authors of this material have designed the explanations to reinforce and supplement the information tested by the questions If you feel you need vii Copyright © 1999 by The McGraw-Hill Companies, Inc Click here for Terms of Use viii INTRODUCTION further information about the material covered, consult and study the references indicated This book is directed primarily toward medical students, especially second year medical students as they prepare for the USMLE Step Since the book will integrate material from many of the basic science medical courses, it will also benefit first and second year medical students as they study for individual courses during the first two years of medical school It will especially be beneficial if they use it to integrate these courses Additionally, since the questions will all be based on patient histories, this book will also be beneficial to students during their third and fourth years to review basic science course material and integrate this into their clinical experience It will also be beneficial for these students as they study for the USMLE Step Earl Brown, MD ACKNOWLEDGMENTS I would like to express my appreciation and gratitude to my colleagues in the Department of Pathology for their support and help over the past decade that I have been director of the sophomore pathology course at the Quillen College of Medicine I would like to especially thank Dr Philip S Coogan, the chairman of our department, who has supported my efforts over the years and has enabled me to progress as a teacher I would especially like to express my deep felt thanks to all the many students who over the years have inspired me with their spirit, their common sense, and their enthusiasm They have showed me time and time again different and better ways to explain concepts and integrate basic science material They have taught me much Finally, I would like to thank my family, my wife Janet and my two children Kevin and Heather, who have supported me through many late-night and weekend typing sessions ix Copyright © 1999 by The McGraw-Hill Companies, Inc Click here for Terms of Use 564 INTEGRATED BASIC SCIENCES The monoaminergic pathways, which use monoamines as the neurotransmitter, include the catecholaminergic and the indolaminergic pathways The catecholaminergic pathways use a monoamine that contains a catechol nucleus (dopamine, norepinephrine, and epinephrine) as a neurotransmitter, whereas the indolaminergic pathways use a monoamine that contains an indole nucleus (serotonin) The major dopaminergic pathways are the nigrostriatal (substantia nigra to the striatum), the mesolimbic (ventral tegmentum to limbic system), and the tuberohypophyseal (arcuate nucleus of hypothalamus to anterior pituitary) The mesolimbic pathway may be involved with behavior and schizophrenia, whereas release of dopamine from the arcuate nucleus inhibits the release of prolactin from the anterior pituitary Norepinephrine pathways involve the locus ceruleus and the lateral tegmental area, whereas serotonin (5-hydroxytryptamine) is found in the raphe nuclei of the brain stem and the pineal gland 51 The answer is E (Mycek, 2/e, pp 83 – 88 Chandrasoma, 3/e, p 935.) Degenerative diseases of the central nervous system (CNS) affect the gray matter and are characterized by progressive loss of neurons in specific areas of the brain Idiopathic Parkinson’s disease is associated with degeneration and loss of pigmented cells in the substantia nigra and the locus ceruleus Lewy bodies — eosinophilic intracytoplasmic inclusions — are found in the remaining neurons of the substantia nigra These degenerations result in decreased synthesis of dopamine, which is an important neurotransmitter of the extrapyramidal system The decreased synthesis of dopamine by neurons originating in the substantia nigra leads to decreased amounts and functioning of dopamine in the striatum This in turn causes a decrease in dopamine inhibition and a relative increase in acetylcholine in the striatum The function of acetylcholine, however, in the striatum is to stimulate GABA (␥-aminobutyric acid) neurons, which are inhibitory The final effect, therefore, of a decreased amount of dopamine is increased GABA inhibition of movement, which leads to bradykinesia (slow movement) Individuals with Parkinson’s disease develop a masklike facial expression, coarse tremors, slowness of voluntary movements, and muscular rigidity, They walk stooped forward with short, shuffling steps Similar degenerative changes and clinical symptoms as seen with idiopathic Parkinson disease can be seen with other disorders that