Muscles | One Shot Lecture

Types of Muscles in the Human Body
Skeletal Muscles:

These muscles are attached to bones and are responsible for voluntary movements. When you walk, run, or lift something, it's your skeletal muscles that make it happen.
Skeletal muscles are striated (striped in appearance) and are under conscious control. You can decide when to move them.

They work in pairs: when one muscle contracts, the opposing muscle relaxes, creating movement.

Smooth Muscles:
Found in the walls of internal organs such as the stomach, intestines, blood vessels, and bladder.
Unlike skeletal muscles, smooth muscles are involuntary, meaning they work automatically without you having to think about it.
These muscles help with things like digestion, controlling blood flow, and regulating airways.

Cardiac Muscle:
Found only in the heart, this muscle is also involuntary.
Cardiac muscle is striated like skeletal muscle, but it functions automatically, pumping blood throughout your body without you having to tell it to do so.
It has a unique structure that allows it to contract in a coordinated manner, which is essential for maintaining a steady heartbeat.

Skeletal Muscle Structure and Mechanism of Contraction

Skeletal Muscle Structure:
Skeletal muscles are made up of bundles of long, cylindrical cells called muscle fibers. Each muscle fiber contains smaller units called myofibrils, which are made up of even smaller structures called sarcomeres. Sarcomeres are the functional units of muscle contraction and are composed of two main types of protein filaments: actin (thin filaments) and myosin (thick filaments).

Each sarcomere is organized in a way that gives skeletal muscle its striated appearance. The overlapping arrangement of actin and myosin filaments allows them to slide past one another during muscle contraction.

Mechanism of Muscle Contraction:
Muscle contraction follows a process known as the Sliding Filament Theory:

Signal Transmission: It all starts when your brain sends a signal through the nervous system to the muscle. This signal travels via motor neurons and reaches the muscle fiber at a point called the neuromuscular junction.

Calcium Release: The signal triggers the release of calcium ions from the sarcoplasmic reticulum (a specialized storage system within the muscle fiber) into the muscle cells.

Binding of Calcium: The calcium ions bind to a protein called troponin, which is located on the actin filaments. This causes a shift in another protein, tropomyosin, exposing the binding sites on the actin filaments.

Cross-Bridge Formation: With the binding sites exposed, the heads of the myosin filaments attach to the actin filaments, forming what’s called a cross-bridge.

Power Stroke: The myosin heads then pivot, pulling the actin filaments toward the center of the sarcomere. This shortens the muscle fiber, resulting in contraction. This action is powered by ATP (adenosine triphosphate), which provides the necessary energy.

Relaxation: After the muscle contracts, ATP is also required to detach the myosin heads from the actin, allowing the muscle to relax. The calcium ions are pumped back into the sarcoplasmic reticulum, and the muscle returns to its resting state.

This entire process happens in a fraction of a second and allows for precise, controlled movements of the body.

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