Basic Sciences Review for Medical Licensure Developed at The University of Oklahoma College of Medicine Suitable Reviews for: United States Medical Licensing Examination (USMLE), Step 1 Anatomy Embryology Neuroanatomy Gross Anatomy Microanatomy Edited by Raymond E. Papka With Contributions by James J. Tomasek Daniel L. McNeill Hubert W. Burden Raymond E. Papka Springer-Verlag New York Berlin Heidelberg London Paris Tokyo Hong Kong Barcelona Budapest Raymond E. Papka, Ph.D. Department of Anatomical Sciences University of Oklahoma Health Science Center P.O. Box 26901 Oklahoma City, OK 73190 USA All contributors share the address above except: Hubert W. Burden Department of Anatomy and Cell Biology East Carolina University Greenville, NC 27858 USA Library of Congress Cataloging-in-Publication Data Anatomy: embryology, gross anatomy, neuroanatomy, microanatomy I edited by Raymond E. Papka ; contributors, Raymond E. Papka ... let al.]. p. cm. - (Oklahoma notes) Includes bibliographical references. lSBN-\3: 978-0-387-94395-4 e-lSBN-\3: 978-1-4612-4194-2 DOl: 10.1007/978-1-4612-4194-2 1. Human anatomy-Outlines, syllabi, etc. 2. Human anatomy Examinations, questions, etc. 3. Embryology, Human-Outlines, syllabi, etc. 4. Embryology, Human-Examinations, questions, etc. I. Papka, Raymond E. II. Series. [DNLM: 1. Anatomy-outlines. 2. Anatomy-examination questions. QS 18 A536 1995] QM31.A53 1995 611-dc20 DNLMIDLC for Library of Congress 94-45449 Printed on acid-free paper. © 1995 Springer-Verlag New York, Inc. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. While the advice and information in this book is believed to be true and accurate at the date of going to press, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Production managed by Jim Harbison; manufacturing supervised by Jacqui Ashri. Camera-ready copy prepared by the editor. 987654321 Preface to the tJ~~ In 1973, the University of Oklahoma College of Medicine instituted a requirement for passage of the Part 1 National Boards for promotion to the third year. To assist students in preparation for this examination, a two-week review of the basic sciences was added to the curriculum in 1975. Ten review texts were written by the faculty: four in anatomical sciences and one each in the other six basic sci ences. Self-instructional quizzes were also developed by each discipline and ad ministered during the review period. The first year the course was instituted the Total Score performance on National Boards Part I increased 60 points, with the relative standing of the school chang ing from 56th to 9th in the nation. The performance of the class since then has remained near the national candidate mean. This improvement in our own stu dents' performance has been documented (Hyde et al: Performance on NBME Part I examination in relation to policies regarding use of test. J. Med. Educ. 60: 439-443, 1985). A questionnaire was administered to one of the classes after they had completed the Boards; 82% rated the review books as the most beneficial part of the course. These texts were subsequently rewritten and made available for use by all stu dents of medicine who were preparing for comprehensive examinations in the Basic Medical Sciences. Since their introduction in 1987, over 300,000 copies have been sold. Obviously these texts have proven to be of value. The main reason is that they present a concise overview of each discipline, emphasizing the content and concepts most appropriate to the task at hand, i.e., passage of a comprehen sive examination over the Basic Medical Sciences. The recent changes in the licensure examination that have been made to create a Step l/Step 2/Step 3 process have necessitiated a complete revision of the Okla homa Notes. This task was begun in the summer of 1991 and has been on-going over the past 3 years. The book you are now holding is a product of that revision. Besides bringing each book up to date, the authors have made every effort to make the tests and review questions conform to the new format of the National Board of Medical Examiners. Thus we have added numerous clinical vignettes and ex tended match questions. A major revision in the review of the Anatomical Sci ences has also been introduced. We have distilled the previous editions' content to the details the authors believe to be of greatest importance and have combined the four texts into a single volume. In addition a book over neurosciences has been added to reflect the emphasis this interdisciplinary field is now receiving. I hope you will find these review books valuable in your preparation for the licensure exams. Good Luck! Richard M. Hyde, Ph.D. Executive Editor Preface This book represents a major revision of the Oklahoma Notes that were previously produced as individual volumes for the review of Embryology, Gross Anatomy, Neuroanatomy, and Microanatomy. Within this single book, information regard ing the four major topics of anatomical sciences has been reorganized and up dated. The authors have endeavored to produce a concise and relevant study-book that will provide students a reasonably thorough review of the components of the anatomical sciences. The book is written in outline form in order to reduce the volume of descriptive prose and to facilitate the student's opportunity to get to the "meat" of the subjects. This review narrative is written expressly for students preparing to take Step 1 of the USMLE. It is a distillation of headlines of essential content for medical Embryology, Gross Anatomy, Neuroanatomy, and Microanatomy. It is written with the assumption that you previously have completed medical school courses that included dissections and microscopy. For most of us, anatomy is quickly forgotten if not used. This outline volume attempts to organize the contents of the anatomy courses into formats useful for review/recall purposes. This is not a traditional review