USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 751:

  A middle-aged, markedly obese male patient presents to the emergency room with pain in the inguinal region. Examination reveals an abnormal bulge which increases in size when the patient performs the Valsava maneuver. The bulge can be reduced manually when the patient is lying supine. However, as soon as the patient stands up and coughs, the bulge reappears. The patient is diagnosed with an inguinal hernia. The chief resident in surgery asks for a determination of whether the hernia is direct or indirect. Which of the following is a useful landmark to distinguish an indirect from a direct inguinal hernia?

  A. anterior superior iliac spine

  B. inferior epigastric vessels

  C. inguinal ligament

  D. pubic tubercle

  E. umbilicus

  Correct Answer: B

  Section: Anatomy The inferior epigastric vessels lie medial to the deep inguinal ring. An indirect inguinal hernia leaves the abdominal cavity through the deep inguinal ring and is thus always localized lateral to the inferior epigastric vessels. Adirect inguinal hernia results from weakness in the posterior wall of the inguinal canal and pushes through the conjoint tendon to reach the superficial inguinal ring. The direct inguinal hernia is thus always located medial to the inferior epigastric vessels. The anterior superior iliac spine (choice A) and pubic tubercle (choice D) are respectively located too far laterally or medially to be of use in distinguishing indirect from direct hernias. The inguinal ligament (choice C) is used to istinguish a femoral hernia which is always located inferior to this structure. The umbilicus (choice E) is the site for an umbilical hernia and not inguinal hernias.

• Question 752:

  Which of the following vessels participate in the arterial circulation of the spleen?

  A. afferent arteriole

  B. efferent arteriole

  C. interlobar arteries

  D. interlobular arteries

  E. sheathed arteriole

  Correct Answer: E

  Section: Anatomy The spleen receives its blood supply from the splenic artery, which branches off from the celiac trunk from the abdominal aorta. At the hilum of the spleen, the splenic artery branches off into trabecular arteries, which enter the spleen along the trabeculae and branch in the parenchyma as central arteries running in the white pulp. The central arteries branch into penicillar arterioles, which give rise to capillaries and sheathed arterioles. The capillaries feed the marginal sinuses as well as the red pulp sinuses. Afferent (choice A) and efferent (choice B) arterioles, and interlobar (choice C) and interlobular (choice D) arteries are vessels found in the kidney.

• Question 753:

  Which of the following is directly involved with the descending modulation of pain transmission?

  A. dopamine

  B. MLF

  C. nucleus raphe magnus

  D. rubrospinal fibers

  E. ventral lateral thalamic nucleus

  Correct Answer: C

  Section: Anatomy The nucleus raphe magnus receives input from the periaqueductal gray and gives rise to descending serotonergic fibers of the raphe spinal projection. The latter fibers activate enkephalinergic spinal cord interneurons that presynaptically inhibit incoming pain fibers at their initial synapse in the spinal cord dorsal horn. The neurotransmitter dopamine (choice A) has not been shown to be involved in the descending systems that modulate pain transmission. The MLF (choice B) is an ascending fiber system in the brainstem that is primarily involved in the control of eye movements. The rubrospinal system (choice D) is a descending fiber tract involved with the control of limb musculature. The ventral lateral nucleus of the thalamus (choice E) is primarily involved with motor function and does not contribute to descending pathways that influence pain transmission.

• Question 754:

  Cilia are anchored to the apical portion of certain types of epithelial cells and they are mobile. Which of the following form the motile cytoskeletal component of the cilia?

  A. intermediate filaments

  B. microfilament

  C. microtubule

  D. neurofilament

  E. tonofilaments

  Correct Answer: C

  Section: Anatomy Acilium is formed by a concentric array of nine microtubule doublets surrounding a central pair of microtubules (9 + 2 organization). Intermediate filaments (choice A) are intermediate in diameter size (10 nm) between the microtubules (25 nm) and the microfilaments (7 nm). They do not confer motility to the cilia. They instead participate in the cytoskeletal integrity of nerve cells, neurofilaments (choice D) or hemidesmosomes, tonofilaments (choice E). Microfilaments (choice B) are found in microvilli and stereocilia.

• Question 755:

  A 79-year-old female patient was admitted to the hospital, presenting with fever, vomiting, dehydration, and distension of the abdomen. An X-ray reveals ileus and exploratory surgery reveals occlusion of vasa recta of the jejunum. Which of the following arteries supply branches to the involved vasa recta?

  A. ileocolic artery

  B. inferior pancreaticoduodenal artery

  C. right colic artery

  D. right gastroepiploic artery

  E. superior mesenteric artery

  Correct Answer: E

  Section: Anatomy Ileus is obstruction of the intestine, in this case due to paralysis resulting from ischemia. The jejunum receives its vascular supply from jejunal branches arising from the superior mesenteric artery. The ileocolic artery (choice A) supplies the ileum, ileocolic junction, and the appendix. The inferior pancreaticoduodenal artery (choice B) provides vascular innervations to the pancreas and duodenum, and forms the anastomosis between the foregut and midgut. The right colic artery (choice C) supplies the ascending colon and the right gastroepiploic artery (choice D) the greater curvature of the stomach and greater omentum.

• Question 756:

  Which of the following is characteristic of damage to the corticospinal (pyramidal) system?

