Cardiophysiology

Question 1

What are the leak ion channels? Which direction do the ions flow?

Answer 1

Na and K ion leak channels
- help maintain resting membrane potential
- Na goes into cell
- K goes out of cell
- more K than Na leak channeks

Question 2

What factors determine resting membrane potential? What cells don’t have a RMP?

Answer 2

• K/Na leak channels
• Na/K-ATPase pump: 3 Na out for every 2 K in against their concentration gradient
• negatively charged proteins

auto rhythmic cells do not have RMP

Question 3

Describe auto rhythmic cells. What is their function?

Answer 3

function: to regulate heart activity via AP’s
contain very little actin/myosin
- replaced with glycogen
capable of depolarizing on their own
- does not require NTs to have graded potential
- NTs can speed up rate

Question 4

What is the cardiac skeleton and what is its function?

Answer 4

band of dense irregular CT around valves that gives structural support and does NOT conduct electricity
- the current through the atrial muscle cells are blocked
- once it reaches the AV node, it starts again via AV bundle

Question 5

What is the sequence of excitation for auto rhythmic cells?

Answer 5

Sinoatrial node (100 BPM)
atrioventricular node
atrioventricular bundle
bundle branches
conduction myofibrils - brings depolarizing current to contrastive cells of the heart

Question 6

Describe the sinoatrial node. Where is it located and what happens when it it triggers an action potential?

Answer 6

pacemaker of the heart - 100 BPM without regulation
located in wall of R atrium below superior VC

specialized muscle fibers of the heart with more leaky Na channels

AP spread downward through atria
- muscles cells joined by gap junctions at intercalated discs

Question 7

What is the role of the atrioventricular node and where is it located? What is AV nodal delay?

Answer 7

located in the right atrial wall near interatrial septum
- depolarized by AP’s of R atrial contractile muscle cells

AV nodal delay: .1 seconds
due to AV autorhythmic fibers smaller in diameter, fewer gap junctions

Question 8

Describe the atrioventricular bundle, bundle branches, and conduction myofibers.

Answer 8

AV bundle - located in iinteratrial septum
- only electrical connection btw atria and ventricles

bundle branches - AV bundle splits into two bundle branches that pass through the septum

conduction myofibers - contain few myofibrils
- supply cardiac and papillary muscles in ventricles

Question 9

Describe funny channels. What ion does it allow to pass though? What kind of channel is it?

Answer 9

funny channels - Na ion channels that typically open at negative resting membrane potential
- voltage gated - opens during hyper polarization
- ligand gated - cAMP binding can open the channels

Question 10

Describe the pre potential permeability in auto rhythmic cells

Answer 10

small # Na channels open - Na enters
- funny channels begin to open at (-) MP
vg - K channels that opened during depolarization phase begin to close
transient Ca channels begin to open

Question 11

Describe the depolarization phase of autorhythmic cells

Answer 11

fast Ca channels open
- vg channels
- cause for action potential

voltage gated K channels closed

Question 12

Describe the repolarization phase autorhythmic cells

Answer 12

Fast Ca channels (vg) close

Vg - K channels open, allowing K to move out and bring MP back to negative

Question 13

Describe the opening/closing of channels in autorhythmic AP in order

Answer 13

at - 60 mV:
- funny channels open: some K leave but mainly Na enters - depolarization
- near - 40 mv: funny channels close, slow Ca open - continue depolarization
- 40 mv: threshold reached - Fast Ca open and depolarize
+ 5 mv: fast Ca close, VG K open and repolarize

Question 14

Describe parasympathetic neuromodulation of auto rhythmic cells. What nerve and what NT is in charge of this, and what are the effects is has?

Answer 14

Postganglionic neurons from the VAGUS nerve release ACETYLCHOLINE
- bind to muscarinic GPCR in autorhytmic cells
- inhibitory alpha unit inhibits adenylate cyclase
- fewer cAMP = decreased number of funny channels
- beta/gamma subunits bind to K channels to cause them to open

takes longer for the cell to depolarize to the threshold potential - longer heart rate

Question 15

Describe the sympathetic neuromodulation of the autorhythmic cells

Answer 15

postganglionic neurons of the sympathetic nervous system release norepinephrine - binds to beta 1 GPCR’s of auto rhythmic cells
- alpha unit activates adenylate cyclase = more cAMP = more/earlier funny channels = faster depolarization
- cAMP activates protein kinase A which P’s transient Ca channels = opens easier/longer

higher heart rate

Question 16

How does caffeine affect the sympathetic nervous system and increase heart rate?

Answer 16

caffeine blocks the activity of phosphodiesterase
- less cAMP deactivation: more funny channels open, more protein kinases activated to P transient Ca channels

Question 17

Describe the intercalated discs in cardiac muscle tissue. What are they made of and what are the function of the components?

Answer 17

join the short, fat, branched cells of cardiac muscle together
- gap junctions - allow communication from one cell to the next
- desmosomes - vertical aspect of desmosome - holds muscle together

Question 18

Describe the contractile muscle cell AP. Does it have a resting membrane potential? How does it compare to a skeletal muscle cell?

Answer 18

RMP: - 90 mv
1. transmission of AP via gap junctions - vg - Na open for rapid depolarization (Na IN)

2. short repolarization due to vg K opening (K out)
3. slow vg Ca open - Ca flows into cell, slowing down repolarization - plateau
   - additional Ca from SR
   - lots of Ca in cytoplasm = activate interaction btw actin and myosin = more contraction
4. Ca ions activate Na-Ca ion exchangers - one Ca out for every 3 Na in
5. repolarization - vg- Ca close, vg - K open

Question 19

What are the Ca transporters that are active during relaxation?

Answer 19

Ca/ATPase pump - uses energy to move 2 Ca out of cell or into ST

Na/Ca cotransporter - removes one Ca from inside cell for every 3 Na to enter
- affected by digitalis

Ca mitochondrial uniport
- hypoxia - affects Na/K ATPase - increased Na = increased Ca
- damages mitochondria due to increase in Ca mitochondrial uniport

Question 20

Describe the effect of digiatlis and its effect on heart contractility

Answer 20

blocks the activity of Na/K ATPase - increases [Na] in the cell
- increased Na means that the Ca/Na cotransporter will not work
- increases [Ca] in cardiac contractile cell - increases FORCE of contraction

Question 21

Describe the sympathetic neuromodulation of cardiac contractile cells

Answer 21

Postganglionic sympathetic releases NE that binds to beta1 GPCR on cardiac contractile cells
- alpha subunit activate adenylate cyclase = more cAMP = more activated protein kinase A
- Protein kinase A increases intracellular Ca by opening Ca channels in SR and plasma membrane
- more Ca = increased contractility

ventricular muscle cells do not have receptors for ACh

Question 22

Do cardiac contractile cells have motor end plates?

Answer 22

no motor end plates
incoming depolarization comes from gap junctions or auto rhythmic cells