USMLE Step 1 Qs (7)

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  • 1/20 Questions

    After a night of fraternity parties, a 20-year-old college sophomore came to the ER the following morning complaining that she could not raise her wrist. There was no history of trauma. On examination, the patient could not extend her fingers or wrist but could flex them. She could also both flex and extend her elbow normally. There were no other motor deficits. The symptoms suggest damage to which of the following nerves?

    • Median nerve
    • Ulnar nerve
    • Radial nerve
    • Axillary nerve
    • Musculocutaneous nerve
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About This Quiz

This USMLE Step 1 quiz assesses knowledge on various medical topics including benign prostatic hypertrophy, homologues of arteries in males, complications of colonic diverticulosis, arterial variations, and anatomy related to the male reproductive system. It is designed for medical students preparing for the USMLE Step 1 exam.

USMLE Step 1 Qs (7) - Quiz

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  • 2. 

    A patient presents in her fifth pregnancy with a history of numbness and tingling in her right thumb and index finger during each of her previous four pregnancies. Currently, the same symptoms are constant, although generally worse in the early morning. Symptoms could be somewhat relieved by vigorous shaking of the wrist. Neurologic examination revealed atrophy and weakness of the abductor pollicis brevis, the opponens pollicis, and the first two lumbrical muscles. Sensation was decreased over the lateral palm and the volar aspect of the first three digits. Numbness and tingling were markedly increased over the first three digits and the lateral palm when the wrist was held in flexion for 30 s. The symptoms suggest damage to which of the following structures?

    • The radial artery

    • The median nerve

    • The ulnar nerve

    • Proper digital nerves

    • The radial nerve

    Correct Answer
    A. The median nerve
    Explanation
    The patient has a classic case of carpal tunnel syndrome, in which the median nerve is compressed as it passes through the carpal tunnel formed by the flexor retinaculum in the wrist. Evidence for involvement of the median nerve is weakness and atrophy of the thenar muscles (abductor pollicis brevis, opponens pollicis) and lumbricals 1 to 3. Sensory deficits also follow the distribution of the median nerve. The median nerve enters the hand, along with the tendons of the superficial and deep digital flexors, through a tunnel framed by the carpal bones and the overlying flexor retinaculum. Symptoms are worse in the early morning and in pregnancy because of fluid retention, resulting in swelling that entraps the median nerve. Flexing the wrist for an extended period exaggerates the paresthesia ("Phelan's" sign) by increasing pressure on the median nerve.

    Neither the ulnar nerve, radial nerve, nor radial artery passes through the carpal tunnel. The ulnar nerve supplies the third and fourth lumbricals and only the short adductor of the thumb. The radial nerve innervates mostly long and short extensors of the digits and the dorsal aspect of the hand. Proper digital nerves lie distal to the carpal tunnel but are only sensory.

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  • 3. 

    A 38-year-old man is seen in the emergency room complaining of severe chest pain. He tends to sit leaning forward. On physical examination he is noted to be tachypneic (breathing rapidly); he has a rapid pulse rate, and on auscultation of the chest, his valve sounds appear distant. A radiograph shows a globular heart shadow. All evidence indicates pericarditis with pericardial effusion. Which of the following vessels is at high risk during the parasternal approach?

    • Anterior interventricular artery

    • Left internal thoracic artery

    • Right coronary artery

    • Right marginal artery

    • Nodal artery

    Correct Answer
    A. Left internal thoracic artery
    Explanation
    The parasternal approach is via the left fourth intercostal space adjacent to the sternum so that the internal thoracic artery may be avoided. The low risk of injuring a major blood vessel is the benefit of the costoxiphoid approach. At the level of the costoxiphoid angle, the internal thoracic artery has bifurcated into the musculophrenic and superior epigastric arteries. The former courses laterally along the costal margin, and the latter enters the rectus sheath somewhat lateral to the tract of the needle. Because the heart is tilted on its right side, the right coronary artery lies directly behind and is protected by the sternum. The right marginal branch of the right coronary artery courses anteriorly along the diaphragmatic surface of the heart, anterior and superior to the needle track. The anterior interventricular (descending) artery, which courses to the apex of the heart under the left nipple, is well out of harm's way.

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  • 4. 

    A 27-year-old man was admitted for neurologic evaluation of a gunshot wound received five days previously. A 9-mm bullet had passed through both the medial and lateral heads of the gastrocnemius muscle. The exit wound on the lateral head of the muscle was somewhat deeper than the entrance wound in the medial head. The bullet had not struck bone or significant arteries although significant tissue damage, suppuration, and swelling were found around the exit wound. Neurologic examination revealed losses of dorsiflexion and eversion of the left foot. The patient could not feel pinprick or touch on the dorsum of the left foot or anterolateral surface of the left leg. Which of the following nerves was most likely involved in the injury?

