Heart Conduction System & ECG (EKG)

Summary

This educational video script delves into the intricacies of the human heart's cardiac conduction system, explaining how it coordinates heartbeats. It introduces the sinoatrial (SA) node as the heart's pacemaker, the role of the atrioventricular (AV) node in delaying signals for organized contractions, and the function of the bundle of His and Purkinje fibers in rapid signal transmission. The script also correlates these processes with an ECG (EKG), describing the significance of the P-wave, QRS complex, and T-wave, and how they reflect atrial and ventricular activity. Realistic anatomical visuals from Anatomage enhance the learning experience.

Takeaways

• 💓 The human heart has been beating continuously since the first heartbeat as a fetus, thanks to the cardiac conduction system.
• 🔍 The cardiac conduction system is a network of specialized tissue that coordinates heartbeats, including the sinoatrial (SA) node, atrioventricular (AV) node, and the bundle of His.
• 📍 The SA node, located in the right atrium, acts as the heart's pacemaker, initiating the heartbeat by sending electrical signals.
• 🚦 The AV node introduces a delay to ensure the atria contract before the ventricles, allowing for efficient blood transfer.
• 🛤️ The bundle of His and bundle branches rapidly transmit the electrical signal from the AV node to the ventricles, preparing them for contraction.
• 🏭 The Purkinje fibers spread the signal throughout the ventricles, ensuring synchronized contraction for effective blood pumping.
• 📊 An ECG (electrocardiogram) measures the heart's electrical activity, with the P-wave, QRS complex, and T-wave corresponding to atrial depolarization, ventricular depolarization, and repolarization, respectively.
• 🩺 The P-wave on an ECG represents atrial depolarization, which leads to atrial contraction and the subsequent pushing of blood into the ventricles.
• 🏋️‍♂️ The QRS complex indicates ventricular depolarization, which is the signal for the ventricles to contract and pump blood out of the heart.
• 🔙 The T-wave signifies the repolarization of the ventricles, marking the end of their contraction phase and the beginning of relaxation.
• 🎥 Anatomage provides 3D models and virtual dissection tables that help visualize the complex structures of the heart in a three-dimensional space.

Q & A

What is the primary function of the sinoatrial (SA) node?

The SA node, also known as the pacemaker of the heart, is responsible for initiating the heartbeat by sending out electrical signals that trigger the contraction of the heart muscle.

How does the cardiac conduction system differ from cardiac muscle tissue?

The cardiac conduction system is non-contractile and functions like nervous tissue, conducting electrical signals rapidly throughout the heart. In contrast, cardiac muscle tissue is contractile and pumps blood but conducts signals more slowly.

What is the purpose of the delay in the atrioventricular (AV) node?

The delay in the AV node ensures that the atria contract and push blood into the ventricles before the ventricles contract. This sequence prevents the atria and ventricles from contracting simultaneously, allowing for efficient blood flow.

Why is the blood color in diagrams often depicted as blue for the right side of the heart and red for the left?

In diagrams, blue is used to represent the right side of the heart, which contains deoxygenated blood, and red is used for the left side, which contains oxygenated blood. However, it's important to note that blood is always red; these are just conventional colors used for illustration.

What is the role of the interatrial pathway in the heart's electrical conduction?

The interatrial pathway facilitates the rapid transmission of electrical signals from the SA node to the left atrium, ensuring that both atria contract in unison to efficiently move blood into the ventricles.

How does the bundle of His contribute to the heart's electrical activity?

The bundle of His, also known as the atrioventricular bundle, receives the signal from the AV node and rapidly transmits it through the left and right bundle branches, which then stimulate the ventricles to contract.

What is the significance of the QRS complex in an ECG?

The QRS complex in an ECG represents the ventricular depolarization, which is the electrical signal passing through the ventricles causing them to contract and pump blood to the body and lungs.

What does the T-wave indicate on an ECG?

The T-wave on an ECG signifies the repolarization of the ventricles, which is the return to the resting state after contraction, marking the end of the cardiac cycle's electrical activity.

How does the heart sound relate to the ECG?

