Anatomy and Physiology 2- SA and VA nodes (lecture-based questions)

These are questions that are closely related to the online lecture of the SA and VA nodes.

What are the four chambers of the heart?

Right atrium, Left atrium, Right Ventricle, and Left venticle

What is the role of the superior vena cava in the heart?

The Superior vena cava’s role in the heart is to transport deoxygenated blood from the upper half of the heart into the right atrium

Where is the SA nod located, and what it its function?

The SA node is located beside where the superior vena cava enter the right atrium. Its function is to act as the heart’s “pacemaker”, automatically depolarizing about 60 times per minute without any input from the nervous system, and initiating the depolarization that causes the atria to contract and thus starting the heartbeat.

How often do SA nodes depolarize per minute without nervous system input?

SA nodes depolarize approx. 60 times per minute without nervous system input.

How does the SA node connect to other cardiac muscle cells, and what is the result of its depolarization?

The SA node connects to other specialized cardiac muscle cells that form small tubes spreading out from the SA node. Two tubes go to the left atrium and branch out and another one goes to the right atrium and branches out. Each time the SA node polarizes, it sends the depolarization along these tubes, causing the cardiac muscles in the atria walls to depolarize and contract. This initiates a heartbeat, causing both atria to contract simultaneously.

What is the internodal pathway, and why is its slow signal important?

The internodal pathway is a series of small muscle tubes that carry electrical signals from the SA node to the AV node int he heart. Its slow signal is important because it gives the atria time to contract and push blood into the ventricles before the ventricles contract. This delay ensures that the heart pumps blood efficiently.

What happened when the signal reaches the AV node?

When the signal reaches the AV node, it causes the AV node to polarize and then quickly send the signal down to the AV bundle. This ensures the ventricles contract after the atria, allowing for efficient blood flow.

Describe the pathway and function of the AV bundle and Purkinje fibers.

The AV bundle, also know as the bundle of His, is a thick tube of cardiac muscle cells located in the interventricular septum. It splits into two smaller tubes that goes to the bottom of the heart (the apex), then curve back up the sides. These tubes are called Purkinje fibers. The function of the AV bundle and Purkinje fibers is to quickly carry the electrical signal from the AV node to the bottom of the ventricle, causing the ventricles to contract from the bottom up. This helps push blood out of the heart to the lungs and the rest of the body.

Why do the ventricles contract from the bottom up?

The ventricles contract from the bottom up to effectively push blood upward and out to the pulmonary arteries and the aorta

What can cause irregular heartbeats, and what are the symptoms of atrial fibrillation (A-fib)?

Irregular heartbeats can be caused by problems with the heart’s natural pacemaker, the SA node. When the SA node doesn’t work properly, it can lead to atrial fibrillation (A-fib), where the upper chambers of the heart beat chaotically. Symptoms include feeling light-headed, unbalanced, and having a slower heart rate, which can make you feel weak or tired.

What is ventricular fibrillation (V-fib), and why is it more serious than A-fib?

Ventricular fibrillation (v-fib) is a condition where the ventricles of the heart, which are responsible for pumping blood out of the body, start to beat very rapidly and irregularly. This chaotic beating means the heart can’t effectively pump blood, which can lead to cardiac arrest. V-fib is more serious than atrial fibrillation (A-fib) because in A-fib, the atria (upper chmabers) beat irregularly but the ventricles can still pump some blood. In V-fib, the ventricles’ inability to pump properly can quickly become life-threatening.

What is the function of a pacemaker in the heart?

A pacemaker is a device that helps control the heart’s rhythm. It monitors the heart’s activity and sends electrical signal to make sure the heart beats at a regular pace

What happens during a complete and partial heart block?

During a complete heart block, the signals from the SA node (which usually control the heartbeat) do not reach the AV node. As a result, the AV node creates its own slower rhythm of 40-50 beats per minute, and the atria do not contract properly.

In a partial heart block, sometimes the signals get through and sometimes they don’t leading to an irregular heartbeat.

How does the sympathetic nervous system influence the heart?

The sympathetic nervous system increases heart rate by sending signals to the SA and AV nodes. It releases a chemical called norepinephrine, which binds to specific receptors on these nodes, telling the heart to beat faster.

How does the parasympathetic nervous system, via the vagus nerve, affect the heart rate?

The parasympathetic nervous system, through the vagus nerve, slows down the heart rate by releasing a chemical called acetylcholine. This chemical binds to receptors on the heart’s pacemaker cells, telling them to beat more slowly.

What would happen to the heart rate if the vagus nerve is cut?

If the vagus nerve is cut, the heart rate would immediately increase by about 20 beats per minute.