USMLE Anatomy Syllabus

Anatomy syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Anatomy in USMLE, not a summary of it.

1. 1

   Musculoskeletal System

   3 topics

   • Bones
   • Muscles
   • Joints
2. 2

   Cardiovascular Anatomy

   3 topics

   • Heart anatomy
   • Blood vessels
   • Lymphatic system
3. 3

   Neuroanatomy

   3 topics

   • Brain
   • Spinal cord
   • Peripheral nerves

Anatomy flashcards for USMLE

24 of 51 cards from the Anatomy deck — real questions with worked answers.

1. How many bones are in the adult human skeleton, and how is it divided?

   206 bones total, divided into the axial skeleton (80 bones: skull, vertebral column, ribs, sternum) and the appendicular skeleton (126 bones: limbs and girdles).

2. Name the four types of bones by shape, with an example of each.

   Long (femur), short (carpals), flat (sternum, skull), and irregular (vertebrae). A fifth category, sesamoid bones (patella), is sometimes added.

3. What is the difference between the diaphysis and epiphysis of a long bone?

   The diaphysis is the tubular shaft (compact bone around a medullary cavity); the epiphyses are the widened ends (spongy/trabecular bone) that participate in joints. The epiphyseal (growth) plate lies between them in growing bone.

4. What are the two mechanisms of bone formation (ossification)?

   Intramembranous ossification (bone forms directly within mesenchyme, e.g., flat skull bones) and endochondral ossification (bone replaces a hyaline cartilage model, e.g., long bones).

5. Name the three functional bone cell types and their roles.

   Osteoblasts build bone matrix (osteoid), osteocytes are mature cells embedded in lacunae that maintain matrix, and osteoclasts (multinucleated) resorb bone.

6. What is the functional unit of compact bone?

   The osteon (Haversian system): concentric lamellae of matrix surrounding a central (Haversian) canal that carries blood vessels and nerves. Volkmann's canals connect adjacent osteons.

7. How many bones make up the vertebral column, and what are the regional counts?

   33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal. Movable vertebrae number 24.

8. What structural feature is unique to the cervical vertebrae?

   Transverse foramina (in the transverse processes), which transmit the vertebral arteries (except at C7, where only small accessory veins pass). C1 (atlas) and C2 (axis, with dens) are also specialized.

9. What are the three types of muscle tissue and their control?

   Skeletal muscle (striated, voluntary, multinucleated), cardiac muscle (striated, involuntary, intercalated discs), and smooth muscle (non-striated, involuntary, single central nucleus).

10. What is the sarcomere, and which lines define its boundaries?

    The sarcomere is the contractile unit of striated muscle, extending from one Z-line (Z-disc) to the next. It contains the A-band (thick myosin), I-band (thin actin only), and H-zone.

11. Describe the sliding filament theory of muscle contraction.

    Myosin heads bind actin, forming cross-bridges, and pull the thin filaments toward the sarcomere center (power stroke). The Z-lines are drawn together, shortening the sarcomere; filament lengths do not change. ATP releases myosin for the next cycle.

12. What ion triggers skeletal muscle contraction, and where is it released from?

    Calcium ($\ce{Ca^2+}$), released from the sarcoplasmic reticulum. It binds troponin C, shifting tropomyosin to expose actin's myosin-binding sites.

13. Define origin versus insertion of a skeletal muscle.

    The origin is the muscle's attachment to the more stationary (usually proximal) bone; the insertion is the attachment to the more movable (usually distal) bone that moves toward the origin during contraction.

14. What is the difference between isometric and isotonic contraction?

    In isometric contraction, muscle tension increases but length stays constant (no movement). In isotonic contraction, the muscle changes length at constant tension, producing movement (concentric = shortening, eccentric = lengthening).

15. Name the three connective tissue layers of a skeletal muscle from inner to outer.

    Endomysium (surrounds individual muscle fibers), perimysium (surrounds fascicles), and epimysium (surrounds the whole muscle).

16. What are the two main structural classifications of joints by material, plus the functional classification?

    Structural: fibrous, cartilaginous, and synovial. Functional (by movement): synarthrosis (immovable), amphiarthrosis (slightly movable), and diarthrosis (freely movable).

17. List the six types of synovial joints with an example of each.

    Hinge (elbow), pivot (atlantoaxial), ball-and-socket (hip/shoulder), saddle (thumb carpometacarpal), condyloid/ellipsoid (wrist/radiocarpal), and plane/gliding (intercarpal).

18. What are the defining features of a synovial joint?

    A fluid-filled joint (synovial) cavity, articular (hyaline) cartilage on bone ends, a joint capsule lined by synovial membrane secreting synovial fluid, and reinforcing ligaments. It is a diarthrosis (freely movable).

19. What is the difference between a symphysis and a synchondrosis?

    Both are cartilaginous joints. A synchondrosis unites bones with hyaline cartilage (e.g., epiphyseal plate, first sternocostal joint). A symphysis unites bones with fibrocartilage (e.g., pubic symphysis, intervertebral discs).

20. Name the three types of fibrous joints.

    Sutures (between skull bones), syndesmoses (bones joined by a ligament/interosseous membrane, e.g., distal tibiofibular), and gomphoses (peg-in-socket, e.g., tooth in alveolus).

21. In which mediastinum does the heart lie, and what covers it?

    The heart lies in the middle mediastinum, enclosed by the pericardium (an outer fibrous pericardium and an inner serous pericardium with parietal and visceral/epicardial layers separated by the pericardial cavity).

22. Trace the path of blood through the four chambers and valves of the heart.

    Right atrium → tricuspid valve → right ventricle → pulmonary valve → lungs → left atrium → mitral (bicuspid) valve → left ventricle → aortic valve → systemic circulation.

23. Which heart valves are the atrioventricular valves, and which are semilunar?

    Atrioventricular: tricuspid (right) and mitral/bicuspid (left). Semilunar: pulmonary and aortic. AV valves are anchored by chordae tendineae to papillary muscles.

24. Describe the normal cardiac conduction pathway.

    SA node (pacemaker, right atrium) → AV node → bundle of His (AV bundle) → right and left bundle branches → Purkinje fibers → ventricular myocardium.

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