Describe the electrical conduction of the heart.

SA Node Atrial Muscle AV node Bundle of His Left & Right Bundle Branches Purkinje Fibers Ventricular Muscle

What is the function of the SA node?

Sino Atrial node is the pacemaker of the heart because of its ability to spontaneously generate AP without stimulation.

Which other part of the heart can spontaneously generate AP?

Atrio Ventricular node (AV node), Bundle of His, and the Purkinje Fibers

Compare the rate of fire between SA node and that of AV node, Bundle of His, and Purkinje Fibers.

The rate of fire of AV node, Bundle of His, and Purkinje Fibers is slower than SA node; SA node sets the pace of the heart.

What is the role of AV node and Purkinje Fibers?

They conduct electrical current between Atria and Ventricles; the Purkinje Fibers specifically branches off AP to all cardiac tissue in ventricle

Why is there a delay in the conduction at AV-node?(Why is electrical conduction slowest at the AV node?)

In order for the atria to empty out blood into ventricle

Which part of the heart has a high rate of electrical conduction?

The Purkinje Fibers and Bundle of His

State some characteristics of cardiac muscle.

Striated (has sarcomere), Nucleated, and Intercalated Disk (contains Gap Junction)

What is an artery?

Blood vessel that carries blood away from the heart

What is a vein?

Blood vessel that blood to the heart

What is the tricuspid valve? What is its function?

Valve between right atrium and right ventricleIt prevents backflow of blood into right atrium

What is the pulmonary semi lunar valve?

Valve between right ventricle and pulmonary artery

What is the bicuspid or mitral valve? What is its function?

Valve between left atrium and left ventricleIt prevents backflow of blood into right atrium

What is the aortic semi lunar valve?

Valve between left ventricle and the aorta

Describe the flow of blood in the heart.

Deoxygenated blood returns to heart via the VENA CAVA SUPERIOR and VENA CAVA INFERIOR.

Blood enters RIGHT ATRIA, and then flows to RIGHT VENTRICULE via TRICUSPID VALVE.

Ventricle pushes blood to into PULMANORY ARTERY (or Pulmonary Trunk) via PULMONARY SEMI LUNAR VALVE

Blood gets oxygenated in the lung, and returns to the heart via PULMONARY VEIN

Blood enters LEFT ATRIA, and then flows to LEFT VENTRICLE via MITRAL VALVE (BICUSPID VALVE)

Ventricle pushes blood into AORTA via AORTIC SEMI LUNAR VALVE.

Name all 12 channels on the cardiac muscle.

Gap JunctionsCa2+ DHPRyanodine ligand gated Ca2+ channelsNorepinephrine Receptors (sympathetic NS)Acetyl Choline Receptors (PARASYMPATHETIC NS)Na+ voltage channelCa2+ ATPaseCa2+ /Na+ exchangerNa+/K+ ATPaseK+ leak channelNa+ Funny channelK+ Funny channelWhat is an EKG or ECG?

EKG electrocardiogram is a recording of the electrical activity of the heart made on the surface of the body.

What are 5 things an EKG tells us about the heart?

1. Heart Rate2. Size of heart chambers3. If ventricles are damaged4. Orientation of the heart in chest5. Conduction of excitation between parts of the heart

What are the different components of an EKG?

P wave: atrial depolarization

PR-Interval: conduction time from SA node through Purkinje to ventricle

QRS-complex: beginning of ventricular depolarization

ST-segment: ventricle completely depolarized

T-wave: ventricular repolarization

QT-interval: beginning of ventricular depolarization to end of ventricular repolarization

What is the RR interval?

Interval between 2 R waves used to calculate heart rate.

What does the R wave help us detect?

R wave allows us to detect heart arrhythmias

What does the Q wave help us detect?

Q wave is a marker for previous myocardial infarction

For the EKG below each RR interval (1 to 2; 2 to 3; and 3 to 4) represent a heart rate. Calculate HR for each RR interval?

Answer: Each red box in EKG represents 0.2 seconds

RR interval 1 to 2 4 boxes; 4 x 0.2 = 0.8 seconds; That means 1 beat/0.8 second.

RR interval 2 to 3 3 boxes; 3 x 0.2 = 0.6 seconds; That means 1 beat/0.6 second.

RR interval 3 to 4 6 boxes; 6 x 0.2 = 1.2 seconds; That means 1 beat/1.2 second.

What is a normal heart rate?

60-100 bpm

What is tachycardia? How would the RR interval look like?

Heart rate above 100 bpm; RR interval would be shorter than normal

What is bradycardia? How would the RR interval look like?

Heart rate below 60 bpm; RR interval would be longer than normal

Normal EKG, HR = 75 bpm

Tachycardia EKG, HR = 300 bpm, RR interval is shorter than normal

Brachycardia EKG, HR = 50 bpm, RR interval is longer than normal

For each of the RR intervals below, state the HR

What is HR if RR interval is 1 block apart? HR = 300 bpmWhat is HR if RR interval is 2 blocks apart? HR = 150 bpmWhat is HR if RR interval is 3 blocks apart? HR = 100 bpmWhat is HR if RR interval is 4 blocks apart? HR = 75 bpmWhat is HR if RR interval is 5 blocks apart? HR = 60 bpm

What are the 2 broad groups of cardiac action potentials?

Fast response cells and slow response cells

What are fast response cells?

Cardiac muscle cells that make up the atria and ventricles

What are slow response cells?

SA and AV nodes

What do fast response and slow response refer to?

Rate of depolarization

Compared to skeletal muscle, are cardiac action potential longer or faster in duration?

