cardiac muscle

Question 1

T or F: cardiac muscle is striated

Answer 1

T

Question 2

How many nuclei are in cardiac muscle?

Answer 2

most of the time 1, sometimes 2

Question 3

is cardiac muscle voluntary or involuntary

Answer 3

involuntary

Question 4

T or F: intermediate filaments and dense bodies are only in cardiac muscle

Answer 4

F - smooth muscle

Question 5

contractions of cardiac muscle produce…

Answer 5

pumping of heart chambers

Question 6

cardiomyocytes are joined by…

Answer 6

intercalated discs (with desmosomes and gap junctions)

Question 7

cardiac muscle are organized from units of …

Answer 7

myofibrils

Question 8

T or F: cardiac muscle cells are autorhythmic

Answer 8

T

Question 9

the ________ arrangement of ventricular muscle allows ventricular contraction to squeeze the blood upward from the apex of the heart

Answer 9

spiral

Question 10

intercalated disks contain __________ that transfer force from cell to cell, and ________ that allow electrical signals to pass rapidly from cell to cell.

Answer 10

desmosomes

gap junctions

Question 11

Do autorhythmic or contractile cells signal for contraction?

Answer 11

autorhythmic - they signal for contraction but don’t actually contract themselves, have smaller and fewer contractile fibers than contractile cells and do not have organized sarcomeres

Question 12

T or F: cardiac and skeletal muscle are multi nucleiated

Answer 12

F, only skeletal

Question 13

Does cardiac or skeletal have larger T-tubules

Answer 13

cardiac, they are larger and branch

Question 14

Does cardiac or skeletal have larger sarcoplasmic reticulum?

Answer 14

skeletal, cardiac has a smaller and underdeveloped SR

Question 15

mitochondria occupy _____ of cardiac cell volume

Answer 15

1/3

Question 16

explain the steps in cardiac excitation contraction coupling

Answer 16

1 - action potential enters from adjacent cell
2 - voltage gated Ca+ channels open and Ca+ enters cell
3 - Ca+ induces Ca+ release through RyR
4 - local release causes Ca+ spark
5 - summed Ca+ sparks create a Ca+ signal
6 - Ca+ ions bind to troponin to initiate contraction
7 - relaxation occurs when Ca+ unbinds from troponin
8 - Ca+ is pumped back into the sarcoplasmic reticulum for storage
9 - Ca+ is exchanged with Na+ by the NCX antiporter
10 - Na+ gradient is maintained by the NaK ATPase

Question 17

cardiac muscle contraction can be _______

Answer 17

graded

Question 18

force generated in cardiac muscle contraction is proportional to ___________ and determined by ____________

Answer 18

proportional to number of active crossbridges

determined by how much Ca+ is bound to troponin

Question 19

frank-starling relationship

Answer 19

sarcomere length affects force of contraction
- at rest cardiac muscle is not at optimal length, preload allows muscle to get closer to optimal length and allows for increased force production

Question 20

T or F: cardiac muscle cannot undergo tetnus

Answer 20

T, you’d die

Question 21

what is cardiac muscle’s resting membrane potential

Answer 21

-96 mV

Question 22

cardiac depolarization occurs due to _______ inflow

Answer 22

Na+

Question 23

initial repolarization of cardiac muscle occurs due to ____

Answer 23

Na+ channels close

Question 24

the plateau period occurs due to:

Answer 24

Ca+ inflow

• sustains refractory period and prevents tetanus

Question 25

the rapid repolarization of cardiac muscle is due to

Answer 25

K+ outflow (Ca+ channels close)

Question 26

T or F: in cardiac muscle the refractory period lasts almost as long as the entire muscle twitch

Answer 26

T, long refractory periods in cardiac muscle prevents tetanus

Question 27

the refractory period of skeletal muscle is a _______ of the muscle twitch and allows for ________

Answer 27

fraction
tetanus

Question 28

What is the pathway for the conduction system of the heart?

Answer 28

SA node -> internodal pathways -> VA node -> AV bundle -> bundle branches -> purkinje fibers

Question 29

autorhythmic cells have unstable membrane potentials called ______________

Answer 29

pacemaker potentials

Question 30

at the beginning of a pacemaker potential _______ channels open and allow _______ to enter until an autorhythmic AP is triggered

Answer 30

leaky I f channels
Na+

Question 31

(autorhythmic cells)
once an AP is triggered _______ channels close and ________ channels open allowing an influx of Ca+. At the peak ________ channels close and ______ channels open allowing an efflux of ________. K+ channels close and I f channels open again to start another cycle.

Answer 31

I f, Ca+
Ca+, K, K

Question 32

myocardial autorhythmic cells have unstable membrane potentials called _______________

Answer 32

pacemaker potentials

Question 33

depolarization of autorhythmic cells is initially due to ______ which allow _______ inflow

Answer 33

open I f channels
Na+

Question 34

at threshold, 2nd type of voltage gated Ca+ channels open which leads to _________

Answer 34

steep depolarization

Question 35

At peak of autorhythmic AP, _______- channels close, slow ______ channels open

Answer 35

Ca+ close, K+ open

which leads to decreased Ca+ inflow and increased K+ inflow.
pacemaker potential returns to lowest point