Histology, cytology & embryology & neuroscience overview

Topics Runtime

Histology & Cytology

Cell components 19:35

Nervous & Muscle Tissue 12:38

Lymphoid Organs & Integument 6:26

Respiratory, GI & Renal Systems 20:06

Anatomy

Gonad - Embryonic 11:50

Back & Nervous System 12:27

Thorax 29:14

Upper Limbs 14:52

Lower Limbs 12:24

Head and Neck 52:53

Neuroscience

Peripheral, Central and Ventricular System 13:03

Spinal Cord 33:47

Brain Stem 1:03:10

Cerebellum & Visual Pathways 18:33

Diencephalon & Basal Ganglia 12:30

Cerebral Cortex & Limbic System 19:58

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USMLE Step 1 Webprep Course

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Topic > Histology & Cytology: Cell components

View all 24 Slides Kaplan USMLE Step 1 Web Prep / USMLE Step 1 Web Prep — Cell components

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Topic > Anatomy: Back & Nervous System

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Topic > Neuroscience: Peripheral, Central and Ventricular System

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USMLE Step 1 Web Prep - Peripheral, Central and Ventricular System

USMLE Step 1 Web Prep — Peripheral, Central and Ventricular System123575 >>> 0:00:00.2

SLIDE 1 of 9

Peripheral Nervous System

● Contains cranial and spinal nerves ● Consist of neurons that give rise to axons which

grow out of neural tube ● Development of neural tube

❍ Notochord induces formation of neural tube from neurectoderm

❍ Edges of neural groove (neural crest cells) close centrally and then peripherally at caudal and rostral ends

❍ Failure to close results in anencephaly causing polyhydramnios and increased levels of alpha-fetoprotein

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Table IV-1-1. Neuroectoderm and Neural Crest Germ Layer Derivatives EctodermNeuroectoderm Neural tube Central nervous system Retina Pineal gland Neurohypophysis Glial CellsNeural crest Adrenal Medulla Ganglia Sensory Autonomic Pigment cells Schwann cells Satellite cells Meninges Pia and arachnoid mater Pharyngealarch cartilage Odontoblasts Parafollicular (C) cells Aorticopulmonary septum

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Endocardial cushions

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Autonomic Nervous System

● Sympathetic outflow from T1 to sweat glands, dilator pupillae and superior tarsal muscles

● Preganglionic fibers are innervated by the descending fibers of the hypothalamus

❍ If interrupted by lesion in brainstem or spinal cord could cause Horner’s syndrome

❍ If lesion occurs in the CNS could result in a central Horner’s syndrome

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Central Nervous System Derivatives of the Brain Vesicles

● Forebrain ❍ Telencephalon—cerebral hemispheres and

lateral ventricles ❍ Diencephalon—thalamus, hypothalamus,

and epithalamus including the pineal gland, mammilary bodies, retina, and optic nerve

● Midbrain ❍ Mesencephalon—midbrain and cerebral

aqueduct ● Hindbrain

❍ Metencephalon—pons and cerebellum ❍ Myelencephalon—medulla

● *Neurohypophysis derives from neural tube, but adenohypophysis is of ectodermal origin

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Malformations of the Vertebral Column or Spinal Cord

Spina Bifidas—result of defect in cerebral arch, lamina fails to fuse

● Spina Bifida Occulta ❍ Least serious; affects single vertebrae ❍ No noticeable neurologic defects; tuft of hair

where lamina fails to fuse ● Spina Bifida Cystica

❍ Herniation occurs; all have elevated alpha-fetoprotein

❍ Spina Bifida with Menigocele—herniation through meninges

❍ Spina Bifida with Meningomyelocele ■ Arnold-Chiari malformation—

herniation at brainstem includes cerebellar tonsils

❍ Spina Bifida with Myeloschisis ■ Most severe defect ■ Neural tube fails to close at all

❍ *Preventable with administration of folic acid during early stages of pregnancy

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Ventricular System

● Brain and spinal cord float within a protective bath of CSF

● Produced continuously by choroids plexus ● Four ventricles

❍ Two lateral ventricles deep within each cerebral hemisphere

❍ Third ventricle located in midline within diencephalons

❍ Fourth ventricle located on dorsal surface of pons and upper medulla

● Ventricles connected resulting in flow of CSF ● CSF flows from lateral ventricles interventricular



foramen of Monro third ventricle cerebral aqueduct fourth ventricle subarachnoid space either foramen of Magendie or foramina Luschka

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Cerebrospinal Fluid

● Adults produce 90 – 150 mL of total CSF ● About 70 % secreted by choroids plexus located in parts of the lateral, third, and

fourth ventricles, lined by highly vascularized ependymal cells ● Almost all CSF returns to venous system by draining through arachnoid granulations

into superior sagittal dural venous sinus ● Concentration of protein is much lower compared to serum ● Few lymphocytes present; presence of PMN’s always abnormal ● RBCs may be present after traumatic spinal tap or subarachnoid hemorrhage

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CSF Abnormalities

● Hydrocephalus caused by excess volume or pressure of CSF ● Communicating hydrocephalus

❍ Caused by oversecretion of CSF without obstruction in the ventricles or by problems with absorption in subarachnoid space

● Noncommunication hydrocephalus ❍ Caused by obstruction of CSF flow inside ventricular system at foramen of

Monro, cerebral aqueduct, or fourth ventricle ❍ Could also be obstruction at foramina Magendie or Luschka

● Normal Pressure hydrocephalus

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Blood-Brain Barrier (BBB)

● Formed by capillary endothelium connected by tight junctions ● Astrocytes participate in maintenance of BBB



● Numerous long processes with expanded vascular end-feet that attach to walls of capillaries

● Water diffuses across BBB readily; glucose must be actively transported across

Blood-CSF Barrier

● Tight junctions located along the epithelial cells of the choroids plexus form this




Topic > Histology & Cytology: Respiratory, GI & Renal Systems

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USMLE Step 1 Web Prep - Respiratory, GI & Renal Systems

USMLE Step 1 Web Prep — Respiratory, GI & Renal Systems122775 >>> 0:00:02.2

SLIDE 1 of 21 Respiratory System General Features

● Conducting portion (nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles) which carry gases during inspiration and expiration

● Respiratory portion (alveoli) which provides for gas exchange between air and blood

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Nasal cavities--contain two major areas

● Respiratory area ❍ Lined by pseudostratified, ciliated, columnar epithelium ❍ Contain goblet cells that secrete mucus (respiratory epithelium)

● Olfactory area ❍ Composed of bipolar neurons ❍ Synapse with olfactory bulb in brain

122785 >>> 0:01:15.2 SLIDE 3 of 21

Paranasal Sinuses

● Cavities in the frontal, maxillary, ethmoid, and sphenoid bones ● Communicate with nasal cavities

Nasopharynx

● Lined by respiratory epithelium ● Cilia beat toward the oropharynx ● Pharyngeal tonsil--located on posterior wall, lymphoid tissue

Larynx

122790 >>> 0:01:53.2 SLIDE 4 of 21

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Table I-6-1. Histologic Features of Trachea, Bronchi, and Bronchioles Trachea Bronchi Bronchioles

EpitheliaPseudostratified ciliated columnar (PCC) cells, goblet cells

PCC to simple columnar cells

Ciliated, some goblet cells, Clara cells in terminal bronchioles

Cartilage 16–20 C-shaped cartilaginous rings Irregular plates None

Glands Seromucous glands Fewer seromucous glands None

Smooth muscle Between open ends of C-shaped cartilage Prominent

Highest proportion of smooth muscle in the bronchial tree

Elastic fibers Present Abundant Abundant

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Respiratory Bronchioles

● Branch from terminal bronchioles respiratory bronchioles alveolar duct alveolar sacs for gas exchange

Alveoli

● Thin walled sacs, two cell types ❍ Type I cells--thin surface for gas exchange ❍ Type II cells--produce surfactant

Blood-Air Barrier

● Consist of Type I cell, basal lamina, endothelial cell

Alveolar Macrophages

● Found on surface of alveoli ● Derived from monocytes and therefore mesoderm

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SLIDE 6 of 21 Gastrointestinal System

● Digestive tract ● Associated glands

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Table I-7-1a. Digestive Tract—Regional Comparisons Region Major Characteristics Mucosal Cell Types at

SurfaceFunction of Surface Mucosal Cells

Esophagus Stratified squamous epithelium; nonkeratinized skeletal muscle in muscular is externa (upper 1/3); smooth muscle (lower 1/3)

Stomach: body and fundus

Rugae: shallow pits; deep glands

Mucous cells Secrete mucus. Form protective layer against acid. Tight junctions between these cells probably contributes to the acid barrier of the epithelium.