Action potential last longer

State all 9 channels are involved in production of cardiac action potentials and what their functions are?

GAP junction, Ryanodine Ca2+channels, DHP Ca2+ voltage channel, Na+ voltage channel, Na+ funny channel, K+ leakage channel, Na+/K+ ATPase, Ca2+ T voltage channel, K+S

For each of the channels involved in production of cardiac action potentials state their functions?

GAP junction?

Spread depolarization between cardiac myocytes

Na+ funny channel, Na+F?

Found only in SA and AV node, spontaneously open at -40mV

Na+ voltage channel, Na+v?

Everywhere in heart, depolarizes cells

DHP receptor or Ca2+L voltage channel?

Voltage gated channel depolarizes cell

Ca2+T?

Found in SA and AV node - voltage gated calcium channel

Ryanodine Receptor - RyR?

Found in SR of cardiac cell, induce by Ca2+ and is Ca2+ ligand gated channel.

K+s or delayed rectifying K+ channel?

Contributes to repolarization

K+ leakage channel?

Always open, contributes to RMP

Na+/K+ ATPase?

Maintains chemical gradient of sodium and potassium

Describe the graph of fast response action potential.

Fast response graph has 5 phases Phase 0, Phase 1, Phase 2, Phase 3, and Phase 4.

Phase 0: Depolarization Voltage Na+ gated channel open

Phase 1: PEAK; Voltage Na+ gated channel closes, and Ca2+ voltage channel open, KS channel open

Phase 2: DHP channel (Ca2+L voltage channel) open, RyR activated, KS channel open

Phase 3: KS channel still open; DHP channel (Ca2+L voltage channel) close

Phase 4: KS channel close; RMP

Describe the graph of slow response action potential.

Slow response graph has 3 phases Phase 0, Phase 3, and Phase 4.

Phase 0: (SA & AV node) Ca2+T voltage channel Ca2+L voltage channel = Depolarization

Phase 3: KS channel open; DHP channel (Ca2+L voltage channel) close

Phase 4: RMP Na+F OPEN

What initiates slow response action potential?

SA and AV nodes

How is the spontaneous generation of slow response action potential initiated?

Activation of Na+F (Sodium Funny Channel) Followed by activation of Na+ voltage channel.

What does the depolarization trigger?

Activation of Ca2+T (calcium T type voltage channel) in SA and AV node

Followed by activation of Ca2+L (calcium L type voltage channel- DHP receptor)

What 4 channels are open in slow response action potential when AP is triggered?

Na+F (Sodium Funny Channel) Na+ voltage channelCa2+T (calcium T type voltage channel)Ca2+L (calcium L type voltage channel- DHP receptor)

What happens to the concentration of sodium when calcium levels rise?

Sodium levels diminish

What does the influx of Ca2+ trigger? Why?

Activation of RyR; calcium already in the cell is a ligand for ryanodine receptors.

Does RyR need ATP to allow calcium in? Why?

No because Ca2+ is moves down its gradient concentration

When Ca2+T and Ca2+L close, what occurs?

Delayed rectifying K+ channels that were open return the cell to RMP

Why can an action potential be triggered at RMP in slow response action potential?

RMP is about -50mV, and sodium funny channels can open to trigger another AP around that voltage

After the slow response action potential is completed, what happens next?

Cardiac muscle fire FAST RESPONSE ACTION POTENTIALS

What triggers depolarization in fast response action potential?

Spontaneous opening of sodium funny channel and sodium voltage channels

What occurs at Phase 1 of fast response action potential?

Na+V channels close, KS channel open, Ca2+L open

During Phase 2, why does a plateau exist?

Ca2+ influx balances out the efflux of K+

During Phase 3, why does repolarization occur?

Ca2+L close and KS stays open bringing cell back to RMP

How is RMP maintained in fast response action potential?

K+ leakage channel and Na+/K+ ATPase

What are the 3 mechanism to remove Ca2+?

SR Ca2+ ATPaseCell membrane Ca2+ ATPaseNa+/Ca2+ exchanger (3 sodium in: 1 calcium out)

When viewing an EKG, state which interval or wave corresponds to:

Fast response action potential Phase 0 and Phase 1?

QRS complex

Fast response action potential Phase 2?

ST segment

Fast response action potential Phase 3?

T wave

On the fast response action potential graph, what phases corresponds to ABSOLUTE REFRACTORY PERIOD?

Phase 0 to Phase 3

On the fast response action potential graph, what phases corresponds to RELATIVE REFRACTORY PERIOD?

Phase 3

Why cant there be spatial or temporal summation for ventricular contraction?

2 reasons:

1. Long duration of action potential = no temporal summation2. Excitation of heart is independent of nerve stimulation = no spatial summation

Which subunit of autonomic nervous system increase heart rate?

Sympathetic NS

Describe how Sympathetic NS stimulates increase in HR?

Norepinephrine/epinephrine binds to 1 receptors

1 receptors activates G protein that stimulates adenylyl cyclase to produce cAMP

cAMP targets Na+F and Na+V to open longer and sooner = faster and sustained AP

cAMP also targets PKA which activate DHP (Ca2+L channel) adds more to depolarization

PKA also targets KS to repolarize cell faster

How can a quick repolarization of the cardiac cell help increase heart rate?

Shorter absolute refractory period

What increases the contractibility force of the heart rate?

Availability of Ca2+

Describe how parasympathetic NS stimulates decrease in HR?

Acetylcholine binds to M2 receptors

M2 inhibits adenylyl cyclase

M2 also stimulates KS decreasing contractibility force and heart rate