PSIO 532 Study Guide - Midterm Guide: Cardiac Action Potential, Cardiac Muscle Cell, Endoplasmic Reticulum
Graduate Physiology PSL
Cardiac Muscle Contraction
➔ 4. Sketch the temporal relationship between an action potential in a cardiac muscle cell
and the resulting contraction (twitch) of that cell
- As the calcium comes into the cell, contraction begins (we need calcium
to bind to troponin → this causes the muscle contraction)
- The muscle contraction line keeps increasing because more and more
calcium keeps coming into the cell
In the skeletal muscle, the
action potential is really quick and
this leads to the muscle being
repeatedly stimulated (rapidly) →
leads to the buildup of calcium for
contraction (from the sarcolemma)
and other muscle fiber recruitments
In a cardiac cell, you have a
delay so the heart isn’t rapidly
beating → you have this delay so
that the ventricles can fill up with the
blood so that it can be pumped
throughout the body; you also need
to have lots of calcium to coordinate
a contraction to push all this blood
out; lastly, also the long refractory
period in a cardiac muscle prevents tetanus
➔ Outline the sequence of events that occurs between initiation of an action potential in a
cardiac muscle cell and the resulting contraction and then relaxation of that cell
1. Cardiac action potential is initiated in the myocardial cell membrane; it is the influx
of sodium through the sodium channels is what gets the calcium channels to open
(less negative membrane potential) and leads to increase in calcium
2. Entry of Ca2+ into the myocardial cell; around -20 mV, calcium starts to come in and
looks for the sarcoplasmic reticulum
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