  A. Babinski's sign

  B. flaccid paralysis and hypotonia

  C. immediate muscle degeneration and atrophy

  D. intention tremor

  E. loss of deep tendon reflexes

  Correct Answer: A

  Section: Anatomy The Babinski sign--dorsiflexion of the great toe in response to stroking the plantar aspect of the foot-- is a characteristic sign of pyramidal tract involvement. Signs and symptoms of corticospinal tract injury that are nearly always apparent to some degree include spastic paralysis, hypertonia, loss of deep tendon reflexes, and hyperactive abdominal and cremasteric reflexes. Flaccid paralysis and hypotonia (choice B) are commonly seen following lower motoneuron injury, as is loss of deep tendon reflexes (choice E). Muscle degeneration and atrophy (choice C) are not characteristic symptoms of corticospinal tract damage. The presence of an intention tremor (choice D) is a sign of cerebellar damage, and is not seen with corticospinal tract lesions.

• Question 757:

  Which of the following statements concerning muscle spindles is correct?

  A. Activation of type Ia sensory fibers from a given spindle leads to inhibition of the muscle in which that spindle is located.

  B. Alpha motoneurons synapse directly with intrafusal muscle fibers.

  C. Each intrafusal fiber is innervated by two different gamma motoneurons.

  D. Only one type of intrafusal muscle fiber (cell) is present in most muscle spindles.

  E. Type Ia sensory fibers from a spindle form direct synaptic contact with alpha motoneurons in the spinal cord.

  Correct Answer: E

  Section: Anatomy The type Ia sensory fibers from a spindle form direct excitatory synapses with alpha motoneurons. Activation of type Ia sensory fibers (choice A) leads to excitation of the muscle in which that spindle is located. Alpha motoneurons (choice B) synapse with extrafusal muscle fibers, whereas gamma motoneurons synapse with intrafusal muscle fibers. Each intrafusal muscle fiber (choice C) is innervated by only one gamma motoneuron. Each muscle spindle contains a mixture of both nuclear bag and nuclear chain intrafusal fibers, not just one type as indicated in choice D.

• Question 758:

  Which of the following thalamic nuclei subserves a motor function?

  A. dorsomedial nucleus

  B. lateral geniculate nucleus

  C. medical geniculate nucleus

  D. ventral lateral nucleus

  E. ventral posterior medial nucleus

  Correct Answer: D

  Section: Anatomy The ventral lateral nucleus of the thalamus receives projections from the deep cerebellar nuclei and, in turn, sends projections to the motor cortex. It is thus functionally defined as a thalamic motor nucleus. The dorsomedial nucleus (choice A) is considered a limbic nucleus of the thalamus as it receives projections from the amygdala and olfactory cortex, and projects to the prefrontal cortex and hypothalamus. The lateral (choice B) and medial geniculate (choice C) nuclei and the ventral posterior medial nucleus (choice D) are considered sensory nuclei as they receive information mediating vision, audition, and somatosensory signals from the face, respectively. In turn, these three brain areas project to the somatosensory cortex.

• Question 759:

  A neurology resident is testing the jaw-jerk reflex in a patient by tapping gently on the right masseter muscle and observing elevation of the mandible. What is the location of the neuronal cell bodies of the proprioceptive fibers mediating the jaw-jerk reflex?

  A. mesencephalic trigeminal nucleus

  B. motor trigeminal nucleus

  C. principal (main) trigeminal nucleus

  D. spinal trigeminal nucleus

  E. trigeminal (gasserian) ganglion

  Correct Answer: A

  Section: Anatomy The jaw-jerk reflex is a monosynaptic (stretch) reflex for the masseter muscle. Proprioceptive fibers from the muscle travel by way of the trigeminal nerve back to their cell bodies in he mesencephalic trigeminal nucleus. Projections from this nucleus synapse on motor neurons of the motor trigeminal nucleus (choice B) which elicits contraction of the masseter muscle. The principal (main) trigeminal nucleus (choice C) receives light touch sensory information from the face, whereas the spinal trigeminal nucleus (choice D) receives pain and temperature sensations. The trigeminal (gasserian) ganglion (choice E) contains the cell bodies of all sensory neurons projecting to the principal (main) and spinal trigeminal nuclei.

• Question 760:

  During surgical resection of the gastrointestinal tract for treatment of long-standing irritable bowel syndrome, a surgery resident is asked to select a surgical site coinciding with the termination of the vagal innervation. Which of the following does she select?

  A. duodenojejunal junction

  B. ileocolic junction

  C. junction of the second part and third part of the duodenum

  D. left colic (splenic) flexure

  E. right colic (hepatic) flexure

  Correct Answer: D

  Section: Anatomy The left colic (splenic) flexure represents the junction of the midgut to the hindgut during embryonic development. The vagus (tenth cranial) nerve provides the parasympathetic innervation of the digestive tract up to this flexure, whereas the pelvic parasympathetic fibers from S2-S4 innervate the rest of the tract. The duodenaljejunal junction (choice A), ileocolic junction (choice B), and rightcolic (hepatic) flexure (choice E) are anatomical landmarks along the digestive tract without change in parasympathetic innervation. The junction of the second part and third part of the duodenum (choice C) represents the embryonic junction between the foregut and the midgut, but both receive vagal innervation.