Table Of Content®
STEP 1
E
L
M 2018
Lecture Notes
S
U Anatomy
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USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board
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Course ISBN: 978-1-5062-2823-5
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Editors
James White, PhD
Assistant Professor of Cell Biology
School of Osteopathic Medicine
Rowan University
Stratford, NJ
Adjunct Assistant Professor of Cell and Developmental Biology
University of Pennsylvania School of Medicine
Philadelphia, PA
David Seiden, PhD
Professor of Neuroscience and Cell Biology
Rutgers–Robert Wood Johnson Medical School
Piscataway, NJ
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Table of Contents
Part I: Early Embryology and Histology: Epithelia
Chapter 1: Gonad Development 3
Chapter 2: First 8 Weeks of Development 7
Chapter 3: Histology: Epithelia 13
Part II: Gross Anatomy
Chapter 1: Back and Autonomic Nervous System 27
Chapter 2: Thorax 41
Chapter 3: Abdomen, Pelvis, and Perineum 93
Chapter 4: Upper Limb 187
Chapter 5: Lower Limb 203
Chapter 6: Head and Neck 215
Part III: Neuroscience
Chapter 1: Nervous System Organization and Development 235
Chapter 2: Histology of the Nervous System 245
Chapter 3: Ventricular System 257
Chapter 4: The Spinal Cord 263
Chapter 5: The Brain Stem 287
Chapter 6: The Cerebellum 321
Chapter 7: Basal Ganglia 329
v
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Chapter 8: Visual Pathways 337
Chapter 9: Diencephalon 347
Chapter 10: Cerebral Cortex 353
Chapter 11: Limbic System 371
Index 377
Additional resources available at
www.kaptest.com/usmlebookresources
vi
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PART I
Early Embryology and
Histology: Epithelia
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1
Gonad Development
Learning Objectives
❏ Explain information related to indifferent gonad
❏ Interpret scenarios on testis and ovary
❏ Answer questions about meiosis
❏ Interpret scenarios on spermatogenesis
❏ Solve problems concerning oogenesis
INDIFFERENT GONAD
Although sex is determined at fertilization, the gonads initially go through
an indifferent stage weeks 4–7 when there are no specific ovarian or tes-
ticular characteristics. The indifferent gonads develop in a longitudinal
elevation or ridge of intermediate mesoderm called the urogenital ridge.
The components of the indifferent gonads are as follows:
• Primordial germ cells provide a critical inductive influence on
gonad development, migrating in at week 4. They arise from the
lining cells in the wall of the yolk sac.
• Primary sex cords are finger-like extensions of the surface epithe-
lium which grow into the gonad that are populated by the migrat-
ing primordial germ cells.
• Mesonephric (Wolffian) and the paramesonephric (Mullerian)
ducts of the indifferent gonad contribute to the male and female
genital tracts, respectively.
TESTIS AND OVARY
The indifferent gonad develops into either the testis or ovary.
Development of the testis and male reproductive system is directed by the
following:
• Sry gene on the short arm of the Y chromosome, which encodes
for testis-determining factor (TDF)
• Testosterone, which is secreted by the Leydig cells
• Müllerian-inhibiting factor (MIF), which is secreted by the Sertoli
cells
• Dihydrotestosterone (DHT): external genitalia
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Part I l Early Embryology and Histology: Epithelia
Anatomy Immunology
Development of the ovary and female reproductive system requires estrogen.
Ovarian development occurs in the absence of the Sry gene and in the presence
of the WNT4 gene.
Pharmacology Biochemistry
MIF: Müllerian-inhibiting factor
TDF: testis-determining factor
Primordial
Physiology Medical Genetics germ cells
Yolk sac
Urogenital ridge
Pathology Behavioral Science/Social Sciences
Mesonephric duct (Wolffian)
MIF: Müllerian-inhibiting factor Paramesonephric duct
TDF: testis-determining factor (Müllerian)
Microbiology
Indifferent gonad
TDF
Testosterone No factors
MIF
Testis Ovary
and male and female
genital system genital system
Figure I-1-1. Development of Testis and Ovary
Figure I-1-1. Development of Testis and Ovary
MEIOSIS
Meiosis occurs within the testis and ovary. This is a specialized process of cell
division that produces the male gamete (spermatogenesis) and female gamete
(oogenesis). There are notable differences between spermatogenesis and
oogenesis.
Meiosis consists of 2 cell divisions. In meiosis I, the following events occur:
• Synapsis: pairing of 46 homologous chromosomes
• Crossing over: exchange of segments of DNA
• Disjunction: separation of 46 homologous chromosome pairs
(no centromere-splitting) into 2 daughter cells, each containing
23 chromosome pairs
In meiosis II, synapsis does not occur, nor does crossing over. Disjunction does
occur with centromere-splitting.
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Chapter 1 l Gonad Development
Type B
Spermatogonia (46, 2n) (Diploid)
Oogonia
Meiosis I
Primary
spermatocyte DNA replication
(46, 4n)
Primary
oocyte
Synapsis
Crossover
Cell division
Alignment and disjunction
Centromeres do not split
Secondary
spermatocyte
(23, 2n)
Secondary
oocyte
Meiosis II
Cell division
Alignment and
disjunction
Centromeres split
Gamete (23, 1n)
(Haploid)
Figure I-1-2. Meiosis
Figure I-1-2. Meiosis
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