Chief cells Secrete pepsinogen and lipase precursor.

Parietal cells Secrete HCl and intrinsic factor.

Enteroendocrine (EE) cells Secrete a variety of peptide hormones.

Stomach: pylorus Deep pits; shallow branched glands

Mucous cells

Parietal cells

EE cells

Same as above.

Same as above.

High concentration of gastrin.

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Table I-7-1b. Digestive Tract - Regional Comparisons



Region Major Characteristics Mucosal Cell Types at Surface

Function of Surface Mucosal Cells

Small intestine: Villi, plicae, and crypts (Fig I-7-1)

Columnar absorptive cells

Contain numerous microvilli that greatly increase the luminal surface area, facilitating absorption.

Duodenum (Fig I-7-2)

Brunner’s glands, which secrete an alkaline secretion

Goblet cells Secrete acid glycoproteins that protect mucosal lining.

Paneth cells Contains granules that contain lysozyme. May play a role in regulating intestinal bacterial flora.

EE cells High concentration of cells that secrete cholecystokinin and secretin.

See Page 56 of Anatomy Lecture Notes

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Table I-7-1. Digestive Tract—Regional Comparisons Region Major Characteristics Mucosal Cell Types

at SurfaceFunction of Surface Mucosal Cells

Small intestine: jejunum

Villi, well-developed plica, crypts Same cell types as found in the duodenal epithelium

Same as above.

Small intestine: ileum (Fig I-7-3)

Aggregations of lymph nodules called Peyer’s patches

Mucous cells, found over lymphatic nodules and Peyer’s patches

Endocytose and transport antigen from the lumen to lymphoid cells.

Large intestine Lacks villi, has crypts Mainly mucus-secreting and absorptive cells

Transports Na+ (actively) and water (passively) out of lumen.

See Page 56 of Anatomy Lecture Notes

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Submandibular and sublingual glands are of endodermal origin Parotid gland is of ectodermal origin

Table I-7-2. Comparison of the Major Salivary Glands Gland Acinar Cell Type (histologic appearance) Innervation



Parotid Serous (high amylase activity) Glossopharyngeal (IX)

Submandibular Serous and mucous; mainly serous Facial (VII)

Sublingual Mucous and serous; mainly mucous Facial (VII)

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Pancreas

● Exocrine portion consists of parenchymal cells arranged in acini and are protein secreting

● Acini contain pancreatic enzymes that cleave: ❍ Proteins (trypsin, chymotrypsin, carboxypeptidase, elastase) ❍ Carbohydrates (amylase) ❍ Lipids (lipase, lecithinase) ❍ Nucleic acids (ribonuclease, deoxyribonuclease)

● Acini contain much RER and stain basophilic

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Liver

● Largest gland of body ● Liver parenchyma

❍ Divided into small lobules shaped like polygonal cylinders

● Hepatocytes arranged in rows "hepatic cords" ● Sinusoids--receive oxygenated blood from hepatic

artery and deoxygenated blood from portal vein ❍ Kupffer cells ❍ Lipocytes

● Biliary system

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Hepatocytes

● Abundant stores of glycogen and many mitochondria

● Produce proteins for export (albumin, prothrombin, fibrinogen)

● Secrete bile ● Store lipids and carbohydrates ● Convert lipids and amino acids into glucose via

gluconeogenesis ● Detoxify and inactivate drugs by oxidation,

methylation, and conjugation

Sinusoids

● Receive oxygenated blood from hepatic artery and deoxygenated blood from portal vein

❍ Kupffer cells--phagocytize RBC ❍ Lipocytes--lie in perisinusoidal space

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Biliary System

● Bile flows from Bile canaliculi (small channels) Hering's canals Hepatic ducts common

hepatic duct joins with cystic duct (from gallbladder) common bile duct

● Blood flow from periphery to central vein while bile flow is opposite from center out peripherally

122845 >>> 0:13:35.2 SLIDE 15 of 21



Kidney

● Hilum ● Cortex ● Medulla ● Urine flows from medullary pyramids a minor

calyx major calyx ureter bladder

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Uriniferous Tubules

● Nephron ❍ Bowman's capsule ❍ Proximal convoluted tubule ❍ Loop of Henle ❍ Distal convoluted tubule

● Collecting Tubule ●

Also note the afferent arteriole carrying blood toward the glomerulus and efferent arteriole carrying blood away from glomerulus

●

Vasa rectae form a loop and empty into arcuate veins

122855 >>> 0:15:18.2 SLIDE 17 of 21



Glomerulus

● Podocytes wrap around glomerular capillaries ● Interdigitating foot processes form filtration slits ● Materials from capillaries pass into urinary space

"Bowman's space"

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Bowman's capsule

● Between visceral and parietal layers ● Contains ultrafiltrate of blood (not urine)

Basal lamina

● Primary filtration site ● Contains two elements

❍ Type IV collagen--forms meshwork, filters out large molecules

❍ Heparan sulfate--negatively charged, repels negatively charged molecules

● Podocyte foot processes also are negatively charged

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Glomerular Region--Podocyte Relationship to Capillaries

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Glomerular Region--Higher Magnification

122875 >>> 0:19:19.2 SLIDE 21 of 21

Juxtaglomerular Apparatus

● Juxtaglomerular cells ❍ Modified smooth muscle cells within afferent

arteriole ❍ Secrete renin which converts

angiotensinogen to angiotensin I ❍ Angiotensin I is converted by ACE

(Angiotensin converting enzyme) to Angiotensin II

● Polkissen cells ● Macula Densa

❍ Cells of distal tubule thought to be involved in



sensing Na+ concentration


USMLE Step 1 Web Prep - Cell components

USMLE Step 1 Web Prep — Cell components122500 >>> 0:00:00

SLIDE 1 of 24 Introduction to Anatomy Online

122505 >>> 0:00:46.2 SLIDE 2 of 24

Nucleus

● Enclosed by Nuclear Envelope ● Nuclear Lamina "lattice-like" network of proteins ● Nucleolus--site of rRNA synthesis and ribosome

assembly ● Chromatin--DNA plus proteins (histones and non-

histones)

122510 >>> 0:01:34.2 SLIDE 3 of 24

Nucleolus

● Heterochromatin--highly condensed DNA which is transcriptionally inactive; about 10% of nuclear chromatin

● Euchromatin--contains DNA which is transcriptionally more active; about 90% of nuclear chromatin

122515 >>> 0:01:51.2 SLIDE 4 of 24

Cytoplasm Ribosomes

● Consist of 60s and 40s subunits in eukaroytes ● Assembled in nucleus and transported to cytoplasm through nuclear pores ● Polysomes--groups of ribosomes translating the same piece of mRNA; two types:



free (in cytosol) and membrane associated (Rough Endoplasmic Reticulum (RER))

122520 >>> 0:03:03.2 SLIDE 5 of 24

Endoplasmic Reticulum--Two types: Rough and Smooth Rough Endoplasmic Reticulum (RER)

● Single lipid bilayer continuous with outer nuclear membrane with cisternae studded with ribosomes

● Synthesizes proteins destined for the Golgi apparatus, secretion, plasma membrane, and lysosomes

● Prominent in cells specialized for the synthesis of proteins destined for secretion (e.g., pancreatic acinar cells, chief cells of stomach)

122525 >>> 0:03:55.2 SLIDE 6 of 24

Smooth Endoplasmic Reticulum (SER)

● Network of membranous sacs continuous with RER but lack ribosomes

● Contains many enzymes involved in detoxification, glycogen degradation, gluconeogenesis, lipid metabolism, and sequestration and release of Ca2+

122530 >>> 0:04:26.2 SLIDE 7 of 24



Golgi Apparatus

● Consists of disc-shaped smooth cisternae assembled into stacks

● Proteins released by the RER into this complex ● Two distinct faces

❍ the cis (forming) face--convex shape ❍ The trans (maturing) face--concave shape,

contains the trans-Golgi network (TGN)

122535 >>> 0:05:14.2 SLIDE 8 of 24

Functions of the Golgi Apparatus

● Site of post-transcriptional modification and sorting of newly synthesized lipids and proteins

● Modification of the carbohydrate moiety of glycoproteins which is used to determine the destination of different glycoprotein types