affect the extrapyramidal system Von Economo’s encephalitis was a transient infectious disorder occurring from 1915 to 1918 (concurrent with in- CHAPTER MUSCULOSKELETAL 565 fluenza pandemic) that was associated with a postencephalitic parkinsonism Shy-Drager syndrome is characterized by Parkinson-like signs and autonomic dysfunction, such as postural (orthostatic) hypotension, and urinary incontinence Other causes of Parkinson-like signs include trauma (especially in boxers), certain drugs and toxins [MPTP (1-methyl-4phenyl-1,2,3,6-tetrahydropyridine), a meperidine analogue found in illicit drugs], and copper (Wilson’s disease) Huntington’s disease, an autosomal dominant disorder associated with a defective gene on chromosome 4, also involves abnormalities of the extrapyramidal system In contrast to idiopathic Parkinson’s disease, however, Huntington’s disease is associated with atrophy of the caudate nuclei and putamen Patients also develop variable atrophy of the cerebral cortex, particularly the frontal lobes Individuals with Huntington’s disease develop chorea (sudden jerky and purposeless movements) and progressive dementia after the age of 30 In the striatum of these individuals, degeneration of GABA neurons leads to decreased inhibition of muscles, which leads to hyperkinesis (increased movement) Huntington’s disease is one of four diseases that are characterized by long repeating sequences of three nucleotides Therapy for excessive movement (hyperkinetic) disorders can be attempted with dopamine antagonists, which inhibit the functioning of dopamine Decreased dopamine in the striatum theoretically will cause a relative increase in acetylcholine and therefore an increase in excitation in the striatum This will cause increased functioning of GABA and lead to increased inhibition of movement, which is similar to the pathomechanism associated with idiopathic Parkinson’s disease The same end result could theoretically be achieved with inhibition of acetylcholine breakdown (cholinesterase inhibitors such as physostigmine) In contrast, therapy for decreased movement (that is, hypokinetic disorders such as idiopathic Parkinson’s) is to stimulate the functioning of dopamine in the degenerating substantia nigra neurons This can be accomplished by using dopamine agonists, such as bromocriptine, or levodopa, which is metabolized to DOPA, the immediate precursor substance in the synthesis of dopamine Two other drugs used to treat Parkinson’s disease include amantadine, which is an antiviral drug that increases the release of 566 INTEGRATED BASIC SCIENCES dopamine from surviving neurons, and deprenyl, which is a selective inhibitor of monoamine oxidase B, which metabolizes dopamine These drugs increase the normal inhibition in the striatum produced by dopamine, which leads to decreased functioning of GABA in the striatum This leads to decreased inhibition of movement (increased movement) The same result could theoretically be achieved with anticholinergics, such as benztropine Answers to Case Study XVIII 52 The answer is C (Gartner, 2/e, pp 129 – 130 Fix, 2/e, pp 82 – 84.) The glial cells of the central nervous system (CNS) include astrocytes, oligodendrocytes, microglial cells, and ependymal cells Astrocytes, which are the largest of the glial cells and star shaped, provide structural support for the CNS Astrocytes have many processes, some of which form part of the blood – brain barrier that surrounds the capillaries of the brain The astrocytic end feet form the external glial-limiting membrane between the pia mater and the CNS and the internal glial-limiting membrane between the ependyma and the CNS Astrocytes also proliferate (gliosis) in response to acute tissue injury, which forms the “scar tissue” of the brain There is no collagen, however, produced with gliosis Proliferating astrocytes have vesicular nuclei, prominent nucleoli, and a large amount of bright pink cytoplasm (gemistocytic astrocytes) In contrast, protoplasmic astrocytes and fibrillary (fibrous) astrocytes are two types of resting (normal) astrocytes Protoplasmic astrocytes, which are found mostly in the gray matter, have flat, branching processes, while fibrillary astrocytes, which are found in white matter, have long, thin processes The processes of both types of resting astrocytes contain glial fibrillar acidic protein (GFAP) Oligodendroglial cells (oligodendrocytes) are found in both the white matter and the gray matter Oligodendrocytes produce myelin for the axons of the CNS (analogous to the way Schwann cells produce myelin for the axons of the peripheral nervous system) The