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USMLE STEP1 Exam Questions
Step1 (Page 17 )

Updated On: 31-Mar-2026
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PDF with 845 Questions

An 18-year-old male patient was thrown from a horse and suffered extensive damage to the back and pelvic region. After 2 weeks of recovery, it is noted that the patient has a spastic neurogenic urinary bladder. Although the patient is unable to initiate micturition, the bladder periodically empties itself. Where is the lesion affecting control of the bladder in this patient located?

  1. cauda equine
  2. spinal cord, above the level of S2
  3. spinal cord, at the level of S2
  4. spinal cord, at the level of S3
  5. spinal cord, at the level of S4

Answer(s): B

Explanation:

Since the patient presents with a spastic neurogenic bladder, the lesion is in the spinal cord above the level of S2. The micturition reflex works as follows: when the bladder becomes distended, sensory impulses travel back from the bladder to synapse onto preganglionic parasympathetic neurons located at the levels of S2-S4. These neurons, in turn, excite postganglionic parasympathetic neurons which innervate and cause contraction of the detrusor muscle of the urinary bladder, thus emptying the bladder. This primitive reflex loop comes under supraspinal influence in early childhood when the child learns control of the micturition reflex. When the supraspinal influence is removed, as happens with spinal lesions above the level of S2, the primitive reflex loop remains and the neurogenic spastic bladder empties itself reflexively whenever it becomes full. Lesions in the cauda equina (choice A), or in the spinal cord at the level of S2 (choice B), S3 (choice D), or S4 (choice E) will result in a flaccid bladder because of loss of innervation to the detrusor muscle. In this case, the bladder does not contract by itself and the patient will have to be catherized to prevent cystitis.



Papez circuit provides the anatomic substrate for the integration of cognitive, emotional, and expressive brain activities. Which of the following brain structures participates in Papez circuit?

  1. amygdale
  2. caudate nucleus
  3. mammilary nuclei
  4. suprachiasmatic nucleus
  5. ventrolateral thalamic nucleus

Answer(s): C

Explanation:

Papez circuit is formed by efferent fibers of the hippocampus, which project by way of the fornix to the mammillary nuclei in the hypothalamus. Axons from the mammillary nuclei project to the anterior thalamic nucleus, which is connected to the cingulate gyrus. The latter projects back to the hippocampus by way of the parahippocampal gyrus. Papez circuit integrates cortical, hypothalamic, and thalamic functions resulting in the integration of cognitive, emotional, and expressive brain functions. The ventrolateral thalamic nucleus (choice E) is involved in motor pathways, being connected to the deep cerebellar nuclei and the motor cortex. The caudate nucleus (choice B) is a component of the basal ganglia and the extrapyramidal motor control system. Although the amygdala (choice A) is involved in emotional brain functions, it is not part of Papez circuit. The suprachiasmatic nucleus (choice D) is located in the hypothalamus and mediates the circadian rhythm.



Aurologist is teaching her resident to perform a vasectomy. She explains that he has to inject the anesthetic in the skin of the scrotum, in preparation for incision of its lateral aspect. This surgical location allows for easy access to the spermatic cord. Which of the following nerves innervates the skin of the scrotum?

  1. femoral nerve
  2. iliohypogastric nerve
  3. ilioinguinal nerve
  4. obturator nerve
  5. subcostal nerve

Answer(s): C

Explanation:

The anterior aspect of the scrotum is innervated by branches of the ilioinguinal nerve (L1).Other nerves innervating the scrotum are branches of the genitofemoral nerve (L1, L2), pudendal nerve (S2-S4), and posterior femoral cutaneous nerve (S2, S3). The femoral nerve (L2-L4, choice A) supplies sensory innervations to the anteromedial thigh, hip joint, and knee joint. It also innervates muscles of the anterior compartment of the thigh. The iliohypograstric nerve (L1, choice B) provides sensory innervations over the iliac crest and the hypogastric region. The obturator nerve (L2-L4, choice D) supplies motor innervation to the medial compartment of the thigh. The subcostal nerve (T12, choice E) provides motor innervation for the lower part of the external oblique muscle and sensory innervations over the hip and anterior superior iliac spine.



Infiltrating or invasive ductal cancer is the most common breast cancer histological type, comprising 7080% of all cases. Invasive breast cancers usually are epithelial tumors of ductal or lobular origin. Which of the following epithelia line the lactiferous ducts?

  1. pseudostratified
  2. simple squamous
  3. stratified cuboidal
  4. stratified squamous
  5. transitional

Answer(s): C

Explanation:

The lactiferous duct is lined by a two-cell layered cuboidal epithelium. All other epithelial choices are not found in the breast tissue and are thus incorrect.



The abdominal aorta provides for the major blood supply in this region and its branches are organized into paired or unpaired and visceral or parietal branches. Which of the following are paired visceral branches of the abdominal aorta?

  1. celiac trunk
  2. gonadal arteries
  3. inferior phrenic arteries
  4. lumbar arteries
  5. superior mesenteric artery

Answer(s): B

Explanation:

The gonadal arteries are paired visceral branches of the abdominal aorta. Other branches in this category are the suprarenal and renal arteries. The celiac trunk (choice A) and superior mesenteric artery (choice E) are unpaired visceral branches. The inferior phrenic (choice C) and lumbar (choice D) arteries are paired parietal branches.



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