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Comprehensive Human Anatomy Guide

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1. Heart: Structure and Topography. Pericardium

Topography (Location)

• Superior: 2nd rib level (great vessels emerge here)
• Inferior: 5th intercostal space (apex beat felt here)
• Right border: Right atrium
• Left border: Left ventricle + left auricle

External Structure

• Anterior (sternocostal): Mainly RV
• Posterior (base): Mainly LA
• Inferior (diaphragmatic): RV + LV
• Apex: LV, points down-left to 5th intercostal space, mid-clavicular line

• Coronary sulcus (atrioventricular groove): Separates atria from ventricles; contains coronary arteries and coronary sinus
• Anterior interventricular sulcus: Front, separates two ventricles
• Posterior interventricular sulcus: Back, separates two ventricles

Internal Structure

• Receives SVC (superiorly) and IVC (inferiorly)
• Fossa ovalis — oval depression; remnant of foramen ovale (fetal)
• Crista terminalis — smooth muscle ridge
• Pectinate muscles — rough muscular ridges

• Inlet: tricuspid valve (3 leaflets)
• Trabeculae carneae (irregular muscle ridges)
• Papillary muscles → connect to tricuspid cusps via chordae tendineae (prevent valve eversion)
• Outlet: pulmonary valve (3 semilunar cusps) → pulmonary trunk

• Receives 4 pulmonary veins
• Smooth walls posteriorly; auricle is rough
• Outlet: mitral valve (bicuspid — 2 leaflets)

• Thickest wall (~3x thicker than RV — pumps systemic circulation)
• Inlet: mitral valve
• Outlet: aortic valve (3 semilunar cusps) → ascending aorta
• Interventricular septum — mostly muscular, upper part membranous

Pericardium

Fibrous pericardium (outer)
    ↓
Parietal layer of serous pericardium
    ↓
Pericardial cavity (contains ~15–50 mL of fluid — acts as lubricant)
    ↓
Visceral layer of serous pericardium = EPICARDIUM (directly on heart surface)

• Tough, inextensible connective tissue
• Attached inferiorly to central tendon of diaphragm
• Anteriorly attached to sternum by sternopericardial ligaments
• Fused with roots of great vessels (aorta, pulmonary trunk, SVC, IVC)
• Prevents overdistension of the heart

• Parietal layer lines the inside of fibrous pericardium
• Visceral layer (epicardium) covers the heart surface
• Between them: pericardial cavity with serous fluid

• Transverse pericardial sinus: Behind aorta + pulmonary trunk, in front of SVC; surgeons use it to clamp great vessels
• Oblique pericardial sinus: Behind the heart, between pulmonary veins and IVC; blind-ended recess

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2. Arch of the Aorta and Its Branches. Common, External & Internal Carotid Arteries. Subclavian Artery. Arterial Circle of the Brain

Aorta Overview

1. Ascending aorta (gives off coronary arteries)
2. Arch of aorta
3. Descending thoracic aorta
4. Abdominal aorta

Arch of the Aorta

Memory tip: "Bring Lunch, Come Supper Leaving" or simply: BraCh, LCC, LSC

Common Carotid Artery (CCA)

• Right CCA: Branch of brachiocephalic trunk
• Left CCA: Direct branch of aortic arch
• Both ascend in the carotid sheath (with internal jugular vein and vagus nerve)
• Bifurcate at the level of C4 (upper border of thyroid cartilage) into:
  • Internal carotid artery (ICA)
  • External carotid artery (ECA)

• Carotid sinus — baroreceptor (pressure sensor), on ICA origin
• Carotid body — chemoreceptor (O₂/CO₂ sensor)

External Carotid Artery (ECA)

Internal Carotid Artery (ICA)

• No branches in the neck
• Enters skull via carotid canal in petrous temporal bone
• Passes through cavernous sinus
• Enters cranial cavity and supplies the brain

• Ophthalmic artery → orbit and eye
• Anterior cerebral artery (ACA) → medial frontal/parietal lobe
• Middle cerebral artery (MCA) → lateral hemisphere (largest branch; most common stroke vessel)
• Posterior communicating artery (PComA) → connects to posterior circulation

