The Heart- Part 2 Conduction system of the heart

Question 1

what are intercalated discs?

Answer 1

They are made up of desmosomes that connect the cells to eachother and gap junctions that allow ions for movement.

Question 2

Why is a Gap junction important?

Answer 2

Gap junctions coordinate the movement of ions through the heart so the heart can function as a single unit. Aka functional syncytium.

Question 3

Cardiac muscle does not need neuronal stimulation to contract so what are the (2) main cells that make cardiac muscle contract?

Answer 3

1. Cardiac pacemaker cells (aka Autorhythmic cells) they make up the intrinsic conduction system of the heart and do not contract.
2. Contractile cardiac muscle cells do contract.

Question 4

What cool about the ANS (autonomic nervous system) and the heart?

Answer 4

The ANS can alter the heart rate but if disconectted the heart will still beat.

Question 5

Tell me about Cardiac pacemaker cells (autorhythmic cell)

Answer 5

They do not have a stable resting potential. they are always close to threshold with a changing membrane potential. (pacemaker potential) it set the rythem of the heart. it uses a conduction pathway that propagates the action potential from one area to another Via SA node and AV node.

Question 6

How does the Intrinsic cardiac conduction system work in order of propagation?

Answer 6

Sinoatrial (SA) node- (pacemaker) generates impluse at the Internodal pathway. Then sends pulse to Atrioventricular (AV) node, it pauses and impulse travels through the internodal pathway. Pulse then travels down to the AV bundle located at the top of the interventricle septum, then splits into right and left bundle branches and here is where it conducts the action potential from the atrioventricular septum to the apex of the heart. The Subendocardial network ( Purkinje fibers) stem into the lateral sides of the ventricles and conducts the impulse to the ventricles.

Question 7

what is an ectopic pacemaker?

Answer 7

an extra bundle of cardiac pacemaker cells. (an extra node) it can cause an extra beat or take over the SA node’s natural rhythm.

Question 8

How does the action potential affect SA, AV nodes?

Answer 8

it works fastes from SA node to the AV node and then slows due to smaller size of fibers extending from the AV node. This result allow the atria to contract fully before the ventricles.

Question 9

What if your SA node quits?

Answer 9

another bundle can take over at a lower rate it often is too slow for normal heart activity so the SA node is replaced with an artificial pacemaker instead that keeps the heart beating at a normal pace.

Question 10

What is an EKG or (ECG) used to detect?

Answer 10

It records the action potential of the heart.Electrolytes in our tissue carry a charge and can be measured. EKG detect: if the intrinsic conduction pathway is working, enlarged heart, damage to the heart, electrolyte imbalance or arrhythmias.

Question 11

How do you read a (PQRST) (aka) heart beat… gram!

Answer 11

P wave represents Atrial depolarization, the atria usually contracts shortly after P wave begins. an inlarged P wave indicates an enlaged atria. QRS complex- represents ventricular depolarization; atrial repolarization (relaxing) the ventricles contract shortly after the depolarization, and T wave represent ventricular repolarization.

Question 12

what can a EKG or ECG tell about you under a stress test?

Answer 12

during exercise causes the body to increase the demand for oxygen and makes detecting a blockage easier by looking at the tracing of the heart gram.

Question 13

what is arrhythmia (dysrhythmia) ?

Answer 13

abnormal rhythm, can be too slow or too fast or erratic.
Bradycardia - too slow less than 60 bpm
Tachycardia - Too fast greater than 110 bpm

Question 14

define a heart block

Answer 14

a interruption in the conduction system, usually an AV block.

Question 15

Name (3) degrees of heart blocks (aka) an interruption in the conduction system.

Answer 15

1. delay in propagation of the action potential fron the SA node to AV node, a increase in the P-R interval. 2.Sometimes action potential makes it to the AV node and sometimes it doesn’t. PQRS 3. Complete heart block the action potential ventricles and atria do not contract in proper sequence.

Question 16

what is (AFib) atrial fibrillation? What is Ventricular fibrillation (VF)?

Answer 16

when the cardiac muscles within the atria are not contracting in sync. usually seen as a missing P wave. ventricular fibrillation is when the cardiac muscle within the ventricles is not contracting.

Question 17

What is the diffrence between cardiac action potential and skeletal muscle action potential?

Answer 17

Cardiac action potential starts in the SA node and the action potential spreads from one contractile to another via gap junctions.

Question 18

Compare cardiac action potential to skeletal action potential.

Answer 18

Cardiac muscles do not require outside innervation, the are self -stimulatory provided by the pacemaker cells. Cardiac muscle of the heart contract as an entire unit rather than a motor unit. A functional syncytium. The length in time of cardiac action potential is slower that muscular action potential. the absolute refractory period of cardiac muscle is long compared to skeletal muscle.

Question 19

demonstrate Cardiac action potential, how does it work?

Answer 19

Resting membrane potential of cardiac muscle cell is -90mV. this involves depolarization and repolarization of the cell. 1. rapid depolarization occurs, sodium channels open and flow of sodium into cell makes the cell more positive that the resting potential, and channels stay open for a very short time. 2. Then it Plateaus, and the depolarization state is maintained from a influx of calcium, this slows sodium channels and trigger the calcium sensitive channels in Sarcoplasimic recticulum and opens to release calcium. 3. Repolarization- the overall negativity of the cell is restored and potassium flows out of the cell and calcium channels close at the same time.

Question 20

what is “excitation” in cardiac Action potential?

Answer 20

When Calcium binds to troponin and actin and myosin slide past one another.

Question 21

What is a absolute refractory period?

Answer 21

the new contraction does not start until after the first contraction is through.

Question 22

What is Tetanus?

Answer 22

tetanus is not possible because wave summation is not possible, lack of tetanus ensures that the atria contract fully before ventricles contract.

Question 23

Pacemaker potential and their action potentials

Answer 23

Cardiac pacemaker cells do not have a stable resting potential due to opening of sodium channels and closing potassium channels closing at the same time. the fluctuate around their threshold about -40mV. Pacemaker potentials trigger action potential for the pacemaker cell.

Question 24

Depolarization of pacemaker potentials and Repolarization

Answer 24

when the threshold of -40mV is reached, calcium channels open rather than sodium. Calcium channels close and potassium channels open.