Muscle Fiber (Muscle Cell):
- Myofibrils: These are long, thread-like structures that run parallel within the muscle fiber. They contain the contractile proteins actin and myosin.
- Sarcolemma: This is the cell membrane that surrounds each muscle fiber.
- Sarcoplasm: The cytoplasm of a muscle fiber, containing the organelles, including the nuclei, mitochondria, and myofibrils.
- Sarcoplasmic Reticulum: A specialized form of smooth endoplasmic reticulum that stores and releases calcium ions, which are essential for muscle contraction.
Connective Tissue:
- Endomysium: A thin layer of connective tissue that surrounds each individual muscle fiber.
- Perimysium: A thicker layer of connective tissue that surrounds bundles of muscle fibers, called fascicles.
- Epimysium: The outermost layer of connective tissue that surrounds the entire muscle.
Tendons: Tough bands of fibrous connective tissue that connect muscles to bones. Tendons transmit the force generated by the muscle to the bone, causing movement.
Blood Vessels: Muscles are richly supplied with blood vessels, which provide the necessary oxygen and nutrients and remove waste products.
Nerves: Motor neurons innervate muscle fibers, transmitting signals from the brain and spinal cord to the muscle, initiating contraction.
Myofilaments:
- Actin: Thin filaments involved in muscle contraction.
- Myosin: Thick filaments that interact with actin to produce muscle contraction.
- Titin: A large protein that helps stabilize the position of myosin and actin and contributes to muscle elasticity.
- Nebulin: A protein that helps align actin filaments within the myofibril.
Motor Unit: A motor neuron and the muscle fibers it innervates. The number of muscle fibers in a motor unit can vary, affecting the precision of movement.
Neuromuscular Junction: The synapse or connection between a motor neuron and a muscle fiber. It is where the nerve impulse is transmitted to the muscle fiber to trigger contraction.
Mitochondria: Organelles within the muscle fibers that produce ATP through aerobic respiration, providing the energy needed for muscle contractions.
Myoglobin: A protein in muscle cells that binds to oxygen, facilitating its delivery to mitochondria.