Subclavian Artery

• Right: from brachiocephalic trunk
• Left: direct from aortic arch

Arterial Circle of the Brain (Circle of Willis)

Anterior communicating artery (AComA)
        |
Left ACA ←—→ Right ACA
        |
Left ICA           Right ICA
        |                   |
Left PComA         Right PComA
        |                   |
Left PCA ←—→ Right PCA
        |
Basilar artery (from two vertebral arteries)

Clinical: Most berry (saccular) aneurysms occur at junctions in the Circle of Willis — especially at the AComA (most common), followed by PComA.

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3. Thoracic Aorta. Axillary Artery. Arteries of the Upper Limb

Thoracic (Descending) Aorta

Axillary Artery

Arteries of the Upper Limb

Subclavian → Axillary → Brachial
                              |
               Radial ←———→ Ulnar
                    |              |
              Deep palmar arch ← Superficial palmar arch
                              |
                     Digital arteries

• Main artery of the arm (upper limb above elbow)
• Runs with median nerve in the medial bicipital groove
• Divides at the neck of radius (cubital fossa) into radial and ulnar arteries
• Profunda brachii = deep branch supplying posterior compartment (with radial nerve in spiral groove)

• Lateral forearm → wrist → "anatomical snuffbox" → palm
• Forms deep palmar arch (with deep branch of ulnar)
• Used for arterial blood gas sampling and coronary catheterization

• Medial forearm → enters hand via Guyon's canal
• Forms superficial palmar arch (main arch, with superficial branch of radial)

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4. Abdominal Aorta. Common, External & Internal Iliac Arteries. Lower Limb Arteries

Abdominal Aorta

Common Iliac Arteries

• External iliac artery → lower limb
• Internal iliac artery → pelvis

Internal Iliac Artery (Hypogastric)

• Superior/inferior vesical → bladder
• Uterine artery (females)
• Obturator → medial thigh
• Internal pudendal → perineum, external genitalia
• Inferior gluteal → gluteal region

• Superior gluteal → gluteal region (largest branch)
• Iliolumbar, lateral sacral

External Iliac Artery

• Inferior epigastric artery → anterior abdominal wall
• Deep circumflex iliac artery → iliac region

Lower Limb Arteries

Aorta (L4) → Common Iliac → External Iliac
                                    ↓
                            Femoral artery (in femoral triangle)
                                    ↓
                      Deep femoral (profunda femoris) ← thigh muscles
                                    ↓
                    Popliteal artery (behind the knee)
                          /                    \
              Anterior tibial            Posterior tibial
                      ↓                           ↓
              Dorsalis pedis             Peroneal (fibular)
              (dorsum of foot)           + Plantar arteries → plantar arch

• Main artery of the thigh
• Lies in the femoral triangle (bounded by inguinal ligament, sartorius, adductor longus)
• Deep femoral (profunda femoris): biggest branch — supplies thigh muscles and hip
• Passes through the adductor canal (Hunter's canal) → becomes popliteal artery

• Behind the knee in the popliteal fossa
• Terminates by dividing into anterior and posterior tibial arteries

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5. Superior and Inferior Vena Cava

Superior Vena Cava (SVC)

• Formed by union of right and left brachiocephalic (innominate) veins at the level of the right 1st costal cartilage
• Brachiocephalic veins are formed by union of the internal jugular vein + subclavian vein (at the angle of confluence = venous angle of Pirogov)
• SVC descends ~7 cm, enters the right atrium at the level of the 3rd costal cartilage
• Lower half of SVC is within the pericardium
• No valves
• Drains: head, neck, upper limbs, thoracic wall

• Left and right brachiocephalic veins
• Azygos vein (enters just before reaching RA)
• Small mediastinal and pericardial veins

Inferior Vena Cava (IVC)

• Formed at L5 by union of the two common iliac veins
• Ascends on the right of the aorta
• Passes through caval opening in diaphragm at T8
• Enters right atrium from below
• Contains a valve (valve of IVC / Eustachian valve) — rudimentary in adults

Note: The left gonadal vein and left suprarenal vein drain into the left renal vein, not directly into the IVC.