    • Sciatic nerve

    • Femoral nerve

    • Sural nerve

    • Common peroneal nerve

    • Tibial nerve

    Correct Answer
    A. Common peroneal nerve
    Explanation
    The common peroneal (fibular) nerve is the lateral terminal branch of the sciatic nerve. After arising near the apex of the popliteal fossa, it descends on the popliteus muscle and winds superficially around the fibular neck. It is extremely vulnerable in this position and is the most often injured nerve in the lower extremity. The common peroneal nerve innervates all muscles in the anterior and lateral compartments of the leg. In addition, it provides sensory innervation to the dorsum of the foot and the anterolateral surface of the legs via the superficial and sural/lateral sural cutaneous nerves, respectively. The tibial nerve innervates plantar flexors of the posterior compartment. The sciatic nerve generally divides into the tibial and common peroneal nerves superior to the popliteal fossa. Damage to it might result in deficits in both plantar flexion and dorsiflexion. The femoral nerve innervates the quadriceps muscles of the anterior thigh. Damage to it would impair flexion of the thigh at the hip.

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  • 5. 

     Which of the following contains the ovarian neurovascular bundle

    • Broad ligament

    • Mesosalpinx

    • Mesovarium

    • Suspensory ligament

    • Transverse cervical ligament

    Correct Answer
    A. Suspensory ligament
    Explanation
    The mesosalpinx, mesovarium, and suspensory ligament are all continuous with the broad ligament, which is a reflection of peritoneum over the female reproductive organs. The mesovarium attaches the ovary to the broad ligament. The suspensory ligament of the ovary runs from the pelvic brim to the lateral pole of the ovary. It contains the ovarian artery, ovarian vein, ovarian lymphatics, and ovarian nerves (ovarian neurovascular bundle). Volvulus of the ovary (usually associated with an ovarian tumor) may constrict the neurovascular bundle with ovarian infarct and pain referred to the inguinal and hypogastric regions.

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  • 6. 

    A 52-year-old man is brought to the emergency room after being found in the park, where apparently he had lain overnight after a fall. He complains of severe pain in the left arm. Physical examination suggests a broken humerus that is confirmed radiologically. The patient can extend the forearm at the elbow, but supination appears to be somewhat weak; the hand grasp is very weak compared with the uninjured arm. Neurologic examination reveals an inability to extend the wrist (wristdrop). Because these findings point to apparent nerve damage, the patient is scheduled for a surgical reduction of the fracture. The observation that extension at the elbow appears normal but supination of the forearm appears weak warrants localization of the nerve lesion to which of the following?

    • Posterior cord of the brachial plexus in the axilla

    • Posterior divisions of the brachial plexus

    • Radial nerve at the distal third of the humerus

    • Radial nerve in the midforearm

    • Radial nerve in the vicinity of the head of the radius

    Correct Answer
    A. Radial nerve at the distal third of the humerus
    Explanation
    The clinical signs and findings in the patient presented in the question indicate radial nerve damage. The evidence that extension at the elbow appeared normal while supination appeared weak can be used to localize the lesion. The innervation to the medial and long heads of the triceps brachii, principal extensor of the arm, arises from the radial nerve (in the axilla) as the medial muscular branches. The innervation to the lateral head, and to a smaller portion of the medial head, arises from the radial nerve as it passes along the musculospiral groove at mid-humerus. The supinator muscle is innervated by muscular twigs from the deep branch of the radial nerve in the forearm, just before the radial nerve reaches the supinator muscle. Thus, paralysis of the supinator muscle, but not of the triceps brachii, localizes the fracture to the distal third of the humeral shaft between the elbow and musculospiral groove.

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  • 7. 
    The patient is a 45-year-old male with a history of colonic diverticulosis. He complains of fever with pain and swelling in the rectal area. You are concerned that the colonic diverticulum may have become infected (diverticulitis) and ruptured into the space indicated by the * in this CT scan. Which of the following is correct regarding the indicated space? - ProProfs

    The patient is a 45-year-old male with a history of colonic diverticulosis. He complains of fever with pain and swelling in the rectal area. You are concerned that the colonic diverticulum may have become infected (diverticulitis) and ruptured into the space indicated by the * in this CT scan. Which of the following is correct regarding the indicated space?