microglial cells are small, phagocytic glial cells that originate from monocytes Reactive microglial (gitter) cells may have foamy cytoplasm The ependymal cells line the ventricles of the brain and the central canal of the spinal cord They also form the choroidal cells of the choroidal CHAPTER MUSCULOSKELETAL 567 plexus, which are the cells that produce cerebrospinal fluid (CSF) Ependymal cells often contain cilia, which originate from blepharoplasts (basal bodies) and help to circulate the CSF 53 The answer is D (Guyton, 9/e, pp 765 – 767 Ganong, 17/e, pp 182 – 183.) Seizures result from abnormal synchronous discharge of cortical neurons and are classified into two general types: partial (focal) and generalized Partial seizures, which arise from an abnormality affecting only one cerebral hemisphere, are generally caused by focal brain damage, such as a brain tumor in adults Partial seizures are called simple partial seizures if there is no alteration of consciousness during the seizure In contrast, complex partial seizures are associated with alterations of consciousness General seizures, which involve both hemispheres simultaneously, are classified into several clinical types, including tonic – clonic seizures, absence seizures, myoclonic seizures, and atonic seizures Tonic – clonic (grand mal) seizures are characterized by loss of consciousness that is followed by sustained contraction of limb muscles (tonic phase) and then symmetric jerking and relaxing of the limbs (clonic phase) The electroencephalogram (EEG) shows high-voltage, synchronous discharge from both sides of the cortex Absence (petit mal) seizures are characterized by momentary loss of consciousness (blank stare) without loss of posture Absence seizures occur in childhood and display characteristic EEG changes consisting of runs of spikes and waves (spike-and-dome pattern) that occur at a rate of three per second Myotonic epilepsy is characterized by sudden, brief, repetitive contractions of muscles, whereas atonic seizures (drop seizures) are characterized by the sudden loss of muscle tone 54 The answer is E (Cotran, 5/e, pp 1342 – 1349 Chandrasoma, 3/e, pp 938 – 944.) Neoplasms of the central nervous system (CNS) can originate from glial cells (astrocytes, oligodendroglia, and ependymal cells), neural crest cells (Schwann cells or arachnoid cells), or embryonic remnants Astrocytomas, which are CNS neoplasms that originate from astrocytes, are the most common primary brain tumor in adults, and they occur predominantly in the cerebral hemispheres Histologically, astrocytomas vary 568 INTEGRATED BASIC SCIENCES from low grade to very high grade (glioblastoma multiforme) Grade I astrocytomas are the least aggressive and histologically are difficult to differentiate from reactive astrocytosis Grade II astrocytomas show some pleomorphism microscopically, while grade III astrocytomas (anaplastic astrocytomas) are characterized histologically by increased pleomorphism and prominent mitoses Glioblastoma multiforme (grade IV astrocytoma) is a highly malignant tumor that is characterized histologically by endothelial proliferation and serpentine areas of necrosis surrounded by peripheral palisading of tumor cells It frequently crosses the midline (butterfly tumor) Oligodendrogliomas, which most commonly involve the cerebral hemispheres in adults, are slow-growing tumors that have a high recurrence rate Histologically, they consist of sheets of cells that are surrounded by clear halos (“fried-egg” appearance) and have various amounts of calcification, which can be seen on x-ray Meningiomas, which are tumors that arise outside of the brain parenchyma attached to the dura, typically occur in adults and are more common in women These benign neoplasms originate from the meningothelial cells of the arachnoid They are slowgrowing tumors, but, because they may have progesterone receptors, they may exhibit rapid growth during pregnancy Histologically, these tumors have multiple patterns, such as a whorled pattern that is associated with psammoma body formation Ependymomas, which are slow-growing tumors that are found most commonly in childhood and adolescence, are found most frequently in the fourth ventricle, whereas choroid plexus papilloma, a variant of an ependymoma, is found most commonly in the lateral ventricle of young boys Ependymomas can obstruct the flow of the CSF (producing hydrocephalus) or disseminate via the CSF Grossly, these tumors may be solid or papillary masses, while histologically they are characterized by ependymal rosettes (around central spaces), pseudorosettes (around blood