The first heart sound corresponds to the end of the QRS complex when the tricuspid and mitral valves close, while the second heart sound occurs at the end of the T-wave when the aortic and pulmonary valves close.

What is the role of the interatrial and internodal pathways in the heart's electrical conduction system?

The interatrial pathway rapidly transmits the signal from the SA node to the left atrium, while the internodal pathways conduct the signal through the right atrium. Together, they ensure synchronized atrial contraction.

Outlines

00:00

🫀 Introduction to the Cardiac Conduction System

This paragraph introduces the concept of the cardiac conduction system, which is responsible for coordinating heartbeats. It explains that the heart has been beating continuously since fetal development, thanks to a small mass of cardiac tissue known as the sinoatrial (SA) node. The SA node, along with a complex conduction system, ensures the blood is pumped through the arteries. The video aims to educate viewers about the cardiac conduction system and how it relates to ECG (electrocardiogram) readings. Real human cadavers and anatomage images are used to provide a three-dimensional understanding of the heart's structure. The script also covers the basic structure of the heart, including the atria and ventricles, and the flow of blood through these chambers.

05:00

🚀 The Cardiac Conduction System and ECG Waves

This section delves into the three types of tissue in the heart: the cardiac conduction system, cardiac muscle tissue, and non-conductive fibrous tissue. The SA node's role as the heart's pacemaker is emphasized, explaining how it generates electrical signals that initiate each heartbeat. The script describes the pathway of these signals from the SA node through the internodal pathway to the atrioventricular (AV) node, and the purpose of the delay in the AV node to ensure the atria contract before the ventricles. It also discusses the bundle of His and the bundle branches that facilitate rapid signal transmission, leading to the contraction of the ventricles. The paragraph concludes with an overview of how these processes relate to the different waves of an ECG, specifically the P-wave, QRS complex, and T-wave.

10:01

🔬 Detailed Explanation of ECG Intervals and Waves

The paragraph provides a detailed explanation of the different intervals and waves seen in an ECG, correlating them with the electrical activity in the heart. It describes the P-wave, which signifies atrial depolarization, the PR interval during which the atria contract and push blood into the ventricles, and the QRS complex that indicates ventricular depolarization. The script also explains the ST interval, which corresponds to ventricular contraction and the first heart sound, and the T-wave, which represents ventricular repolarization and the second heart sound. The paragraph emphasizes the importance of these intervals and waves for understanding the heart's electrical activity and function.

15:02

📚 Recap and Visualization of Cardiac Processes

In this final paragraph, the script recaps the key points about the cardiac conduction system and the corresponding ECG readings. It summarizes the role of the SA node, the pathways of the electrical signals through the heart, and the significance of the ECG's P-wave, PR interval, QRS complex, ST interval, and T-wave. The paragraph also highlights the importance of practice in understanding these concepts. The video includes real-time visualizations of the heart's contractions and the electrical signals that drive them, provided by Anatomage, to help viewers grasp the complexity of the cardiac conduction system. The script ends with a call to action for viewers to practice labeling the parts of the cardiac conduction system and to explore more videos on the topic.

Keywords

💡Cardiac Conduction System

The Cardiac Conduction System is a network of specialized heart cells that generate and coordinate electrical impulses to regulate the heartbeat. In the video, it is described as the orchestrator of the heart's rhythmic contractions, ensuring that the atria and ventricles contract in a coordinated manner. The script mentions the SA node, AV node, and the bundle of His as key components of this system.

💡Sinoatrial (SA) Node

The Sinoatrial (SA) Node is often referred to as the heart's natural pacemaker. It is an autorhythmic cell cluster that initiates the heartbeat by sending electrical signals throughout the heart. The video script describes how the SA node's self-rhythmic nature ensures a consistent heartbeat, even without external input, by increasing the permeability to sodium and calcium ions.

💡Atrial Node

The Atrial Node, also part of the Cardiac Conduction System, is mentioned in the script as a secondary pacemaker that can take over if the SA node fails. It is located in the right atrium and is involved in the transmission of electrical signals from the SA node to the ventricles.

