Anatomy & Physiology 3: Electrophysiology of the Heart

This flashcard set covers the fundamentals of action potentials, the cardiac conduction system, myocardial contraction mechanisms, and EKG wave components based on the lecture material.

Excitable cells

The 2 cell types, neurons and muscle cells, that are capable of generating an action potential.

Resting Membrane Potential (RMP)

An imbalance on opposing sides of a cell membrane, created by the Sodium/Potassium pump and Potassium leaky channels, typically between $-70\,mV$ and $-90\,mV$.

Threshold

A specific membrane potential (approximately $-50\,mV$) that, when reached, triggers voltage-gated $Na^+$ or $Ca^{2+}$ channels to open.

Depolarization

The phase of an action potential where sodium ($Na^+$) or calcium ($Ca^{2+}$) rushes into the cell, making the interior more positive.

Repolarization

The phase where $Na^+$ or $Ca^{2+}$ channels close and $K^+$ channels open, allowing $K^+$ to leave the cell and return it to a polarized state.

Neurotransmitters

Chemicals released from synaptic vesicles at the end of an axon that trigger $Na^+$ channels to open on the receiving excitable cell.

Myocardium

Heart muscle, $1\%$ of which is specialized conducting system and $99\%$ of which are contractile fibers.

Regulatory proteins

The proteins troponin and tropomyosin, which are contained within the myocardium along with the sliding filaments actin and myosin.

Functional Syncytium

A group of cardiac muscle cells that function electrically and mechanically as a single unit.

Gap junctions

Structures located at intercalated discs that allow ions and small molecules to move between muscle fibers, enabling direct communication.

Autorhythmicity

The property of the heart's specialized conducting system to initiate its own electrical impulses.

Sinoatrial (SA) Node

The pacemaker of the heart that initiates electrical impulses due to an unstable resting membrane potential.

Pacemaker potential

An unstable resting membrane potential in the SA node caused by a natural leakiness to $Na^+$, preventing a resting state.

Absolute Refractory Period

The time during depolarization and repolarization when a second action potential cannot be generated by the cell.

Relative Refractory Period

The phase during hyperpolarization when a second action potential can only be generated if the stimulus is strong enough.

Plateau Effect

A unique phase in cardiac action potentials where $Ca^{2+}$ channels open alongside $K^+$ channels, allowing $Ca^{2+}$ to enter and lengthening the duration of the action potential.

Troponin

The protein that $Ca^{2+}$ (from both entry and the sarcoplasmic reticulum) binds to, causing tropomyosin to move so myosin can attach to actin.

P wave

The segment of an EKG representing depolarization spreading from the SA node through the atria.

QRS complex

The segment of an EKG representing ventricular depolarization, followed immediately by ventricular systole.

T wave

The segment of an EKG representing ventricular repolarization.

Conduction Pathway

The electrical sequence of the heart: Sinoatrial (SA) Node $\rightarrow$ Atrioventricular (AV) Node $\rightarrow$ Bundle of His $\rightarrow$ Left and Right Bundle Branches $\rightarrow$ Purkinje Fibers.