Cardiac Myocyte Action Potential and Contraction

Vocabulary flashcards covering the cellular mechanics, ionic benchmarks, ion channel behaviors, and electrophysiological stages of the cardiac myocyte action potential.

Cardiac myocytes

The muscle cells within the heart that perform the physical squeezing and contraction.

Calcium (in cardiac contraction)

The essential trigger ion that initiates the transition from a relaxed cell state with spread-apart proteins to a squeezed state with overlapping proteins.

Depolarization

The electrical process of changing the cell membrane potential from a negative value toward a positive value.

Repolarization

The electrical process of changing the cell membrane potential from a positive value back down toward a negative value.

Gap junctions

Microscopic physical connections between neighboring heart cells that permit ions like sodium and calcium to leak across.

Threshold

The membrane potential level of $-70\,mV$ that triggers the opening of fast voltage-gated sodium channels.

Fast sodium channels

Voltage-gated channels that open rapidly at $-70\,mV$, allowing sodium to gush into the cell and drive the membrane potential into positive territory before quickly closing.

Voltage-gated potassium channels

Channels that open when the cell reaches positive territory (around $+20\,mV$), allowing potassium to exit the cell and initiate repolarization.

Voltage-gated calcium channels

Channels that open during the action potential to let calcium enter the cell, balancing outward potassium flow and creating a plateau around $+5\,mV$.

Stage 4

The baseline resting phase of the relaxed cardiac muscle cell, maintained at approximately $-90\,mV$ primarily by potassium permeability.

Stage 0

The rapid depolarization phase triggered at the $-70\,mV$ threshold, driven by the massive inward rush of sodium ions through fast voltage-gated sodium channels.

Stage 1

The initial repolarization phase that occurs when fast sodium channels close and voltage-gated potassium channels open, lowering the membrane potential to around $+5\,mV$.

Stage 2

The plateau or flatline phase during which inward calcium influx through voltage-gated channels balances outward potassium efflux at approximately $+5\,mV$.

Stage 3

The rapid repolarization phase where voltage-gated calcium channels close while voltage-gated potassium channels remain open, driving the potential back down to $-90\,mV$.

Fast action potential

The designation given to the ventricular cardiac myocyte action potential because Stage 0 depolarizes extremely quickly due to fast voltage-gated sodium channels.