💡Atrioventricular (AV) Node

The Atrioventricular (AV) Node is a critical component of the Cardiac Conduction System that receives signals from the atria and transmits them to the ventricles, but with a slight delay. This delay, as explained in the script, ensures that the atria contract and push blood into the ventricles before the ventricles contract.

💡Bundle of His

The Bundle of His is a part of the Cardiac Conduction System that receives signals from the AV node and quickly transmits them to the ventricles. The script describes how this structure branches into the left and right bundle branches, which are essential for the rapid depolarization of the ventricles.

💡Depolarization

Depolarization is the process by which cardiac cells lose their electrical potential, leading to muscle contraction. The script explains that the SA node's depolarization initiates a heartbeat and that this process occurs in both the atria and ventricles, though at different times to ensure proper blood flow.

💡Repolarization

Repolarization is the return of cardiac cells to their resting state after depolarization. It is highlighted in the script as the process that follows the contraction of the heart muscle, allowing the muscle to relax and prepare for the next contraction cycle.

💡ECG/EKG

An Electrocardiogram (ECG or EKG) is a graphical representation of the heart's electrical activity. The video script uses the ECG to illustrate the different phases of the heartbeat, including the P-wave, QRS complex, and T-wave, each corresponding to specific events in the Cardiac Conduction System.

💡P-Wave

The P-Wave on an ECG represents atrial depolarization. The script explains that the P-wave corresponds to the electrical signal traveling through the atria, causing them to contract and push blood into the ventricles.

💡QRS Complex

The QRS Complex on an ECG indicates ventricular depolarization. As described in the script, the QRS complex is a significant spike that represents the rapid spread of electrical signals through the ventricles via the Bundle of His and Purkinje fibers, leading to their contraction.

💡T-Wave

The T-Wave on an ECG represents ventricular repolarization. The script mentions that the T-wave corresponds to the ventricles returning to their resting state after contraction, which is the final electrical event in a heartbeat cycle.

Highlights

The heart's rhythm is maintained by a small mass of cardiac tissue called the sinoatrial (SA) node.

The cardiac conduction system coordinates heartbeats through a complex network within the heart.

An ECG (Electrocardiogram) or EKG represents the electrical activity of the heart.

The heart is divided into right and left sides, each with an atrium and ventricle, colored to represent oxygen levels.

Blood flows through specific pathways, from the vena cava to the right atrium, then to the right ventricle and out through the pulmonary artery.

The left side of the heart receives oxygenated blood from the lungs and pumps it through the aorta to the rest of the body.

The cardiac conduction system is non-contractile and functions like nervous tissue to conduct signals.

Cardiac muscle tissue is contractile and also plays a role in signal conduction.

Fibrous tissue in the heart is non-conductive, ensuring the atria and ventricles do not contract simultaneously.

The SA node, or the heart's pacemaker, sends signals for each heartbeat without external input.

The internodal pathway transmits the signal from the SA node to the AV node through three branches in the right atrium.

The interatrial pathway quickly conducts the signal from the SA node to the left atrium.

The AV node introduces a delay to ensure the atria contract before the ventricles.

The bundle of His and bundle branches quickly transmit the signal down the heart's septum.

Purkinje fibers extend from the bundle branches to distribute the signal throughout the ventricles.

The ECG's P-wave corresponds to atrial depolarization, the QRS complex to ventricular depolarization, and the T-wave to ventricular repolarization.

The PR interval represents the time from atrial depolarization to the beginning of ventricular depolarization.

The ST interval is when the ventricles are contracting, pushing blood through the aorta and pulmonary artery.

The first and second heart sounds correspond to the closing of the heart valves during different stages of the cardiac cycle.

