physiology secrets

PHYSIOLOGY SECRETS
What is Hill’s hyperbola? How it is applicable in muscles? Compare and apply it for different kinds of muscles in our body.
Ans-Hyperbola is an open curve and it continues indefinitely to infinity. It is related to F-V (force-velocity curve) of muscles.
Skeletal muscle-F-V curve shows inverse relation between velocity of shortening and force (after load). (Fig-1)
Vmax(maximum velocity of shortening.)If no load is applied, the muscle will shorten at its greatest possible speed, a velocity known as Vmax.in this graph the value is extrapolated bcz muscle cannot contract in the absence of any load. (Fig-1)
Y-intercepts represent extrapolated value for maximum velocity-Vmax.Algebrically Y intercepts is a point where X is zero.
Fmax i.e. Po :( Maximum isometric force).represents the point where after load is so great that the muscle cannot shorten.
X-intercepts is a point where Y is zero.
Smooth muscle’s F-V curve is compared with skeletal muscle. (fig-2) here the peak force may be similar but velocity of shortening is 100 times lower than skeletal muscle.
Cardiac muscle-F-V curve is influenced by changes in initial length (preload) and the changes in the contractility. (Fig3-A, 3-B)
If preload is increased (within physiological limits) Fmax increases, as well as velocity of shortening, but doesn’t alter the Vmax. (Fig-3-A)
Changes in ionotropism also alter the F-V.If ionotropic effect of cardiac muscle is increased, there is parallel shift up and right and increase in both Fmax and V max. (Fig 3-B).