cardiac muscle

Question 1

major difference between cardiac EC coupling and skeletal EC coupling

Answer 1

in cardiac: Calcium (and AP) is essential for the opening of L type voltage gated calcium channels at the T tubules vs in skeletal muscle the AP alone is sufficient to open the voltage gated calcium channels i.e. extracellular calcium is not required to open the voltage gated calcium channel.

Question 2

the more calcium present in the cytosol

Answer 2

the greater the contraction and force generated

Question 3

various NTs and hormones can modulate contraction

Answer 3

e.g. Beta 1 promote an increase in intracellular calcium which will ——> induce greater contraction of cardiac muscle

Question 4

calcium induced calcium release

Answer 4

extracellular calcium entering cell via voltage gated calcium channel is essential for calcium release from SR

10% of calcium for contraction comes from extracellular entry
90% of calcium for contraction comes from SR

although only 10% is sourced extracellular, the contractile process is dependent on extracellular calcium entry

Question 5

Cardiac AP and contraction

Answer 5

the cardiac AP phase is almost = to the contraction phase (vs skeletal the AP is only 2 - 5 ms with contraction being 20 - 100ms)

this is because cardiac calcium channel is L type

Question 6

cardiac muscle contractions cannot tetanise

Answer 6

cardiac muscle refractory period remains for the duration of AP i.e. very long refractory period due to prolonged plateau phase

Question 7

cardiac AP exists as

Answer 7

plateau phase