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6. Portal Vein. Venous Anastomoses. Fetal Circulation

Portal Vein

• Superior mesenteric vein (SMV) — from small intestine + right colon
• Splenic vein — from spleen + inferior mesenteric vein (left colon, sigmoid, rectum)

Porto-Systemic (Venous) Anastomoses

Fetal Circulation

Placenta (O₂ rich)
    → Umbilical vein
    → Ductus venosus (bypasses liver)
    → IVC
    → Right atrium
    → Foramen ovale → LEFT atrium (most of the oxygenated blood)
    → Left ventricle → Aorta → Body

Some blood: RA → RV → Pulmonary trunk
            → Ductus arteriosus → Aorta (bypasses lungs)

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7. Lymphatic System: Trunks, Tributaries, Regional Lymph Nodes, Thoracic Duct

Overview

• Returns interstitial fluid to blood
• Transports dietary fats (chylomicrons) from gut
• Provides immune surveillance

Lymphatic Trunks (9 paired/unpaired trunks):

Thoracic Duct

• Left + right lumbar trunks
• Intestinal trunk

1. Ascends through the aortic hiatus of the diaphragm (with aorta)
2. Runs in the posterior mediastinum between the aorta (left) and azygos vein (right)
3. At T5, crosses to the left side
4. Ascends behind the left carotid sheath
5. Terminates at the left venous angle (junction of left internal jugular + left subclavian veins)

• Left jugular trunk
• Left subclavian trunk
• Left bronchomediastinal trunk

Regional Lymph Nodes (key groups):

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8. Right Lymphatic Duct

• Right jugular trunk (head/neck right side)
• Right subclavian trunk (right upper limb)
• Right bronchomediastinal trunk (right thorax)

• Right side of head and neck
• Right upper limb
• Right thorax
• Right side of heart
• Right lung
• Right upper lobe of liver

The rest of the body (everything else = ~75%) drains via the thoracic duct into the left venous angle.

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9. Sense Organs. Organ of Vision. Eyeball Structure. Auxiliary Apparatus. Vestibulcocochlear Organ. Outer, Middle & Inner Ear

Classification of Sense Organs

Organ of Vision — The Eye

Eyeball Structure

• Sclera (posterior 5/6): White, tough, maintains shape; extraocular muscles attach here
• Cornea (anterior 1/6): Transparent, avascular, most refractive surface of the eye

• Choroid: Posterior, highly vascular; nourishes outer retina; dark (absorbs scattered light)
• Ciliary body: Contains ciliary muscle (controls lens shape for accommodation) and produces aqueous humor
• Iris: Pigmented ring with central pupil; contains sphincter pupillae (constricts — parasympathetic CN III) and dilator pupillae (dilates — sympathetic)

• 10 layers, including:
  • Photoreceptors: rods (dim light, peripheral vision) and cones (color, detail, central)
  • Bipolar cells → Ganglion cells → axons form optic nerve
• Fovea centralis: Point of sharpest vision (highest cone density); located in the macula lutea
• Optic disc (blind spot): Where optic nerve exits; no photoreceptors

• Anterior chamber: Between cornea and iris; contains aqueous humor (produced by ciliary body; drains via canal of Schlemm at the iridocorneal angle)
• Posterior chamber: Between iris and lens
• Vitreous chamber: Behind lens; filled with vitreous humor (gel-like, maintains shape)

• Biconvex, transparent, avascular, elastic
• Suspended by zonular fibers (suspensory ligaments of Zinn) from ciliary body
• Accommodation: ciliary muscle contracts → zonules relax → lens becomes more convex → focuses near objects

Auxiliary (Accessory) Apparatus of the Eye

Mnemonic: "LR₆SO₄" = Lateral Rectus → CN6, Superior Oblique → CN4, rest → CN3

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Vestibulocochlear Organ (CN VIII) — Ear