● Two diseases result from malfunction of Golgi apparatus

❍ I-cell disease--lack of mannose-6-phosphate on lysosomal hydrolases

❍ Hyperproinsulinemia--defect of peptidase in the Golgi region causing elevated concentrations of serum pro-insulin

122540 >>> 0:06:16.2 SLIDE 9 of 24



Lysosomes

● Spherical membrane-enclosed organelles containing 60 different hydrolytic enzymes

● Primary lysosomes--inactive, formed by budding from trans side of Golgi

● Secondary lysosomes--formed after fusing with substance to be degraded

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Peroxisomes

● Heterogeneous group of small, spherical organelles ● Contain enzymes responsible for transfer of

hydrogen atoms to molecular oxygen to form hydrogen peroxide

● Catalase is the major peroxisomal enzyme ● Synthesized on free polysomes ● Functions include synthesis and degradation of

hydrogen peroxide, β-oxidation of fatty acids, phospholipid exchange, and bile acid synthesis

● Peroxisome deficiency

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Mitochondria

● Only cytoplasmic organelle to have two membranes, synthesize ATP, contain own dsDNA, make some of their own proteins

● Outer membrane--contains channels formed by porins

● Inner membrane--impermeable to most ions due to high lipid cardiolipin

● Cristae--numerous infoldings of inner membrane, involved in election transport

● Metabolic activity proportional to number of cristae per mitochondrion

122555 >>> 0:09:48.2 SLIDE 12 of 24

Mitochondria

● Intermembrane compartment--space between inner and outer membranes and contains enzymes that use ATP to phosphorylate other nucleotides

● Matrix--enclosed by inner membrane, contains dehydrogenases used to oxidize, causes regeneration of NAD+ and FAD

● Maternal transmission of mitochondrial DNA ● Most mitochondrial proteins synthesized in the cytoplasm ● Intramitochondrial granules--may represent storage of Ca2+ and Mg2+ ions

122560 >>> 0:11:13.2 SLIDE 13 of 24

Cytoskeleton

● Provides supportive network composed of microtubules, intermediate filaments, and microfilaments

● Microtubules ❍ Found in all eukaryotic cells ❍ Tubulin polymers--rapid assembly and disassembly of α-tubulin and β-tubulin ❍ Defective in Chédiak-Higashi syndrome ❍ Important in spindle formation during meiosis and mitosis ❍ Involved in intracellular vesicle and organelle transport ❍ Kinesin and dynein--ATPases responsible for generating force that drives



transport ❍ Utilized in ciliary and flagellar movement

122565 >>> 0:12:44.2 SLIDE 14 of 24

Cytoskeleton

● Intermediate filaments ❍ Cellular role primarily structural but contain several tissue-specific proteins

■ Cytokeratins, desmin, vimentin, neurofilaments, and glial fibrillary acidic protein

❍ Microfilaments ■ Composed of F-actin and G-actin ■ Two types of movement

■ Local movement (e.g., endocytosis, phagocytosis, cytokinesis, and, amoeboid movement)--inhibited by cytochalasin B

■ Sliding filament movement--actin in almost every cell

122570 >>> 0:14:26.2 SLIDE 15 of 24

Cell Surface

● Basement Membrane ❍ Sheet-like structure underlying all epithelia ❍ Basal lamina--composed of type IV collagen,

proteoglycans, glycoproteins (laminin) ❍ Reticular lamina--composed of delicate

reticular fibers

122575 >>> 0:15:01.2 SLIDE 16 of 24



122580 >>> 0:15:08.2 SLIDE 17 of 24

Lateral Surface Specializations

● Tight Junction (Zonula Occludens) ❍ Formed by fusion of opposed cell

membranes ❍ Constitutes the anatomic component of many

barriers in the body ❍ Note the sealing strands on freeze-fracture

micrograph ● Zonula Adherens

❍ Lies basal to zonula occludens ❍ Band-like junction that serves in attachment

of adjacent epithelial cells

122585 >>> 0:16:00.2 SLIDE 18 of 24



Lateral Surface Specialization

● Desmosomes (Macula adherens) ❍ Formed by juxtaposition of two disc shaped

plaques contained within the cytoplasm of each adjacent cell

❍ Intermediate filaments (tonofilaments) radiate away from the plaque

❍ Desmosomes--most common, hold cells together

122590 >>> 0:16:32.2 SLIDE 19 of 24

Gap Junctions

● Area of communication between adjacent cells ● Allows passage of very small particles and ions ● Hexagonal lattice of tubular protein subunits called

connexons

122595 >>> 0:16:57.2 SLIDE 20 of 24

Gap Junctions

● Connexons create hydrophilic channels connecting the cytoplasm of adjacent cells

● Permit the direct passage of ions and small molecules between cells to conduct electrical impulses

● A.k.a. "communicating junctions" ● Well-developed in tissues where cells are

electrically coupled (e.g., cardiac and smooth muscle)



122600 >>> 0:17:27.2 SLIDE 21 of 24

Apical (Free) Surface Specializations

● Microvilli ❍ Apical cell surface evaginations ❍ Thick glycocalyx coat ❍ Contain actin microfilaments ❍ Anchored in apical cell cytoplasm to terminal

web which is anchored to zonula adherens of cell membrane

122605 >>> 0:18:03.2 SLIDE 22 of 24

Apical Surface Specializations

● Cilia ❍ Apical cell surface projections of the cell

membrane that contain microtubules ❍ Inserted on centriole-like basal bodies

present below the membrane surface ❍ Contain two central microtubules surrounded

by a circle of nine peripheral microtuble doublets

122610 >>> 0:18:28.2 SLIDE 23 of 24



Movement of Cilia

● Peripheral doublets are fused so that they share a common tubule wall and form two subtubules, A and B

● Adjacent doublets are connected to one another by nexin links

● Movement results from interaction of dynein arms with B subtubules

● Pair of dynein arms attached to each A subtubule arms bind to ATP adjacent doublets slide

● Cilia move back and forth to propel fluid and particles in one direction

● Important in clearing mucus from the respiratory tract`

122615 >>> 0:19:18.2 SLIDE 24 of 24

Kartagener's Syndrome

● Aberrant dynein arms in cilia and flagella ● "Immobile cilia syndrome"

❍ Chronic sinusitis ❍ Bronchiectasis ❍ Infertility ❍ Situs inversus




Topic > Histology & Cytology: Nervous & Muscle Tissue

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Topic > Histology & Cytology: Lymphoid Organs & Integument

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USMLE Step 1 Web Prep - Lymphoid Organs & Integument

USMLE Step 1 Web Prep — Lymphoid Organs & Integument122730 >>> 0:00:07.2

SLIDE 1 of 9

Lymphoid Organs

Thymus

● Encapsulated and contains trabeculae ● Cortical and medullary regions ● Derived from 3rd pharyngeal arch ● Located in anterior mediastinum, usually superior,

atrophied in adults ● Lacks germinal centers ● Protects developing T cells by the blood-thymus

barrier

122735 >>> 0:00:59.2 SLIDE 2 of 9

Lymph Node

● Outer cortex contains most of the nodules and numerous germinal centers

● Populated mostly by B lymphocytes in the germinal center

● Paracortex populated by T lymphocytes 'thymic dependent area'

● Contains dendritic cells which act as antigen presenting cells

● High endothelial veins are the site of repopulation of lymph nodes (paracortical)

122740 >>> 0:02:00.2 SLIDE 3 of 9

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Spleen

● Extensive blood supply ● White pulp

❍ Lymphoid tissue, ensheaths central arteries and associated nodules and germinal centers

❍ Periarterial sheath populated mostly by T lymphocytes

❍ Peripheral white pulp and germinal centers populated mainly by B lymphocytes

122745 >>> 0:02:35.2 SLIDE 4 of 9

Spleen

● Red pulp ❍ Consists of splenic cords and venous sinusoids ❍ Defective RBC trapped in splenic cords are destroyed by macrophages ❍ Healthy RBC leave through splenic vein unchanged and go to liver ❍ Breakdown product of RBC is bilirubin which is later conjugated in the liver

122750 >>> 0:03:19.2 SLIDE 5 of 9

Integument

● Skin (epidermis and dermis) ● Associated appendages (sweat glands, sebaceous glands, hairs, and nails)