    • It is called the paracolic gutter

    • The space is largely filled with muscle

    • The space is located superior to the pelvic diaphragm

    • Pus from the abscessed diverticuli in that space can extend anteriorly to the perineal body, inferior to the urogenital diaphragm

    • Pus from the abscessed diverticuli in that space can extend superiorly anterior to the sacrum

    Correct Answer
    A. Pus from the abscessed diverticuli in that space can extend anteriorly to the perineal body, inferior to the urogenital diaphragm
    Explanation
    The ischioanal fossa is a fat-filled space that extends from below the levator ani muscle (puborectalis, pubococcygeus, and iliococcygeus muscles). It also extends anteriorly in the area between the pelvic diaphragm (superiorly) and the urogenital diaphragm (inferiorly). It cannot extend superiorly above the pelvic diaphragm and, therefore, cannot extend superiorly anterior to the sacrum.

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  • 8. 

    Benign prostatic hypertrophy results in obstruction of the urinary tract. This specific condition is associated with enlargement of which of the following?

    • Entire prostate gland

    • Lateral lobes

    • Median lobe

    • Posterior lobes

    Correct Answer
    A. Median lobe
    Explanation
    Benign prostatic hypertrophy is the result of enlargement of the median lobe, which may compress the prostatic urethra to the point of obstruction. This hypertrophic tissue may also protrude into the urinary bladder to prevent complete emptying. The posterior lobes are commonly associated with malignant transformation. The lateral (anterior) lobes tend to be asymptomatic.

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  • 9. 

     Paresthesia, hyperesthesia, or even painful sensation in the anterolateral region of the thigh may occur in obese persons. It results from an abdominal panniculus adiposus that bulges over the inguinal ligament and compresses which of the following underlying nerves?

    • Femoral branch of the genitofemoral nerve

    • Femoral nerve

    • Iliohypogastric nerve

    • Ilioinguinal nerve

    • Lateral femoral cutaneous nerve

    Correct Answer
    A. Lateral femoral cutaneous nerve
    Explanation
    The lateral femoral cutaneous nerve passes beneath the inguinal ligament just medial to the anterior superior iliac spine. It innervates the lateral aspect of the thigh. The iliohypogastric nerve innervates a portion of the gluteal, inguinal, and pubic regions. The ilioinguinal nerve and the femoral branch of the genitofemoral nerve supply the upper portions of the anterior thigh. The sensory distribution of the femoral nerve is the anterior thigh and medial leg.

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  • 10. 

    After a night of fraternity parties, a 20-year-old college sophomore came to the ER the following morning complaining that she could not raise her wrist. There was no history of trauma. On examination, the patient could not extend her fingers or wrist but could flex them. She could also both flex and extend her elbow normally. There were no other motor deficits. Which of the following muscles is spared by the type of injury described above?

    • Extensor digitorum communis

    • Extensor carpi radialis

    • Extensor pollicis longus

    • Triceps

    • Anconeus

    Correct Answer
    A. Triceps
    Explanation
    When the radial nerve is compressed in the radial groove (e.g., by supporting the outstretched arm on a hard object), only the triceps is spared because the branch of radial nerve supplying this muscle originates proximal to the nerve's position in the groove. Branches to all the other muscles innervated by the radial nerve occur distal to that point and thus would be affected by compression of the nerve in the groove.

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  • 11. 

    Innervation to the rotator cuff muscle that medially rotates the arm is provided by which of the following nerves?

    • Axillary nerve

    • Suprascapular nerve

    • Thoracodorsal nerve

    • Upper and lower subscapular nerves

    Correct Answer
    A. Upper and lower subscapular nerves
    Explanation
    The upper and lower subscapular nerves innervate the subscapularis muscle, which is the only muscle of the rotator cuff group that medially rotates the arm. The lower subscapular nerve also innervates the teres major muscle, which is not part of the rotator cuff group. The suprascapular nerve innervates the supraspinatus and infraspinatus muscles that abduct and laterally rotate the arm, respectively. The teres minor muscle, innervated by the axillary nerve, also laterally rotates the arm. The thoracodorsal nerve, originating from the posterior cord between the upper and lower subscapular nerves, innervates the latissimus dorsi muscle.

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  • 12. 
    . The diagram below represents a frontal section through the bladder and prostate gland. Which lettered structure that forms the external urethral sphincter? - ProProfs

    . The diagram below represents a frontal section through the bladder and prostate gland. Which lettered structure that forms the external urethral sphincter?

