🧠 Final Tip for Students
To remember the flow of blood through the heart:
“RA → RV → Lungs → LA → LV → Body”
- RA: Right Atrium
- RV: Right Ventricle
- LA: Left Atrium
- LV: Left Ventricle
🫀 Control of Heartbeat: Heart Excitation and Contraction
The human heart is an amazing organ that beats on its own, without us needing to think about it. But how does it know when to beat and how fast? That’s what this lesson is all about.
🔋 Initiation of Heartbeat — The Heart’s Natural Battery
The heartbeat starts from a special group of cells called the Sinoatrial Node (SA Node). This group of cells works like a natural battery or timer inside your heart. It is also called the pacemaker of the heart.
📍 Where is it located?
The SA Node is found in the upper wall of the right atrium (one of the upper chambers of the heart).
⚡ What does it do?
- It sends electrical signals (impulses).
- These impulses spread across the walls of both atria.
- As a result, both atria contract at the same time and push blood into the ventricles.
🧠 Real-life example:
Imagine a school bell system. When the bell rings, all students move at the same time. Similarly, when the SA node sends a signal, both atria respond at the same time and contract.
🧠 Transmission of Impulses — The Heart’s Electrical Wiring
After the signal starts at the SA node, it needs to travel through the heart so that the ventricles also contract. Let’s follow the path of this impulse:
1️⃣ Atrioventricular Node (AV Node)
- Located at the bottom of the wall between the two atria (called the interatrial septum).
- It receives the signal from the SA node.
⏱️ Delay for Proper Timing
Before sending the signal forward, the AV node pauses the signal for 0.15 seconds.
🧠 Why delay?
To give the atria time to empty their blood into the ventricles before the ventricles start contracting.
💡 Real-life example:
It’s like pressing the clutch before changing gears in a car—if you don’t do it at the right time, the car will jerk or stop. Timing is important!
2️⃣ Atrioventricular Bundle (Bundle of His)
- From the AV node, the signal moves into a bundle of muscle fibers called the AV Bundle, also known as the Bundle of His.
- This bundle is found in the interventricular septum (the wall between the two ventricles).
3️⃣ Right and Left Bundle Branches
- The AV bundle splits into two branches:
- One goes to the right ventricle
- One goes to the left ventricle
4️⃣ Purkinje Fibers
- These are very fine, fast-conducting fibers that spread through the walls of the ventricles.
- When they receive the signal, they cause the ventricles to contract simultaneously.
🧠 Real-life example:
Think of the electrical wiring in a house. The main switch (SA node) sends power through wires (AV node, Bundle of His, branches, Purkinje fibers) to different rooms (atria and ventricles) to switch on the lights (heart contractions).
🔁 How Everything Works Together – A Summary
- SA Node starts the heartbeat → sends impulse to atria → atria contract.
- Signal goes to AV Node, pauses briefly.
- Then passes through Bundle of His, branches, and Purkinje Fibers.
- Finally, ventricles contract and push blood to the lungs and rest of the body.
This entire sequence happens every time your heart beats – which is about 70–80 times per minute when you’re resting!