USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 31:

  A 64-year-old male patient suffering from diabetes has developed a cataract in the left eye. Which of the following is the most likely location of a cataract?

  A. lens anterior epithelium

  B. lens capsule

  C. substance

  D. posterior chamber

  E. vitreous cavity

  Correct Answer: C

  Section: Anatomy A cataract is an opacification of the lens caused by a change in the solubility of the lens proteins filensin and crystallins (, , and ). These proteins are synthesized by the cortical lens fibers in the lens substance. Their change in solubility and aggregation result in increased light scattering, forming the cataract, which can only occur in the lens substance. The lens anterior epithelium (choice A) consists of a simple cuboidal epithelium. When these cells reach the equatorial region of the lens, they differentiate into the cortical lens fibers, which then synthesize filensin and the crystallins. The lens capsule (choice B) is a thick and transparent membrane enclosing the lens. The posterior chamber (choice D), located anterior to the lens, and the vitreous cavity (choice E), located posterior to the lens, are not involved in cataract formation.

• Question 32:

  A professional football player was diving for a touchdown when his face mask was grabbed and wrenched, causing neck hyperextension and rotation to the right. When brought to the sideline, the player complained of a burning sensation radiating down the right upper extremity and neurological examination revealed right lateral weakness of this limb. Movements affected were arm rotation and flexion, elbow flexion, forearm supination, and thumb flexion. The patient is diagnosed with a brachial plexus injury at the level of C6. 29. Which of the following muscles can perform arm and elbow flexion along with forearm supination?

  Which of the following innervates the muscle identified in question 29?

  A. median

  B. musculocutaneous

  C. radial

  D. suprascapular

  E. ulnar

  Correct Answer: B

  Section: Anatomy The musculocutaneous nerve innervates the biceps brachii along with the coracobrachialis and the brachialis. It continues into the forearm as the lateral antebrachial cutaneous nerve. In this brachial plexus injury, the sudden hyperextension and right rotation of the neck narrow the intervertebral foramina through which exit the cervical nerves. Injury at the level of C6 will affect the musculocutaneous nerve along with the suprascapular nerve, resulting in impairment of the movements described. The median nerve (choice A) and ulnar nerve (choice E) innervate muscles not in the arm but in the forearm and hand. In the arm, the radial nerve (choice C) is the nerve to the only muscle in the extensor compartment, the triceps brachii. The suprascapular nerve (choice D) innervates two muscles of the rotator cuff, the supraspinatus and infraspinatus. It is affected in a brachial plexus injury at the C6 level.

• Question 33:

  A third-year medical student is asked to review the computerized tomographic (CT) results of a patient with a possible abdominal aortic aneurysm. Which of the following arrows in Following figure points to the abdominal aorta?

  

  A. 1

  B. 2

  C. 3

  D. 4

  E. 5

  Correct Answer: B

  Section: Anatomy Arrow 2 points to the abdominal aorta, located anterior to the lumbar vertebra. Arrows 1 (choice A) and 5 (choice B) indicate the left and right kidneys respectively. Arrow 3 points to the inferior vena cava; the junctions of the left and right renal veins to the inferior vena cava are seen in this CT scan. Arrow 4 points to a loop of the small intestine, filled with contrast-enhancing material.

• Question 34:

  A young resident doing a fellowship in neuropathology is asked to review histological slides from the cerebral cortex of a 79-year-old nursing home resident, who died of multiinfarct dementia. The resident is asked to estimate the density of neurons in the infracted brain area. To prepare himself for the task, he first reviews slides from the normal areas of the cerebral cortex. Referring to following figure,which of the following structures does he correctly identify as neurons?

  

  A. 1

  B. 2

  C. 3

  D. 4

  E. 5

  Correct Answer: D

  Section: Anatomy Routine neuropathological identification of cells in the central nervous system is based on nuclear morphology using a stain such as the hematoxylin-eosin (HandE) stain shown in Fig. 1-10. The largest nuclei belong to neurons. Nuclei of glial cells are smaller and decrease in size from astroglia (choice A), to oligodendroglia (choice B), to microglia (choice C). Endothelial cells of the penetrating vasculature of the brain represent choice E.

• Question 35:

  An 8-year-old male patient is brought to a rural hospital with a history of recurrent infection. The patient has a characteristic facies with a high, broad nasal bridge, long face, narrow palpebral fissures, and an abnormally small mandible. The patient also has a cleft palate. The patient is diagnosed with DiGeorge syndrome, an inherited immunodeficiency disease due to a chromosome 22q11.2 deletion. In this syndrome, the production of which of the following cells is affected in the thymus?

  A. B cells

  B. endothelial cells

  C. macrophages

  D. neutrophils

  E. T cells

  Correct Answer: E

  Section: Anatomy In DiGeorge syndrome, the cortical epithelial cells of the thymus fail to develop and the thymus is hypoplastic. As a result, bone marrow-derived T-cell precursors cannot differentiate and functional T- cell production is markedly reduced. The development of B cells (choice A) is not affected in DiGeorge syndrome. Endothelial cells (choice B) forming the vascular walls are not affected by thymic maldevelopment, nor are the cells of myeloid lineage, the macrophages (choice C), and the neutrophils (choice D).