    • A

    • B

    • C

    • D

    • E

    Correct Answer
    A. A
    Explanation
    The anterior portion of the deep transverse perineal muscle (A) is closely associated with the urethra and forms the external urethral sphincter. Voluntary control of this muscle is mediated by the pudendal nerve. The muscles of the superficial pouch generally are associated with the penis or clitoris. The deep perineal pouch is formed by the deep transverse perineal muscle (A). This muscle, along with its inferior and superior fascial layers, forms the urogenital diaphragm. Extending from the ischiopubic ramus to meet its counterpart of the opposite side in a midline raphe, the deep transverse perineal muscle reinforces the urogenital hiatus of the pelvic diaphragm formed by the central defect in the levator ani muscle (C). Although the obturator internus muscle (B), a lateral rotator of the thigh, does not contribute to the support of the pelvic viscera, the tendinous arch of the obturator fascia provides an origin for the levator ani muscle. The bulbospongiosus muscle (E), which overlies the erectile tissue of the corpus spongiosus urethrae, functions to compress the penile urethra to expel residual urine. The ischiocavernosus muscles (D), which overlie the corpora cavernosa, along with the bulbospongiosus muscle, may assist in maintenance of erection by retarding venous return from the erectile tissue.

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  • 13. 

     Which of the following types of femoral fracture is most likely to result in avascular necrosis of the femoral head in adults?

    • Acetabular

    • Cervical

    • Intertrochanteric (between the trochanters)

    • Subtrochanteric

    • Midfemoral shaft

    Correct Answer
    A. Cervical
    Explanation
    Fractures of the femoral neck will completely interrupt the blood supply to the femoral head in adults. If the capsular retinaculum also is torn, avascular necrosis of the head will certainly occur because the only remaining blood supply to the head (through the ligamentum teres) is inadequate to sustain it. The nearer the fracture to the femoral head, the more likely will be disruption of the retinacular blood supply.

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  • 14. 

    A 52-year-old man is brought to the emergency room after being found in the park, where apparently he had lain overnight after a fall. He complains of severe pain in the left arm. Physical examination suggests a broken humerus that is confirmed radiologically. The patient can extend the forearm at the elbow, but supination appears to be somewhat weak; the hand grasp is very weak compared with the uninjured arm. Neurologic examination reveals an inability to extend the wrist (wristdrop). Because these findings point to apparent nerve damage, the patient is scheduled for a surgical reduction of the fracture. On examination of muscle function at the metacarpophalangeal (MP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints, the findings expected in the presence of radial nerve palsy would include which of the following?

    • Inability to abduct the digits at the MP joint

    • Inability to adduct the digits at the MP joint

    • Inability to extend the MP joint only

    • Inability to extend the MP, PIP, and DIP joints

    • Inability to extend the PIP and DIP joints

    Correct Answer
    A. Inability to extend the MP joint only
    Explanation
    Radial nerve palsy produces an inability to extend the metacarpophalangeal joints, owing to paralysis of the extensor digitorum communis muscle. However, the lumbrical and interossei muscles, which are served by the median and ulnar nerves and insert into the dorsal expansions (extensor hoods) of the proximal phalanges, are able simultaneously to flex the metacarpophalangeal joints and to extend the interphalangeal joints. Also, abduction of the digits, a function of the dorsal interossei, and adduction, a function of the palmar interossei, are both mediated by the ulnar nerve and, therefore, unaffected.

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  • 15. 

    In the male, which of the following is the homologue of the vaginal artery?

    • Obturator artery

    • Internal pudendal artery

    • Middle rectal artery

    • Umbilical artery

    • Inferior vesical artery

    Correct Answer
    A. Inferior vesical artery
    Explanation
    All of the listed choices are branches of the internal iliac artery. The inferior vesical artery in the male supplies the seminal vesicle, prostate, fundus of the bladder, distal ureter, and the vas deferens. In the female, the vaginal artery supplies the vagina, urinary bladder, and pelvic portion of the urethra. The obturator artery gives off muscular and nutrient branches within the pelvis and then leaves the pelvis via the obturator canal to supply the thigh. The internal pudendal artery crosses the piriformis muscle, exits the pelvic cavity via the greater sciatic foramen, and enters the ischiorectal fossa via the lesser sciatic foramen. It supplies the external genitalia (penis and clitoris). The middle rectal artery supplies the inferior rectum and forms important anastomoses with other rectal arteries. The umbilical artery gives off the superior vesical artery in both sexes. Its distal portion degenerates to form the medial umbilical ligament.

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  • 16. 

