Skeletal Muscle Function and Contraction

Skeletal Muscle Function

• Skeletal muscles are voluntary muscles that can be controlled consciously
• Functions:
  • Movement: contraction and relaxation of muscles to facilitate movement
  • Stabilization: maintenance of posture and balance
  • Support: support for joints and bones
  • Protection: protection of organs and surrounding tissues

Muscle Contraction

• Types of muscle contractions:
  • Isotonic contraction: muscle contracts and shortens
  • Isometric contraction: muscle contracts but does not shorten
  • Concentric contraction: muscle shortens while contracting
  • Eccentric contraction: muscle lengthens while contracting
• Muscle contraction process:
  1. Neuromuscular transmission: nerve impulse reaches muscle fiber
  2. Muscle action potential: electrical signal travels along muscle fiber
  3. Muscle contraction: muscle fiber contracts and shortens

Neuromuscular Transmission

• Process of transmitting nerve impulses to muscle fibers
• Steps:
  1. Nerve impulse reaches neuromuscular junction (NMJ)
  2. Release of acetylcholine (ACh) from nerve terminal
  3. Binding of ACh to receptors on muscle fiber
  4. Generation of muscle action potential
  5. Muscle contraction

Muscle Fatigue

• Decreased ability of muscle to generate force
• Causes:
  • Metabolic fatigue: accumulation of lactic acid and ATP depletion
  • Neuromuscular fatigue: failure of neuromuscular transmission
  • Mechanical fatigue: muscle damage and inflammation
• Factors contributing to muscle fatigue:
  • Intensity and duration of exercise
  • Electrolyte imbalance
  • Dehydration
  • Muscle damage and inflammation

Electrolytes and Their Role

• Electrolytes: ions that carry electric charge
• Important electrolytes for musculoskeletal physiology:
  • Sodium: regulates muscle contraction and relaxation
  • Potassium: regulates muscle contraction and relaxation
  • Calcium: essential for muscle contraction
  • Magnesium: involved in muscle contraction and relaxation
• Functions of electrolytes:
  • Regulate muscle contraction and relaxation
  • Maintain muscle membrane potential
  • Involved in muscle metabolism and energy production

Abnormal Electrolytes and Their Effect on Musculoskeletal Pathophysiology

• Electrolyte imbalance can lead to musculoskeletal disorders
• Effects of abnormal electrolyte levels:
  • Hypokalemia (low potassium): muscle weakness, fatigue, and cramps
  • Hyperkalemia (high potassium): muscle weakness, fatigue, and paralysis
  • Hypocalcemia (low calcium): muscle cramps, weakness, and tetany
  • Hypercalcemia (high calcium): muscle weakness, fatigue, and decreased reflexes
  • Hypermagnesemia (high magnesium): muscle weakness, fatigue, and decreased reflexes
• Musculoskeletal disorders associated with electrolyte imbalance:
  • Muscle cramps
  • Muscle weakness
  • Muscle fatigue
  • Tetany

Skeletal Muscle Function

• Skeletal muscles are voluntary muscles controlled consciously
• Functions:
  • Facilitate movement through contraction and relaxation
  • Maintain posture and balance
  • Provide support for joints and bones
  • Protect organs and surrounding tissues

Muscle Contraction

• Types of muscle contractions:
  • Isotonic: muscle contracts and shortens
  • Isometric: muscle contracts but doesn't shorten
  • Concentric: muscle shortens while contracting
  • Eccentric: muscle lengthens while contracting
• Muscle contraction process:
  • Neuromuscular transmission: nerve impulse reaches muscle fiber
  • Muscle action potential: electrical signal travels along muscle fiber
  • Muscle contraction: muscle fiber contracts and shortens

Neuromuscular Transmission

• Transmits nerve impulses to muscle fibers
• Steps:
  • Nerve impulse reaches neuromuscular junction (NMJ)
  • Release of acetylcholine (ACh) from nerve terminal
  • Binding of ACh to receptors on muscle fiber
  • Generation of muscle action potential
  • Muscle contraction

Muscle Fatigue

• Decreased ability to generate force
• Causes:
  • Metabolic fatigue: lactic acid accumulation and ATP depletion
  • Neuromuscular fatigue: failure of neuromuscular transmission
  • Mechanical fatigue: muscle damage and inflammation
• Contributing factors:
  • Exercise intensity and duration
  • Electrolyte imbalance
  • Dehydration
  • Muscle damage and inflammation

Electrolytes and Their Role

• Electrolytes: ions carrying electric charge
• Important electrolytes:
  • Sodium: regulates muscle contraction and relaxation
  • Potassium: regulates muscle contraction and relaxation
  • Calcium: essential for muscle contraction
  • Magnesium: involved in muscle contraction and relaxation
• Functions:
  • Regulate muscle contraction and relaxation
  • Maintain muscle membrane potential
  • Involved in muscle metabolism and energy production

Abnormal Electrolytes and Their Effect

• Electrolyte imbalance leads to musculoskeletal disorders
• Effects of abnormal electrolyte levels:
  • Hypokalemia: muscle weakness, fatigue, and cramps
  • Hyperkalemia: muscle weakness, fatigue, and paralysis
  • Hypocalcemia: muscle cramps, weakness, and tetany
  • Hypercalcemia: muscle weakness, fatigue, and decreased reflexes
  • Hypermagnesemia: muscle weakness, fatigue, and decreased reflexes
• Associated musculoskeletal disorders:
  • Muscle cramps
  • Muscle weakness
  • Muscle fatigue
  • Tetany