Outer Ear

• Auricle (pinna): Elastic cartilage covered by skin; collects and funnels sound waves
• External acoustic meatus: Canal (~2.5 cm) from pinna to tympanic membrane; lined with skin, contains ceruminous glands (produce ear wax)
• Tympanic membrane (eardrum): Semitransparent, obliquely set membrane; vibrates with sound waves; consists of 3 layers (outer epithelium, middle fibrous layer, inner mucosa)

Middle Ear (Tympanic Cavity)

• Air-filled cavity in the petrous temporal bone
• Ossicles (3 smallest bones in body):
  • Malleus (hammer): Handle attached to tympanic membrane; head articulates with incus
  • Incus (anvil): Middle bone
  • Stapes (stirrup): Footplate sits in oval window → transmits vibrations to inner ear
• Muscles: Tensor tympani (CN V₃ → dampens vibration), Stapedius (CN VII → dampens loud noise)
• Auditory (Eustachian) tube: Connects middle ear to nasopharynx; equalizes air pressure
• Mastoid air cells: Communicate with middle ear

Inner Ear (Labyrinth)

• Bony labyrinth — outer shell of bone; filled with perilymph (similar to CSF/ECF)
• Membranous labyrinth — inner sac system; filled with endolymph (high K⁺, like ICF)

• 3 scalae: Scala vestibuli, Scala tympani, Scala media (cochlear duct, membranous)
• Organ of Corti — on basilar membrane inside cochlear duct; contains inner and outer hair cells → detect sound vibrations → CN VIII (cochlear branch)
• Tonotopic organization: High frequency detected at base; low frequency at apex

• Utricle and Saccule → maculae with otoliths (otoconia) → detect gravity and linear acceleration
• 3 Semicircular canals (anterior, posterior, lateral) → ampullae with cristae (hair cells in cupula) → detect rotational head movements
• → CN VIII (vestibular branch) → vestibular nuclei → cerebellum + brainstem + spinal cord + eye muscles

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10. Organs of Smell and Taste. Skin and Its Derivatives. Breast

Organ of Smell (Olfaction)

• Located in the olfactory epithelium in the upper nasal cavity (superior nasal concha region)
• Contains olfactory receptor neurons (Type I sense organ) — bipolar neurons with cilia projecting into mucus
• Odorant molecules dissolve in mucus → bind receptors → action potential
• Axons pass through cribriform plate of ethmoid → olfactory bulb → olfactory tract → primary olfactory cortex (piriform cortex, amygdala) — no thalamic relay (unique among senses)

Organ of Taste (Gustation)

• Taste buds located on papillae of the tongue:
  • Fungiform papillae (anterior 2/3) — mushroom-shaped
  • Circumvallate (vallate) papillae (posterior, at sulcus terminalis) — largest, surrounded by moat
  • Foliate papillae (lateral tongue edges)
  • Filiform papillae — no taste buds (tactile)
• 5 basic tastes: Sweet, Sour, Salty, Bitter, Umami
• Taste receptor cells (Type II) → synapse onto sensory neurons

• Anterior 2/3 tongue: CN VII (chorda tympani branch — taste) + CN V₃ (lingual nerve — general sensation)
• Posterior 1/3: CN IX (glossopharyngeal — taste + sensation)
• Epiglottis/pharynx: CN X (vagus)
• All taste signals → solitary nucleus (medulla) → thalamus → gustatory cortex (insula)

Skin (Integument)

1. Stratum basale: Stem cells + melanocytes (produce melanin)
2. Stratum spinosum: Keratinocytes connected by desmosomes
3. Stratum granulosum: Keratohyalin granules form
4. Stratum lucidum: Only in thick skin (palms/soles)
5. Stratum corneum: Dead keratinocytes; protective outer barrier

Breast (Mamma)

• Located in the anterior chest wall between the 2nd and 6th ribs, from lateral sternal border to mid-axillary line
• The breast lies on the pectoralis major muscle and fascia (also partly on serratus anterior)
• Axillary tail (of Spence): Extension of breast tissue into the axilla

