Muscle Physiology
What is a muscle twitch?
A single, brief contraction and relaxation cycle in a muscle fiber in response to a single stimulus.
What does “wave summation” mean in muscle physiology?
It’s the increased muscle tension produced when a second stimulus occurs before the first contraction has fully relaxed
Define tetanus in the context of muscle contraction.
A sustained muscle contraction resulting from rapid, repeated stimulation without relaxation
What is muscle fatigue?
A decrease in the muscle’s ability to generate force after prolonged activity.
In a lab setting, what instrument is used to record muscle contractions?
A myograph.
Name the three phases of a muscle twitch.
Latent period, contraction phase, and relaxation phase
What happens to tension if a second stimulus arrives before the muscle has relaxed from the first?
The second contraction adds to the first, increasing total tension (summation).
What is the difference between incomplete (unfused) and complete (fused) tetanus?
Incomplete tetanus has small relaxations between contractions; complete tetanus has none, forming a smooth plateau.
Which metabolic changes in the muscle fiber lead to fatigue during tetanus?
Decreased ATP, accumulation of inorganic phosphate and lactic acid, and ionic imbalance.
How can the frequency of stimulation be changed in such experiments?
By adjusting the rate of electrical impulses delivered by a stimulator.
How does the length of a sarcomere affect muscle tension?
Optimal sarcomere length allows maximum cross-bridge formation; too short or too stretched reduces tension.
How does increasing the frequency of stimulation lead to wave summation?
Repeated stimulation keeps calcium ions in the sarcoplasm, allowing stronger and more sustained contractions.
At what stimulation frequency does complete tetanus occur?
When the stimulation frequency is so high that the muscle has no time to relax — typically 80–100 stimuli per second in skeletal muscle.
How do ATP depletion and lactic acid accumulation contribute to fatigue?
ATP shortage limits cross-bridge cycling; lactic acid lowers pH, inhibiting enzyme activity and contractile proteins
Why is it important to control stimulus voltage and frequency in muscle physiology experiments?
To isolate the effects of recruitment and frequency on contraction strength without damaging the muscle.
Explain how calcium ions contribute to muscle contraction.
Ca²⁺ binds to troponin, causing tropomyosin to move, exposing binding sites on actin for myosin heads to attach.
Differentiate between incomplete and complete tetanus in terms of wave summation.
Incomplete tetanus shows partial relaxation between stimuli; complete tetanus shows no relaxation, with smooth sustained tension.
Why can’t complete tetanus be sustained indefinitely in living muscles?
Because ATP stores deplete and lactic acid accumulates, leading to fatigue.
Explain the role of oxygen debt in muscle recovery.
Extra oxygen is needed post-exercise to restore ATP, creatine phosphate, and convert lactic acid to pyruvate.
Name a clinical condition caused by Clostridium tetani and explain how it differs from physiological tetanus.
Tetanus (lockjaw); it’s caused by a neurotoxin leading to uncontrolled spasms, unlike normal physiological sustained contraction
Describe the sliding filament theory in detail
Muscle contraction occurs as myosin heads pull actin filaments toward the center of the sarcomere using ATP, shortening the muscle fiber.
Explain physiologically why wave summation increases muscle force (mention Ca²⁺ availability and elastic elements).
More frequent stimuli prevent full Ca²⁺ reuptake, keeping more cross-bridges active, while elastic elements remain partially stretched, adding to tension.
Explain how the state of tetanus demonstrates temporal summation of action potentials.
Each successive action potential arrives before relaxation, summing their effects over time to produce continuous contraction.
Discuss how continuous tetanic stimulation can lead to decreased contractile force despite constant stimulation.
Due to depletion of energy reserves, Ca²⁺ handling inefficiency, and reduced sensitivity of contractile proteins.
How does the concept of tetanus help in understanding graded muscle contractions in the human body?
It shows how varying stimulation frequency produces smooth, graded muscle tension — from twitches to sustained contraction.