122755 >>> 0:03:37.2 SLIDE 6 of 9



Epidermis

● Ectodermal origin ● Five layers

❍ Stratum basale (germanativum) ❍ Stratum spinosum ❍ Stratum granulosum ❍ Stratum lucidum ❍ Stratum corneum

122760 >>> 0:04:05.2 SLIDE 7 of 9

Epidermis--Cell Types

● Keratinocytes--principle cell type, responsible for production of keratin proteins ● Melanocytes--derivatives of neural crest ectoderm, produce melanin but distribute it

to the keratinocytes ● Langerhans cells--antigen presenting cells ● Merkel cells--function in concert with nerve fibers

Epidermis lacks blood vessels and contains free nerve endings

122765 >>> 0:05:16.2 SLIDE 8 of 9

Dermis

● Mesodermal origin ● Contains receptors

❍ Meissner's corpuscle--touch receptors ❍ Pacinian corpuscle--receptors for vibration ❍ Both receptors associated with primary sensory neurons and convey

information back to spinal cord

Hypodermis

● Layer of loose vascular tissue infiltrated with adipocytes

122770 >>> 0:05:51.2



SLIDE 9 of 9 Table I-5-1. Features of Eccrine and Apocrine Sweat Glands

Eccrine ApocrineSize 0.4 mm diameter 3-5 mm diameter

Location Essentially everywhere with some exceptions (e.g., glans penis)

Axillary, areolar, and anal region

Site of opening Skin surface Hair follicles

DischargeWatery, little protein, mainly H2O, NaCl, urea, NH3, uric acid Viscous, odor producing

Innervation Cholinergic Adrenergic




Topic > Anatomy: Gonad - Embryonic

View all 15 Slides Kaplan USMLE Step 1 Web Prep / USMLE Step 1 Web Prep — Gonad - Embryonic



USMLE Step 1 Web Prep - Gonad - Embryonic

USMLE Step 1 Web Prep — Gonad - Embryonic122880 >>> 0:00:00.2

SLIDE 1 of 15

Gonad Development

● Primordial germ cells arise in the wall of the yolk sac

● At week 4 germ cells migrate into the indifferent gonad

● Forms a longitudinal elevation of intermediate mesoderm called urogenital ridge

● Develop into either testes or ovary

122885 >>> 0:00:28.2 SLIDE 2 of 15

Testes--development directed by three factors

● Testes determining factor (TDF) which is encoded by the Sry gene on the short arm of the Y chromosome

● Testosterone which is secreted by Leydig cells ● Müllerian-inhibiting factor (MIF) secreted by Sertoli cells, repress

development of structures that develop from paramesonephric duct

Ovary--indifferent gonad develops into ovary in the absense of factors

IMAGE TO COME

122890 >>> 0:01:13.2 SLIDE 3 of 15

Meiosis

● Produces male gamete (spermatogenesis) and female gamete (oogenesis)

● Consists of 2 cell divisions, meiosis I and meiosis II

IMAGE TO COME

122895 >>> 0:01:30.2 SLIDE 4 of 15



Meiosis I

● S phase prior to meiosis I where DNA replication occurs

● During prophase ❍ Synapsis occurs--46 homologous

chromosomes pair off ❍ Crossing over--exchange of segments of

DNA ❍ Disjunction--separation of chromosomes

without centromere splitting ● During metaphase and anaphase

❍ Chromosome number decreases from 46 to 23

❍ Total DNA not changed since duplicate

122900 >>> 0:02:29.2 SLIDE 5 of 15

Meiosis II

● Disjunction occurs with centromere splitting resulting in normal size chromosomes

● No DNA replication prior to meiosis II ● Gametes each contain half the chromosome

number and half the original DNA

122905 >>> 0:03:01.2 SLIDE 6 of 15

Spermatogenesis

● Primordial germ cells arrive at indifferent gonad at week 4, remain dormant until puberty

● At puberty, cells differentiate into type A spermatogonia—serve as stem cells for life ● Some type A spermatogonia develop into type B spermatogonia which enter meiosis

I to form primary spermatocytes ● Each primary spermatocyte forms two secondary spermatocytes



● Each secondary spermatocyte forms two spermatids ● Spermatids undergo spermiogenesis—resulting in mature sperm

122910 >>> 0:03:48.2 SLIDE 7 of 15

Oogenesis

● Primordial germ cells arrive in indifferent gonad at week 4, differentiate into oogonia ● Oogonia enter meiosis I to form primary oocytes (all formed by month 5 of fetal life) ● Arrested in prophase (diplotene) of meiosis I until puberty ● At puberty, each month, a primary oocyte completes meiosis I to form a secondary

oocyte and polar body ● Secondary oocyte arrested in meiosis II (metaphase) ● Process will not complete unless fertilization occurs in uterine tube, then completes

meiosis II to form mature oocyte and polar body

122915 >>> 0:05:20.2 SLIDE 8 of 15

Week 1: Beginning of Development Zygote formation

● Fertilization occurs in the ampulla of uterine tube ● After fertilization male and female pronuclei fuse to

form zygote

Cleavage

● Series of mitotic divisions creating increasing smaller blastomeres (Blastula)

● At the 32 cell stage formation of morula with its inner cell mass and outer cell mass

● Blastocyst forms when fluid secreted with the morula foms the blastocyst cavity

❍ Inner cell mass becomes embryoblast--forms embryo

❍ Outer cell mass becomes trophoblast--forms part of placenta

122920 >>> 0:06:24.2



SLIDE 9 of 15

Implantation

● Zona pellucida must degenerate for implantation to occur

● Blastocyst usually implants within the posterior wall of the uterus

● Implants within the functional layer of the endometrium during the secretory (progestational) phase of menstrual cycle

● Trophoblast differentiates into the cytotrophoblast and syncytiotrophoblast (secretes human chorionic gonadotropin which maintains the corpus luteum)

122925 >>> 0:07:03.2 SLIDE 10 of 15

Week 2: Formation of Bilaminar Embryo Bilaminar Embryonic Disk

● Embryoblast differentiates into the epiblast and hypoblast

● Amniotic cavity forms above the epiblast ● Yolk sac forms below the hypoblast

Growth into the endometrium

● Syncytiotrophoblast continues its growth into the endometrium to make contact with endometrial blood vessels and glands

● No mitosis occurs in the syncytiotrophoblast (inside the cytotrophoblast)

● Cytotrophoblast is mitotically active

122930 >>> 0:08:03.2 SLIDE 11 of 15

Extraembryonic Mesoderm and Chorion Formation

● New layer of cells derived from the epiblast ● Extraembryonic somatic mesoderm lines the cytotrophoblast, forms the connecting



stalk, and covers the amnion ● Extraembryonic visceral mesoderm covers the yolk sac ● Connecting stalk suspends the conceptus within the chorionic cavity ● Wall of chorionic cavity is called the chorion, which consists of extraembryonic

somatic mesoderm, cytotrophoblast, and syncytiotrophoblast

122935 >>> 0:08:41.2 SLIDE 12 of 15

Weeks 3-8: Embryonic Period Gastrulation

● Process that establishes the three primary germ layers--ectoderm, mesoderm, and endoderm

● Cells migrate toward the primitive groove and give appearance as primitive streak

● Some cells displace hypoblast endoderm ● Other epiblast cells fill space between epiblast and

hypoblast mesoderm ● Cells left behind ectoderm

122945 >>> 0:09:55.2 SLIDE 13 of 15

Ectoderm

● Gives further rise to neuroectoderm and neural crest cells

Mesoderm

● Gives rise to paraxial mesoderm--form somites ● Intermediate mesoderm ● Lateral mesoderm

Endoderm

122950 >>> 0:10:24.2 SLIDE 14 of 15

Organ Systems Development

● All major organ systems begin to develop during the embryonic period



● Craniocaudal and lateral body folding ● By week 8, embryo has distinct human appearance

122940 >>> 0:10:43.2 SLIDE 15 of 15

Table II-4-1. Development of the Fetal Structures From the Three Germ Layers Ectoderm Mesoderm EndodermEpidermis, hair, nails Cochlear duct, semicircular ducts Enamel of teeth Adenohypophysis Lens of the eye Parotid gland Mammary glands Epithelial lining of lower anal canal

Muscle (smooth, cardiac, skeletal) Extraocular muscles (preotic somites) Muscles of the tongue (occipital somites) Connective tissue, dermis of skin Bone, cartilage Blood and lymph vessels Heart Adrenal cortex Spleen Kidney Dura mater Testes, ovaries

Epithelial lining of:Gastrointestinal tract Trachea, bronchi, lungs Biliary apparatus Urinary bladder, urethra Vagina Auditory tube Middle ear cavity Parenchyma of:Liver Pancreas Submandibular gland Sublingual gland Thyroid Parathyroid

Neuroectoderm:

All neurons within brain and spinal cord Retina Neurohypophysis Astrocytes, oligodendrocytes

Neural crest:

Ganglia: dorsal root, cranial, autonomic Schwann cells Pia and arachnoid Adrenal medulla Parafollicular cells (calcitonin) Aorticopulmonary septum Dilator and sphincter pupillae mm. Ciliary muscle

Further detail of the development into adult structures is presented in the gross anatomy section.


