Cardiovascular 2

Question 1

What are the phase of myocyte AP?

Answer 1

Phase 4: the resting membrane
potential, largely determined by
permeability to K+

Phase 0: activation of voltage-gated Na+
channels, inward current moves Vm
towards ENa
Phase 1: early repolarisation due
largely to inactivation of Na+ channels,
K
\+ channels slow Vm changes

Phase 2: ‘plateau’ phase; inward
current through slowly activating and
inactivating voltage-gated Ca++ channels
Note: phase 1 is less prominent in
ventricular myocytes than shown here

Phase 3: repolarisation phase;
inactivation of Ca++ channels and
increase in permeability to K+

Question 2

What happens if there isn’t one twitch per AP?

Answer 2

tetany

Question 3

characteristics of cardiac muscle?

Answer 3

Interleaved actin & myosin
• T-tubules
• Sarcoplasmic reticulum (SR): Ca2+
store (CICR)
• T-tubules and SR associate in diads
often found near Z bands
• AP & CICR – evokes excitationcontraction
coupling

Question 4

what is a syncytium?

Answer 4

cytomplasmic mass containing several nuclei (fusion of cells)

Question 5

what type of contraction happens in cardiac muscle?

Answer 5

All or nothing

Question 6

What are the differences between a ventricular myocyte and SA node?

Answer 6

1. the resting membrane potential
2. ‘fast’ inward Na+ channels
3. ca2+ channels plateau phase
4. different lengths of refractory period