vessels), and blepharoplasts (basal bodies of cilia, which are rod-shaped structures found near the nucleus) Medulloblastomas, which are tumors that originate exclusively in the cerebellum, most commonly occur in children These tumors are highly malignant, but are very radiosensitive Histologically, the tumor cells are small, have scant cytoplasm, and may form rosettes and perivascular pseudorosettes CHAPTER MUSCULOSKELETAL 569 Answers to Case Study XIX 55 The answer is B (Fix, 2/e, pp 205 – 208 Isselbacher, 13/e, p 2349.) The facial nerve (cranial nerve VII) has at least four separate and unique functions The facial nerve innervates all of the muscles of facial expression, as well as the stapedius, stylohyoid, posterior belly of the digastric, and the platysma The facial nerve also supplies parasympathetic fibers to the submandibular and sublingual salivary glands, to the lacrimal glands, and to the mucous glands of the nasal cavity The facial nerve receives taste sensation from the anterior two-thirds of the tongue, and touch sensation from the auricle of the ear and the external tympanic membrane The motor portion of the facial nerve originates in the motor nucleus of the seventh nerve, which lies anterior and lateral to the abducens nucleus in the pons After leaving the midbrain, the facial nerve enters the internal auditory meatus with the acoustic nerve, travels through the facial canal, exits the brain through the stylomastoid foramen, passes through the parotid gland, and terminates in six branches: temporal, zygomatic, buccal, mandibular, cervical, and posterior auricular 56 The answer is C (Costanzo, 1/e, p 34 Guyton, 9/e, pp 686 – 687 Ganong, 17/e, p 185.) The motor system is composed of upper motor neurons (UMNs) and lower motor neurons (LMNs) UMNs consist of neurons that originate in the precentral gyrus of the frontal lobe and send processes through the pyramidal tracts, which decussate at the medulla and descend via the lateral corticospinal tracts to synapse with LMNs in the anterior horn of the spinal cord UMN lesions are characterized by spastic paralysis, increased deep tendon reflexes in the absence of muscle atrophy, and extensor (up) plantar reflexes (the Babinski response) Spastic paralysis refers to paralysis with increased muscle tone due to the unopposed activity of the extrapyramidal system on LMNs LMNs are large alpha motor neurons that are located in the ventral horns of the spinal cord and the brain-stem motor nuclei (facial nucleus, trigeminal motor nucleus, nucleus ambiguus, and hypoglossal nucleus) Two types of motor neurons are found in the anterior horn of the spinal cord: alpha motor neurons and gamma motor neurons The alpha motor neurons 570 INTEGRATED BASIC SCIENCES give rise to large type A alpha (A␣) nerve fibers that innervate the large skeletal muscle fibers, whereas gamma motor neurons give rise to type A gamma (A␥) fibers that innervate small, specialized skeletal muscle fibers called intrafusal fibers, which are part of the muscle spindle Lesions of the alpha motor neurons (LMN lesions) are characterized by muscle weakness, flaccid paralysis, muscle atrophy, absent deep tendon reflexes, and flexor (down) plantar reflexes 57 The answer is A (Fix, 2/e, pp 207 – 208 Chung, 3/e, pp 274 – 275 Isselbacher, 13/e, pp 2349 – 2350.) The physical finding of facial asymmetry is suggestive of an abnormality involving the facial nerve The facial nucleus, which is located within the pons, is divided in half as the upper neurons innervate the upper muscles of the face while the lower neurons innervate the lower portion of the face Each half receives input from the contralateral motor cortex, while only the upper half receives input from the ipsilateral motor cortex As a result, an upper motor neuron (UMN) lesion of the motor cortex will produce a defect involving only the contralateral lower half of the face UMN lesions involving the facial nerve may result from strokes that involve the cortex or the internal capsule In contrast, lesions that affect the facial nerve from its origin in the facial nucleus throughout its remaining length will produce symptoms of a lower motor neuron (LMN) lesion referred to as Bell’s palsy (facial paralysis) Patients present with facial asymmetry due to weakness and paralysis that involves the ipsilateral upper and lower quadrants of the face Patients may develop Bell’s phenomenon — which refers to the clinical finding that if the patient tries to close their eyes, then the affected eye will look up and out — and mild pain behind the ear Patients may also develop decreased lacrimation, loss