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USMLE STEP1 Exam Questions
Step1 (Page 12 )

Updated On: 31-Mar-2026
Page 12 of 171
PDF with 845 Questions

In the central auditory pathways, second-order neurons are located in which of the following?

  1. cochlear (spiral) ganglion
  2. cochlear nuclei
  3. inferior colliculi
  4. nuclei of lateral lemniscus
  5. superior olivary nuclei

Answer(s): B

Explanation:

Second-order neurons in the central auditory pathways are located in the dorsal and ventral cochlear nuclei. They receive afferents from the first-order neurons located in the cochlear (spiral) ganglion (choice A). Secondorder fibers from the cochlear nuclei project in turn to the inferior colliculi (choice C), nuclei of lateral lemniscus (choice D), and superior olivary nuclei (choice E).



Arrow 2 in following figure points to which of the following structures?

  1. glomerulus
  2. juxtaglomerular cells
  3. lacis cells
  4. macula densa
  5. vascular pole of the renal corpuscle

Answer(s): D

Explanation:

The macula densa indicated by arrow 2 is a modified segment of the distal tubule at the site of its passage adjacent to the vascular pole of the renal corpuscle. The name arises from the close spacing of nuclei of the epithelial cells forming this part of the distal tubule. These cells are thought tosense the chloride content in the passing filtrate and generate signals that regulate the caliber of the afferent arteriole. The glomerulus (choice A, arrow 1) is a network of capillaries derived from the afferent arteriole and suspended within Bowman's capsule by its vascular pole. The juxtaglomerular cells (choice B) form a cuff around the afferent arteriole prior to its entrance into the glomerulus and they secrete renin. Lacis cells (choice C, arrow 4) are extraglomerular mesangial cells with an uncertain function. The vascular pole (choice E, arrow
3) feeds blood to the glomerulus and carries blood away from it. As part of the juxtaglomerular apparatus, it is closely apposed to the macula densa.



A gang member is rushed to the emergency room suffering from multiple stab wounds made by an ice pick. Athird-year medical student rotating through emergency medicine is puzzled by the sight of a milky white substance exuding from a stab wound just superior to the right sternoclavicular joint. Which of the following structures is possibly injured at this location?

  1. the common carotid artery
  2. the cupola of the right lung
  3. the internal jugular vein
  4. the right lymphatic trunk
  5. the thoracic duct

Answer(s): D

Explanation:

The right lymphatic trunk is ruptured and chyle is exuding from the wound. Blood would flow from a wound involving the common carotid artery (choice A) or internal jugular vein (choice C). Astabbing lesion of the cupola of the right lung (choice B) would result in pneumothorax. The thoracic duct (choice E) does carry chyle. However, the thoracic duct drains into the bifurcation of the internal jugular and subclavian veins on the left side, above the left sternoclavicular joint.



A 72-year-old male patient has suffered a cerebral infarct affecting the left cerebral hemisphere. On examination of the patient, it is noticed that his verbal output is fluent and paraphasic. His comprehension of speech is normal but repetition is severely impaired. Naming is also impaired, although when given a list, the patient is able to select the correct name. Special consultation with a neurologist results in a diagnosis of conduction aphasia. Which of the following brain structures is affected?

  1. arcuate fasciculus
  2. Broca's area
  3. nucleus ambiguous
  4. red nucleus
  5. Wernicke's area

Answer(s): A

Explanation:

The arcuate fasciculus connects Wernicke's area to Broca's area, integrating comprehension of speech with motor speech. A lesion in this connecting bundle results in this unusual condition of conduction aphasia, characterized by impairment of repetition and naming. Broca's area (choice B) is the motor speech area and lesion in this area will result in motor speech impairment. However, this patient's verbal output is fluent. Alesion in the nucleus ambiguus (choice C) will result in dysarthria and also loss of a fluent verbal output. The red nucleus (choice D) is a mesencephalic motor nucleus, which does not participate in the central pathways for speech. Wernicke's area (choice E) is the speech comprehension area, which is intact in this patient because he comprehends spoken language.



Which of the following is characterized by an absence of lymphoid follicles and germinal centers?

  1. axillary lymph node
  2. Peyer's patches
  3. pharyngeal tonsil
  4. spleen
  5. thymus

Answer(s): E

Explanation:

The thymus provides for development of new T lymphocytes in an environment shielded from foreign antigens. Like bone marrow, the thymus is a primary lymphoid organ, and not a site of reactions to foreign antigens. Lymphoid follicles are sites of B lymphocyte proliferation in response to antigen stimulation.
These occur in the lymph nodes (choice A), Peyer's patches (choice B), tonsils (choice C), and white pulp of the spleen (choice D).



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