Muscle Force and Mechanisms of Contraction Flashcards
What is agonist vs antagonist vs synergist muscle?
agonist - muscles for which contraction leads to motion
antagonist - muscle that moves joint opposite to agonist motion
synergist - muscle that assists another muscle to accomplish a movement
What constitutes the load of skeletal muscle?
- Skeleton
- External load
- Load to overcome passive resistance to contraction of agonist muscle
- Load to overcome passive resistance to stretch of the antagonist muscle
What is meant by pinnation?
Pennate muscle form a common oblique angle with a tendon, so contraction does not move tendons as far as parallel muscles, but produces a greater physiological cross-sectional area
What is the law of laplace? How is it transformed for hearts?
Tension = Pressure * Radius
Wall stress = (Pressure * radius) / (wall thickness)
Thus, greater wall thickness = reduced stress on vessels
For a pennate muscle contractile force, what two vectors run at 90 degree angles?
Tension runs at a right angle to the targeted force (in the direction of the tendon)
What is the function of tension generated on veins?
Important in maintaining blood flow from feet back to heart
What is muscle hypertrophy?
An increase in the number of sarcomeres (not muscle fibers / myocytes though)
What is the function of cardiac contraction and what happens in response to increased blood pressure?
Contracts longitudinally create tension to counteract wall stress. There are concentric layers of cardiac muscles to create tension. Since blood pressure increases wall stress, cardiac cells hypertrophy to counteract that stress
What is the function of arterial smooth muscle? Why don’t capillaries need smooth muscle?
Creates tension to offset wall stress. Capillaries need no smooth muscle because capillaries have a tiny radius and thus require little tension to offset the pressure
What is the function of titin?
Traverses the entire sarcomere to keep the thin and thick filaments aligned
What are the steps of the crossbridge cycle of the actinomyosin ATPase, starting with the actin being exposed by troponin-C binding calcium? What is the power stroke?
Crossbridges form:
- Activated myosin head binds to actin
- Power stroke - MYOSIN undergoes conformational change, releasing phosphate and using energy to pull actin backwards
Crossbridges break:
- ATP binds myosin, causing it to unbind actin
- ATP is hydrolyzed on myosin, returning to resting state and ADP is released.
What is continued contraction dependent on?
Typically, the amount of calcium available. ATP is generally not limiting.
In excitation-contraction coupling of cardiac muscle, what channels are open during the peak rate of force development and the peak rate of relaxation?
Peak rate of force development - contraction phase - L-type (longlasting) Ca+2 channels on T-tubules, and RyR receptor on SR
Peak rate of relaxation - SERCA - Sarcoplasmic / endoplasmic reticulum ca+2 ATPase, to pump Ca+2 back into the SER
What does the maximum rate of rise of the myocyte twitch depend on?
The isoform of the myosin in the myocyte - fast twitch vs slow twitch
What is the function of the sarcolemma / T-tubules of the sarcolemma for EC coupling?
Voltage gated sodium channels trigger L-type Ca+2 channels, which are longlasting dihydropyridine receptors (DHPR). These serve to cause the influx of “trigger calcium” which binds to Ryanodine receptors (ryanodine-sensitive Ca+2 channel)