Transcripts

your heart has beat continuously for

your entire life from that very first

heartbeat back when you were a fetus

developing in the uterus until this very

day that constant Rhythm that keeps the

blood pumping through your arteries is

thanks to a small mass of cardiac tissue

called the CYO atrial node along with a

complex cardiac conduction system that

runs through your heart coordinating

your heartbeat in this video we're going

to build out the cardiac conduction

system piece by piece learn how it all

works and then use that to understand

the different parts of an ECG or EKG and

throughout the video we'll look at real

human cavers and other fac images

provided by anatomage the creator of the

world's first virtual dissection table

so you can see all these structures are

arranged three-dimensionally in the body

and by the end of this video you're

going to know this whole process by

heart well by brain because that's where

memories are stored but you know what I

mean let's jump to the Whiteboard and

get started so let's start by drawing

out the heart here we have an outline of

the main structure of the heart on the

cardiac muscle we've got the right

atrium and the right ventricle and the

left atrium and the left ventricle and

of course we have the right side in blue

because it's low oxygen blood the left

side in red because it's high oxygen

blood that's just come from the lungs

and remember our blood is always red

never blue that's just the colors we use

in the diagrams blood is going to come

into the right side through the superior

and inferior venne cavis into the right

atrium it'll pass through the tricuspid

valve into the right ventricle and the

right ventricle is going to pump it out

through the pulmonary artery to go to

the lungs to receive some oxygen the

blood is going to get back to the heart

through the pulmonary veins and go into

the left atrium from the left atrium

it'll pass through the bicuspid or mitol

valve into the left ventricle and then

the the left ventricle is going to pump

it very forcefully out through the aorta

so it can travel throughout the rest of

the body and deliver the oxygen and

nutrients and hormones and all the other

stuff that's in our blood in between the

left side and the right side of the

heart we have the septum that really

divides the heart into those two halves

and here we can see in the anatomage

models the right atrium and the right

ventricle sitting sort of anterior to

the left side where we have the left

atrium and the left ventrical now for

the rest of the video I'm going to

assume you know those structures pretty

well but if you want to refresh your a

whole lesson on all that check out my

pathway of blood Through the Heart video

links down below for that now in the

heart there's three different types of

tissue that we're concerned about in

this video first we have the cardiac

conduction system itself that's going to

be in yellow on this diagram and that's

non-contractile cardiac tissue in other

words these aren't muscle cells that are

Contracting they're going to be more

like nervous tissue that's going to be

conducting signals throughout the heart

second we have the cardiac muscle tissue

this is going to be contractile tissue

it's going to be tissue that contracts

and and pumps blood but it also conducts

signals as well the card conduction

system which is just about 1% of the

total kind of cells in here that's going

to conduct the signals very quickly

whereas the cardiac muscle it will take

a little bit longer for the signals to

pass through the muscle tissue itself

and the cardiac muscle tissue that's

going to be the vast majority of tissue

in the heart now there is some

non-conductive tissue in the heart and

that's going to be the fibrous tissue

and that's going to run from the atrial

floor between the atrium and the

ventricles now the fact that this

fibrous tissue right there is

non-conductive is very important we

don't want the Atria and the ventricles

to be contracting at the same time we

want the Atria to contract and push the

blood into the ventricles and then the

ventricles to contract and push all that

blood out of the heart if this tissue

right here was conductive then we would

have the Atria and ventricles

Contracting at the same time wouldn't be

good and the only way that signal can

pass through here is through the cardiac

conduction system through this yellow

section right there that's the only part

where the signal travels through that

fibrous connective tissue so that

fibrous connective tissue separates the

Atria from the ventricles and into two

sections that we call the atrial sensium

as well as the ventricular sensium a

sensium is just a big sort of hardto

pronounce word that means a group of

cells that are all electrically

connected to each other so all of the

cardiac muscle in this atrial sensium

are connected electrically meaning that

if one of the cells depolarizes it

depolarizes the next cardiac muscle cell

and that depolarizes the next one and

eventually they'll all be depolarized

cuz they're all electrically connected

same thing in the ventricular sens when

one of those cells depolarizes that'll

depolarize the next cell and the next

cell and the next cell until it's all

depolarized now the signal passing

between cardiac muscle cells is sort of

slow I kind of mentioned that earlier

