#26

Question 1

Diastole

Answer 1

Relaxation phase of the heart
The heart refills with blood

Question 2

Systole

Answer 2

Contraction phase of the heart
The heart pumps blood out to the rest of the body

Question 3

Cardiac Cycle

Answer 3

The complete sequence of events in one heartbeat from the start of one contraction to the next

Question 4

Sinoatrial (SA) node

Answer 4

specialized cluster of cells that is located in the right atrium and generates electrical impulses
Pacemaker cells

Question 5

Pacemaker cells

Answer 5

specialized cardiac muscle cells that generate spontaneous electrical signals to control the heart rate

Question 6

What is the start and end of the cardiac cycle?

Answer 6

The cardiac cycle starts and ends in full diastole

Question 7

Pacemaker potential

Answer 7

• The spontaneous depolarization of cardiac pacemaker cells (mainly in the SA node) that occurs in between heartbeats.
• Drives the membrane to a threshold that initiates an action potential
  Responsible for hearts automatic beat which allows for rhythmic firing w/o external nervous system input

Question 8

Action potential

Answer 8

Rapid electrical signal that causes heart muscle cells to contract

Question 9

How does the action potential spread in the heart?

Answer 9

Originates in the SA node and spreads via gap junctions

Question 10

What is the role of the SA node?

Answer 10

To generate electrical impulses and set a rhythm for the entire heart

Question 11

What is the difference between action potential vs pacemaker potential?

Answer 11

AP: requires an external stimulus to reach threshold, rapid
PMP: slow, spontaneous and rhythmic depolarizations in pacemaker cells which leads to self generated action potentials

Question 12

Pacemaker cell membrane potential after a heartbeat

Answer 12

-60mV, at its most negative

Question 13

Funny current

Answer 13

electric current in the heart that flows through the HCN channel or pacemaker channel/funny channels

Question 14

What is a funny channel?

Answer 14

HCN channel
ion channels in the heart’s SA node

Question 15

What happens with the funny channels/current?

Answer 15

In response to -60mv membrane potential, “funny” channels open which allow for a slow inward leakage of sodium (Na+) ions, gradually making the cell interior less negative

Question 16

What is threshold after the funny channels open?

Answer 16

-40mV

Question 17

What happens as the cell becomes more positive from funny channels opening?

Answer 17

Calcium (Ca2+) channels open which provides further positive charge

Question 18

What is threshold for this pacemaker potential?

Answer 18

-40mV

Question 19

What happens when the cell reaches -40mV?

Answer 19

this is threshold, triggering a rapid action potential

Question 20

What are T-type channels?

Answer 20

T for transient
- opens in response to small, low voltage depolarizations
- transient becayse they quickly inactivate and produce a short-lived calcium current

Question 21

What are L-type Voltage gated Calcium channels channels?

Answer 21

L for long
- transmembrane proteins that allow Calcium ion influx in response to membrane depolarization
- long lasting length of activation and long time for channels to open

Question 22

What happens after the -40mV threshold?

Answer 22

L(ong)-type voltage gated calcium channels open which allow for a rapid influx of calcium ions in the cell, causing rapid depolarization peak

Question 23

What happens after rapid depolarization?

Answer 23

The action potential spreads via gap junctions
- causes atrial muscle cells to contract

Question 24

How does the cell membrane repolarize?

Answer 24

L-type voltage gated calcium channels close, potassium channels open which allows potassium to leave the cell, becoming negative again

Question 25

What are the 5 phases of a cardiac action potential?

Answer 25

Phase 4: Resting membrane potential Phase 0: Rapid depolarization Phase 1: Early repolarizarion Phase 2: Plateau Phase 3: Repolarization

Question 26

Why is there a plateau phase?

Answer 26

To prolong depolarization

Question 27

Why would depolarization need to be prolonged?

Answer 27

preventing tetanus, ensuring sustained contraction

Question 28

Calcium-induced calcium release

Answer 28

when a small amount of calcium flows into the cell, it increases local intracellular concentration - influx of calcium bines to ryanodine receptors on sarcoplasmic reticulum membrane - this opens them and triggers even more calcium from stored reserves in the SR - calcium binds to troponin-C, uncovering actin-myosin binding sites and initiating cross-bridge cycling and muscle contraction

Question 29

What ion channels are active in Phase 4: Resting membrane potential?

Answer 29

the membrane is kept at a stable negative potential by inwardly rectifier potassium channels

Question 30

What ion channels are active at phase 0?

Answer 30

Voltage-gated fast sodium channels open rapidly

Question 31

What ion channels are active at phase 1?

Answer 31

T[ransient]-type outward potassium channels open briefly causing slight rapid decrease in membrane potential

Question 32

What ion channels are active during phase 2?

Answer 32

L[ong]-type calcium channels open which allow calcium to enter the cell delayed rectifier potassium channels allow potassium to leave

Question 33

What ion channels are inactive at Phase 3?

Answer 33

L[ong]-type calcium channels close

Question 34

How long is a cardiac. action potential?

Answer 34

200-400ms

Question 35

Why does the AV node cause a 100ms delay in the spread of depolarization?

Answer 35

it ensures the atria have fully emptied their blood into the ventricles before the ventricles are signalled to contract. maximizes cardiac output and prevents backflow

Question 36

P-wave

Answer 36

represents atrial depolarization

Question 37

QRS complex

Answer 37

represents rapid ventricular depolarization

Question 38

T-wave

Answer 38

ventricular repolarization

Question 39

Tachycardia

Answer 39

Heart rate more than 100 BPM

Question 40

Bradycardia

Answer 40

Heart rate less than 60 BPM

Question 41

Arrhythmias

Answer 41

unusual patterns of cardiac electrical activity

Question 42

sinus arrhythmia

Answer 42

interval between heart beats varies 5% during respiratory cycle and up to 30% during deep restoration