smooth muscle

Question 1

smooth muscle cross section

Answer 1

one circular and the other
longitudinal layers running at right
angles to each other

Question 2

t tubule version in smooth muscle

Answer 2

caveolae - increases surface area

Question 3

dense bodies

Answer 3

act like z-lines to
“anchor” actin to sarcolemma

Question 4

contractile proteins

Answer 4

Less organized – actually allows for greater shortening:
Can operate over large range of lengths

Question 5

Initiation of contraction

Answer 5

voltage gated Ca2+ channels
Trigger for contraction is an increase in intracellular calcium
Can be neural, hormonal or spontaneous

Question 6

contraction scheme

Answer 6

ca2+ enters through calcium channels and binds to activates calmodulin. The activated calmodulin then activates myosin light chain kinase
(MLCK). MLCK is an enzyme

Question 7

REGULATION IS MYOSIN (NOT ACTIN) BASED

Answer 7

Myosin does not hydrolyse ATP (to become energized) unless it is first phosphorylated

Question 8

MLCK activates what

Answer 8

myosin by phosphorylating it, which in turn activates the myosin ATPases
Activated myosin forms cross bridges with actin of the thin filaments and shortening begins in the usual fashion.

Question 9

when does Contraction end

Answer 9

when a myosin light chain
phosphatase dephosphorylates the myosin light
chain

Question 10

MLCK, myosin light chain kinase
MLCP, myosin light chain phosphatase

Answer 10

Increased MLCK activity (Ca 2+ regulated) will favour contraction
Increased MLCP activity will favour relaxation
When intracellular Ca 2+ drop MLCP activity will dominat

Question 11

stretch of smooth muscle

Answer 11

initially resist but with time adapts to length change