and that's why we need this cardiac

conduction system to conduct those

signals very quickly so that the Atria

can contract as one unit and the

ventricles especially can contract as

one unit but again the atrial cisum will

depolarize first Contracting the Atria

and then the ventricular sensium will

depolarize Contracting the ventri Les

now let's take a look at the individual

parts of the cardiac conduction system

first here we have the Sino atrial node

now the Sino atrial node is autorhythmic

meaning that it's going to be sending

pulses by itself even without input from

some other source autorhythmic meaning

self- rhythmic in other words that saay

note is the pacemaker of the heart it

sends a signal every time our heart

beats now there will be input from the

brain from the cardiac regions of the

brain they'll be sending signals to the

heart to speed up that saay node or to

slow down that SA node but even without

input from the brain the SA node is

going to be sending signals itself

causing our heartbeat rhythm this

consistent Rhythm happens by increasing

permeability in the SA node of sodium

ions and calcium ions so those sodium

and calcium ions are slowly entering

into the SA node and it prevents

pottassium from leaving the cells in the

SA node so there's a slow buildup of

positive charge over time as sodium and

calcium come into the SA node and then

as soon as reaches a threshold membrane

potential the SA node will send an

action potential now the signals will

eventually get to another node called

the atrio ventricular or AV node more on

that in just a moment but next let's

talk about the internodal pathway this

is going to be how the signal transmits

from the SA node to the AV node and if

you look at that internodal pathway

there's three branches of it and they're

all passing through the right atrium now

on my diagram they look sort of planer

or flat with each other but if we look

on the anatomage images we'll see that

these are actually three-dimensional um

running through that right atrium which

we can see right there so the SA node

depolarizes sends a signal through the

internal Pathway to the AV node and

that's going to depolarize the right

atrium now eventually that

depolarization would make itself over to

the left atrium but that's going to take

a long time without the interatrial

pathway which is going to run from the

SA node over into the left atrium that

interatrial pathway will conduct the

signal very quickly into the left atrium

and deol ize it most of the diagrams I

looked up have the interatrial pathway

coming directly from the SA node but one

thing I noticed in the anatomage images

is that the interatrial pathway is

actually branching off of one of the

internodal branches even though most of

the diagrams you look up on this show it

coming from the SA node directly great

so the signal comes from the SA node

it's going to travel through the

interatrial pathway as well as the

internodal pathway depolarizing both

Atria so that they can contract that

signal then is going to make it to the

AV node now we've talked about the

cardiac conduction system needing to

send these signals very quickly but the

AV node sort of does the opposite

there's going to be a delay in the AV

node now what would be the benefit of

that well like I said earlier we want

the Atria to contract before the

ventricles contract so that delay is

going to really separate the atrial

contraction from the ventricular

contraction that way we can get all the

blood from the Atria to the ventricles

and then the ventricles can pump it all

out from The Av node the signal is going

to pass into the bundle of hiss also

known as the atrio ventricular bundle

that bundle is immediately going to

separate into the right and left bundle

branches now unlike the AV node which

passes the signal very slowly the bundle

of His and the bundle branches are going

to transmit that signal very quickly

down the septum of the heart also as the

signal is traveling through the septum

it's not going to be stimulating the

ventricles to contract just yet the

ventricles will be stimulated to

contract when the signal is passing its

way back up that's going to allow the

pumping to happen from the apex of the

heart on the way back up to kind of

force the blood out through the

pulmonary artery and the aorta this way

the tricuspid and mitro valves will also

snap shut during this time to prevent

the blood from back flowing into the

Atria now extending out of the left and

right bundle branches we have something

called the Peri fibers and the pingi

fibers are going to take that signal

traveling through the bundle branches

and spread it out throughout the muscle

of the right and left ventricles that's

going to conduct that signal many many

times faster than if we were only

relying on the ventricular Sensi or the

connections between all of the cardiac

cells so quick recap of all that the SA

node or the pacemaker of the heart will

send out a signal that'll pass through

the interatrial pathway to stimulate the

left atrium it'll also pass through the

internodal pathways to stimulate the

right atrium the signal will make it to

the AV node where it's going to pass

very slowly to cause a delay before the

ventricles will contract the signal will

pass through the bundle of hiss and the

left and right bundle branches on the

