MCATExamkrackers
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Hi there! I’m Austin, one of the MCAT instructors at Examkrackers. In our class, we’ve been getting questions about the differences between a normal action potential that occurs in your neurons and the action potential that happens in the heart. While the principles of ion movements are similar, there are some key differences. We wanted to share a helpful diagram and some MCAT pointers that have helped our students.
MCAT Think: Draw the shape of the myocardial action potential, label the phases, and describe the movement of the ions.
Notice that the shape of the heart muscle action potential is not the same as the one for nerves. There’s a key difference – the plateau phase! Remember that heart muscle must contract, so calcium needs to enter the cytoplasm to help actin and myosin interact. Let’s walk through the phases of the action potential.
Phase 0: Rapid Na+influx through open fast Na+channels
Phase 1: Transient K+channels open and K+efflux begins to return the membrane potential to 0 mV
Phase 2: Influx of Ca2+through Ca2+ channels balances the K+efflux to create the plateau phase.
Phase 3: Ca2+ channels close and rectifier K+channels remain open to return the membrane potential to -90 mV
Phase 4: Na+and Ca2+channels are closed, while open K+rectifier channels maintain the negative resting potential
The MCAT is most interested in the plateau phase, where a balance exists between potassium efflux and calcium influx. This phase creates a stable membrane potential that is not seen in neuronal action potentials. Draw out the neuron action potential as a next step to test yourself on the differences between the two.
MCAT Think: Draw the shape of the myocardial action potential, label the phases, and describe the movement of the ions.
Notice that the shape of the heart muscle action potential is not the same as the one for nerves. There’s a key difference – the plateau phase! Remember that heart muscle must contract, so calcium needs to enter the cytoplasm to help actin and myosin interact. Let’s walk through the phases of the action potential.
Phase 0: Rapid Na+influx through open fast Na+channels
Phase 1: Transient K+channels open and K+efflux begins to return the membrane potential to 0 mV
Phase 2: Influx of Ca2+through Ca2+ channels balances the K+efflux to create the plateau phase.
Phase 3: Ca2+ channels close and rectifier K+channels remain open to return the membrane potential to -90 mV
Phase 4: Na+and Ca2+channels are closed, while open K+rectifier channels maintain the negative resting potential
The MCAT is most interested in the plateau phase, where a balance exists between potassium efflux and calcium influx. This phase creates a stable membrane potential that is not seen in neuronal action potentials. Draw out the neuron action potential as a next step to test yourself on the differences between the two.
