Pacemaker Cells and contractile cells

https://iu.pressbooks.pub/humanphys/chapter/cardiac-pacemaker-and-muscle-cells/ 

https://open.oregonstate.education/aandp/chapter/19-2-cardiac-muscle-and-electrical-activity/

Pacemaker Cells:

These specialized cells are responsible for initiating and regulating the rhythmic contractions of the heart.

Only about one percent of the heart muscle cells are pacemaker cells, while the rest are contractile cells.

Unlike skeletal muscles and neurons, pacemaker cells do not have a stable resting potential. Instead, they exhibit a phenomenon called autorhythmicity.

Here’s how it works:

Pacemaker cells contain a series of Na+ channels that allow a slow influx of sodium ions, causing the membrane potential to rise gradually from an initial value of around -60 mV to about -40 mV.

This slow depolarization brings the cell closer to the threshold.

When the threshold is reached, voltage-gated Ca2+ channels open, leading to rapid depolarization until the membrane potential reaches approximately +5 mV.

At this point, the Ca2+ channels close, and voltage-gated K+ channels open, allowing potassium ions (K+) to flow out, leading to repolarization.

Once the membrane potential reaches approximately -60 mV again, the K+ channels close, and the slow Na+ channels reopen, initiating the drift phase once more.

The lack of a stable resting potential in pacemaker cells accounts for their ability to spontaneously depolarize and contract, setting the pace for the heart’s rhythm1.

Contractile Cells:

These cells are responsible for the forceful contractions that propel blood throughout the body.

Their action potential differs significantly from that of pacemaker cells:

Rapid depolarization occurs, followed by brief repolarization and plateau phases.

The plateau phase is crucial for the long refractory periods required for effective blood pumping by cardiac muscle cells before they can fire again.

Contractile cells are connected to neighboring pacemaker cells via gap junctions, allowing them to locally depolarize adjacent cells2.

In summary:

Pacemaker cells initiate and regulate the heart’s rhythmic contractions.

Contractile cells generate forceful contractions to pump blood throughout the body. Together, they orchestrate the intricate dance of the heart’s beating rhythm! 🫀🎵34

Learn more  the heart’s beating rhythm! 🫀🎵34

1

iu.pressbooks.pub

2

en.wikipedia.org

3

thisvsthat.io

4

pediaa.com

pacemaker cell and contractile cell

Pacemaker Action Potential

What cells make up the heart?

 Instructions

What cells make up the heart?

The heart is composed of specialized cells called cardiomyocytes or myocardiocytes.

And why are these cells important?

In summary, cardiomyocytes play a crucial role in maintaining blood circulation by contracting rhythmically and efficiently. They are essential for the heart’s function and overall health. 😊

Conductive Cardiomyocytes:

These cells are involved in the heart’s electrical conduction system.

They include the sinuatrial node, atrioventricular node, and Purkinje fibers.

Conductive cardiomyocytes have leaky ion channels, fewer myofibrils, and reduced potential resistance

Below watch a short video to learn about two sets of heart cells and how they work together to lead to heart beats. You'll then answer a few short questions to check your understanding.

 

Contractile vs Pacemaker cells (6 min)Links to an external site.

How are contractile cells and pacemaker cells related?

Which cause heart contractions?

Which set the heart rate?

How are the two sets of cells physically connected at the cellular level? As a result, how do ions flow from one cell to another?