text-there are few illustrations or diagrams. The student is encouraged to thoughtfully engage the narrative, highlight words/phrases as ap propriate, and incorporate mental images of structures and their functions as you read. If the mental images fail to focus clearly as you read the narrative, students should consult atlases and more comprehensive texts used in your medical school courses. Questions for self-examination are placed separately at the end of the book. These questions are intended to be integrative so students should not expect to review a section of the anatomical sciences and then take a self-examination on that section alone. We wish you the best in your review! R.E.P. J.J.T. D.L.M. H.W.B. Contents Preface to the Oklahoma Notes ............. ........................................... .............. v Preface ........................................................................................................... vii Embryology James J. Tomasek Gametogenesis, Reproductive Cycle and Fertilization ................. ................ 1 Early Development of the Conceptus: Weeks 1-2 ........................................ 6 Extraembryonic Membranes and Umbilical Cord ....................................... 8 Placenta ...... .................... ................................................................................ 10 Formation of the Trilaminar Embryo ........................................................... 12 Development of General Body Form, Body Cavities and Diaphragm .......... 15 Nervous System ............................................................................................. 18 Musculoskeletal System ................................................................................ 23 Integumentary System ................................................................................... 27 Development of the Head and Neck .............................................................. 29 Development of the Face, Palate, Tongue, and Thyroid Gland .................... 33 Respiratory System ........................................................................................ 36 Digestive System and Mesenteries System ...... .......................... .......... ......... 38 Urogenital System ......................................................................................... 43 Development of the Heart ............................................................................. 47 Development of the Vasculature ................................................................... 51 Gross Anatomy Hubert W. Burden Basic Concepts of the Nervous System and Imaging ................................... 55 Back and Upper Limb .................................................................................... 57 Head and Neck ............................................................................................... 67 Thorax ............................................................................................................ 79 Abdomen ........................................................................................................ 84 Pelvis and Perineum 92 Lower Limb ....................................................... ............................................. 99 Neuroanatomy DanielL. McNeill Histology of the Nervous System .................................................................. 106 Gross Features of the Brain and Brainstem .................................................. 109 Vasculature and Ventricular System of the CNS .......................................... 110 Spinal Cord and Peripheral Nerves ............................................................... 114 Cranial Nerves ............................................................................................... 124 Medulla Oblongata ........................................................................................ 136 Pons ................................................................................................................ 137 Mesencephalon .............................................................................................. 138 Diencephalon ................................................................................................. 139 Basal Ganglia ................................................................................................. 142 Cerebellum ..................................................................................................... 144 x Contents Cerebrum ....................................................................................................... 148 Limbic System ................................................................................................ 152 Autonomic Nervous System .......................................................................... 153 Microanatomy Raymond E. Popko Cytology ......................................................................................................... 158 Epithelium ...................................................................................................... 162 Connective Tissue Proper ............................................................................. 163 Cartilage ......................................................................................................... 165 Bone ............................................................................................................... 166 Peripheral Blood ............................................................................................ 170 Hematopoiesis ............................................................................................... 172 Immune System (Lymphatic System) ............................................................ 174 Muscle Tissue ................................................................................................ 