5. Cardiac Muscle Excitation/Contraction

Question 1

pacemaker cells

Answer 1

initiate depolarization

contain fewer contractile fibers
no organized sarcomeres
faster conduction rate

Question 2

pacemaker cell locations

Answer 2

SA node
AV node
internodal pathways
autohythmic cells
purkinje fibers
bundle of his

Question 3

contractile cells

Answer 3

forceful contraction

Question 4

contractile cell locations

Answer 4

muscle cells
atria/ventricle

Question 5

contractile cardiac muscle cells

Answer 5

fibers arranged in sarcomeres
gap junctions
- quickly spreads depolarization

Question 6

contractile cell action potential

Answer 6

phase 0: depolarization
phase 1: initial repolarization
phase 2: plateau
phase 3: repolarization
phase 4: RMP

Question 7

absolute refractory period
(cardiac muscle cells)

Answer 7

0.2-0.25 s

Question 8

relative refractory period
(cardiac muscle cells)

Answer 8

0.05 s

Question 9

absolute refractory period

Answer 9

inactivation gate is closed

Question 10

relative refractory period

Answer 10

some channels closed
some channels open

not as responsive

Question 11

skeletal refractory vs cardiac refractory

Answer 11

cardiac - longer refractory period
-prevents tetanic stimulation
skeletal - shorter refractory period
- allows tetanic stimulation

Question 12

cold cardioplegia solution

Answer 12

increases ECF K+:
from 5mEq/L to 16+mEq/L

Question 13

cold cardioplegia solution mechanism

Answer 13

incr ECF K+
decr [K+] gradient
K+ flows inside –> depolarization
– contracts heart
heart repolarizes to -20mV
– incomplete because [K+] inside higher than normal
Vg Na+ stuck in the inactivation state
– stuck in refractory period
heart cannot contract

Question 14

genetic hypertrophic cardiomyopathy

Answer 14

enlarged ventricle that hypertrophies inward

obstructs outflow to aorta (decr CO)
reduces filling volume
prone to arrhythmia (incr refractory)
may alter papillary muscles (mitral valve prolapse)

Question 15

genetic hypertrophic cardiomyopathy
mutations

Answer 15

MYH7: beta myosin heavy chain
TNNT2: cardiac muscle troponin T
TNNI3: cardiac muscle troponin I
TPM1: tropomyosin alpha-1 chain
TTN: titin
ACTC1: cardiac alpha actin
MYBPC3: myosin binding protein C
MLC-2: myosin regulatory light chain 2

Question 16

types of genetic hypertrophic cardimyopathy

Answer 16

sigmoidal: 40-50%
reverse curve: 30-40%
apical: 10%
neutral: 10%

Question 17

mechanisms to alter contraction

Answer 17

augmenting force (Stroke volume)
decreasing force

Question 18

augmenting force

Answer 18

increase Ca++

beta agonists
- Epi
- NE

Question 19

SA nodal cells intrinsic depolarization rate

Answer 19

60-80/min

Question 20

AV nodal intrinsic depolarization rate

Answer 20

40-55/min

Question 21

purkinje fibers intrinsic depolarization rate

Answer 21

15-35/min

Question 22

overall pacemaker

Answer 22

SA nodal cells

Question 23

what happens if you block the SA node?

Answer 23

heart still beats

AV node takes over == slower

Question 24

what happens if you block the SA and AV nodes?

Answer 24

heart still beats

purkinje fibers take over == much slower

Question 25

purkinje fibers

Answer 25

found in ventricles

have similar ion conductance to contractile cells

have funny current like conductile cells

Question 26

why is SA nodal depolarization fastest?

Answer 26

more Na+ leak channels

reaches threshold faster

Question 27

SA node location

Answer 27

atria

Question 28

AV node location

Answer 28

ventricle