USMLE Step 1 Anatomy Practice Questions

A 55-year-old man presents with difficulty swallowing solids and liquids, along with regurgitation of undigested food. Barium swallow reveals a dilated esophagus with distal tapering ('bird's beak' sign). Manometry confirms aperistalsis in the esophageal body and incomplete relaxation of the lower esophageal sphincter (LES). Degeneration of which neural structure is most likely responsible for this condition (Achalasia)?

• (A) Myenteric (Auerbach's) plexus
• (B) Submucosal (Meissner's) plexus
• (C) Dorsal motor nucleus of the vagus
• (D) Nucleus ambiguus

During a surgical procedure involving the axilla, the surgeon must be careful to avoid injuring the long thoracic nerve. Damage to this nerve would result in paralysis of which muscle, leading to a characteristic 'winged scapula'?

• (A) Serratus anterior
• (B) Latissimus dorsi
• (C) Pectoralis major
• (D) Deltoid

A patient suffers a fracture of the surgical neck of the humerus. Which nerve and artery pair are most at risk of injury in this location?

• (A) Axillary nerve and posterior circumflex humeral artery
• (B) Radial nerve and deep brachial artery
• (C) Median nerve and brachial artery
• (D) Ulnar nerve and superior ulnar collateral artery

A 20-year-old college student presents with fever, headache, and neck stiffness. A lumbar puncture is performed to analyze cerebrospinal fluid (CSF). To safely obtain CSF, the needle is typically inserted between which two vertebral levels in an adult?

• (A) L3 and L4
• (B) L1 and L2
• (C) T12 and L1
• (D) S1 and S2

Following a penetrating injury to the right side of the neck superior to the clavicle, a patient experiences hoarseness and difficulty swallowing. Examination reveals that the right side of the palate droops and the uvula deviates to the left upon phonation. Which cranial nerve is most likely injured?

• (A) Vagus nerve (CN X)
• (B) Glossopharyngeal nerve (CN IX)
• (C) Hypoglossal nerve (CN XII)
• (D) Spinal accessory nerve (CN XI)

A 45-year-old woman undergoes thyroid surgery. Postoperatively, she complains of tingling sensations in her hands and feet (paresthesias) and exhibits carpopedal spasm upon blood pressure cuff inflation (Trousseau's sign). These symptoms are most likely due to inadvertent damage to or removal of which structures located posterior to the thyroid gland?

• (A) Parathyroid glands
• (B) Recurrent laryngeal nerves
• (C) Superior laryngeal nerves
• (D) Thyroglossal duct remnants

A patient presents with weakness in extending the wrist and fingers ('wrist drop'). Sensory examination reveals loss of sensation over the posterior forearm and the dorsolateral aspect of the hand. Injury to which nerve is the most likely cause?

• (A) Radial nerve
• (B) Median nerve
• (C) Ulnar nerve
• (D) Musculocutaneous nerve

During inspiration, the diaphragm contracts and moves downward, increasing the vertical dimension of the thoracic cavity. Which nerve provides motor innervation to the diaphragm?

• (A) Phrenic nerve
• (B) Intercostal nerves
• (C) Vagus nerve
• (D) Long thoracic nerve

A 60-year-old man with a history of hypertension presents with sudden onset severe tearing chest pain radiating to his back. Imaging reveals a dissection of the aorta originating just distal to the left subclavian artery (Stanford Type B). This dissection primarily involves which layer of the aortic wall where the initial tear occurs?

• (A) Tunica intima
• (B) Tunica media
• (C) Tunica adventitia
• (D) Vasa vasorum

A medical student is dissecting the inguinal region. They identify the spermatic cord passing through the superficial inguinal ring, an opening in the aponeurosis of which abdominal wall muscle?

• (A) External oblique muscle
• (B) Internal oblique muscle
• (C) Transversus abdominis muscle
• (D) Rectus abdominis muscle

A patient involved in a high-speed motor vehicle accident sustains a pelvic fracture. Examination reveals inability to adduct the thigh and sensory loss over the medial aspect of the thigh. Which nerve is most likely compromised?

• (A) Obturator nerve
• (B) Femoral nerve
• (C) Sciatic nerve
• (D) Superior gluteal nerve

Which structure forms the floor of the anatomical snuffbox, a triangular depression on the radial aspect of the wrist, making it palpable within this space?