of taste sensation in the anterior two-thirds of the tongue, and painful sensitivity to sounds Most patients with Bell’s palsy recover completely within year Answers to Case Study XX 58 The answer is B (Fix, 2/e, pp 103 – 106, 115 – 117, 121.) The spinal cord is composed of both gray matter and white matter The gray matter, which is centrally located and H shaped, is divided into three horns on each side: the dorsal horn, the lateral horn, and the ventral horn CHAPTER MUSCULOSKELETAL 571 The dorsal horn receives sensory input, while the lateral horn receives viscerosensory input, such as from the preganglionic sympathetic neurons The cell bodies of lower motor neurons are found in ventral horn (anterior horn cells) The white matter of the spinal cord consists of bundles of myelinated axons that may group together to form columns The columns of the spinal cord include the posterior (dorsal) columns, the anterior (ventral) columns, and the lateral columns These columns may contain ascending or descending tracts Most of the ascending tracts carry sensory information to the brain These tracts are generally organized as a chain of three neurons, the first of which (first-order neuron) is always located in the dorsal root ganglia The major ascending tracts of the spinal cord are the dorsal columns, the spinothalamic tracts (ventral and lateral), the spinocerebellar tracts (dorsal and ventral), and the cuneocerebellar tracts The major descending tracts include the corticospinal tracts (lateral and ventral), the rubrospinal tracts, and the vestibulospinal tracts 59 The answer is C (Ganong, 17/e, pp 122 – 131 Fix, 2/e, pp 113 – 119.) The ascending tracts of the spinal cord send sensory information to the brain The lateral spinothalamic tracts are involved with pain and temperature sensation The first-order neurons of this pathway have their cell bodies in the dorsal root ganglia They synapse with second-order neurons that are located in the dorsal horn From there, the axons decussate in the ventral white commissure and ascend as the lateral spinothalamic tracts They end in the thalamus (posterior ventral nuclei), which then sends fibers to the postcentral gyrus Unilateral destruction of the lateral spinothalamic tract leads to contralateral loss of pain and temperature Proprioception has a conscious component and an unconscious components The conscious proprioception pathway involves neurons located in the dorsal root ganglia that send axons up ipsilateral dorsal columns These columns also send tactile information, namely, touch, vibration, and pressure sense These fibers synapse in the gracile and cuneate nuclei of the medulla From there, fibers decussate to form the medial lemniscus, which terminates in the ventral posterolateral (VPL) nucleus of the thalamus Axons then travel via the internal capsule to the postcentral gyrus (the somatosensory cortex) Unilateral destruction of the dorsal columns produces ipsilateral loss of tactile discrimination, position sense, and vibration sense (either in the legs, the arms, or both) Unconscious propri- 572 INTEGRATED BASIC SCIENCES oception, which is involved in coordination, travels via dorsal and ventral spinocerebellar tracts to the cerebellum The dorsal spinothalamic tract is uncrossed, but the ventral spinocerebellar tract crosses at the ventral white commissure Therefore, a lesion of the dorsal spinocerebellar tract will produce ipsilateral leg dystaxia, whereas a lesion of the ventral spinocerebellar tract will produce contralateral leg dystaxia Light-touch fibers travel via two tracts: uncrossed fibers in the ipsilateral posterior columns and crossed fibers in the contralateral ventral spinothalamic tracts Light touch is often spared in unilateral spinal cord lesions, because there are two routes to carry this sensory information to the brain 60 The answer is A (Fix, 2/e, pp 127 – 135 Isselbacher, 13/e, pp 2357 – 2358.) Syringomyelia refers to a cleftlike cavity (syrinx) that is located in the inner portion of the spinal cord At first, the syrinx involves only the crossing fibers of the ventral white commissure, which contain the fibers involved with pain and temperature sensation (at the level of the lesion) Syringomyelia, which is associated with the Arnold-Chiari malformation, is usually found in the cervical area (C5-T5) Therefore, the loss of pain and temperature sensations affects only the upper trunk and both arms Touch sensation is not affected, as some fibers involved with touch not cross Extension of the syrinx, however, can involve the ventral horn of the spinal cord and cause a lower