Cardiac Muscle

Question 1

What connects cardiac myocytes?

Answer 1

intercalated discs

Question 2

what two things to intercalated discs have?

Answer 2

desmosomes and gap junctions

Question 3

pathway of electrical signal in the heart

Answer 3

SA node
Internodal tract
AV node
common bundle of his
bundle branches
purkinje fibers
contraction

Question 4

does the SA node have an RMP?

Answer 4

nah never has a flat line

Question 5

why is there a delay at the AV node?

Answer 5

this delay allows for adequate ventricle filling prior to contraction of the ventricle

Question 6

which two locations in the heart do not have a consistent RMP?

Answer 6

SA and AV nodes

Question 7

are cardiac APs longer or shorter than neuronal APs?

Answer 7

much much longer…allows for more contractility and blood output

Question 8

name the 5 phases of cardiac AP

Answer 8

0-depolarization
1-partial repolarization
2-plateau
3- rapid repolarization
4- RMP

Question 9

what channel is opening during phase 0 of heart AP?

Answer 9

voltage gated Na channels

Question 10

3 channel changes during phase 1 of cardiac AP?

Answer 10

Na voltage gated are inactivated
outward K+ channels open
Calcium (L-type) channels open

Question 11

channel opening/closing during phase 2 of the cardiac AP?

Answer 11

outward K+ channels closing
voltage Na+ inactivated still
voltage gated Calcium channels open
delayed rectifier K+ channels opening

Question 12

channel opening/closing during phase 3 of cardiac AP?

Answer 12

Ca voltage channels inactivated
outward K channels inactivated
delayed rectifier K+ channels open

Question 13

phase 4 channel that is open?

Answer 13

internal rectifier K+ channel

Question 14

how does calcium cause cardiac muscle contraction?

Answer 14

it enters through the calcium voltage gated channels and then induces the opening of the SR calcium channels (ryanodine)…calcium induced calcium release

Question 15

3 ways cardiac cells decrease Calcium concentration following contraction?

Answer 15

SERCA pump
secondary active transport with the Na influx and Ca efflux
primary transport of calcium out with ATPase

Question 16

what is the name of the special channel in SA node cells?

Answer 16

Hyperpolarization activated cyclic nucleotide gated channels

HCN channels

Question 17

what is the role of HCN channels in the SA node?

Answer 17

open at negative potentials and allow Na and K to pass through…they are sensitive to NE and Epi so are a point of contact for ANS control of cardiac

Allows a little more Na to pass so it leads to rise in MP

Question 18

when are the HCN channels open in the SA node?

Answer 18

during the weird RMP time where the MP is rising a bit toward the AP

Question 19

T-type Ca channels definition and when are they open?

Answer 19

transient channels that open briefly just before the AP occurs at negative voltages like -50mV