178 Nerve Tissue (see Section on Neuroanatomy) .............................................. 181 Cardiovascular System ... ... ............ ..... ..... ........ ............. ....... .... .......... ... ......... 182 Integumentary System ... ............... ..... ............... ....... ................. ........ ..... .... .... 185 Respiratory System ........................................................................................ 187 Gastrointestinal System . ...... ...... ......... ....... ........... .... ... ... ...................... ......... 189 Urinary System .............................................................................................. 198 Endocrine System .. ......... ... ................. ....... ..... ...... ............................ ............. 202 Female Reproductive System ............ ....... .................................. ....... ... ......... 207 Male Reproductive System ............................................................................ 213 Review Questions .................................................................... 218 Answers to Review Questions ................................................ 231 EMBRYOLOGY GAMETOGENESIS, REPRODUCTIVE CYCLE AND FERTILIZATION I. CELLS AND CHROMOSOMES A. Diploid Cells In humans, the cells comprising all renewing cell populations (including the precursors of germ cells) are diploid (2N) and possess a total of 46 chromosomes. = diploid (2N) 46 chromosomes = autosomal chromosomes 44 (22 homologous pairs) = sex chromosomes 2 = females XX (homologous) = males XY (nonhomologous) B. Haploid Cells (Gametes) The gametes (sperm and ova) are highly specialized reproductive cells containing only one half (N or 23) the number of chromosomes found in renewing cell populations. The reduction in chromosome number is accomplished by two specialized cell cycles which are referred to as Meiosis I and Meiosis II. = haploid (N) 23 chromosomes = autosomal chromosomes 22 (one member from each pair) = sex chromosomes 1 females = X (always) males = XorY C. Chromosome Morphology 1. centro meres 2. arms 3. chromatids D. Mitosis The two most important events occurring during mitosis are DNA replication (interphase) and centromeric division (late metaphase). When DNA replication and centromeric division occur during the same cell cycle, the number of chromosomes in both daughter cells will remain constant (diploid) and the daughter cells will be identical genetically. E. Meiosis During the two specialized cell cycles of gametogenesis (meiosis I and meiosis II), DNA replication and centromeric division occur in separate cell cycles. DNA replication occurs during meiosis I; centromeric division occurs during meiosis II. When cells divide without centromeric division, the number of chromosomes transmitted to daughter cells must be reduced by one-half. The resulting haploid daughter cells will NOT be genetically identical, each cell receives only one member (maternal or paternal) from each of the 23 chromosome pairs. 1 II. ABNORMALITIES IN CHROMOSOME NUMBER (ANEUPLOID CELLS) A. Nondisjunction The most common event producing abnormal chromosome numbers (aneuploidy) is nondisjunction. When nondisjunction occurs, the chromosomes are unequally distributed between the daughter cells so that one cell receives an extra chromosome (trisomy) and the other cell is missing that chromosome (monosomy). NONDISJUNCTION CAN OCCUR ANYTIME A CELL DIVIDES (MITOTICALLY OR MEIOTICALLY) AND CAN AFFECT EITHER AUTOSOMAL OR SEX CHROMOSOMES. It is generally accepted that one of the most frequent causes for nondisjunction is delayed or asynchronous division of centromeres during late metaphase. B. Meiotic Nondisjunction During gametogenesis, nondisjunction results in the production of two abnormal gametes (haploid plus one or haploid minus one chromosome). If one of the abnormal gametes participates in fertilization an aneuploid zygote is produced which either possesses an extra chromosome (sex or autosomal trisomy) or lacks a chromosome (sex or autosomal monosomy). Individuals developing from these abnormal zygotes will be either trisomic or monosomic for the chromosome involved. 1. Zygotes with autosomal aneuploidy. Although 22 pairs of autosomal chromosomes are present in human zygotes and any chromosome can be affected by nondisjunction (all have been reported in aborted material), only a few (trisomic only) complete development to present as postnatal medical problems. a) Autosomal Monosomy. True monosomic conditions involving any of the 22 autosomal chromosomes have not been reported to complete intrauterine development and are generally considered to be invariably lethal. b) Autosomal Trisomy. Trisomic conditions for autosomal chromosomes are usually but not invariably lethal. The only common autosomal trisomic condition with long term survival is trisomy 21 (Down's syndrome). Trisomy 13 (Patau's syndrome) and trisomy 18 (Edward's syndrome) are occasionally reported but these individuals rarely survive beyond the first few months of postnatal life. c) Maternal Age. The increased frequency of nondisjunction with advancing maternal age is usually attributed to the fact that the first meiotic division of all ova begins during fetal life. Ova produced during the later years of the reproductive life span are very old and have been subjected to the cumulative environmental (radiation, chemicals, therapeutic drugs, viral infections) and physiological (endocrine changes) effects of aging. 2. Zygotes with Sex Chromosome Aneuploidy. In contrast to the small number of aneuploid conditions resulting from unequal distribution of the 22 pairs of autosomes, nondisjunction affecting the single pair of sex chromosomes may produce zygotes and adult individuals of at least four basic genotypes. Monosomic and trisomic conditions for sex chromosomes are well known clinically and are relatively common. 2