SA node cell to atrial cardiac muscle cell signaling

Definition

Target type: biologicalprocess

Any process that mediates the transfer of information from an SA node cardiomyocyte to an atrial cardiomyocyte. [GOC:BHF, GOC:mtg_cardiac_conduct_nov11]

The Sinoatrial (SA) node, located in the right atrium, is the heart's natural pacemaker. It generates electrical impulses that trigger heartbeats, initiating the cardiac cycle. These impulses are transmitted to the atrial cardiac muscle cells, causing their contraction and subsequently pumping blood to the ventricles.

The signaling process between the SA node and atrial muscle cells involves a coordinated sequence of events:

1. **SA Node Action Potential Generation:** The SA node cells are specialized pacemaker cells that exhibit spontaneous depolarization due to a unique combination of ion channels. These channels allow for inward movement of sodium (Na+) and calcium (Ca2+) ions, gradually increasing the cell's membrane potential until it reaches the threshold for action potential generation.

2. **Action Potential Conduction:** The action potential generated by the SA node cells spreads rapidly through the atrial muscle cells via specialized gap junctions, which allow the passage of ions and electrical signals between cells. These gap junctions ensure synchronized contraction of the atria.

3. **Atrial Muscle Cell Excitation:** As the action potential reaches the atrial muscle cells, it causes a rapid influx of Ca2+ ions through voltage-gated calcium channels. This calcium influx triggers a cascade of events that ultimately lead to muscle contraction:
- **Calcium-Induced Calcium Release:** The influx of Ca2+ into the sarcoplasm (the cytoplasm of muscle cells) triggers the release of even more Ca2+ from the sarcoplasmic reticulum, an intracellular organelle that stores calcium.
- **Cross-Bridge Formation:** The increased intracellular calcium concentration enables the binding of calcium to troponin, a protein that regulates the interaction of actin and myosin filaments, the contractile proteins of muscle cells.
- **Muscle Contraction:** This binding allows the myosin heads to attach to actin filaments, forming cross-bridges. The interaction between actin and myosin results in muscle contraction.

4. **Repolarization and Relaxation:** Once the SA node action potential has passed, the atrial muscle cells repolarize. This involves the efflux of potassium (K+) ions, restoring the resting membrane potential. The reduction of calcium in the sarcoplasm leads to the detachment of myosin heads from actin filaments, allowing the muscles to relax and prepare for the next contraction cycle.

This intricate signaling process ensures the efficient and coordinated contraction of the atria, which is essential for propelling blood to the ventricles and maintaining the rhythm of the heart.'
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Proteins (1)

Compounds (12)