Muscle Tissue Types

• Excitable tissues are capable of generating and conducting electrical impulses.
• Excitable tissues include nervous, muscle, and neuroendocrine tissues (like the adrenal medulla).

Muscle Basics

• Muscle is an excitable tissue responsible for maintaining posture, locomotion, and movement of internal organs.
• There are three main types of muscle: skeletal, smooth, and cardiac

Muscle Types

• Skeletal muscle attaches to bones, moves the body, is striated, and is controlled voluntarily.
• Smooth muscle is found in the walls of visceral organs, blood vessels, and respiratory airways.
• Smooth muscle contracts involuntarily to move substances, and is not striated.
• Cardiac muscle is found in the heart and is responsible for pumping blood.

Muscle Components

• Muscle is composed of muscle cells (myocytes), connective tissue, blood vessels, and nerve tissues.
• Myocytes are tubular cells known as muscle fibers.
• Myocytes can be multinucleated (e.g., skeletal muscle) or uninucleated (e.g., smooth and cardiac muscles).
• Myocytes in cardiac muscle are called cardiomyocytes.

Muscle Fibers

• Muscle fibers consist of the sarcolemma (plasma membrane), sarcoplasm (cytoplasm), myofibrils, and sarcomeres.
• Myofibrils are long, thread-like structures containing contractile units called sarcomeres.
• Sarcomeres are the functional units of muscle contraction.

Contractile Filaments

• Contractile filaments are protein filaments responsible for muscle contraction and relaxation.
• There are three main types: thin (actin), thick (myosin), and the tropomyosin-troponin complex.
• Actin filaments interact with myosin to produce muscle contraction.
• Myosin filaments generate the force of contraction.
• The tropomyosin-troponin complex regulates the interaction between actin and myosin filaments.

Actin Filaments

• Actin filaments are composed of two strands of actin proteins twisted together in a helix.
• Each actin protein has a globular head that interacts to form a strong bond, holding the filament together, and a long tail.

Types of Actin Filaments

• G-actin (Globular actin) is the monomeric form of actin proteins with a globular shape.
• G-actin polymerizes to form F-actin.
• F-actin (Filamentous actin) is the polymerized form of actin protein, consisting of a long chain of monomeric actin filaments involved in cellular processes.

Myosin Filaments

• Myosin filaments, also called thick filaments, are protein molecules that interact with actin to produce muscle contraction and relaxation.
• Each myosin molecule has a tail and two elongated globular heads.
• Myosin filaments are composed of a heavy chain, light chain, and a head.

Myosin Components

• The myosin heavy chain provides the structural framework.
• The myosin light chain binds to the heavy chain and helps regulate muscle contraction.
• The myosin head interacts with actin filaments to produce muscle contraction.

Myosin Types

• Myosin II is the most common type, found in skeletal, cardiac, and smooth muscle cells.
• Myosin I is in some non-muscle cells, like epithelial cells and neurons.
• Myosin V is in some non-muscle cells, like neurons and melanocytes.

Tropomyosin

• Tropomyosin is a long, helical protein that wraps around actin filaments in muscle cells and helps regulate muscle contraction.

Tropomyosin Isoforms

• Tropomyosin-1 (TPM1) is expressed in skeletal muscle.
• Tropomyosin-2 (TPM2) is expressed in cardiac muscle.
• Tropomyosin-3 (TPM3) is expressed in smooth muscle.

Troponin

• Troponin is bound to tropomyosin on actin filaments and is a complex of three proteins (troponin C, I, and T).
• Troponin plays a role in regulating muscle contraction.

Troponin Components

• Troponin C (TnC) binds to calcium ions and triggers a conformational change in the troponin complex.
• Troponin I (TnI) inhibits the interaction between actin and myosin filaments in the absence of calcium ions.
• Troponin T (TnT) binds to tropomyosin and helps regulate its movement.

Troponin Function

• Troponin regulates muscle contraction by controlling the interaction between actin and myosin filaments.
• Troponin C binding to calcium triggers a conformational change that causes tropomyosin to move away from myosin binding sites on actin, allowing muscle contraction.

Role of Actin and Myosin

• Contractile filaments are organized into the sarcomere within muscle cells.
• During muscle contraction, actin and myosin filaments interact, causing the sarcomere to shorten, leading to muscle contraction.

Overview of muscle tissue as an excitable tissue. Covers types like skeletal, smooth, and cardiac. Details muscle components, cells, and their functions in body movement and organ function.