Skeletal Muscle Structure and Contraction

• Skeletal muscles facilitate movement, maintain posture, produce heat, and stabilize joints.

Key Muscle Components

• Epimysium is the outer layer that covers the muscle.
• Tendons connect muscles to bones.
• Perimysium surrounds muscle fascicles.
• Endomysium surrounds individual muscle fibers.
• Fascicles are bundles of muscle fibers.
• Fibers constitute muscle cells.
• Myofibrils are long muscle structures containing contractile units.
• Sarcomeres are the functional units responsible for muscle contraction.
• Actin and myosin are the proteins essential for muscle contraction.
• Myofilaments are thread-like strands composed of proteins.
• Z-lines define the boundaries of sarcomeres.

Muscle Structure Hierarchy

• Myofilaments assemble to form sarcomeres.
• Sarcomeres combine to form myofibrils.
• Myofibrils bundle together to form fibers.

Components in Muscle Contraction

• T-tubules spread signals throughout the muscle fiber.
• Sarcoplasmic reticulum stores calcium ions necessary for contraction.
• Neuromuscular junction is where signal transmission occurs.
• Sodium and calcium are essential for muscle contraction.

Muscle Contraction Process

• Muscle contraction occurs in the following steps: Signal, calcium release, myosin binds to actin, power stroke, and relaxation.
• Calcium binds to troponin, enabling actin and myosin to interact and facilitate muscle contraction.
• Myoglobin stores oxygen, and glycosomes store glycogen, providing energy for muscle activity.

Myogram Phases

• Latent phase is the delay between stimulus and the start of contraction.
• Contraction phase involves the shortening of the muscle.
• Relaxation phase is when the muscle returns to its normal state.
• During the latent phase, calcium is released, but contraction has not yet begun.
• Treppe illustrates increased contractions with repeated muscle stimulation.

Muscle Contractions

• A muscle twitch is a single, brief contraction.
• Sustained contraction, also known as tetanus, involves continuous force generation.
• Motor units regulate the strength of muscle contractions.
• A motor unit comprises a nerve and the muscle fibers it controls; muscle tone keeps muscles prepared for action.
• Increased frequency of signals leads to stronger contractions through wave summation and multiple motor unit summation.

Muscle Fatigue

• Muscle fatigue is the inability of a muscle to contract.
• Causes of muscle fatigue: low ATP levels, lactic acid buildup, and ion imbalances.

Exercise Types

• Aerobic exercise uses oxygen and is suitable for long durations.
• Anaerobic exercise does not use oxygen and is used for short bursts of activity.

Contraction Types

• Isometric contractions involve no movement, such as holding a plank.
• Isotonic contractions involve movement, such as lifting weights.

Oxygen Debt

• Oxygen debt refers to the extra oxygen required to restore muscle energy reserves after exercise.