motor neuron (LMN) lesion with hyporeflexia and muscle atrophy In contrast to syringomyelia, the Brown-Sequard syndrome refers to lesions that involve one-half of the spinal cord, such as would occur with hemisection of the spinal cord at T10 The symptoms produced by this abnormality may be ipsilateral or contralateral to the lesion, depending on whether the affected area is a crossed tract or an uncrossed tract Ipsilateral symptoms include ipsilateral flaccid paralysis at the level of the lesion (due to involvement of the ventral horn), ipsilateral spastic paralysis below the lesion (due to involvement of the lateral corticospinal tract), ipsilateral cutaneous anesthesia at the level of the lesion (due to involvement of the dorsal horn), and ipsilateral loss of proprioceptive, vibratory, and two-point discrimination below the lesion (due to involvement of the dorsal column) Contralateral symptoms include contralateral loss of pain and temperature below the lesion (due to involvement of the lateral spinothalamic tracts) CHAPTER MUSCULOSKELETAL 573 Answers to Case Study XXI 61 The answer is B (Fix, 2/e, pp 231 – 233 DeMyer, 1/e, pp 187 – 191.) The cerebellum lies within the posterior fossa with the medulla, pons, and midbrain The cerebellum contains three paired nuclei: the fastigial nucleus, the interpositus nucleus, and the dentate nucleus The interpositus nucleus contains the emboliform and globose nuclei, whereas the dentate nucleus is the largest and most lateral of the cerebellar nuclei Anatomically, the cerebellum can be divided into longitudinal zones by transverse clefts or fissures These longitudinal zones connect with specific cerebellar nuclei The median (vermal) zone projects to the fastigial nucleus, while the paramedian (paravermal) zone projects to the emboliform and globose nuclei The lateral zone of the hemisphere projects to the dentate nucleus The cerebellum can also be divided sagittally into two lateral hemispheres and a midline vermis, and it can be divided functionally into three regions The anterior lobe, which lies anterior to the primary fissure of the cerebellum, receives proprioceptive input from muscles and tendons via the dorsal and ventral spinocerebellar tracts The posterior lobe, which lies between the primary fissure and the posterolateral fissure, receives input from the cerebral cortex via the pontine nuclei and middle cerebellar peduncles The flocculonodular lobe, which contains the nodules of the vermis and the flocculus, has connections with the vestibular nucleus 62 The answer is B (Costanzo, 1/e, pp 50 – 51 Fix, 2/e, pp 233 – 234.) Histologically, the cerebellar cortex is divided into the molecular layer, the Purkinje cell layer, and the granular layer The Purkinje cell layer is the middle layer of the cerebellar cortex and is found between the molecular layer and the granular cell layer It contains the Purkinje cells, which are the only output from the cerebellar cortex Purkinje cells are GABAnergic and their output, which is to the cerebellar and vestibular nuclei, is always inhibitory They are excited by parallel and climbing fibers and are inhibited by basket and stellate cells The climbing fibers and the mossy fibers are the input connections to the cerebellar cortex The climbing fibers, which originate from the inferior olive of the medulla (olivocerebellar tract), participate in cerebellar motor learning, whereas the mossy fibers originate from many areas of the brain stem and 574 INTEGRATED BASIC SCIENCES spinal cord (spinocerebellar and pontocerebellar tracts) The granular cell layer, which is the innermost layer of the cerebellar cortex, contains granule cells, Golgi type II cells, and glomeruli, in which the axons of the mossy fibers make synaptic connections with the dendrites of the granular cells and Golgi type II cells The molecular layer, which is the outermost layer of the cerebellar cortex, contains stellate (outer) cells and basket (inner stellate) cells The main functions of the cerebellum are maintenance of posture, balance, and muscle tone, and coordination of voluntary muscle activity Dysfunction of the cerebellum leads to ataxia (awkwardness of posture and gait), intention tremor, and dysmetria (“overshooting” of purposeful movement) 63 The answer is E (Cotran, 5/e, pp 1353 – 1354 Chandrasoma, 3/e, pp 909 – 910.) The phakomatoses are a group of autosomal dominant disorders that are characterized by the formation of multiple hamartomas or neoplasms that primarily involve the nervous system and skin The most common phakomatosis is neurofibromatosis (von Recklinghausen’s disease), which