Electrical Activity of Cardiac Cells

Question 1

Slow vs. Fast APs (which ones each are)

Answer 1

Nodals vs. cardiac muscle

Question 2

Slow APs

Answer 2

Have CaV to depol which are slower than NaV. Also have slower Kvs

Question 3

If

Answer 3

“Funny” current activated from hyperpolarization cyclonucleotide gated channels (HCN)

Question 4

HCN Channels

Answer 4

Opens at hyperpol and closes at depol (opposite of Kv despite having similar voltage sensors) and allows Na and Ca but mainly Na

Question 5

3 Currents -> Pacemaker Activity

Answer 5

Upon threshold, CaV activate to depol, which activates Kvs to hyperpol, which activates HCN to slowly depol

Question 6

5 Stages of Fast Cardiac Muscle AP

Answer 6

0 - upstroke, Na influx
1 - slight dip from Na closure (and a little K efflux)
2 - plateau from Ca influx
3 - rapid repol from slow K efflux
4 - resting

Question 7

NE Effects

Answer 7

Stimulates Gs which increases cAMP, so HCNs more activated so increased freq of APs/HR. However this could lead to shitty filling, so cAMP activates PKA which activates CaV and KV giving an elevated plateau (stronger contraction) and faster repol (faster AP, more time to fill)

Question 8

ACh Effects

Answer 8

Activates Gi which decreases cAMP, so HCN less activated leading to less freq of APs/lower HR