USMLE Step 1 Web Prep - Back & Nervous System

USMLE Step 1 Web Prep — Back & Nervous System122955 >>> 0:00:00.2

SLIDE 1 of 10

Vertebral Column

● Embryology ❍ Sclerotome cells migrate medially to

surround the spinal cord and notochord during the fourth week of development

❍ Notochord persists in the areas between the vertebral bodies, forming the nucleus pulposus

● Vertebrae ❍ 7 cervical ❍ 12 thoracic ❍ 5 lumbar ❍ 5 sacral ❍ Sometimes 2 coccygeal

122960 >>> 0:00:40.2 SLIDE 2 of 10

Intervertebral Foramen

● Contains spinal cord ● Formed by lamina, pedicles, and vertebral body ● Bounded superiorly and inferiorly by the pedicles ● Transmits the spinal nerves

Intervertebral Disks

● Nucleus pulposus surrounded by annulus fibrosus ● Herniation is almost always in a posterolateral

direction ● Passing through a rupture in the annulus fibrosus ● Since not reinforced posteriolaterally, herniated

nucleus often comes to lie in the intervertebral foramen where it may compress a spinal nerve

● Zygapophyseal joint disease can also compress spinal nerves

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122965 >>> 0:01:54.2 SLIDE 3 of 10

Spinal Nerves and Spinal Cord Spinal Nerves

● Arise from the spinal cord by way of dorsal and ventral roots

● Dorsal root ❍ Contains sensory nerve fibers with cell

bodies in the dorsal root ganglion ❍ Conveys information from periphery to spinal

cord ● Ventral root

❍ Contains motor fibers with cell bodies in the gray matter of the spinal cord

❍ Conveys information from spinal cord to periphery

● Spinal nerves divide into rami ❍ Dorsal rami innervate deep muscles of the

back and overlying skin ❍ Ventral rami make up all the major plexuses

in the body ❍ Each contains both sensory and motor fibers

122970 >>> 0:03:57.2 SLIDE 4 of 10

Spinal cord

● Made up of gray and white matter ● Gray matter

❍ "Butterfly" shaped ❍ Contains cell bodies and interneurons

● White matter ❍ Surrounds gray matter ❍ Contains ascending and descending tracts

122975 >>> 0:04:32.2



SLIDE 5 of 10 Meninges

● Pia Mater ❍ Innermost layer fused to surface of the spinal cord ❍ External to this is the subarachnoid space which is filled with CSF

● Arachnoid layer ● Dura Mater

❍ Outermost layer, strongest ❍ Normally no subdural space, but such a space can be created when bleeding

occurs into this space ❍ External to the dura is the epidural space--contains fat and veins

Cauda Equina

● Below the inferior limit of the spinal cord at L1-L2, but within the subarachnoid space is the cauda equina which is composed of dorsal and ventral roots

122980 >>> 0:05:37.2 SLIDE 6 of 10

Lumbar Puncture

● Needle is passed through the interlaminar space in the midline while the vertebral column of the patient is flexed

● Needle must pass through the following layers: ❍ Skin superficial fascia deep fascia supraspinous

ligament interspinous ligament interlaminar space epidural space dura arachnoid subarachnoid space (contains CSF)

122985 >>> 0:06:20.2 SLIDE 7 of 10



Autonomic Nervous System

● Responsible for the motor innervation of smooth muscle, cardiac muscle, and glands of the body

● Composed of two divisions ❍ Sympathetic ❍ Parasympathetic

● Both divisions have two neurons in the peripheral distribution of the motor innervation

❍ Preganglionic motor neuron with the cell body in the CNS

❍ Postganglionic motor neuron with the cell body in a ganglion in the peripheral nervous system which innervates the target organ

122990 >>> 0:07:34.2 SLIDE 8 of 10

Sympathetic Nervous System

● Thoracolumbar outflow ● Preganglionic nerve cell bodies lie within the spinal cord

from T1-L2 ● Most preganglionic fibers synapse in the sympathetic

chain parallel to the spinal cord ● Some preganglionic fibers pass through sympathetic

chain and innervate the GI tract where they synapse in ganglia in the abdomen “prevertebral ganglia”

● Outflow at T1 has preganglionic fibers that run up sympathetic chain and synapse in the superior cervical ganglion

● Postganglionic fibers from here innervate areas of the head including sweat glands and two eye muscles: dilator pupillae and superior tarsal muscle

❍ Damage to these fibers can result in Horner's syndrome

122995 >>> 0:09:25.2 SLIDE 9 of 10



Sympathetic Outflow

● Preganglionic sympathetic cell bodies are found in the lateral horn of the gray matter of the spinal cord

● Outflow pass through ventral root spinal nerve white rami communicantes sympathetic chain

● Postganglionic sympathetic flows back to spinal cord through gray rami communicantes

123000 >>> 0:10:05.2 SLIDE 10 of 10

Parasympathetic System

● Craniosacral outflow ● Preganglionic cell bodies either in brain stem or

come from S2-S3-S4 (pelvic splanchnics) ● Cranial nerve III outflow

❍ Originates in Edinger-Westfall nucleus of midbrain

❍ Efferent limb of pupillary response and near response (accommodation)

● Cranial nerve VII outflow ❍ Damage to this pathway results in inability to

produce tears ● Cranial nerve IX innervates the parotid gland,

thoracic, and abdominal viscera ● Cranial nerve X innervates down through thorax

and abdomen to the level of the left colic flexure ● S2-S3-S4 innervate below the left colic flexure




Topic > Anatomy: Thorax

View all 31 Slides Kaplan USMLE Step 1 Web Prep / USMLE Step 1 Web Prep — Thorax

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USMLE Step 1 Web Prep - Thorax

USMLE Step 1 Web Prep — Thorax123005 >>> 0:00:00.2

SLIDE 1 of 31 Chest Wall Breast

● Mammary gland ● Modified sweat gland specialized in women for the production and secretion of milk ● Variable amount of fat surrounds the glandular tissue and is responsible for the

shape and size of the female breast ● There are 15-20 lactiferous ducts

❍ Drains a glandular lobule of the breast tissue ❍ Radiate outward from the nipple ❍ Terminal portion of each duct, the lactiferous sinus, is dilated

● Cooper's ligaments ❍ Suspensory ligaments of the breast ❍ Attach mammary gland to skin and run from the skin to the deep fascia

123010 >>> 0:00:55.2 SLIDE 2 of 31

Breast Arterial and Lymphatic Supply Arterial Supply

● Most of the blood supply comes from branches of the internal thoracic artery ● Lateral thoracic and thoracoacromial branches of axillary artery also supply ● Intercostal arteries also contribute

Lymphatic drainage

● Extremely important ● Most lymph drains to axillary nodes of the pectoral group ● Those of the deep surface drain to the apical group of axillary nodes ● Medial surface lymph drains to parasternal nodes which accompany the internal

thoracic vessels

123015 >>> 0:01:41.2 SLIDE 3 of 31



Skeletal Structure--Ribs

● True ribs (1 - 7)--have costal cartilage ● False ribs (8 - 12) are not attached by costal

cartilage ● Floating ribs (11 - 12)

123020 >>> 0:02:26.2 SLIDE 4 of 31

Muscles and Nerves Intercostal Muscles

● External Intercostal Muscles--run anteriorly and inferiorly ● Internal Intercostal Muscles--run posteriorly and inferiorly ● Innermost Intercostal Muscles--deep layers

Intercostal Nerves

● Pass between the internal intercostals and innermost intercostals ● Run along costal groove which is the inferior border of the rib ● When performing thoracentesis must pass needle along superior margin of rib