may occur in two different clinical forms Neurofibromatosis type (NF-1) is characterized by the formation of multiple neurofibromas in the skin and peripheral nerves The majority of the neurofibromas that develop in these individuals are histologically identical to neurofibromas that occur sporadically, but one type — plexiform neuroma — is characteristic of NF-1 Patients may also develop hyperpigmented macules of the skin (café-au-lait spots), pigmented nodules of the iris (Lisch nodules), and other neoplasms of the central nervous system, such as gliomas of the optic nerve, meningiomas, and astrocytomas The abnormal gene, called NF-1, is a tumor-suppressor gene located on chromosome 17 and encodes for a protein called neurofibromin Neurofibromatosis type (NF-2) is an autosomal dominant disorder that is characterized by the development of bilateral acoustic neuromas, which are tumors of Schwann cells that arise at the cerebellopontine angle Individuals with NF-2 may also develop optic nerve gliomas, meningiomas, and astrocytomas Von Hippel-Lindau disease is characterized by the formation of multiple hemangiomas in the retina and brain, a benign tumor of the cerebellum (capillary hemangioblastoma), angiomas and cysts of the kidney and liver, CHAPTER MUSCULOSKELETAL 575 and renal cell carcinoma The abnormal gene in these individuals is thought to be the raf-1 oncogene, which is located on chromosome Capillary hemangioblastomas are associated with the paraneoplastic production of erythropoietin, which causes the patient to develop polycythemia Microscopically, hemangioblastomas show a mixture of capillary vessels with intervening “stroma” cells that have abundant vacuolated cytoplasm Tuberous sclerosis is an autosomal dominant disorder that is characterized by the formation of multiple firm, white nodules (tubers) in the cortex and subependymal nodules of gliosis that protrude into the ventricles (“candle drippings”) Other signs associated with tuberous sclerosis include the triad of seizures, mental retardation, and congenital white spots or macules (leukoderma) Facial angiofibromata (adenoma sebaceum) also occur, along with rhabdomyomas of the heart and angiomyolipomas of the kidney Sturge-Weber syndrome is characterized by the formation of multiple venous angiomas in the leptomeninges, large ipsilateral angiomas of the skin (port-wine nevi of the face), and mental retardation Answers to Case Study XXII 64 The answer is B (Sternberg, 1/e, pp 161 – 163 Gartner, 2/e, pp 267 – 268.) The circumventricular organs (CVOs) are a group of specialized structures of the central nervous system that are located around the ventricles and have blood vessels that lack the typical blood – brain barrier of capillaries in the cortex The five components of the CVOs are the pineal gland, area postrema, subfornical organ, organum vasculosum of the lamina terminalis, and the median eminence and infundibulum of the hypothalamus The pineal gland (epiphysis) is located off of the roof of the third ventricle between the posterior end of the corpus callosum and the posterior commissure, to which it is connected by a stalk Histologically, the pineal gland contains pinealocytes, which synthesize serotonin and melatonin, neuroglial (interstitial) cells, and small concretions called corpora arenacea (“brain sand”) 576 INTEGRATED BASIC SCIENCES 65 The answer is D (Ganong, 17/e, pp 425 – 427 Gartner, 2/e, pp 267 – 268.) The pineal gland contains the highest concentration of serotonin (5hydroxytryptamine) in the body, which is synthesized by the pinealocytes from tryptophan Pinealocytes also convert serotonin into melatonin (N-acetyl-5-methoxytryptamine) The pinealocytes secrete both serotonin and melatonin into the blood and the cerebrospinal fluid, but their synthesis and secretion are different during the day This pineal gland synthesizes and secretes serotonin during the day and melatonin during the night This diurnal variation is thought to be responsible for the daily sleep – wake cycle, which is controlled by the release of norepinephrine from postganglionic sympathetic nerves (nervi onarii) that innervate the pineal gland The neurologic circuits involved in the sleep – wake cycle begin with the retinohypothalamic fibers, which transmit light impulses from the retina to the suprachiasmatic nucleus of the hypothalamus From there, sympathetic fibers travel in the intermediolateral gray column of the spinal cord, where they terminate on preganglionic sympathetic neurons from the superior cervical ganglion Postganglionic fibers then travel via the nervi conarii to the