• (A) Scaphoid bone
• (B) Lunate bone
• (C) Trapezium bone
• (D) Radial styloid process

The portal vein, carrying nutrient-rich but deoxygenated blood from the gastrointestinal tract to the liver, is typically formed by the confluence of which two major veins?

• (A) Superior mesenteric vein and splenic vein
• (B) Inferior mesenteric vein and splenic vein
• (C) Superior mesenteric vein and inferior mesenteric vein
• (D) Hepatic veins and splenic vein

A patient presents with double vision (diplopia), particularly when looking downward and inward (e.g., reading or walking downstairs). Examination reveals impairment of downward and medial rotation of the eye. Dysfunction of which cranial nerve and muscle is responsible?

• (A) Trochlear nerve (CN IV) and Superior oblique muscle
• (B) Oculomotor nerve (CN III) and Inferior oblique muscle
• (C) Abducens nerve (CN VI) and Lateral rectus muscle
• (D) Oculomotor nerve (CN III) and Medial rectus muscle

Which anatomical structure marks the transition from the duodenum to the jejunum?

• (A) Ligament of Treitz (suspensory muscle of the duodenum)
• (B) Pyloric sphincter
• (C) Ileocecal valve
• (D) Sphincter of Oddi

The blood supply to the sinoatrial (SA) node, the primary pacemaker of the heart, most commonly arises from which coronary artery?

• (A) Right coronary artery (RCA)
• (B) Left anterior descending artery (LAD)
• (C) Left circumflex artery (LCX)
• (D) Posterior descending artery (PDA)

A patient undergoes surgery for a pituitary adenoma via a transsphenoidal approach. This surgical route involves passing instruments through the nasal cavity and then through which paranasal sinus to reach the sella turcica?

• (A) Sphenoid sinus
• (B) Ethmoid sinus
• (C) Maxillary sinus
• (D) Frontal sinus

Which ligament contains the ovarian artery and vein, providing the primary vascular supply to the ovary?

• (A) Suspensory ligament of the ovary (infundibulopelvic ligament)
• (B) Ovarian ligament
• (C) Broad ligament
• (D) Round ligament of the uterus

The common peroneal (fibular) nerve wraps around the neck of the fibula before dividing into its superficial and deep branches. Injury at this location typically results in weakness of which foot/ankle movements?

• (A) Dorsiflexion and eversion
• (B) Plantarflexion and inversion
• (C) Dorsiflexion and inversion
• (D) Plantarflexion and eversion

Which part of the nephron is primarily responsible for reabsorbing the majority (approximately 65-70%) of the filtered sodium, chloride, water, bicarbonate, glucose, and amino acids?

• (A) Proximal convoluted tubule (PCT)
• (B) Loop of Henle (thin descending limb)
• (C) Distal convoluted tubule (DCT)
• (D) Collecting duct

The Circle of Willis, an anastomotic ring of arteries at the base of the brain, provides collateral circulation. Which artery directly connects the anterior cerebral arteries (ACAs) of the two hemispheres?

• (A) Anterior communicating artery (ACom)
• (B) Posterior communicating artery (PCom)
• (C) Middle cerebral artery (MCA)
• (D) Basilar artery

A 6-year-old boy presents with recurrent respiratory infections and situs inversus (major visceral organs reversed). Chest X-ray shows dextrocardia. This condition, Kartagener syndrome, is caused by a defect in which microtubular structure?

• (A) Dynein arms
• (B) Nexin links
• (C) Radial spokes
• (D) Basal bodies

Which muscle is the primary flexor of the hip joint?

• (A) Iliopsoas
• (B) Gluteus maximus
• (C) Hamstrings (Biceps femoris, Semitendinosus, Semimembranosus)
• (D) Quadriceps femoris (Rectus femoris)

The thoracic duct, the largest lymphatic vessel in the body, collects lymph from the entire lower body and the left side of the upper body. It typically empties into the venous system at the junction of which two veins?

• (A) Left internal jugular vein and left subclavian vein
• (B) Right internal jugular vein and right subclavian vein
• (C) Left brachiocephalic vein and superior vena cava
• (D) Azygos vein and superior vena cava

Which cranial nerve is responsible for the sensory limb of the corneal reflex (blinking in response to touching the cornea)?

