Muscle Fatigue Flashcards
What are the general characteristics of skeletal muscle fibers?
Skeletal muscle fibers are long, multinucleated cells with peripheral nuclei, extending from tendon to tendon, and can vary from millimeters to tens of centimeters in length and 5-80 µm in diameter.
Describe the different types of muscle fibers in skeletal muscle.
Slow-twitch fibers (Type I) are red, fatigue-resistant, and suited for endurance, while fast-twitch fibers (Type II) are white, generate high force quickly, and fatigue faster, being ideal for rapid movements.
What is excitation-contraction coupling?
Excitation-contraction coupling is the process by which an action potential triggers calcium release from the sarcoplasmic reticulum, initiating muscle contraction.
Define the resting membrane potential (RMP) and its determinants in muscle cells.
RMP is the potential at which no net current flows across the membrane, determined by ion concentration gradients and membrane permeability, primarily for K+, Na+, and Cl−.
Explain the Goldman-Hodgkin-Katz (GHK) equation in muscle physiology.
The GHK equation calculates RMP by considering the concentration differences and relative permeability of K+, Na+, and Cl−, providing insight into ion flow across the muscle cell membrane.
What are the roles of the different muscle fiber types in mammals?
Slow-twitch fibers support postural or repetitive activities with endurance, while fast-twitch fibers provide rapid, high-force contractions for explosive activities.
Describe tetanic contraction and its significance in muscle function.
Tetanic contraction occurs when muscle fibers are stimulated at a high rate, resulting in a sustained contraction (complete tetanus) or partial fusion of twitches (incomplete tetanus) for prolonged force generation.
How does the sarcoplasmic reticulum (SR) contribute to muscle contraction?
The SR stores calcium ions and releases them in response to an action potential, enabling muscle contraction. It reabsorbs calcium afterward to allow muscle relaxation.
What are the primary types of muscle fatigue?
High-frequency fatigue (rapid onset/recovery), metabolic fatigue (due to metabolite buildup), and long-duration fatigue (often caused by muscle damage or prolonged activity).
Describe high-frequency fatigue and its causes.
High-frequency fatigue occurs rapidly due to potassium buildup in the t-tubules, which inactivates sodium channels and prevents further action potentials, thus reducing calcium release.
Explain the concept of metabolic fatigue in muscle fibers.
Metabolic fatigue results from the accumulation of metabolites like phosphate, ADP, AMP, and H+, which reduce calcium release and impair contractile function.
What role does ATP play in muscle contraction and fatigue?
ATP is essential for muscle contraction, fueling the cross-bridge cycle and calcium reuptake. Depletion of ATP or buildup of ADP and AMP contributes to fatigue by impairing calcium release.
What are the effects of lactate on muscle fatigue?
While often blamed for fatigue, lactate is a byproduct of anaerobic metabolism that serves as fuel for the heart and brain, and helps regulate glucose production in the liver.
Define eccentric contraction and its association with muscle fatigue.
Eccentric contraction occurs when a muscle lengthens under tension, as seen in downhill walking, which can cause muscle damage and contribute to long-duration fatigue.
Describe the effects of prolonged calcium elevation on muscle.
Prolonged high levels of intracellular calcium activate calpain proteases, damaging muscle proteins and disrupting excitation-contraction coupling, leading to fatigue and muscle weakness.
