Problem 167 - Objective Biology for NEET

Question

Assertion: SA node is called pacemaker of heart. Reason: It is responsible for initiating and maintaining the rhythm of heart

Step-by-Step Solution

Answer

The Assertion-Reason link is valid as the SA node is known as the pacemaker of the heart because it is responsible for initiating and maintaining the heart's rhythm.

Step 1: Understanding the Assertion

The 'Sinoatrial (SA) node,' often referred to as the 'pacemaker of the heart,' is indeed a section of cardiac muscle cells found in the right atrium of the heart. These cells are distinct because they have the unique capability to spontaneously generate electrical impulses.

Step 2: Understanding the Reason

The 'reason' states that the SA node is responsible for initiating and maintaining the rhythm of the heart, this is indeed true. The electrical impulses generated by the SA node, cause the heart muscle to contract and thus initiate the heartbeat. This node determines the rate of heart contractions, thereby maintaining the rhythm of the heart.

Step 3: Validating the Assertion-Reason Link

Since the assertion and the reason are both independently correct and the reason correctly explains the assertion, it can be concluded that the Assertion-Reason link is valid.

Key Concepts

Pacemaker of the Heart

The Sinoatrial (SA) node is famously known as the "pacemaker of the heart."
Located in the right atrium, it consists of specialized cardiac muscle cells.
What makes the SA node remarkable is its ability to initiate electrical impulses without any external stimulus. These impulses begin the process of heart contraction and are crucial for establishing a regular heartbeat.
By setting the pace at which the heart beats, the SA node ensures that the entire heart works in harmony, effectively pumping blood throughout the body.

Cardiac Muscle Cells

Cardiac muscle cells make up a significant portion of heart tissue, including the SA node.
These cells are distinct from other muscle types, like skeletal muscles, because of their ability to communicate and work together in an organized manner.
A unique feature of cardiac muscle cells in the SA node is their ability to spontaneously generate electrical signals.
This means that they do not rely on signals from the brain to initiate a heartbeat. Instead, they act autonomously, ensuring the heart rhythm is consistent and reliable.

• Specialized cells in the SA node possess automatic impulse generation.
• These cells maintain cohesion and coordination throughout the heart muscle.

Electrical Impulses

Electrical impulses are the driving force behind the heart's ability to pump blood.
These impulses originate in the SA node and spread across the heart, prompting contraction.
Think of these impulses as natural electrical signals that tell the heart muscle when to contract and pump blood. As they move, they ensure that each part of the heart contracts in the correct sequence.
This precise sequence is crucial for capturing and ejecting blood efficiently from chambers like the atria and ventricles.

• Electrical impulses initiate in the SA node.
• These signals ensure synchronized heart functions.

Heart Rhythm

Heart rhythm refers to the consistent, coordinated beat that keeps blood moving throughout the body.
The SA node establishes this rhythm by creating a regular sequence of electrical impulses. These impulses set the basic rate at which the heart contracts.
Without a proper rhythm, the heart wouldn't be able to efficiently supply the body with the necessary oxygen and nutrients.
Abnormal heart rhythms can lead to health problems, so the pacemaking role of the SA node is vital for healthy cardiovascular function.

• Regular heart rhythm is crucial for effective blood circulation.
• The SA node maintains steady heart function.