123025 >>> 0:03:24.2 SLIDE 5 of 31

Respiratory System Embryology of the Lungs

● Forms from the laryngotracheal diverticulum in the ventral wall of the foregut

● Tracheoesophageal septum divides foregut into the esophagus and trachea

● Distal end of the laryngotracheal diverticulum enlarges to form the lung bud two bronchial buds main bronchi lobar bronchi segmental bronchi



● Tertiary bronchi related to bronchopulmonary segments of the lung

Tracheoesophageal Fistula

● Associated with esophageal atresia and polyhydramnios

● Most commonly located between the esophagus and distal third of the trachea (90%)

● Gagging and cyanosis from reflux of gastric contents; pneumonitis frequent

● Abdominal distention results from air entering the abdominal cavity

123030 >>> 0:05:15.2 SLIDE 6 of 31

Table III-2-1. The Four Stages of Lung Development Stage CharacteristicsGlandular (weeks 5–17) Respiration is not possible

Premature fetuses cannot survive

Canalicular (weeks 13–25) Respiration is not possible

Premature fetuses rarely survive

Terminal sac (weeks 24–birth) Type I and type II pneumocytes are present

Respiration is possible

Premature fetuses born between weeks 25 and 28 can survive with intensive care

Alveolar (birth–8 years)

Note: Lung development continues after birth

Respiratory bronchioles, terminal sacs, alveolar ducts, and alveoli increase in number

Chest radiograph is more dense in children

123035 >>> 0:06:14.2 SLIDE 7 of 31



Pleural Cavity

● Space between the parietal and visceral layers of pleura

● Introduction of air into the pleural cavity may cause the lung to collapse (pneumothorax)

Pleural Reflections

● Areas where the pleura change direction from one wall to the other

● Costal pleura is continuous with the mediastinal pleura behind the sternum

● Costal line of reflection is where the costal pleura becomes continuous with the diaphragmatic pleura from rib 8 in the midclavicular line, to rib 10 in the midaxillary line, and to rib 12 lateral to the vertebral column

123040 >>> 0:07:12.2 SLIDE 8 of 31

Pleural Recesses

● Potential spaces not occupied by lung tissue except during deep inspiration

● Costodiaphragmatic recess ● Costomediastinal recess

Innervation of Parietal Pleura

● Intercostal nerves supply the costal and peripheral portions of the diaphragmatic pleura

● Phrenic nerve supplies the central portion of the diaphragmatic pleura and the mediastinal pleura

123045 >>> 0:07:44.2 SLIDE 9 of 31



Lungs

● Right lung is divided into three lobes by the oblique and horizontal fissures into superior, middle, and inferior lobes

● Left lung is divided into two lobes by the oblique fissure into upper and lower lobes

● Bronchopulmonary segments ❍ Ten on the right ❍ Eight on the left ❍ Supplied by the segmental bronchus, artery,

and vein

123050 >>> 0:08:24.2 SLIDE 10 of 31

Lungs

● Arterial supply ❍ Right and left pulmonary arteries from the pulmonary trunk deliver

deoxygenated blood to the lungs ❍ Bronchial arteries branch from the thoracic aorta and supply the bronchi and

nonrespiratory portions of the lung ● Venous drainage

❍ Four pulmonary veins that carry oxygenated blood away from the lungs and into the left atrium of the heart

123055 >>> 0:08:54.2 SLIDE 11 of 31

Lungs

● Lymphatic drainage ❍ Superficial--to bronchopulmonary nodes and then to tracheobronchial nodes ❍ Deep--to pulmonary nodes and then to bronchopulmonary nodes

● Innervation ❍ Parasympathetic stimulation has bronchoconstrictor effect ❍ Sympathetic stimulation has bronchodilator effect

123060 >>> 0:09:30.2



SLIDE 12 of 31

Embryology of the Heart Formation of Heart Tube

● Lateral plate mesoderm fuses in the midline to form the primitive heart tube which becomes the endocardium of the adult heart

● Mesoderm surrounding primitive heart tube secretes cardiac jelly and forms the myocardium of the adult heart

● Mesoderm from coelomic wall forms the epicardium of the adult heart

● Primitive heart grows and bends to the right (dextral looping)

123065 >>> 0:10:01.2 SLIDE 13 of 31

Table III-2-2. Adult Structures Derived From the Dilatations of the Primitive Heart Embryonic Dilatation Adult Structure

Truncus arteriosusAorta

Pulmonary trunk

Bulbus cordisSmooth part of right ventricle (conus arteriosus)

Smooth part of left ventricle (aortic vestibule)

Primitive ventricleTrabeculated part of right ventricle

Trabeculated part of left ventricle

Primitive atriumTrabeculated part of right atrium

Trabeculated part of left atrium

Sinus venous

Smooth part of right atrium (sinus venarum)

Coronary sinus

Oblique vein of left atrium

123070 >>> 0:11:40.2



SLIDE 14 of 31

Atrial Septum

● Septum primum (SP) grows toward atrioventricular (AV) septum—gap between is called the foramen primum (FP); it is obliterated when the SP fuses with the AV septum

● Shortly thereafter foramen secundum (FS) forms in the center of SP

● Septum secundum (SS) forms to the right of the SP and fuses after birth with the SP to form atrial septum

● Foramen ovale (FO) is the opening between the upper and lower parts of the SS

❍ During fetal life, blood shunted from right atrium (RA) to left atrium (LA) through the FO and FS (right-to-left shunt)

❍ Closure takes place soon after birth; facilitated by increased LA pressure that results from changes in pulmonary circulation

123075 >>> 0:13:40.2 SLIDE 15 of 31

Interventricular septum

● Muscular Interventricular (IV) Septum develops in the floor of the ventricle and grows toward the AV cushions; opening is called IV foramen

123080 >>> 0:14:38.2 SLIDE 16 of 31



Truncus arteriosus

● Positioning occurs when neural crest cells migrate into truncal and bulbar ridges

● Form aorticopulmonary (AP) septum ● Membranous IV septum forms by fusion of right and

left bulbar ridges and AV cushion; closes the IV foramen

❍ Divides truncus into aorta and pulmonary trunk

❍ Forms in a spiral manner ❍ Results in correct positioning of pulmonary

trunk and aorta ● If AP septum does not form in spiral manner, may

cause transposition of great vessels

123085 >>> 0:15:26.2 SLIDE 17 of 31

Fetal Circulation

● Oxygenated blood from mother enters fetus through umbilical vein inferior vena cava RA through FO LA (1st right-to-left shunt) LV aorta most blood goes to brain

● Deoxygenated blood from head and neck superior vena cava RA RV pulmonary trunk shunted through ductus arteriosus aorta (2nd right-to-left shunt) return to placenta via umbilical arteries

● If ductus arteriosus fails to close after birth, results in a left-to-right shunt due to the increased system pressure

123090 >>> 0:16:55.2 SLIDE 18 of 31

Table III-2-3. Adult Vestiges Derived From the Fetal Circulatory System Changes After Birth Remnant in AdultClosure of right and left umbilical arteries Medial umbilical ligaments

Closure of left umbilical vein Ligamentum teres



Closure of ductus venosus Ligamentum venosum

Closure of foramen ovale Fossa ovale

Closure of ductus arteriosus Ligamentum arteriosum

*Between two medial umbilical ligaments lies the median umbilical ligament containing the urachus

123095 >>> 0:17:40.2 SLIDE 19 of 31

Mediastinum

● Middle Mediastinum contains ❍ Pericardium and heart ❍ Phrenic nerve (arises from ventral rami of

cervical nerves 3, 4, and 5) ● Anterior Mediastinum--contains fat and areolar

tissue ● Posterior Mediastinum contains

❍ Thoracic aorta with its bronchial, esophageal, and posterior intercostal branches

❍ Esophagus, throacic duct, and azygous system of veins

❍ Sympathetic trunks located paravertebrally, just outside the posterior mediastinum

123100 >>> 0:19:38.2 SLIDE 20 of 31

Mediastinum

● Superior Mediastinum contains ❍ Thymus, which usually atrophies in the adult ❍ Superior vena cava ❍ Arch of the aorta with three branches:

brachiocephalic trunk, left common carotid, and left subclavian artery

❍ Vagus, trachea, esophagus, and thoracic duct

123105 >>> 0:20:39.2



SLIDE 21 of 31

Heart Borders of the Heart

● Right border formed by RA ● Left border formed by LV and auricle of LA ● Superior border formed by right & left auricles and

the conus arteriosus of the RV ● Apex is the tip of LV ● Anterior wall is formed primarily by RV ● Posterior wall formed by LA