• Question 36:

  An 8-year-old boy is referred to a neurologist by his family physician because he has developed progressive slow and clumsy walking. On examination, the patient has difficulty with standing and running. While standing, he adopts a wide-based gait with constant shifting of position to maintain his balance. Sitting or standing, he also displays a constant tremor of the head and trunk. When asked to walk, his feet strike the ground in an uneven and irregular rhythm; if he attempts to correct his imbalance, he displays wild and abrupt movements. A magnetic resonance image (MRI) reveals demyelination in the dorsal columns, corticospinal and spinocerebellar tracts. The child is diagnosed with Friedreich's ataxia, an autosomal recessive neurological disorder resulting from mutation of a gene locus on chromosome 9. Second-order neurons of the dorsal (posterior) spinocerebellar tracts are located in which of the following?

  A. deep cerebellar nuclei

  B. dorsal root ganglion

  C. nucleus cuneatus

  D. nucleus dorsalis (Clarke's column)

  E. Rexed's lamina IX of the spinal cord

  Correct Answer: D

  Section: Anatomy The nucleus dorsalis (Clarke's column, Rexed's lamina VII of the spinal cord) contains the cell bodies of the second order neurons of the dorsal (posterior) spinocerebellar tract. Axons from these neurons ascend ipsilaterally in the lateral funiculus of the spinal cord, join the restiform body of the inferior cerebellar peduncle, and terminate in the vermis of the cerebellum as mossy fibers. The dorsal (posterior) spinocerebellar tract conveys proprioception from muscle spindles and Golgi tendon organs. Collateral branches of this tract also terminate in the deep cerebellar nuclei (choice A). The dorsal root ganglion (choice B) contains the cell bodies of sensory neurons, including the first-order neurons of the dorsal (posterior) spinocerebellar tract. The nucleus cuneatus (choice C) contains the second order neurons of the dorsal column pathways, responsible for conveying sensations of fine touch, pressure, and vibration sense. Rexed's lamina IX of the spinal cord (choice E) contains the spinal cord motorneurons responsible for the innervations of voluntary muscles.

• Question 37:

  Sean is 8 years old. He is referred by his school because he is habitually disruptive in class. Which of the following is the most useful area to explore at this point?

  A. his attention span

  B. his criminal record

  C. his relationship with his mother

  D. history of cruelty to animals

  E. history of enuresis

  Correct Answer: A

  Section: Behavioral Science and Biostatics Acommon cause of disruptiveness is attention deficit hyperactivity disorder (ADHD), which is characterized by inattention and hyperactivity. Enuresis (choice E), cruelty to animals (choice D), and trouble with the law (choice B) are often found in the childhoods of those who are eventually diagnosed as having an antisocial personality, but disruptiveness in class is more indicative of hyperactivity. Exploring Sean's relationship to his mother (choice C) may be useful, but not as much as assessing his attention span.

• Question 38:

  Thomas is a 9-year-old child of normal physical stature and health. He is unruly at school and refuses to abide by instructions given to him by his teachers. In addition, he has had inattention, hyperactivity, and impulsivity since the age of 5. Which of the following is the most likely diagnosis?

  A. anaclitic depression

  B. attention deficit hyperactivity disorder

  C. conduct disorder

  D. generalized anxiety disorder

  E. separation anxiety disorder

  Correct Answer: B

  Section: Behavioral Science and Biostatics The diagnostic criteria for ADHD include inattention, hyperactivity, and impulsivity invarious areas, and the symptoms must have been present before the age of 7. The specific history of inattention and hyperactivity tend to rule out choices A, C, D, and E, although there may be some elements of conduct disorder.

• Question 39:

  In following figure, arrow 2 points to which of the following specific structures A. central vein

  

  B. hepatic lobule

  C. portal tract

  D. sinusoid

  E. Space of Disse

  Correct Answer: A

  Section: Anatomy Arrow 2 points to the central vein which defines the center of each hepatic lobule (choice B). Arrows 1 and 3 point to portal tracts (choice C), which are located at the angles of the margins of the hepatic lobule. The sinusoids (choice D) originate from the margins of the lobules and converge to the central vein by running between the plates of hepatocytes. The space of Disse (choice E) is found between the sinusoid lining cells and the surfaces of the hepatocytes. It is best seen in electron micrographs and not in a photomicrograph.

• Question 40:

  Alarge vascular infarct involving the posterior limb of the internal capsule on the right side is likely to produce which of the following deficits?

  A. deviation of the protruded tongue to the right

  B. hypertonia and hyperreflexia in the right upper limb

  C. paralysis of facial expression muscles on the lower left portion of face

  D. paraplegia involving the lower extremities

  E. spastic hemiplegia involving the right side of the body

  Correct Answer: C

  Section: Anatomy Capsular lesions of the corticobulbar system produce the "central seven" symptoms. Loss of the descending cortical fibers to the contralateral facial nucleus (cranial nerve VII) primarily affects the muscles of facial expression in the lower portion of the face, particularly those around the angle of the mouth and the nasolabial fold. Deviation of the protruded tongue (choice A), hypertonia/hyperreflexia (choice B), and spastic hemiplegia (choice E) are symptoms that result from a capsular lesion, but they would be seen contralateral to the affected capsule, and in this case would involve the left side of the body.

  Paraplegia (choice D) is not typically seen following a unilateral capsular lesion.