Muscle Cell (Myocyte)
Muscle Cells (Definition): Muscle cells, also known as myocytes, are specialized cells designed for contraction and force production.
- Skeletal Muscle Cells: These cells are long, cylindrical, and have a striated (or striped) appearance due to their highly organized structure into functional units known as sarcomere. Additionally, these cells are multi-nucleated to increase the rate of protein synthesis and growth. Further, these cells have the highest number of mitochondria per cell in the human body to aid in energy production. However, the most important difference between skeletal muscle cells and other muscle cell types is that they can be voluntarily recruited. That is, skeletal muscle is the only type of muscle that can be consciously activated via the intent to move.
- "Muscle Fibers" versus "Myofibrils:" Note that skeletal muscle cells are also known as "muscle fibers" because of their long fiber-like shape (0.001 - 0.01 cm thick but 2 - 12 cm long). However, "myofibrils" are an organelle within a muscle cell (muscle fiber). Myofibrils are strands of repeating sarcomeres that run parallel to one another and are bundled into muscle fibers by the sarcolemma and endomysium - a thin layer of areolar (loose) connective tissue.
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Additional Information:
The human body consists of four main types of cells: epithelial cells (e.g., skin), nerve cells (e.g., sciatic nerve), connective tissue cells (e.g., tendons), and muscle cells (e.g., biceps brachii). Muscle tissue is classified into three distinct types: smooth muscle tissue, cardiac muscle tissue, and skeletal muscle tissue. Skeletal muscle cells are unique due to their highly organized structure, their ability to generate force through contraction, and their ability to be voluntarily controlled.
Muscle contraction results from an interaction between two proteins, actin and myosin, which are collectively known as "contractile filaments." These contractile filaments are organized parallel to one another in the smallest functional unit of a muscle cell, known as a sarcomere . When a motor nerve is stimulated (action potential ), it signals to all of the sarcomeres in all of the innervated muscle cells (a motor unit) to contract. This is known as excitation-contraction coupling . Contraction occurs when myosin (a "motor protein") changes in shape and pulls actin toward the center of the sarcomere, sliding the filaments passed one another. This process of contraction is known as the sliding filament theory .
Understanding muscle cell structure and function has many practical implications, including the "all-or-none Principle ," the effects of disease and injury on the excitation-contraction coupling and physical rehabilitation, and understanding motor unit recruitment and muscle cell hypertrophy and the effects on human performance.