• 15–20 lobes of glandular tissue (modified sweat glands) arranged radially
• Each lobe has a lactiferous duct → converges at the nipple
• Lactiferous sinuses: Small dilations just beneath the areola — milk storage
• Separated by fibrous septa (Cooper's ligaments) — support breast; when invaded by cancer → skin dimpling
• Surrounded by fat (gives shape)

• Nipple: Projection; contains 15–20 lactiferous duct openings
• Areola: Pigmented ring; contains Montgomery's glands (modified sebaceous glands)

• Internal thoracic (mammary) artery → medial breast
• Lateral thoracic artery → lateral breast
• Intercostal arteries

• ~75% drains to axillary lymph nodes (especially anterior/pectoral group)
• ~25% to internal mammary (parasternal) nodes
• Also to: posterior intercostal, clavicular, supraclavicular nodes
• Sentinel lymph node = first axillary node to receive drainage; biopsied in breast cancer staging

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11. General Overview of the Nervous System. Spinal Cord

Overview of the Nervous System

Nervous System
├── Central Nervous System (CNS)
│   ├── Brain
│   └── Spinal Cord
└── Peripheral Nervous System (PNS)
    ├── Somatic (voluntary — skeletal muscles, skin)
    └── Autonomic (involuntary — viscera, smooth muscle, glands)
        ├── Sympathetic ("fight or flight")
        └── Parasympathetic ("rest and digest")

• Neurons — functional units; consist of cell body, dendrites (input), axon (output)
• Neuroglia (glia) — supportive cells: astrocytes, oligodendrocytes (CNS myelin), Schwann cells (PNS myelin), microglia (immune), ependymal cells (CSF production)

Spinal Cord

Macrostructure and Topography

• Extends from the medulla oblongata (foramen magnum) to L1–L2 (conus medullaris) in adults
• Below L2: Cauda equina (bundle of lumbar/sacral nerve roots floating in CSF)
• The filum terminale (glial/connective tissue strand) anchors the cord to the coccyx
• Length: ~45 cm in adults; diameter: ~1 cm

• Cervical enlargement (C4–T1): For upper limb innervation (brachial plexus)
• Lumbosacral enlargement (L1–S3): For lower limb innervation (lumbar/sacral plexus)

• 8 Cervical (C1–C8)
• 12 Thoracic (T1–T12)
• 5 Lumbar (L1–L5)
• 5 Sacral (S1–S5)
• 1 Coccygeal

• Dorsal (posterior) root — carries sensory fibers; has dorsal root ganglion (DRG) with sensory cell bodies
• Ventral (anterior) root — carries motor fibers

Gray Matter (H-shaped in cross-section)

White Matter

Meninges (Coverings of Spinal Cord)

Lumbar puncture is performed at L3–L4 or L4–L5 (safely below the conus medullaris at L1–L2) to sample CSF from the subarachnoid space.

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12. Base and Midline Section of the Brain. Cranial Nerves. Medulla Oblongata

Brain Divisions

12 Pairs of Cranial Nerves

Mnemonic for names: "On Old Olympus' Towering Tops A Finn And German Viewed Some Hops" Mnemonic for type (S/M/B): "Some Say Marry Money But My Brother Says Big Brains Matter More"

Medulla Oblongata

• Anterior median fissure — continuous with spinal cord
• Pyramids (bilateral): Contain corticospinal fibers; pyramidal decussation (motor cross) occurs at lower medulla — explains contralateral control
• Olives (inferior olivary nuclei) — oval bulges lateral to pyramids; involved in cerebellar coordination
• Post-olivary groove: CN IX, X, XI emerge here
• Pre-olivary groove: CN XII emerges here

• Lateral medullary syndrome (Wallenberg): Blockage of PICA (posterior inferior cerebellar artery) → ipsilateral face loss of pain/temp + contralateral body loss + vertigo + dysphagia + Horner's syndrome
• Damage to medullary vital centers → life-threatening (respiratory arrest, cardiac arrest)

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