Cardiac Muscle

Question 1

Characteristics of myocytes

Answer 1

found in the heart wall, striated, one/two nuclei, feature Y-shaped branching, join other cells at intercalated discs, autorhymic, under involuntary control

Question 2

Characters like skeletal muscle

Answer 2

striations, sarcomere structure

Question 3

Explain the steps in the cardiac action potential

Answer 3

rapid depolarization from opening of V-gated Na channels, plateau from opening of V-gated Ca2+ channels and closing of some K channels, repolarization from opening of more V-gated K channels and blocking Ca2+ channels

Question 4

Unlike skeletal

Answer 4

shorter fibers, often branched/gap junction, uni-/bi-nucleate, Ca2+ plateau, cardiac pacemaker cells drive beating, autonomic sympathetic and parasympathetic neurons modulate beating; hormones modulate beating

Question 5

Intercalated Discs

Answer 5

include desmosomes and gap junctions

Question 6

why are gap junctions important in cardiac muscle cells?

Answer 6

they allow direct electrical communication between cells and the passive spread of Na+ and Ca2+ from neighboring cells (electrical coupling)

Question 7

how does branching help cardiac cells

Answer 7

more effectively spread signal to neighbors

Question 8

What are the two major ways pace can be altered?

Answer 8

1. Autonomically: sympathetically: norepinephrine (fight or flight)
   parasympathetically: acetylcholine (rest or digest)
2. Hormonally: usually up: epinephrine/ thyroid hormone

Question 9

What does ACh cause skeletal muscle to do

Answer 9

contract

Question 10

what does ACh cause cardiac muscle cells to do

Answer 10

down regulate