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M04.05.01 Skeletal muscles structure function and relationship: Ultrastructure of a Myofibril
Overview of Muscle Tissue
Muscle tissue is specialized for contraction and generates the force required for movement and various bodily functions. There are three main types of muscle tissue: skeletal, cardiac, and smooth muscle. Each type has distinct structural features and functions.
Skeletal Muscle Structure
Structure:
- Fibers: Long, cylindrical, multinucleated cells with striations.
- Connective Tissue: Encased in connective tissues (epimysium, perimysium, endomysium).
- Sarcomeres: Basic contractile units organized in a repeating pattern.
Function:
- Voluntary control
- Responsible for body movements and posture
Microscopic Appearance:
- Longitudinal Section:
- Striations: Alternating dark (A bands) and light bands (I bands) due to the arrangement of actin and myosin filaments.
- Multinucleation: Multiple nuclei located at the periphery of the fibers.
- Sarcomeres: The repeating units between Z lines which are the functional units of muscle contraction.
- Cross Section:
- Polygonal shape of muscle fibers.
- Peripheral nuclei.
- Presence of connective tissue (endomysium) around each muscle fiber.
Cardiac Muscle Structure
Structure:
- Fibers: Short, branched, and interconnected cells with a single nucleus.
- Intercalated Discs: Specialized junctions that connect cardiac muscle cells.
- Striations: Similar to skeletal muscle but with unique features for electrical coupling.
Function:
- Involuntary control
- Pumps blood through the circulatory system
Microscopic Appearance:
Smooth Muscle Structure
Structure:
- Fibers: Spindle-shaped cells with a single nucleus, and no striations.
- Arrangement: Organized in sheets, typically found in walls of hollow organs.
Function:
- Involuntary control
- Regulates the diameter of blood vessels, movement of food through the digestive tract, and other involuntary movements
Microscopic Appearance:
Comparison of Muscle Types
| Feature | Skeletal Muscle | Cardiac Muscle | Smooth Muscle |
|---|---|---|---|
| Control | Voluntary | Involuntary | Involuntary |
| Location | Attached to bones | Heart | Walls of hollow organs |
| Cell Structure | Long, cylindrical, multinucleated | Short, branched, single nucleus | Spindle-shaped, single nucleus |
| Striations | Present | Present | Absent |
| Special Features | Organized sarcomeres | Intercalated discs, syncytium | Can contract without neural input |
| Function | Body movements, posture, heat production | Pumping blood | Regulation of internal movements |
Points to Remember
- Skeletal muscle is under voluntary control and is responsible for body movement.
- Cardiac muscle is found only in the heart and has unique structures like intercalated discs for synchronized contraction.
- Smooth muscle is involuntary, lacks striations, and controls the function of internal organs.
Bibliography
- Ross, M. H., & Pawlina, W. (2015). Histology: A Text and Atlas. Lippincott Williams & Wilkins.
- Marieb, E. N., & Hoehn, K. (2018). Human Anatomy & Physiology. Pearson.
- Tortora, G. J., & Derrickson, B. (2017). Principles of Anatomy and Physiology. Wiley.
By understanding the distinct structures and functions of the three types of muscle tissue, medical students can better appreciate their roles in health and disease.