D5.1 - Movement and Muscle Tissue

Skeletal Muscle Functions

• Skeletal muscles oppose gravity, enabling upright posture.
• Muscle contractions cause movement of limbs, eyes, face, and enable breathing.
• Muscle contractions generate heat, maintaining body temperature.
• Muscles pad bones and protect internal organs.
• Tendons connect muscles to bones for joint stability.

Skeletal Muscle Cooperation

• All skeletal muscles pull, not push.
• Movement occurs through muscle pairs contracting and relaxing.
• For example, biceps contract to bend the elbow, while triceps contract to straighten the arm.

Muscle Composition

• Muscles are composed of muscle fibers.
• Muscle fibers consist of myofibrils.
• Myofibrils are made of myofilaments (actin and myosin).
• Actin (thin) & Myosin (thick) filaments interact for muscle contraction.

Muscle Fiber Contraction Mechanism

• Muscle contractions involve the interaction of actin and myosin myofilaments.
• Actin is a thin, string-like protein.
• Myosin is a thick, filamentous protein with heads that connect to actin.
• These interactions cause the sliding of actin and myosin filaments, shortening the muscle.

Sliding Filament Model

• Actin myofilaments slide past myosin myofilaments.
• Actin and myosin are anchored in the muscle by Z-lines.
• The movement of Z-lines causes muscle contractions.
• These anchored Z-lines are connected to membranes, causing the entire muscle to contract.

Calcium Ions and Contraction

• In a relaxed muscle, tropomyosin blocks myosin binding.
• Calcium ions bind to troponin.
• This movement of troponin exposes myosin binding sites on actin.
• Myosin heads can then bind to actin and cause contraction.

Energy for Muscle Contraction

• ATP provides energy for muscle contraction.
• ATP production methods vary:
  • Creatine phosphate (anaerobic, short bursts)
  • Aerobic cellular respiration (long-term)
  • Fermentation (in oxygen deprivation)

Creatine Phosphate

• Anaerobic process occurring before oxygen use.
• Muscle builds up creatine phosphate when at rest.
• When muscles contract, breakdown of creatine phosphate generates ATP.
• Provides energy for about 8 seconds of intense activity.

Aerobic Cellular Respiration

• Takes place in mitochondria.
• Primary source of ATP for prolonged muscle activity.
• Myoglobin (muscle's oxygen-binding protein) temporarily stores oxygen, providing oxygen to mitochondria when needed.

Fermentation

• Provides ATP when oxygen is unavailable.
• Glucose is broken down to lactate.
• Lactate buildup in the sarcoplasm makes it acidic, leading to muscle fatigue.

Oxygen Deficit

• Fermentation provides energy, but oxygen is limiting.
• Athletes have more mitochondria, thus less reliance on fermentation.
• Blood pH remains more stable in these cases.
• Replenishing creatine phosphate and removing lactate removes the oxygen deficit.

Explore the critical functions of skeletal muscles, including their roles in movement, posture, and temperature regulation. This quiz also covers muscle composition, the mechanism of contraction, and the teamwork of muscle pairs. Test your understanding of how muscles work together to facilitate bodily functions.