way back up they'll pass through the

pingi fibers that's going to stimulate

the cardiac muscle and the ventricles to

contract and pump the blood out through

the pulmonary artery as well as the

aorta now let's take a look at an ECG or

an EKG this is the thing that you've

seen in like doctor movies and stuff

where you see the beep beep and if it

stops you hear it go beep because the

heart has stopped beating but it's a

measure of the electrical activity

happening in the heart and it's got

three regions here it's got the p-wave

the QRS complex as well as the t-wave

and these three sections correspond to

different things happening in the

cardiac conduction pathway so again we

have the p-wave the Q complex in the

t-wave you can see that happening one

more time there I just really like that

animation so what we're going to do is

we're going to connect this to the

cardiac conduction pathway looking at

the p-wave QRS complex and the t-wave

we're going to start with the p-wave the

p-wave is going to correspond to the

depolarization of the Atria so we've got

the depolarization happening and you can

see those signals traveling through

those different Pathways causing

depolarization of the Atria so that's

the main thing happening here in the

p-wave the Atria will depolarize next we

have what we call the pr interval the PR

interval is going to start at the

beginning of the p wve and last all the

way really until the Q part right here

we call it the PR interval I think

because sometimes on ECGs the qwave

might be hard to identify or might not

show up so we refer to this as the PR

interval you also might see something

called the pr segment so just as a quick

clarification the PR interval starts at

the beginning of p and lasts until R

whereas the pr segment is just from the

end of P to the beginning of R so PR

interval would be this PR PR segment

would just be this now during the PR

interval the Atria are going to contract

and that's going to send blood from the

right atrium Into The ventricle and the

blood from the left atrium into the left

ventricle basically any blood that was

still left in the atrium is going to get

squeezed out through the contraction of

the Atria the Contracting of the Atria

will really start early on in the p wve

and last throughout this section right

here also during this section of the PR

interval which is the pr segment is

where we have that AV noal delay

happening because as soon as the QRS

complex hits then we're going to be

depolarizing the ventricles speaking of

which let's move on to the QRS complex

in the QRS complex you see this huge R

Spike that's because of the signal

passing through the bundle of His and

the bundle branches and then through the

bingi fibers stimulating all of this

cardiac muscle that electrical activity

is going to be much greater in the

ventricles because the ventricles have

more cardiac tissue they also have to

pump the blood a lot farther the Atria

just had to pump the blood from one

chamber to another the ventricles have

to pump the blood to the lungs and then

also Al through the aorta throughout the

whole body so they need a very strong

contraction so we need a lot of

electrical activity to cause that to

happen so during the QRS complex that

signal is going to pass through the left

and right bundle branches and through

theingi fibers that's going to

depolarize the ventricles also the Atria

are going to repolarize repolarization

is the opposite of depolarization

depolarization is when tissue becomes

more positive and in this case causes it

to contract repolarization is when it

returns back to its resting membrane

potential and that muscle is going to

relax and stop Contracting so we have

depolarization of the ventricles as well

as repolarization of the Atria basically

ventricles contract but the Atria will

be stopping their contraction now that

QRS complex that big spike in the r is

caused by the ventricles depolarizing we

can't really see the effect of the Atria

repolarizing on the EKG because it's

sort of hidden by that big

depolarization of the ventricles but

both of those things are happening

during that QRS complex up next we have

something called the St interval that St

interval is going to start with s and

last all the way to the end of the

t-wave a subset of that is the ST

segment which would just be this section

in right there lasting until the

beginning of the t-wave during the St

interval we're going to have the

ventricles Contracting that's going to

cause blood to be pumped through the

aorta as well as blood to be pumped

through the pulmonary artery that very

forceful contraction is going to be

starting kind of at the end of the QRS

complex and Lasting until the t-wave

happens the t-wave is when we're going

to be repolarizing the ventricles and

stopping the contraction but those

ventricles will be contracting during

that St interval now when the ventricles

contract that's where we're going to

hear our first heart sound the love of

the ldub ldub we represent that with S1

for the first sound of the heart and

that sound is caused by the tricuspid

and mitol valves snapping shut right

before the ventricles will contract and

pump the blood out we need those valves

to close of course because we don't want

the blood to rush back into the Atria we

want all that blood to be forced out

