Myogenic stimulation and the electrocardiogram

Overview

Importance of the delay imposed at the atrioventricular node and advantage of the ventricles contracting from the apex upwards.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What does it mean to say that cardiac muscle is myogenic?

   Model answer

   It means the muscle contracts rhythmically of its own accord, without needing a nerve impulse to initiate each beat.

2. 2

   Where is the sinoatrial node located?

   Model answer

   The sinoatrial node lies in the wall of the right atrium, near the entry of the vena cava.

3. 3

   Why is the sinoatrial node described as the pacemaker of the heart?

   Model answer

   It generates the wave of excitation at a faster rate than any other region, so it sets the rhythm the whole heart follows.

4. 4

   Describe what happens when the wave of excitation spreads over the atria.

   Model answer

   It causes both atria to contract together, producing atrial systole.

5. 5

   Why can the wave of excitation not pass directly from the atria to the ventricles?

   Model answer

   A band of non-conducting fibrous tissue separates the atrial and ventricular muscle, so excitation can cross only at the atrioventricular node.

6. 6

   Where is the atrioventricular node found?

   Model answer

   The atrioventricular node lies at the base of the right atrium, close to the septum between the atria.

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