123110 >>> 0:21:25.2 SLIDE 22 of 31

Chambers of the Heart

Refer to page 140 of Anatomy Lecture Notes

123115 >>> 0:22:48.2 SLIDE 23 of 31

Surface Projections of Heart Sounds

● Aortic and Pulmonic valves project mainly through the 2nd intercostal space on each side of the sternum (right and left respectively)

● Tricuspid valve projects through the sternum near the level of the 5th intercostal space

● Mitral valve projects at the 5th intercostal space in the midclavicular line

123120 >>> 0:23:21.2 SLIDE 24 of 31



Arterial Supply of the Heart Right Coronary Artery

● Supplies the RA, RV, SA node, AV node, and parts of the LA and LV

Left Coronary Artery

● Divides into two branches ❍ Anterior interventricular (descending) artery ❍ Circumflex artery

● Supplies most of the LV, LA, and the interventricular septum

123125 >>> 0:24:09.2 SLIDE 25 of 31

Venous Drainage of the Heart

● Coronary sinus ❍ Main vein of the coronary circulation ❍ Travels in posterior coronary sulcus ❍ Drains in RA

● Great cardiac vein ● Small cardiac vein ● Middle cardiac vein

123130 >>> 0:24:35.2 SLIDE 26 of 31



Conducting System of the Heart

● SA node ❍ Located at superior end of the cristae

terminalis where SVC enters RA ❍ Supplied by nodal branch of right coronary

artery ● AV node

❍ Located in the interatrial septum near the opening of the coronary sinus

❍ Signal is delayed here going to His bundle

123135 >>> 0:25:33.2 SLIDE 27 of 31

Conducting System of the Heart

● Bundle of His ❍ Conducts impulses to bundle branches

● Right and left bundle branches ❍ Supply RV and LV respectively ❍ Moderator band, found in the RV, contains

the right bundle branch ● Purkinje fibers

Innervation

● Sympathetic stimulation increases heart rate ● Parasympathetic stimulation decreases heart rate

123140 >>> 0:26:24.2 SLIDE 28 of 31



Diaphragm

● Composed of muscular portion and central tendon ● Innervated by phrenic nerve arising from segments

C3-C4-C5 ● Apertures

❍ Caval hiatus--at T8: transmits IVC, and right phrenic nerve

❍ Esophageal hiatus--at T10: transmits esophagus, anterior, and posterior vagus nerves

❍ Aortic hiatus--at T12: transmits aorta, azygous vein, and thoracic duct

123145 >>> 0:27:25.2 SLIDE 29 of 31

Posterioanterior view of chest Identify structures:

● Aortic arch ● Left pulmonary artery ● Border of right atrium ● Left atruim ● Left ventricle

123150 >>> 0:27:47.2 SLIDE 30 of 31



Chest CT at T6 Note positions:

● RV is most anterior chamber ● LA is most posterior chamber ● RA is right border of heart ● Descending aorta displayed slightly left of vertebral

column ● Esophagus directly behind heart

123155 >>> 0:28:41.2 SLIDE 31 of 31

On all scans

● Major vessels ❍ Aorta (arch, ascending, descending parts) ❍ SVC, brachiocephalic artery and vein ❍ Left common carotid and left subclavian arteries ❍ Pulmonary arteries and trunk

● Major heart chambers ● Major structures

❍ Esophagus, trachea ● Major bony structures

❍ Scapula, ribs




Topic > Anatomy: Upper Limbs

View all 15 Slides Kaplan USMLE Step 1 Web Prep / USMLE Step 1 Web Prep — Upper Limbs

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USMLE Step 1 Web Prep - Upper Limbs

USMLE Step 1 Web Prep — Upper Limbs123160 >>> 0:00:00.2

SLIDE 1 of 15

Upper Limb Brachial Plexus

● Suprascapular nerve branches off the superior trunk

● Musculocutaneous nerve branches off the lateral cord

● Median nerve branches off the lateral and medial cords

● Ulnar nerve branches off medial cord ● Median nerve branches off the lateral and medial

cords ● Radial nerve branches off the posterior cord ● Axillary nerve branches off the posterior cord ● Long thoracic nerve branches off nerve roots C6-

C7-C8

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Lesions of the Brachial Plexus Upper Trunk (C5, C6)

● Erb’s palsy results ● Arm is medially rotated, abducted, extended, and

pronated due to injury ● Axillary, suprascapular, and musculocutaneous

nerves involved ● Lateral rotators, flexors, and abductors affected ● “Waiter’s tip” or “Porter’s tip” sign

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Lower Trunk (C8, T1)

● Thoracic outlet syndrome results ● Involves muscles of the forearm and hand ● "Claw hand" or "Ape hand" sign ● May include a Horner's syndrome ● Could be combined with flattening of the thenar

eminence if T1 involved

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Table III-4-1. The Motor Innervation by the Five Terminal Nerves Terminal Nerve Muscles InnervatedMusculocutaneous nerve All the muscles of the anterior compartment of the arm

Median nerve

All the muscles of the anterior compartment of the forearm except 1 [1//2] muscles (flexor carpi ulnaris and the ulnar [1/2] of the flexor digitorum profundus)

The 3 thenar compartment muscles and the 1st and 2nd lumbricals

Ulnar nerveThe 1[1/2] muscles of the forearm not innervated by the median nerve

All the muscles of the hand except those innervated by the median nerve

Axillary nerve Deltoid and teres minor

Radial nerve The posterior muscles of the arm and forearm

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Table III-4-2. The Collateral Nerves of the Brachial Plexus Collateral Nerve Muscles or Skin InnervatedDorsal scapular nerve Rhomboids

Long thoracic nerve Serratus anterior

Suprascapular nerve Supraspinatus and infraspinatus

Lateral pectoral nerve Pectoralis major

Medial pectoral nerve Pectoralis major and minor

Upper subscapular nerve Subscapularis



Middle subscapular (thoracodorsal) nerve Latissimus dorsi

Lower subscapular nerve Subscapularis and teres major

Medial brachial cutaneous nerve Skin of medial arm

Medial antebrachial cutaneous nerve Skin of medial forearm

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Sensory Innervation of the Hand

● Palmar surface ❍ Radial nerve--1st dorsal web space ❍ Median nerve--lateral palm and anterior

surface of index and middle fingers ❍ Ulnar nerve--medial palm

● Dorsal surface ❍ Ulnar nerve--medial surface ❍ Median nerve--lateral surface

● Nail beds--branch of the median nerve ● Index finger--dual innervation by median and radial

nerves

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Nerve Injuries

● Radial nerve at: ❍ Axilla--loss of extensors at the elbow, wrist and digits

■ Weakened extension at the shoulder ■ Weakened supination ■ Sensory loss of posterior arm, forearm, and hand ■ Cardinal sign: "wrist drop"

❍ Elbow--loss of extensors at the wrist and digits ■ Mimics injury caused by fracture of humerus lacerating radial nerve ■ Sign is "wrist drop" without shoulder involvelment

❍ Wrist--sensory loss on posterior hand in 1st dorsal web space

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Nerve Injuries

● Median nerve at: ❍ Elbow—loss of flexion of the digits, thenar muscles, and 1st and 2nd

lumbricals; no loss at shoulder or elbow ■ Loss of opposition of thumb ■ Flattening of thenar eminence ■ Cardinal sign: "Ape hand"

❍ Wrist--only affect muscles of the hand ■ Occurs in the carpal tunnel ■ No sensory loss for the palm of the hand--innervation does not pass

through carpal tunnel ■ Sign is "Ape hand"

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Nerve Injuries

● Ulnar nerve at: ❍ Elbow--loss of abduction and adduction of digits; no loss at shoulder or elbow

■ Cardinal sign: "claw hand" of 4th and 5th digits ❍ Wrist--loss of abduction and adduction of digits

■ Loss of 3rd and 4th lumbricals ■ Loss of interossei muscles

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Nerve Injuries

● Musculocutaneous nerve at: ❍ Axilla

■ Greatly weakened shoulder flexion ■ Severely weakened flexion at elbow due to involvement of biceps

brachii and brachialis muscles ■ Greatly weakened supination ■ Sensory loss of lateral forearm

❍ Axillary nerve—loss of abduction of the arm from 7-70 degrees; results from damage caused by fracture of surgical neck of humerus



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Arterial Supply to the Upper Limb