through the aorta and pull AR artery so

again that first heart sound is going to

kind of happen right around the end of

that QRS complex as the valves are

snapping shut finally the last section

of this is the t-wave and the t-wave is

going to be the repolarization of the

ventricles or in other words sort of the

turning off of ventricular contraction

after the ventricles are finished

Contracting we're going to have the

second heart sound the dub of ldb just

like the first heart sound the second

heart sound is going to be caused by

Valve snapping shut but in this case

that's going to be the pulmonary valve

snapping shut as well as the aortic

valve valve snapping shut so the

ventricles are relaxing and we don't

want the blood that's been pumped out of

the ventricles to pass back into them

through the aorta or pulmonary artery so

we snap those valves shut to keep the

blood out of the ventricles there and

that second heart sound is going to be

happening kind of right at the end of

the t-wave somewhere right in there all

right so a lot going on in that process

let's do a quick recap we have the soo

atrial node where the signal will start

we have the interatrial pathway the

signal will travel there to depolarize

the left atrium we have the internal

pathway the signal will travel through

the noal Pathways to depolarize the

right atrium the signal will travel to

the AV node where it is slowed down or

delayed so the Atria can finish

Contracting before the ventricles get

depolarized and contract we have the

bundle of His which is going to separate

into the left and right bundle branches

the bundle and the branches are going to

transmit the signal very quickly because

we want the ventricles to contract as

one contract all unit as quickly as

possible signal passes down the septum

and then on the way back up it's going

to pass through pereni fibers which are

going to distribute the signal

throughout the heart muscle to help the

ventricles contract all at once from the

Apex up all of this electrical

conduction is going to cause the ECG the

electrocardiogram the ECG will start

with the p-wave this is where the Atria

are depolarizing up next we have the PR

interval this is where the Atria are

Contracting and it's going to be pushing

blood from the right atrium to the right

ventricle and from the left atrium to

the left ventricle next is the QRS

complex this is going to be where the

ventricles are depolarizing and it's

going to be where the Atria are

repolarizing or sort of turning off once

the ventricles are depolarized we move

into the St interval and this is where

the ventricles are going to be

contracting causing blood to pass up

through the aorta and pumping blood out

through the pulmonary artery as well and

at the beginning of that St interval is

where we have the first heart sound

which is caused by the tricuspid and

mitro valves snapping shut up next we

have the t-wave the t-wave is going to

be where the ventricles are repolarizing

or turning off or stopping their

contraction and as those ventricles

relax we're going to have the second

heart sound which is the dub of love dub

and that's caused by the aortic and the

pulmonary semilunar valves snapping shut

now let's take a look at some video from

anatomize so we can see all of this

pumping and Contracting and stuff

happening in action so we have the

signal starting in the SA node and we're

going to see the depolarization of the

Atria the Atria are going to be

contracting and it's hard to see that

Contracting of the Atria it's going to

be much less forceful than the

Contracting of the ventricles later on

the signals passing through the Atria

into the AV node where we have that AV

noal delay and then the signals passing

through the bundle branches and the

pingi fibers which is going to cause

that QRS complex and then we have the

ventricles Contracting during the St

interval and finally The ventricle is

relaxing until we have another signal

from the SA node and we get a new p wve

and this process starts all over again

and now let's watch that process

happening in real time it's just a cool

process imagine this is happening in

your heart like every time it beats

multiple times per second it's just wild

now the only way to really learn this

stuff is to practice yourself so here's

the diagram that you can use pause the

video test yourself see if you can label

all the parts of the cardiac conduction

system as well as explain what's

happening through the different parts of

the electroc cardiogram and here's all

that information back so you can check

and see how you did thanks again to

anatomage for sponsoring this video they

make these amazing virtual dissection

tables they have a science table they

also have anatomage lessons lots of

awesome stuff go check those out in the

website link below and special thanks to

my supporters on patreon link in the

description if you're interested in

joining all my supporters on patreon get

access to the diagrams both labeled and

unlabeled from all my videos including

this one thanks for learning about the

heart in this video I've got more videos

on the heart and cardiovascular system

and other parts of the body so uh check

those out on the channel if you're

interested and may your Sino atrial node

continue sending signals for years and

years to come and I'll see you in the

next video