Problem 36 - Objective Biology for NEET

Question

Contractile fibrils of muscles are called (a) Neurofibrils (b) Collagen fibres (c) Myofibrils (d) Elastin

Step-by-Step Solution

Answer

(c) Myofibrils

Step 1: Understanding The Terms

Neurofibrils are key components of the nerve cell structure; they are not related to muscle contraction. Collagen fibres and Elastin are proteins found in connective tissues and, though important in many bodily functions, they don't directly contribute to muscle contraction. Myofibrils, however, are the parts of muscle cells that contract. Therefore only myofibrils have a direct role in muscle contraction.

Step 2: Choosing The Correct Answer

Given above descriptions, it is clear that only Myofibrils are the contractile portions of muscle cells. So, the correct answer is (c) Myofibrils.

Key Concepts

Myofibrils

Myofibrils are the essential contractile units within muscle cells, playing a critical role in muscle contraction. Imagine tiny threads packed tightly into each muscle cell, working like mini-machines. These threads are primarily made up of proteins known as actin and myosin, which slide past one another to facilitate contraction. This movement is powered by ATP, the energy currency of cells, allowing muscles to extend and contract as needed.
Each myofibril is divided into sections called sarcomeres, which are the actual functional units of contraction.
The sarcomeres contain repeating patterns of actin and myosin, creating a striation pattern often visible under a microscope, giving skeletal muscles their characteristic striped appearance.

• Actin: A thin filament protein that is pulled during contraction.
• Myosin: A thick filament protein that pulls actin closer during muscle contraction.
• ATP: Required for myosin to attach, pull, and release the actin filament.

These myofibrils work in concert to produce the muscle movements necessary for daily activities and complex physical tasks. Understanding their function is paramount for grasping how muscles operate on a cellular level.

Muscle Structure

A muscle is composed of various components that come together to allow for movement and support. At the microscopic level, myofibrils are bundled together to form muscle fibers, which are then grouped to create muscle fascicles. It's this organizational structure that allows muscles to contract efficiently and with strength.
Each muscle fiber is a single cell and can contain multiple myofibrils, each contributing to the overall contraction of the muscle. These muscle fibers are wrapped in a connective tissue layer called the endomysium.
The next level of organization comes from the fascicles, which are bundles of muscle fibers, and these are surrounded by another layer of connective tissue known as the perimysium.

• Fascicle: A bundle of muscle fibers.
• Endomysium: Connective tissue wrapping individual muscle fibers.
• Perimysium: Connective tissue surrounding each fascicle.

Finally, multiple fascicles together form a muscle, covered by a further connective tissue layer called the epimysium. This hierarchical arrangement ensures muscles are both strong and flexible, able to perform a wide range of motion while maintaining structural integrity.

Connective Tissue Proteins

Connective tissue proteins are crucial in maintaining the structure and function of muscles, providing support and protection. Among these, collagen and elastin are key players found in the connective tissues that wrap around muscle fibers and fascicles.

• Collagen: Known for its strength and rigidity, collagen forms the backbone of connective tissues, ensuring that muscles are held together securely. It helps with the transmission of force from muscle to bone, aiding in movement.
• Elastin: As the name suggests, elastin gives tissues elasticity, allowing them to stretch and return to their original shape. This is especially important in parts of the body requiring flexibility such as the lungs and skin.

While these proteins do not directly cause muscle contraction, they are indispensable in maintaining the overall structure and function of muscle tissues.
They ensure that the muscles can withstand tension and return to their original condition after being stretched, which is vital for repeated cycles of contraction and relaxation during physical activities.