Cardiac contraction
Created @August 23, 2024 11:19 AM
SPREAD OF CARDIAC EXCITATION
The myocardium consists of two main components: nodal cells that generate automaticity (the ability to produce action
potentials without external stimuli) and contractile cells.
Automaticity originates from:
1. The SA node (sinoatrial node): It generates impulses at the fastest rate, causing depolarization of the right atrium.
These impulses travel to Bachmann's bundle, leading to left atrial depolarization, and then through the internodal
pathway to:
2. The AV node (atrioventricular node): It delays impulses by about 0.1s (allowing time for atrial contraction) before
sending them to the bundle of His. This structure conducts impulses into the right bundle branch (RBB) and the left
bundle branch (LBB) (from the interventricular septum to the heart's apex) and finally to the Purkinje fibers.
NOTE: Both atria contract simultaneously with equal intensity (as do both ventricles).
Link: https://socratic.org/questions/where-in-the-heart-is-the-sinoatrial-node-located
pacemaker cell’s action potential
The action potential starts with sodium ions moving through "funny" channels. This causes the membrane potential to
change from -60 mV (the resting membrane potential for myocardial cells) to -55 mV. Next, T-type calcium channels open,
allowing calcium ions to flow in until the membrane potential reaches the threshold of -40 mV. L-type calcium channels then
open, and more calcium ions enter the cell until it becomes fully depolarized. Finally, potassium channels open, and K+ ions
start leaving the cell, initiating its repolarization again
Cardiac contraction 1
Created @August 23, 2024 11:19 AM
SPREAD OF CARDIAC EXCITATION
The myocardium consists of two main components: nodal cells that generate automaticity (the ability to produce action
potentials without external stimuli) and contractile cells.
Automaticity originates from:
1. The SA node (sinoatrial node): It generates impulses at the fastest rate, causing depolarization of the right atrium.
These impulses travel to Bachmann's bundle, leading to left atrial depolarization, and then through the internodal
pathway to:
2. The AV node (atrioventricular node): It delays impulses by about 0.1s (allowing time for atrial contraction) before
sending them to the bundle of His. This structure conducts impulses into the right bundle branch (RBB) and the left
bundle branch (LBB) (from the interventricular septum to the heart's apex) and finally to the Purkinje fibers.
NOTE: Both atria contract simultaneously with equal intensity (as do both ventricles).
Link: https://socratic.org/questions/where-in-the-heart-is-the-sinoatrial-node-located
pacemaker cell’s action potential
The action potential starts with sodium ions moving through "funny" channels. This causes the membrane potential to
change from -60 mV (the resting membrane potential for myocardial cells) to -55 mV. Next, T-type calcium channels open,
allowing calcium ions to flow in until the membrane potential reaches the threshold of -40 mV. L-type calcium channels then
open, and more calcium ions enter the cell until it becomes fully depolarized. Finally, potassium channels open, and K+ ions
start leaving the cell, initiating its repolarization again
Cardiac contraction 1
