Electrical Initiation Of The Heart

Question 1

What is the testing membrane potential of the nodal cells

Answer 1

-60mv

Question 2

What is the resting membrane potential of the contractile cells

Answer 2

-90mv

Question 3

Why is the resting membrane potential of the nodal cells less negative then the contractile cells

Answer 3

So that nodal tissue channels can operate in a semi-activated state even during the resting phase of the action potential (of the contractile cells)

Question 4

What are the phases in the nodal cells

Answer 4

Phase 0 - open voltage gated sodium channels
Phase 1 - opening of the k+ channels
Phase 2 - plateau as the k+ and the Ca2+ channels would be open, charges would cancel out
Phase 3 - closing of the Ca2+ channels
Phase 4 - refractory period

Question 5

How would the charged ions go to the surrounding cells

Answer 5

Through gap junctions

Question 6

What phase would show the pacemaker potential

Answer 6

Phase 4

Question 7

What happens in the contractile cells

Answer 7

Positive ions in (-90 to -70m)
Na+ ions in (-70 to +10mv)
K+ channels would open and k+ in
Some calcium in

Question 8

What would happen in the nodal cells

Answer 8

Funny sodium in (-60 to -55)
Type T calcium channels (-55 to -40mv)
Potential reached at -40
Type L channels would open (-40 to +40mv)
Positive ions move out

Question 9

What do the calcium ions that move into the contractile cells do

Answer 9

Bind to the RyR receptors of the SR
Calcium would then be released
Bind to the troponin ….

Question 10

What is functional syncytium

Answer 10

When cardiomyocytes would recieve signals at the same time
Contract in a synchronised way

Question 11

What happens in the repolarisation of the nodal cells

Answer 11

L-type calcium would close at +40
K+ channels open and K+ would move out
Repolarise
When hits the -60 (resting) the funny sodium would open again

Question 12

What happens in the repolarisation of the contractile cells

Answer 12

L-type calcium close
Calcium taken up (by the SR and ECF through the calcium-sodium exchanger and the calcium-proton exchanger)
K+ closes and exits

Question 13

What is the action of the alpha 1 and vasoconstriction

Answer 13

PLC - ip3 and dag so would have more calcium channels opened
(Stops the action of the myosin light chain kinase)

Question 14

What cells would also have the beta 2 adrenoreceptors

Answer 14

Liver
Skeletal
Myocardium

Question 15

What structures would have the alpha 1 adrenoreceptors

Answer 15

Artery’s and the veins