Muscular System and Muscle Cell Function Quiz

Muscular System and Homeostasis

• The muscular system plays a crucial role in maintaining whole body homeostasis by regulating body temperature, maintaining posture, and facilitating movement.

Tissue Types in Skeletal Muscles

• A whole skeletal muscle is composed of multiple tissue types, including:
  • Skeletal muscle fibers (cells)
  • Connective tissue (epimysium, perimysium, and endomysium)
  • Nerve tissue
  • Blood vessels
• Multiple tissue types are necessary for the proper function of skeletal muscles, as they provide structural support, facilitate nerve conduction, and enable blood flow.

Structure of Skeletal Muscle Fibers

• A skeletal muscle fiber (cell) is composed of:
  • Sarcolemma (plasma membrane)
  • Sarcoplasm (cytoplasm)
  • Myofibrils (containing actin and myosin filaments)
  • Mitochondria
  • Sarcoplasmic reticulum (SR)
  • T-tubules (transverse tubules)
• The presence of these parts enables the cell to contract, generate force, and recover from contraction.

Excitation, Excitation-Contraction Coupling, and Relaxation

• The process of muscle contraction involves:
  • Excitation: depolarization of the sarcolemma, generation of an action potential
  • Excitation-contraction coupling: release of Ca2+ from the SR, binding of Ca2+ to troponin and tropomyosin, and exposure of myosin binding sites
  • Contraction: interaction of myosin heads with actin filaments, generating force
  • Relaxation: removal of Ca2+, inhibition of myosin binding sites, and return to resting state
• Important molecules involved in this process include:
  • Acetylcholine (ACh)
  • Calcium ions (Ca2+)
  • Troponin
  • Tropomyosin

Motor Units

• Motor units can be classified as small or large, based on:
  • Number of muscle fibers innervated by a single motor neuron
  • Size of the muscle fibers
  • Force generated by the motor unit
• Small motor units are involved in fine and precise movements, while large motor units are involved in powerful and gross movements.

Acetylcholine (ACh)

• ACh is a neurotransmitter released by motor neurons, which binds to nicotinic receptors on the sarcolemma, triggering muscle contraction.

Resting Membrane Potential (RMP)

• The RMP is a critical component of muscle cell function, enabling the cell to respond to stimuli and generate an action potential.
• The RMP is maintained by a balance of potassium and sodium ions, and is vital for muscle contraction.

ATP Supply and Exercise

• The mechanism of ATP supply to muscles depends on the duration of exercise:
  • Short-duration exercise: anaerobic respiration, phosphocreatine breakdown
  • Long-duration exercise: aerobic respiration, oxidative phosphorylation

Fatigue during Long-Duration Exercise

• Fatigue occurs when the muscle's ATP supply is depleted, leading to a decline in muscle force and contraction velocity.

Slow and Fast Twitch Fibers

• Slow twitch fibers:
  • Have a high mitochondrial density
  • Are specialized for endurance and low-intensity activities
  • Are found in postural muscles
• Fast twitch fibers:
  • Have a low mitochondrial density
  • Are specialized for high-intensity, short-duration activities
  • Are found in muscles involved in powerful movements

Endurance and Resistance Exercises

• Endurance exercises:
  • Increase mitochondrial density and capillarization
  • Improve muscle efficiency and ATP supply
  • Enhance muscle endurance
• Resistance exercises:
  • Increase muscle fiber size and strength
  • Improve muscle power and force generation
  • Enhance muscle resistance to fatigue