Question

Read the following statements and select the correct option. Statement 1 : Cardiac muscle of the heart is striated and has intercalated discs between its fibres (cells). Statement 2 : It provides quick, powerful and rhythmic contractions to the heart. (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1 . (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1 . (c) Statement 1 is correct and statement 2 is incorrect. (d) Both statements 1 and 2 are incorrect.

Short answer

Both statements 1 and 2 are correct, but statement 2 is not the correct explanation of statement 1, so the answer is option (b).

Step-by-step solution

Verification of Statement 1

Examine the first statement: Cardiac muscle of the heart is striated and has intercalated discs between its fibers (cells). Verify this information with established biological facts: Cardiac muscle tissue, which is only found in the heart, indeed has striations similar to skeletal muscle and contains intercalated discs. Intercalated discs are specialized structures that facilitate communication and strong connections between adjacent cardiac muscle cells. Hence, Statement 1 is correct.

Verification of Statement 2

Review the second statement: It provides quick, powerful, and rhythmic contractions to the heart. Confirm the statement against biological knowledge: Cardiac muscle is responsible for pumping blood throughout the body, which requires quick, powerful, and rhythmic contractions. This is an accurate description of the cardiac muscle function, thus Statement 2 is also correct.

Relation between Statement 1 and Statement 2

Determine if Statement 2 is the correct explanation of Statement 1: Statement 1 describes the structural features of cardiac muscle, while Statement 2 describes the functional characteristics. While the structures in Statement 1 do contribute to the function in Statement 2, Statement 2 is not a direct explanation of the structural attributes listed in Statement 1. Therefore, while both statements are correct, Statement 2 is not the correct explanation of Statement 1.

Key concepts

Striated Muscle

Understanding the striated muscle helps in comprehending the unique characteristics of different muscle types in the body. Striated muscle tissues are so named because of their striped appearance under the microscope, which is due to the arrangement of proteins (myofilaments) within the muscle cells. These myofilaments are organized into repeating units called sarcomeres, which are the basic functional units of muscle contraction.

In the human body, we have two types of striated muscles: skeletal and cardiac. Skeletal muscles are under voluntary control, and they are responsible for body movements. Cardiac muscle, which is the focus of the exercise, shares some similarities with skeletal muscle, such as the striated pattern, but it operates under involuntary control. It is designed to work autonomously and tirelessly to pump blood throughout the life of an individual.

What sets cardiac muscle apart is not just its location in the heart, but its endurance and capability to function continuously without fatigue. While their striated appearance may be similar at first glance, understanding the microscopic and physiological differences is crucial for grasping the complex behavior of cardiac muscle.

Intercalated Discs

Intercalated discs are highly specialized structures unique to cardiac muscle tissue. These discs play a crucial role in maintaining the health and function of the heart. They appear as dark bands under the microscope and are located at the junctions where individual heart muscle cells, or cardiomyocytes, connect.

These discs have three main functions:

• Enabling strong physical attachments between cells through desmosomes, which prevent the cells from pulling apart during contractions.
• Facilitating electrical coupling with gap junctions that allow the rapid transmission of electrical impulses. This ensures synchronized contractions, producing a coordinated heartbeat.
• Maintaining the structural integrity of the heart's muscle tissue by binding the cells tightly together.

The importance of intercalated discs cannot be overstated. Without them, the heart would lose its ability to contract in a powerful and synchronized manner, leading to a compromised ability to circulate blood efficiently. As the exercise correctly explains, these structures support the quick and powerful contractions mentioned in Statement 2, even though that function is not a direct explanation of the presence of the discs.

Muscle Contraction

Muscle contraction is the process by which muscle fibers produce force and movement, either by shortening or by creating tension. In the context of cardiac muscle, this contraction is what enables the heart to pump blood throughout the body. The process of muscle contraction involves complex interactions at a molecular level, primarily the sliding of actin and myosin filaments past one another.

This sliding mechanism is powered by the breakdown of ATP (adenosine triphosphate), which provides the necessary energy. The cycle of contraction and relaxation in cardiac muscle is rhythmic and intrinsic, meaning that it is governed by the heart's natural pacemaker cells, not by external stimuli or conscious control.

Phases of Cardiac Muscle Contraction

In a simplified explanation, cardiac muscle contraction follows these phases:

• Electrical impulses initiate the contraction.
• Calcium ions are released and bind to the protein troponin, which triggers the sliding of actin and myosin filaments.
• ATP is utilized to generate force, causing the heart chambers to contract and pump blood.
• The muscle then relaxes once the calcium ions are pumped out, preparing for the next cycle.

The synchronized and orderly contractions ensure that blood is efficiently moved from the heart to the lungs for oxygenation and then circulated to the rest of the body. An understanding of this process underlines the importance of the structural characteristics of the cardiac muscle as they relate to its essential function.