pineal gland 66 The answer is E (Cotran, 5/e, pp 1168 – 1169 Rubin, 2/e, pp 1146 – 1147.) Tumors of the pineal may originate from either the pinealocytes or the neuroglial (interstitial) cells, but pineal tumors arise more commonly from sequestered embryonic germ cells These germ-cell tumors of the pineal are most often similar clinically and histologically to seminomas, which are radiosensitive tumors that originate in the testes A similar tumor that originates in the ovaries is called a dysgerminoma, whereas the same tumor in the pineal gland is called a germinoma Tumors that originate from the normal pineal cells (pinealomas) are called pineoblastomas or pineocytomas Pineoblastomas resemble medulloblastomas or neuroblastomas, whereas pineocytomas resemble astrocytomas BIBLIOGRAPHY Akesson EJ, et al: Thompson’s Core Textbook of Anatomy, 2/e Philadelphia, JB Lippincott, 1997 Alberts B, et al: Molecular Biology of the Cell, 3/e New York, Garland, 1994 Andreoli TE, et al: Cecil’s Essentials of Medicine, 3/e Philadelphia, WB Saunders, 1993 Champe PC, Harvey RA: Biochemistry, 2/e Philadelphia, JB Lippincott, 1994 Chandrasoma P, Taylor CR: Concise Pathology, 3/e Stamford (CT), Appleton & Lange, 1998 Chung KW: Gross Anatomy, 3/e Baltimore, Williams & Wilkins, 1995 Costanzo LS: Physiology, 1/e Philadelphia, Williams & Wilkins, 1995 Cotran RS, Kumar V, Robbins SL: Pathologic Basis of Disease, 5/e Philadelphia, WB Saunders, 1994 Damjanov I, Linder J (eds): Anderson’s Pathology, 10/e St Louis, CV Mosby, 1996 DeMyer W: Neuroanatomy, 1/e Philadelphia, Harwal, 1988 Fawcett DW: A Textbook of Histology, 12/e New York, Chapman & Hall, 1994 Fix JD: Neuroanatomy, 2/e Baltimore, Williams & Wilkins, 1995 Ganong WF: Review of Medical Physiology, 17/e Norwalk (CT), Appleton & Lange, 1995 Gartner LP, Hiatt JL: Color Textbook of Histology, 1/e Philadelphia, WB Saunders, 1997 Gartner LP, et al: Cell Biology and Histology, 2/e Philadelphia, Harwal, 1993 Grippi MA: Pulmonary Pathophysiology, 1/e Philadelphia, JB Lippincott, 1995 Guyton AC, Hall JE: Textbook of Medical Physiology, 9/e Philadelphia, WB Saunders, 1996 Henderson JM, et al: Gastrointestinal Pathophysiology, 1/e Philadelphia, Lippincott-Raven, 1996 Henry JB, et al (eds): Clinical Diagnosis and Management by Laboratory Methods, 19/e Philadelphia, WB Saunders, 1996 Hetts SW: To Die or Not to Die: An Overview of Apoptosis and Its Role in Disease JAMA 279(4):300 – 307, 1998 Isselbacher KJ, et al (eds): Harrison’s Principles of Internal Medicine, 13/e New York, McGraw-Hill, 1994 Jorde LB, et al: Medical Genetics, 1/e St Louis, CV Mosby, 1995 577 Copyright © 1999 by The McGraw-Hill Companies, Inc Click here for Terms of Use 578 BIBLIOGRAPHY Katzung BG: Basic and Clinical Pharmacology, 6/e Norwalk (CT), Appleton & Lange, 1995 Larsen WJ: Human Embryology, 1/e New York, Churchill Livingstone, 1993 Lee GR, et al (eds): Wintrobe’s Clinical Hematology, 9/e Philadelphia, Lea & Febiger, 1993 McClatchey KD, et al: Clinical Laboratory Medicine, 1/e Baltimore, Williams & Wilkins, 1994 McPhee SJ, et al: Pathophysiology of Disease, 2/e Stamford (CT), Appleton & Lange, 1997 Moore KL: Clinically Oriented Anatomy, 3/e Baltimore, Williams & Wilkins, 1992 Murray PE, et al: Medical Microbiology, 1/e St Louis, CV Mosby, 1990 Murray RK, et al: Harper’s Biochemistry, 23/e Norwalk (CT), Appleton & Lange, 1993 Mycek MJ, et al: Pharmacology, 2/e Philadelphia, Lippincott-Raven, 1997 Porterfield SP: Endocrine Physiology, 1/e St Louis, Mosby, 1997 Rosenfeld GC, Loose-Mitchell DS: Pharmacology, 3/e Baltimore, Williams & Wilkins, 1998 Rosse C, Gaddum-Rosse P: Hollinshead’s Textbook of Anatomy, 5/e Philadelphia, Lippincott-Raven, 1997 Rubin E, Farber JL: Pathology, 2/e Philadelphia, JB Lippincott, 1994 Shayman JA: Renal Pathophysiology, 1/e Philadelphia, JB Lippincott, 1995 Sternberg SS, et al: Histology for Pathologists, 2/e Philadelphia, LippincottRaven, 1996 Stites PS, et al: Basic and Clinical Immunology, 8/e Norwalk (CT), Appleton & Lange, 1994 .. .INTEGRATED BASIC SCIENCES PreTest® Self-Assessment and Review NOTICE Medicine is an ever-changing science As new research and clinical experience broaden our knowledge, changes in treatment and. .. particular importance in connection with new or infrequently used drugs INTEGRATED BASIC SCIENCES PreTest® Self-Assessment and Review EDITOR Earl J Brown, MD Associate Professor Department of Pathology... numerous plasma cells, lymphocytes, and plasmacytoid lymphocytes 20 INTEGRATED BASIC SCIENCES Case Study XIII INFECTIOUS MONONUCLEOSIS Integrated Basic Science Content Review ANATOMY/HISTOLOGY/EMBRYOLOGY