    Which of the following empties into the penile urethra?

    • Ampulla of the vas deferens

    • Bulbourethral gland

    • Ejaculatory duct

    • Prostate gland

    • Seminal vesicle

    Correct Answer
    A. Bulbourethral gland
    Explanation
    The bulbourethral glands, lying in the deep pouch, drain into the penile urethra. Spermatozoa mature in the epididymis. Emission moves the spermatozoa to the ampulla of the vas, where they are stored prior to ejaculation. On receiving the duct from the seminal vesicle, the passage becomes the narrow ejaculatory duct, which passes through the prostatic parenchyma to empty into the prostatic urethra.

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  • 17. 

    Which of the following arteries may occasionally arise as a branch of the external iliac artery or inferior epigastric artery instead of as a branch of the internal iliac artery?

    • Internal pudendal artery

    • Obturator artery

    • Superior gluteal artery

    • Umbilical artery

    • Uterine artery

    Correct Answer
    A. Obturator artery
    Explanation
    The obturator usually arises from the anterior trunk of the internal iliac artery. However, in 25 to 30% of the population, it arises from the inferior epigastric or the external iliac artery. There is considerable variation as to the origins of the branches of the posterior and anterior trunks of the internal iliac artery. The internal pudendal artery, umbilical artery, and uterine artery almost always arise from the anterior trunk. The superior gluteal usually arises from the posterior trunk.

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  • 18. 

    In the upper extremity, each major nerve passes between two heads of a muscle. The median nerve passes between which of the following?

    • Long and medial heads of the triceps brachii muscle

    • Medial and posterior division of the coracobrachialis muscle

    • Ulnar and humeral heads of the flexor carpi ulnaris muscle

    • Ulnar and humeral heads of the pronator teres muscle

    Correct Answer
    A. Ulnar and humeral heads of the pronator teres muscle
    Explanation
    In the arm, the musculocutaneous nerve passes through the coracobrachialis muscle. The radial nerve, which lies in the musculospiral groove, passes between the long and medial heads of the triceps brachii muscle in company with the profunda brachii artery. It is here that the nerve and artery are in jeopardy in the event of a midhumeral fracture. In the forearm, the median nerve courses between the humeral and ulnar heads of the pronator teres. As the ulnar nerve courses behind the medial epicondyle, it passes between the humeral and ulnar heads of the flexor carpi ulnaris as it enters the forearm. In each instance, the nerve innervates the muscle that it pierces.

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  • 19. 

    A 38-year-old man is seen in the emergency room complaining of severe chest pain. He tends to sit leaning forward. On physical examination he is noted to be tachypneic (breathing rapidly); he has a rapid pulse rate, and on auscultation of the chest, his valve sounds appear distant. A radiograph shows a globular heart shadow. All evidence indicates pericarditis with pericardial effusion. Pericardiocentesis (to drain the exudate) via the costoxiphoid approach passes through which of the following structures?

    • The interchondral portion of an internal oblique muscle

    • The left costodiaphragmatic recess

    • The rectus sheath and rectus abdominis muscle

    • The visceral pericardium

    • The left costomediastinal recess

    Correct Answer
    A. The rectus sheath and rectus abdominis muscle
    Explanation
    In the costoxiphoid approach to the pericardial cavity, a needle angled upward and toward the left passes between the xiphoid process and the costal margin, through the rectus sheath and rectus abdominis muscle, and through the fibrous and serous layers of the parietal pericardium. Because the line of pleural reflection swings away from the midline anteroinferiorly on the left side, the needle should not enter either the left pleural cavity or the left lung. The parasternal approach to the pericardial cavity will pass through the external intercostal membrane and the interchondral portion of an internal intercostal muscle.

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  • 20. 

    The odontoid process (dens) is correctly described by which of the following statements?

    • It articulates with the occipital portion of the skull

    • It is separated from the atlas by an intervertebral disk

    • It projects from the inferior surface of the atlas

    • It represents the vertebral body of the first cervical vertebra

    Correct Answer
    A. It represents the vertebral body of the first cervical vertebra
    Explanation
    The odontoid process (dens) of the axis, the second cervical vertebra, is the remnant of the body of the first cervical vertebra (atlas). Developing from a separate ossification center, it fused to the body of the axis. The fact that there is no intervertebral disk between the atlas and axis probably facilitates the fusion. The dens, projecting from the superior surface of the axis, provides a pivot about which rotation occurs at the atlantoaxial joint. Fracture and posterior dislocation of the dens may crush the spinal cord with fatal results.

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