Muscle Types and Structure

Muscle Types

• Three main muscle types exist: skeletal, smooth, and cardiac.
• Skeletal muscles, attached to bones, enable voluntary movement and are striated (striped).
• Smooth muscles, within internal organs and blood vessels, control involuntary actions like digestion and blood pressure. They are non-striated.
• Cardiac muscle, unique to the heart, is responsible for its pumping action. It's striated, like skeletal muscle, but allows for rhythmic, involuntary contractions.

Muscle Structure

• Muscles consist of bundles of muscle fibers (cells).
• Muscle fibers are composed of myofibrils, with repeating sarcomeres.
• Sarcomeres contain actin and myosin, contractile proteins arranged for contraction.
• Connective tissues—epimysium (entire muscle), perimysium (bundles of fibers), and endomysium (individual fibers)—compartmentalize and support muscles.

Muscle Contraction

• Muscle contraction involves myosin heads binding to actin filaments, pulling them inwards (sarcomere shortening), powered by ATP.
• Calcium ions initiate contraction by binding to regulatory proteins on actin, allowing myosin binding.
• The sliding filament theory describes the mechanism: actin and myosin slide past each other without changing length.

Neuromuscular Junction

• Nervous system signals trigger muscle contraction.
• The neuromuscular junction is where a motor neuron synapses with a muscle fiber.
• Neurotransmitters, like acetylcholine, are released, binding to receptors on the muscle fiber to initiate a muscle action potential.
• This potential spreads, triggering calcium release and contraction.

Muscle Metabolism

• Muscles require constant energy (ATP) supply.
• Muscle metabolism uses aerobic respiration (oxygen-using) and anaerobic respiration (without oxygen).
• Anaerobic respiration generates lactic acid, which can cause fatigue and soreness.
• Glycogen, a glucose form, stores supplemental energy for muscles.

Muscle Fatigue

• Muscle fatigue reduces muscle's force-generating ability.
• Depletion of ATP, metabolic byproduct buildup (like lactic acid), and electrolyte imbalances cause fatigue.
• Insufficient blood supply, dehydration, and lack of rest also contribute.

Muscle Tone

• Muscle tone is slight tension at rest, vital for posture and position maintenance.
• The nervous system regulates muscle tone by maintaining baseline muscle stimulation.

Muscle Disorders

• Various disorders affect muscles, including muscular dystrophy (genetic, progressive muscle weakness and degeneration).
• Myasthenia gravis is a neuromuscular disorder, impairing transmission and causing muscle weakness.
• Muscle cramps and strains are also muscle-related conditions.