Start learning →

USMLE Step 1 — free MCQ practice

Choose from 187 questions across 5 subjects and 6 topics. Open any question for its answer and worked solution, or keep learning through bite-sized lessons and reviews with Quill.

Start learning USMLE Step 1 with Quill →

USMLE Step 1 subjects

Physiology (54)Anatomy & Physiology (42)Microbiology (41)Epidemiology and Biostatistics (34)Behavioural Science (16)

Explore popular topics

The Digestive SystemThe Endocrine SystemVirologyMeasures of RiskPsychological DisordersCardiac Muscle and Electrical Activity

Try a USMLE Step 1 question

Which structure is known as the pacemaker of the heart?Read the answer and worked solution →The atrioventricular bundle passes through which structure before dividing into branches?Read the answer and worked solution →Which fibers finally spread the impulse to the myocardial contractile cells of the ventricles?Read the answer and worked solution →The AV node can transmit impulses maximally at about what rate?Read the answer and worked solution →

Worked practice questions

Which structure is known as the pacemaker of the heart?

  1. The sinoatrial node
  2. The atrioventricular node
  3. The bundle of His
  4. The Purkinje fibers
Show answer and solution

Correct answer: A. The sinoatrial node

1. Normal cardiac rhythm is established by the sinoatrial node, a specialized clump of myocardial conducting cells. 2. The SA node has the highest inherent rate of depolarization, so it is known as the pacemaker of the heart. 3. The AV node and Purkinje fibers conduct more slowly and follow its lead. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 19 "The Cardiovascular System: The Heart", section 19.2 Cardiac Muscle and Electrical Activity_

Open this question →

The atrioventricular bundle passes through which structure before dividing into branches?

  1. The interatrial septum
  2. The arch of the aorta
  3. The interventricular septum
  4. The coronary sinus
Show answer and solution

Correct answer: C. The interventricular septum

1. Arising from the AV node, the atrioventricular bundle is also called the bundle of His. 2. It proceeds through the interventricular septum before dividing. 3. It then splits into the left and right bundle branches on their way to the apex. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 19 "The Cardiovascular System: The Heart", section 19.2 Cardiac Muscle and Electrical Activity_

Open this question →

Which fibers finally spread the impulse to the myocardial contractile cells of the ventricles?

  1. Internodal pathways
  2. Chordae tendineae
  3. Trabecular fibers
  4. Purkinje fibers
Show answer and solution

Correct answer: D. Purkinje fibers

1. The bundle branches descend to the apex and connect with the Purkinje fibers. 2. The Purkinje fibers are additional myocardial conductive fibers that spread the impulse to the contractile cells. 3. They have a fast inherent conduction rate, reaching the whole ventricle quickly. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 19 "The Cardiovascular System: The Heart", section 19.2 Cardiac Muscle and Electrical Activity_

Open this question →

How to practise

  1. Choose a USMLE Step 1 question and try to work out your answer.
  2. Open the question to check the correct answer and read its worked solution.
  3. Continue in the app for bite-sized lessons, explanations and review with Quill. You can start without creating an account.