Skeletal Muscle: Cellular Components and Functions

• Study notes on cellular components, proteins, and functions of skeletal muscle

• Skeletal muscle is composed of various cellular components, each with specific functions

Myoglobin

• Myoglobin is the protein responsible for storing oxygen in muscle tissue

Sarcomere

• Sarcomeres are composed of:
  • Z discs which mark the boundaries of each sarcomere
  • A band which contains the entire length of the thick filaments
  • I band which contains only thin filaments

Myofilaments

• Thick filaments are primarily composed of myosin
• Thin filaments are primarily composed of actin, troponin, and tropomyosin

Troponin & Tropomyosin

• Troponin and tropomyosin regulate skeletal muscle contraction by controlling the interaction of actin and myosin

Sarcoplasmic Reticulum & T Tubules

• Sarcoplasmic reticulum stores and releases calcium ions, essential for muscle contraction
• T tubules transmit action potentials from the sarcolemma into the cell interior, facilitating uniform muscle contraction

Smooth Muscle

• Calmodulin binds to calcium in smooth muscle, initiating a cascade of events that allows cross-bridge formation and contraction

Motor Unit & Neuromuscular Junction

• Motor unit is a single motor neuron and all the muscle fibers it innervates
• Neuromuscular junction is the synapse between a motor neuron and a muscle fiber, where communication occurs

Neurotransmitters

• Acetylcholine is the primary neurotransmitter that activates skeletal muscle, initiating the process of contraction

Muscle Relaxation

• Muscle relaxation occurs when the nerve signal ceases, acetylcholine is no longer released, and calcium ions are pumped back into the sarcoplasmic reticulum
• Tropomyosin shifts back to block the myosin-binding sites on actin, preventing cross-bridge formation

Oxygen Debt

• Oxygen debt refers to the additional oxygen required after exercise to restore metabolic conditions to the resting state

Muscle Twitch

• Muscle twitch is a single contraction-relaxation cycle in a muscle fiber, consisting of a latent period, a contraction phase, and a relaxation phase

Muscle Summation

• Spatial summation involves multiple motor units being activated simultaneously to increase muscle force
• Temporal summation (wave summation) involves high-frequency stimulation of a single motor unit, leading to increased force production

Anaerobic Respiration

• Lactic acid is a byproduct of anaerobic breakdown of glucose in muscle cells, contributing to muscle fatigue

Gap Junctions

• Gap junctions in smooth and cardiac muscle facilitate the spread of electrical signals, enabling coordinated contraction

Muscle Types & Regeneration

• Skeletal muscle has limited regenerative abilities via satellite cells
• Smooth muscle has good regenerative abilities
• Cardiac muscle has very limited, if any, regenerative abilities