Muscle Types and Structure

There are three types of muscle tissues:
- Cardiac Muscle
- Skeletal Muscle
- Smooth Muscle

Found in the heart; responsible for pumping blood.
Structure:
- Striated appearance
- Cells are branched and interconnected through intercalated discs which allow for synchronized contractions.
- Each cell has one nucleus.
Functionality:
- Cells can conduct electrical signals due to action potentials.
- Acts as a functional syncytium - if one cell depolarizes, all depolarize and contract.

Attached to bones; responsible for voluntary movements.
Structure:
- Long, cylindrical, striated fibers with multiple nuclei.
- Innervated by motor neurons from the somatic nervous system.
Functionality:
- Contractions are faster compared to cardiac and smooth muscles.
- Controlled voluntary actions (e.g., moving limbs).

Found in the walls of hollow organs (e.g., GI tract, blood vessels).
Structure:
- Non-striated appearance
- Cells have a single nucleus.
Functionality:
- Involuntary muscle, controlled by the autonomic nervous system.
- Functions include regulating blood flow, digestion, and other involuntary actions.

Origin of Skeletal Muscle Cells:
- Begins with a pluripotent stem cell.
- Differentiates into satellite cells (muscle precursor cells).
- Satellite cells elongate to form myotubes, which eventually mature into muscle fibers with numerous nuclei.

Three layers of connective tissue associated with skeletal muscles:
- Epimysium: Surrounds the entire muscle.
- Perimysium: Surrounds bundles of muscle fibers (fascicles).
- Endomysium: Surrounds each individual muscle fiber.
These layers serve to isolate muscle fibers, provide structure, and contain blood vessels and nerves.

Sarcomeres: Basic structural and functional units of muscle contraction.
- Composed of thick (myosin) and thin (actin) filaments arranged longitudinally.
- Sliding Filament Theory: Muscle fibers shorten during contraction as actin slides over myosin.
Sarcoplasmic Reticulum:
- Specialized endoplasmic reticulum found in muscle cells that stores calcium ions, crucial for muscle contractions.
Transverse Tubules (T Tubules):
- Invaginations of the sarcolemma that convey electrical signals deep into the muscle fiber.
- Functionally, they are associated with the terminal cisternae of the sarcoplasmic reticulum, forming a triad essential for excitation-contraction coupling.

Diagrams of muscle structure will help visualize:
- The relationship between the different connective tissue layers.
- The arrangement of myofibrils within muscle cells.
- The organization of myosin and actin filaments within sarcomeres.
Understanding these structures will aid in grasping the mechanisms of muscle contraction and the distinct roles of different muscle types in the body.