Heart electricity stuff

Question 1

Initiation of the Action Potential

Answer 1

SA node cells exhibit autorhythmicity (spontaneous firing)
In cardiac cells, calcium mediates firing and no outside signal is necessary
Remember in neurons it was sodium and a neuronal input was necessary

Question 2

3 steps of electrical events at the SA node

Answer 2

3 steps
1. reaching threshold
2. depolarization
3. repolarization

Question 3

Reaching threshold (SA)

Answer 3

Step 1:
-slow voltage-gated Na+ channels open. Inflow of Na+ changes membrane potential from -60mV to -40mV

Question 4

Resting membrane potential of nodal cell

Answer 4

-60mV

Question 5

Depolarization (SA)

Answer 5

Step 2:
-Fast voltage-gated Ca2+ channels open. Inflow of calcium changes membrane potential from -40mV to just above 0 mV

Question 6

Repolarization (SA)

Answer 6

Step 3:
-Fast voltage-gated calcium channels close. Voltage-gated potassium (k+) open allowing for K+ outflow. Membrane potential returns to resting membrane potential (-60mV) and K+ channels close

Question 7

Spread of the action potential steps

Answer 7

4 steps:
1) Sinoatrial (SA) node and atrial myocardium
2) Atrioventricular (AV) node
3) Bundle Branches and Purkinje fibers
4) Ventricular myocardium

Question 8

Sinoatrial (SA) node and atrial myocardium

Answer 8

Step 1:
an action potential is generated at the SA node. It spreads via gap junction between cardiac muscle cells through the atria to the AV node

Question 9

Atrioventricular (AV) node

Answer 9

Step 2:
AP is delayed at the AV node before passing to the AV bundle within the inter ventricular septum

Question 10

Bundle Branches and Purkinje fibers

Answer 10

Step 3:
The AV bundle conducts the AP to Left and right bundle branches and then to the purkinje fibers

Question 11

Ventricular myocardium

Answer 11

Step 4:
The AP is spread via gap junctions between cardiac muscle cells throughout the ventricles

Question 12

Cardiac muscle cell at rest

Answer 12

Cardiac muscle RMP is -90mV

Question 13

Depolarization of cardiac muscle cells

Answer 13

Step 1:
Fast voltage-gated Na+ channels open and it rapidly enters. MP goes from -90 -> +30

Question 14

Plateau of cardiac muscle cells

Answer 14

Step 2:
Voltage gated K+ open, K+ flows out. Slow voltage-gated ca2+ enter cell with no electrical change, depolarized state maintained

Question 15

Repolarization of cardiac muscle

Answer 15

Step 3:
Voltage gated Ca2+ channels close. Voltage gated K+ remain open and K+ seeps out. Membrane potential returns to rest (-90mV)