• (A) Trigeminal nerve (CN V1 - ophthalmic division)
• (B) Facial nerve (CN VII)
• (C) Optic nerve (CN II)
• (D) Oculomotor nerve (CN III)

A patient presents with pain and tenderness over the lateral epicondyle of the humerus, exacerbated by gripping and wrist extension ('tennis elbow'). This condition involves inflammation of the common origin of which group of muscles?

• (A) Wrist extensors
• (B) Wrist flexors
• (C) Finger flexors
• (D) Forearm pronators

Which structure is located within the hepatoduodenal ligament, along with the common bile duct and hepatic artery proper?

• (A) Portal vein
• (B) Inferior vena cava
• (C) Splenic vein
• (D) Superior mesenteric artery

The dermatome supplying sensation to the umbilicus corresponds to which spinal cord level?

• (A) T10
• (B) T4
• (C) L1
• (D) S1

Which artery is the primary blood supply to the head and neck of the femur?

• (A) Medial circumflex femoral artery
• (B) Lateral circumflex femoral artery
• (C) Obturator artery (artery to the head of the femur)
• (D) Profunda femoris artery

The biceps brachii muscle performs flexion at the elbow joint and supination of the forearm. Which nerve innervates this muscle?

• (A) Musculocutaneous nerve
• (B) Radial nerve
• (C) Median nerve
• (D) Ulnar nerve

Which valve prevents the backflow of blood from the left ventricle into the left atrium during ventricular systole?

• (A) Mitral valve (bicuspid valve)
• (B) Tricuspid valve
• (C) Aortic valve
• (D) Pulmonary valve

The muscles of facial expression are derived from which pharyngeal (branchial) arch?

• (A) Second pharyngeal arch
• (B) First pharyngeal arch
• (C) Third pharyngeal arch
• (D) Fourth and sixth pharyngeal arches

Which specific region of the adrenal gland is responsible for synthesizing and secreting mineralocorticoids, primarily aldosterone?

• (A) Zona glomerulosa
• (B) Zona fasciculata
• (C) Zona reticularis
• (D) Adrenal medulla

A patient presents with inability to abduct the arm beyond the initial 15 degrees and weakness in external rotation of the shoulder. Injury to which rotator cuff muscle and its innervating nerve is most likely?

• (A) Supraspinatus muscle and Suprascapular nerve
• (B) Infraspinatus muscle and Suprascapular nerve
• (C) Subscapularis muscle and Upper/Lower Subscapular nerves
• (D) Teres minor muscle and Axillary nerve

Which ligament prevents anterior displacement of the tibia relative to the femur?

• (A) Anterior cruciate ligament (ACL)
• (B) Posterior cruciate ligament (PCL)
• (C) Medial collateral ligament (MCL)
• (D) Lateral collateral ligament (LCL)

The main pancreatic duct (duct of Wirsung) typically joins with which other duct before emptying into the second part of the duodenum via the major duodenal papilla (ampulla of Vater)?

• (A) Common bile duct
• (B) Accessory pancreatic duct (duct of Santorini)
• (C) Cystic duct
• (D) Common hepatic duct

Which layer of the epidermis contains stem cells responsible for regenerating the more superficial layers?

• (A) Stratum basale (stratum germinativum)
• (B) Stratum spinosum
• (C) Stratum granulosum
• (D) Stratum lucidum

Which artery provides the main blood supply to the structures in the anterior compartment of the leg (e.g., tibialis anterior, extensor hallucis longus, extensor digitorum longus)?

• (A) Anterior tibial artery
• (B) Posterior tibial artery
• (C) Fibular (peroneal) artery
• (D) Popliteal artery

A patient has lost sensation over the tip of their nose. This area is innervated by a branch of which division of the trigeminal nerve (CN V)?

• (A) Ophthalmic division (V1)
• (B) Maxillary division (V2)
• (C) Mandibular division (V3)
• (D) Facial nerve (CN VII)

During a cholecystectomy (gallbladder removal), the surgeon must carefully identify and ligate the cystic artery. This artery most commonly arises from which larger artery within the triangle of Calot?

• (A) Right hepatic artery
• (B) Left hepatic artery
• (C) Common hepatic artery
• (D) Gastroduodenal artery