● Subclavian artery ❍ Branch of brachiocephalic trunk ❍ Pass over 1st rib, under clavicle--changes

name to axillary artery ● Axillary artery

❍ From the 1st rib to lower edge of teres major--changes name to brachial artery

❍ Several branches ● Brachial artery

❍ A branch is profunda brachii artery which travels with radial nerve

❍ Also divides at the cubital fossa into radial and ulnar arteries

● Radial artery supplies the deep palmar arch ● Ulnar artery supplies the superficial palmar arch

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Collateral Circulation

● Shoulder--subscapular (axillary) and suprascapular (subclavian)

● Hand--palmar arches ● Mammaries--lateral thoracic artery is principle blood

supply to mammaries but would be ligated in radical mastectomy

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Joints of the Upper Limb Shoulder

● Note bony structures ● Scapula articulates with humerus at glenohumeral

joint ● Humeral head stabilized in glenoid fossa by rotator

cuff muscles ❍ Supraspinatus--initiates abduction ❍ Infraspinatus--lateral rotator ❍ Teres minor--lateral rotator ❍ Subscapularis--medial rotator

● Dislocation often inferior and may cause damage to axillary nerve

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Elbow

● Note bony structures ● Composed of humeroradial joint and humeroulnar

joint which permit flexion and extension ● Proximal radioulnar joint which permits pronation

and supination ● Dislocation may cause damage to ulnar and

median nerves as well as brachial artery resulting in “Volkman’s contracture” of the hand

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Wrist and Hand

● Carpal tunnel is space bounded by flexor retinaculum anteriorly and the carpal bones posteriorly

❍ Nine tendons pass through here ■ Four tendons of the flexor digitorum

superficialis ■ Four tendons of the flexor digitorum

profundus ■ Tendon of the flexor pollicis longus

❍ Median nerve also passes through just below flexor retinaculum

● Scaphoid bone is most frequently fractured--may cause avascular necrosis

● Lunate bone is most frequently dislocated anteriorly—may compress median nerve




Topic > Anatomy: Lower Limbs

View all 14 Slides Kaplan USMLE Step 1 Web Prep / USMLE Step 1 Web Prep — Lower Limbs

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USMLE Step 1 Web Prep - Lower Limbs

USMLE Step 1 Web Prep — Lower Limbs123235 >>> 0:00:00.2

SLIDE 1 of 14

Lower Limb Lumbosacral Plexus

● Femoral nerve--posterior divisions L2-L4 ● Obturator nerve--anterior divisions L2-L4 ● Tibial nerve--anterior divisions L4-S3 ● Common peroneal nerve--posterior divisions L4-S2 ● Tibial and common peroneal nerve travel together

as sciatic nerve; pass through greater sciatic foramen and course through thigh

● Common peroneal nerve divides above popliteal fossa

❍ Superficial peroneal nerve—supplies lateral surface and muscles of leg

❍ Deep peroneal nerve--supply anterior compartment of leg

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Table III-5-1(a). Terminal Nerves of Lumbosacral Plexus Terminal Nerve Origin Muscles InnervatedFemoral nerve L2 through L4 posterior divisions Anterior compartment of thigh (quadriceps femoris,

sartorius, pectineus)

Obturator nerve L2 through L4 anterior divisions Medial compartment of thigh (gracilis, adductor longus, adductor brevis, anterior portion of adductor magnus)

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Table III-5-1(b). Terminal Nerves of Lumbosacral Plexus Terminal Nerve Origin Muscles Innervated

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Tibial nerve L4 through S3 anterior divisions

Posterior compartment of thigh (semimembranosus, semitendinosus, long head of biceps femoris, posterior portion of adductor magnus)

Posterior compartment of leg (gastrocnemius, soleus, flexor digitorum longus, flexor hallucis longus, tibialis posterior)

Plantar muscles of foot

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Table III-5-1(c). Terminal Nerves of Lumbosacral Plexus Terminal Nerve Origin Muscles Innervated

Common peroneal nerve L4 through S2 posterior divisions Short head of biceps femoris

Superficial peroneal nerve Lateral compartment of leg (peroneus longus, peroneus brevis)

Deep peroneal nerve Anterior compartment of leg (tibialis anterior, extensor hallucis, extensor digitorum, peroneus tertius)

123255 >>> 0:03:02.2 SLIDE 5 of 14

Table III-5-2(d). Collateral Nerves of Lumbosacral Plexus Collateral Nerve Origin Muscles or Skin InnervatedSuperior gluteal nerve L4 through S1 posterior divisions Gluteus medius, gluteus minimus, tensor

fasciae latae

Inferior gluteal nerve L5 through S2 posterior divisions Gluteus maximus

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Nerve Injuries

● Superior gluteal nerve ❍ Affects gluteus medius and minimus muscles ❍ Destabilizes pelvis ❍ Patient cannot keep pelvis level when standing on one leg ❍ "Trendelenburg gait"

● Inferior gluteal nerve



❍ Affects gluteus maximus ❍ Produces a weakened hip extension ❍ Difficulty rising from a sitting position, climbing stairs, or running

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Nerve Injuries

● Femoral nerve ❍ Affects quadriceps muscles ❍ Loss of extension of the knees ❍ Sensory loss of anterior thigh, medial leg, and foot (saphenous branch)

● Obturator nerve ❍ Loss of adduction of the thigh ❍ Sensory loss on medial thigh

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Nerve Injuries

● Sciatic nerve ❍ Loss of flexion of the knee and function below the knee ❍ Weakened extension of thigh

● Tibial nerve only ❍ Loss of plantar flexion of foot

● Common peroneal nerve only ❍ Affects dorsiflexion of foot ❍ Commonly damaged since passes around head of femur and injured during

trauma or improper cast placement ❍ Sign is "foot drop"

● Deep proneal nerve only--"foot drop" ● Superficial peroneal nerve only--loss of eversion of the foot

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Sensory Innervation of Lower Leg and Foot--Nerve Injuries

● Common peroneal nerve results in loss of sensation over the entire dorsum of the foot

● Tibial nerve results in loss of sensation to plantar surface of foot

● Femoral nerve results in loss of sensation to medial part of leg

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Arterial Supply and Major Anastamoses

● Cruciate anastamosis ❍ Inferior gluteal artery ❍ Profunda femoris artery ❍ Medial femoral circumflex artery ❍ Lateral femoral circumflex artery

● Popliteal artery passes deep within the popliteal fossa behind the knee

❍ May be damaged by supracondylar fracture of the femur

● Femoral triangle contains the femoral artery, femoral vein, and femoral nerve

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Joints of the Lower Limb Hip

● Ball and socket joint formed by the head of the femur and the acetabulum

● Dislocation is usually posterior--called "dashboard injury" and may injure the sciatic nerve

● Fracture may damage the neck of the femur and compromise the blood supply, which arises from the circumflex vessels, resulting in avascular necrosis of the head of the femur

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Joints of the Lower Limb Knee

● Formed by articulation of the medial and lateral femoral condyles, the medial and lateral tibial condyles and the patella

● Capsule is strengthened by the medial and lateral collateral ligaments which resist abduction and adduction

● Anterior cruciate ligament (intracapsular) ❍ Attaches to the anterior tibia and prevents its

anterior displacement ❍ Rupture results in "anterior drawer sign"

● Posterior cruciate ligament (intracapsular) ❍ Attaches to the posterior tibia and prevents

its posterior displacement

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Joints of the Lower Limb Knee

● Medial meniscus ❍ "C-shaped" ❍ More firmly anchored to tibia and attached to

medial collateral ligament ❍ More susceptible to injury since less mobile

● Lateral meniscus ❍ "O-shaped" ❍ Less firmly anchored and not attached to

lateral collateral ligament ● Terrible triad

❍ Tear in the medial collateral ligament, medial meniscus, and anterior cruciate ligament

123300 >>> 0:11:20.2 SLIDE 14 of 14

Joints of the Lower Limb

● Talocrural joint ❍ Formed by the distal ends of the tibia and

fibula and the talus ❍ "Hinge joint"--dorsiflexion and plantar flexion

occur here ❍ Medial collateral (deltoid) ligament prevents

abduction and when sprained results in an eversion injury

❍ Lateral collateral ligament prevents adduction and when sprained results in an inversion injury (very common)

● Subtalar joint ❍ Compound joint formed by talocalcaneal joint

and the talocalcaneonavicular joint ❍ Inversion and eversion are permitted at this

joint ● Transverse tarsal joint


Histology, cytology & embryology & neuroscience overview

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