Smooth Muscle II

Question 1

How does smooth muscle contraction start

Answer 1

increase in intracellular Ca++

Question 2

what is the primary source of Ca++ for smooth muscle

Answer 2

extracellular

Question 3

what happens when intracellular Ca++ is increased

Answer 3

binds to calmodulin

Question 4

what does calmodulin-Ca++ do

Answer 4

bind to and activated MLCK

Question 5

what does MLCK do

Answer 5

phosphorylates myosin and allows for activation of myosin ATPase, thus binding of actina nd myosin

Question 6

how long can the attachment-detachment cycle using ATP continue

Answer 6

as long as myosin is phosphoryalted

Question 7

what is different about ATPase in smooth vs. skeeltal muscle

Answer 7

it’s not always active in smooth muscle

Question 8

decreased MLCk activation and myosin phosphatease activity can lead to what

Answer 8

relaxation of tonic contraction

Question 9

what is happening in relaxation o fmuscle

Answer 9

intracellular Ca++ decreases

you get dephosphorylation of myosin by myosin phosphase

Question 10

what happens in latch bridge

Answer 10

low MLCK, ATPase, and myosin phosphatase activity
cross-bridge is maintained in contracted state
think of it like a very slow power stroke

Question 11

difference of smooth muscle contraction in comparision to skeletal muscle

Answer 11

smooth muscle has long, tonic contractions that can occur for hours or days

Question 12

difference of smooth muscle energy

Answer 12

low energy to produce same tension as in skeletal muscle due to cross-bridge characteristics

Question 13

stress-relaxation response of smooth muscle

Answer 13

happens in response to stretching/filling to maintain constant pressure (bladder)

Question 14

why is the onsut and duration of smooth muscle relatively long

Answer 14

due to rate of atin/.myosin attachement/detachment and availability of Ca++

Question 15

does smooth muscle have structured NMJ?

Answer 15

no

Question 16

how are nerve fibers arranged on smooth muscle

Answer 16

diffuse branches of merve fibers lie over sheets of smooth muscle

Question 17

what does smooth muscle have instead of end-feet

Answer 17

nerve fiber has multiple varicosities along the axes of a nerve fiber

Question 18

diffuse junctions

Answer 18

nerve fiber does not direcetly contact smooth muscle

Question 19

contract junctions

Answer 19

nerve fiber does contact smooth muscle in multi-unit smooth muscle

Question 20

in general if acetylcholine excites a tissue waht will NE do

Answer 20

inhibit it

Question 21

electromechanical stimulation event

Answer 21

open up Ca++ channels and cause contraction

Question 22

electromechanical inhibition effect

Answer 22

close Ca++/Na+ channels or open K+ channels in order to cause a hyperpolarization and inhibit

Question 23

pharmacomehcanical stimulation

Answer 23

you don’t have to have a change in membrane potential in order to get contraction

Question 24

what are teh 2 sources of Ca++ in smooth muscle

Answer 24

extracellular fluid (primary)
sarcoplasmic reticulum

Question 25

functions of Ca++ in smooth muscle

Answer 25

• membrane depolarization

- contraction

Question 26

what are the 2 types of APs

Answer 26

• spike potential

- AP with plateus

Question 27

how does Ca++ affect the plateu phase

Answer 27

helps prolonge it

Question 28

slow wave

Answer 28

not an AP because you have not hit threshold yet

Question 29

what function can slow waves serve

Answer 29

act as pacemakers

Question 30

what can cause slow waves

Answer 30

sodium pumping, rhythmic changes in ion conductance