Chapter 13 - Blood, Heart, and Circulation Flashcards
Compare the two “populations”/types of cells found in cardiac muscle. Provide function and examples
modified/specialized myocardial cells:
- conducts AP at different AP velocities
- ex: SA node, AV node, AV bundles, Purkinje fibers
non-specialized myocardial cells:
- contracts myocardial cells
- ex: make up the walls of atria and ventricles, are branched, and connected via gap junctions
What type of cells in cardiac muscle communicate and are connected through gap junctions?
non-specialized myocardial cells
Where are gap junctions located in?
intercalated discs
What is an SA node?
Is known as the pacemaker which consists of specialized myocytes that can generate their own APs (spontaneous/automatic) that travel to non-specialized myocytes in atrial walls and AV node.
True or False: Myocardial contraction is dependent on specialized myocardial cells and non-specialized myocardial cells
true; specialized myocardial cells are needed to generate an AP that travels to non-specialized myocardial cells in order to generate a contraction
Which specialized myocardial cell in involved with initiating an AP that travels to non-specialized myocytes in atrial walls and the AV node? Be specific.
SA node
Where does the AP from the SA node travel to?
- AV node
- Non-specialized myocytes in atrial walls
What is PP (pacemaker potential)?
Refers to the initial depolarization of an SA node action potential that is triggered by hyperpolarization from a previous AP and opening of HCN channels on SA node cells
What can cAMP influence in the body?
heart-rate because it can increase the SA node AP frequency
(increase in cAMP will lead to steeper slope of PP -> an AP will occur quicker -> and contraction of heart will increase)
What is needed for an HCN channel to open up in SA nodal cells?
a previous hyperpolarization
Describe an HCN channel and some of its characteristics. What would happen to the slope of the PP if there were low amounts of cAMP?
HCN Channel (hyperpolarization-activated cyclic nucleotide-gated channel) = VG-Na+ channel
- Open on SA node cells @ -60mV
- Sensitive to camp
Low amounts of cAMP = flat slope (becomes less steep)
Why is there no RMP in the SA nodal AP graph
No RMP because initial depolarization is a slow, “spontaneous” depolarization that occurs automatically without NS input; specialized nodal cells are never at rest
The initial depolarization in an SA node action potential is referred to as?
pacemaker potential (PP)
The initial depolarization in smooth muscle action potential is referred to as?
graded potentials/depolarization
The initial depolarization in skeletal muscle action potential is referred to as?
end plate potentials (EPP)
What type of action potentials do NOT have RMP?
SA node action potential
What type of action potentials do NOT have threshold?
Myocardial (non-specialized) action potentials
What value do HCN channels open up in an SA node action potential? What happens here?
-60mV
HCN channels open -> influx of Na+ (VG-Na2+ ch)
What value is threshold in an SA node action potential? What happens here?
-40mV
VG-Ca2+ channels open
What value is peak in an SA node action potential? What happens here?
+20mV
VG-Ca2+ close
VG-K+ open
Describe the SA node action potential
- prior hyperpolarization initiates the opening of HCN channels (VG-Na2+ ch) at -60mV -> influx of Na2+
- pacemaker potential occurs (initial depolarization) until it reaches -40mV -> VG-Ca2+ open an influx of Ca2+
- depolarization occurs and at +20mV (peak), VG-Ca2+ will close and VG-K+ open -> K+ efflux -> repolarization
- VG-K+ slow to close -> hyperpolarization
- Action potential can now spread to AV node OR non-specialized myocytes in atrial walls where they spread to other cells (via gap junctions)
What channel is slow to close in a SA node action potential?
VG-K+ channels
How do APs spread from one cardiac myocyte to another in the atrial walls?
Through gap junctions in intercalated discs
Why is there no initial depolarization/threshold in the myocardial AP graph
Because the AP in myocardial cells (non-specialized) can spread directly to the next cell through gap junctions in intercalated discs