20.6 AP in skeletal and cardiac muscle

Question 1

what are the basic steps of skeletal muscle depolarization?

Answer 1

v-gated Na+ channels open

v-gated K+ begin to open

Question 2

what are the basic steps of skeletal muscle repolarization?

Answer 2

v-gated Na+ channels close
v-gated K+ channels continue to open
v-gated K+ channels close @ the end of repolarization and return membrane potential to its resting value

Question 3

what are the basic steps of cardiac muscle depolarization? how is this different from skeletal muscle?

Answer 3

v-gated Na+ channels open
v-gated K+ CLOSE
V-GATED Ca++ begin to open

Question 4

what are the basic steps of early repolarization and plateau phase of cardiac muscle?

Answer 4

v-gated Na+ close
some v-gated K+ open CAUSING EARLY REPOLARIZATION
v-gated Ca++ are still open, producing plateau by slowing further repolarization

Question 5

what are the basic steps of final repolarization of cardiac muscle?

Answer 5

v-gated Ca++ finally close

many v-gated K+ channels open and return the membrane potential to its resting value

Question 6

what are the differences between skeletal and cardiac muscles in the way AP are conducted? why?

Answer 6

in cardiac, AP are conducted cell-to-cell @ intercalated disks with gap junctions
in skeletal, AP is conducted only along the length of a single fiber
cardiac needs to cntx as one
skeletal needs to cntx as individual fibers, to create more delicate and specific motions

Question 7

what is the rate of AP propagation in cardiac and skeletal muscle cells?

Answer 7

cardiac AP propagation is slow because of gap junctions and small diameter of fibers
skeletal AP propagation is faster due to larger diameter fibers

Question 8

what is the difference between Ca++ secretion into the sarcoplasm from the sarcoplasmic reticulum in skeletal and cardiac muscle?

Answer 8

cardiac uses CICR (Ca++ induced Ca++ release) where Ca++ crosses plasma membrane at the T-tubule into the sarcoplasm and stimulates release of Ca++ from the sarcoplasmic reticulum
in skeletal muscle AP travel down the T-tubule and that is what triggers Ca++ channels to open at the sarcoplasmic reticulum and release Ca++ into the sarcoplasm