Muscle Physiology Flashcards

Flashcards to review key concepts from the Muscular System lecture.

What is a motor unit?

One motor neuron and all the muscle fibers it stimulates.

What does NMJ (neuromuscular junction) consist of?

One axon terminal and one muscle fiber.

What is the relationship between the size of a motor unit and the degree of control?

Inverse relationship; fewer fibers per unit = more precise control.

What two factors determine the degree of muscle shortening (graded responses)?

Frequency of muscle stimulation and number of muscle fibers being stimulated.

What characterizes unfused/incomplete tetanus?

Some relaxation occurs between contractions.

What characterizes fused/complete tetanus?

No evidence of relaxation between contractions.

What is muscle tone?

Continuous partial contractions that stabilize joints and keep muscles healthy.

What are the three jobs that ATP does in a muscle fiber?

Provide energy for cross-bridge detachment, supply energy for the Ca2+ pump in the sarcoplasmic reticulum, provide energy for the Na+/K+ pump in the sarcolemma and T tubules.

What are the three methods for regenerating ATP in muscle contraction?

Direct phosphorylation by creatine phosphate, aerobic pathway, anaerobic glycolysis/lactic acid formation.

How does creatine phosphate (CP) work to regenerate ATP?

CP transfers phosphate to ADP, regenerating ATP; it lasts for ~15 seconds.

Describe the aerobic pathway for ATP regeneration.

Starts with glycolysis then Kreb’s cycle + electron transport chain in mitochondria; glucose broken down to CO2 and water; produces 32 ATP/glucose.

What are the waste products of the aerobic pathway?

CO2 and H2O (converted to carbonic acid/bicarbonate).

During prolonged exercise, what becomes a primary fuel source for muscles?

After ~30 minutes of exertion, fatty acids from adipose tissue.

Briefly describe anaerobic glycolysis/lactic acid formation.

Glucose broken down to pyruvic acid, which is then converted to lactic acid; produces 5% as much ATP as the aerobic pathway.

What is the central nervous system cause of muscle fatigue (psychological)?

Perceived inability to do muscular work due to psychological factors.

What are the true muscular fatigue causes of muscle fatigue?

Depletion of Ca2+ from the sarcoplasmic reticulum or an imbalance of Na+/K+.

What is the synaptic fatigue cause of muscle fatigue (at the NMJ)?

Depletion of ACh in the synapse.

What is oxygen debt?

Amount of O2 needed to replenish oxygen & creatine phosphate reserves, convert lactic acid to glucose, and replenish ATP via aerobic respiration.

What are the differences between slow- and fast-twitch muscle fibers due to?

Myoglobin, mitochondria, capillaries, and rate of hydrolysis of ATPase in myosin.

What are the characteristics of slow-twitch muscle fibers?

Better blood supply, more mitochondria, slower response time, fatigue-resistant, myoglobin present.

What are the characteristics of fast-twitch muscle fibers?

Less adequate blood supply, fewer mitochondria,Respond faster but tire quickly.

What largely determines the ratios of slow- and fast-twitch muscle fibers in humans?

Genetics.