Cardiac Electrical System – SG

Inside the heart, there is an electrical conduction system that causes the heart to contract. The heart muscle is made up of special smooth muscle cells that can transmit electrical signals known as cardiac cells. The is part of the autonomic nervous system and has its own pacemakers that cause the heart to contract.

The heart is part of the autonomic nervous system it is not set at a fixed rate. The rate can be affected by hormones and the nervous system. The medulla sets the rate for the sino-atrail node (SAN) through the antagonistic actions of the autonomic nervous system.

The autonomic nervous system has 2 sets of nerves :
the sympathetic system never pathway the releases noradrenaline to increase the heart rate and the parasympathetic pathway that releases acetylcholine that decreases the heart rate.

The heartbeat starts in the top right atrium at the SA node. The SA node will send an electrical impulse that will set the rate at which the heart will beat. The impulse then travels through the walls of both atriums causing the atriums to contract known as atrial systole.

The impulse passes through the atrioventricular node (AVN). The AVN is located in the lower part of the right atrium and is the gatekeeper allowing the impulse to pass through into the ventricles. Once the impulse is passed through the AVN it passes through conduction fibers that travel down the septum (the central wall of the heart) and splits into left and right fibers that wrap around the ventricles and cause them to contact (Ventricular systole).

Heart’s Electrical System

The Marvels of the Heart’s Electrical System: A Symphony of Life

At the heart of our existence lies an astonishing electrical system that orchestrates the rhythmic dance of life within us. The cardiac electrical system is a complex network of specialized cells that generate and transmit electrical impulses, enabling our hearts to beat with remarkable precision and regularity. Let’s delve into the intricacies of this extraordinary system and understand how it keeps the music of life playing harmoniously.

1. The Sinoatrial (SA) Node – The Heart’s Natural Pacemaker:

  • Located in the right atrium, the SA node initiates each heartbeat.
  • It generates electrical impulses at a regular rate, setting the heart’s rhythm.

2. Atrioventricular (AV) Node – The Gatekeeper:

  • Positioned between the atria and ventricles, the AV node acts as a gateway for the electrical impulses.
  • It briefly delays the impulses, allowing the atria to contract and fill the ventricles completely before ventricular contraction.

3. The Bundle of His and Purkinje Fibers – Propagation of Impulses:

  • After passing through the AV node, the electrical impulses travel down the bundle of His, a bundle of specialized fibers.
  • These fibers then split into the Purkinje fibers, spreading throughout the ventricles.
  • The Purkinje fibers deliver the electrical signal to the ventricular muscle cells, causing the ventricles to contract and pump blood out of the heart.

4. The Cardiac Cycle – A Step-by-Step Journey:
The cardiac electrical system coordinates the heart’s actions through a series of steps, known as the cardiac cycle:

  • Step 1: Atrial Contraction (Atrial Systole)
  • The SA node generates an electrical impulse that causes the atria to contract.
  • Blood is forced into the ventricles through the open atrioventricular valves (tricuspid and mitral valves).
  • Step 2: Ventricular Contraction (Ventricular Systole)
  • The electrical impulse reaches the ventricles through the AV node, causing them to contract.
  • The atrioventricular valves close to prevent blood from flowing back into the atria.
  • The semilunar valves (aortic and pulmonary valves) open, allowing blood to be pumped out of the heart.
  • Step 3: Relaxation Phase (Diastole)
  • The ventricles relax, allowing them to fill with blood again.
  • The atria continue to receive blood from various parts of the body.

5. ECG (Electrocardiogram) – Capturing the Heart’s Electrical Activity:

  • An ECG is a non-invasive diagnostic test that records the heart’s electrical activity.
  • It provides valuable information about the heart’s rhythm, rate, and any potential abnormalities.
  • ECG waves represent different phases of the cardiac cycle: P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization).

6. Regulation of Heart Rate:

  • The heart rate is influenced by the autonomic nervous system, which comprises the sympathetic and parasympathetic divisions.
  • The sympathetic nervous system increases heart rate during times of stress or physical activity.
  • The parasympathetic nervous system decreases heart rate during rest and relaxation.

The cardiac electrical system is a symphony of precise electrical signals that keeps our hearts beating in perfect harmony. This symphony ensures that blood flows rhythmically throughout our bodies, providing essential oxygen and nutrients to every cell. Understanding how this intricate system works empowers us to appreciate the marvels of our bodies and inspires us to take care of our hearts through a healthy lifestyle and regular check-ups. Let us cherish the music of life within us, conducted by the heart’s magnificent electrical orchestra.