Question

The long cylindrical fibres that form a muscle is made up of (a) Tinofibriles (b) Collagen fibres (c) Fibroblasts (d) Myofibrils

Short answer

The long cylindrical fibres that form a muscle are made up of (d) Myofibrils.

Step-by-step solution

Understand the question

The question is asking, 'What are the long cylindrical fibres that form a muscle made of?' It is necessary to understand the basic biology about the structure of muscles to answer this question.

Evaluate the options

Next, you evaluate the options provided by using your knowledge of muscle structure: (a) Tinofibriles (b) Collagen fibres (c) Fibroblasts (d) Myofibrils.

Choose the correct answer

By evaluating the options, we know that the correct answer is (d) Myofibrils. This is because Myofibrils are the long cylindrical fibres that form a muscle. They are composed of sarcomeres, which are the basic functional units of muscle fibres.

Key concepts

Myofibrils

Understanding myofibrils is essential when delving into the complexities of muscle anatomy and physiology. Myofibrils are specialized structures that reside within muscle fibers and are crucial to muscle contraction. They are composed of long chains of sarcomeres, which are connected end-to-end to form the myofibril. Each myofibril is encapsulated within a muscle fiber, and numerous myofibrils can be found within a single muscle fiber, contributing to its overall strength and contractility.

These cylindrical organelles are densely packed with protein filaments known as actin (thin filaments) and myosin (thick filaments), which interact during muscle contraction to shorten or lengthen the muscle. It is through the sliding filament theory that the role of myofibrils in contraction is explained where actin slides over myosin to change the muscle length and generate movement. This microscopic process is the fundamental mechanism underlying all voluntary muscle movement.

Sarcomeres

Sarcomeres are the smallest contractile units of striated muscle tissue and are fundamental components of myofibrils. Each sarcomere is delimited by Z-discs, which are repeating segments that give striped (striated) muscle tissue its distinctive appearance under a microscope.

The sarcomere houses actin and myosin myofilaments that are essential for muscle contraction. The arrangement of these filaments creates a pattern of light and dark bands: I bands (light), containing thin actin filaments; A bands (dark), made of overlapping thick myosin and thin actin filaments; and the H zone, a lighter region within the A band where only myosin is present.

During muscle contraction, the sarcomeres shorten, bringing the Z-discs closer together. This shortening is due to the actin filaments sliding over the myosin filaments, a process regulated by calcium ions and ATP (adenosine triphosphate). Understanding the structure and function of sarcomeres is pivotal for comprehending muscle contraction at a molecular level.

Muscle Fibers

Muscle fibers are the cells of skeletal muscles and have a unique, elongated appearance. They are the basic building blocks of muscles and contain multiple nuclei due to their development through the fusion of myoblasts, which are embryonic muscle cells.

These fibers are encapsulated by a plasma membrane known as the sarcolemma, which envelops the fiber's contents, including myofibrils, mitochondria, and sarcoplasmic reticulum (involved in calcium storage and release). Muscle fibers are categorized into different types based on their contractile and metabolic properties:

• Type I fibers (slow-twitch): These are rich in myoglobin, resistant to fatigue, and are used for endurance and continuous activities.
• Type II fibers (fast-twitch): These fibers can be further categorized into IIa and IIb, where IIa fibers have moderate resistance to fatigue, and IIb fibers, which are powerful and quick to contract but fatigue rapidly.

Each muscle fiber type has unique characteristics suited for various functions, from maintaining posture to sprinting.

Biology NEET Preparation

For students preparing for NEET, or the National Eligibility cum Entrance Test, a solid grasp of muscle structure is integral for the Biology section of the examination. Concepts such as myofibrils, sarcomeres, and muscle fibers are essential topics in the NEET syllabus, often featuring in both the theoretical and practical components of the exam.

To excel in these topics, it’s advisable for students to:

• Understand the hierarchal structure of muscles, from the molecular level up to whole organs.
• Memorize the role and composition of various muscle components and their functions in contraction and relaxation.
• Visualize and familiarize themselves with diagrams depicting muscle anatomy and the sliding filament theory.
• Practice mock tests and previous years' papers for a better understanding of the types of questions asked regarding muscle physiology.
• Review and clarify doubts with teachers or through reliable educational platforms to master the concepts methodically.

Strong conceptual knowledge paired with consistent practice can help students score high marks in the Biology section of NEET, ensuring a thorough understanding of muscle structure.