10 Smooth Muscle

Question 1

phasic contraction

Answer 1

contraction followed by relaxation

Question 2

tonic contraction

Answer 2

sustained contraction

Question 3

features of smooth muscle (5)

Answer 3

1/ uninuclear
2/ no striations
3/ no T-tubules
4/ lots of caveolae
5/ numerous cell-to-cell junctions

Question 4

dense bands from adjacent cells combine to form

Answer 4

intermediate junctions (mechanical coupling) - for transmission of force between cells

Question 5

a gap junction provides

Answer 5

electrical (ionic) coupling

Question 6

major storage site for Ca2+ ions in smooth muscle

Answer 6

SR

Question 7

2 receptors in the SR

Answer 7

IP3 and ryanodine

Question 8

binding of IP3 to its receptors allows

Answer 8

release of intracellular Ca2+ needed for contraction

Question 9

three types of myofilaments in smooth muscle

Answer 9

actin, myosin, intermediate

Question 10

thin filaments contain

Answer 10

actin, tropomyosin
calponin, caldesmon
NO TROPONIN!

Question 11

instead of troponin, smooth muscle has

Answer 11

calponin and caldesmon

Question 12

thick filaments are composed of

Answer 12

two heavy chain subunits

two light chain subunits

Question 13

intermediate filaments are

Answer 13

a cytoskeletal component

Question 14

neurotransmitters that cause contraction

Answer 14

excitatory transmitters

Question 15

neurotransmitters that cause relaxation

Answer 15

inhibitory transmitters

Question 16

these are also not present in smooth muscle

Answer 16

NMJs

Question 17

multi-unit smooth muscle

Answer 17

• neurogenic (requires nerve stimulus to initiate contraction, like striated muscle)
• walls of large blood vessels, large airways of respiratory tract, eye muscles

Question 18

single unit (unitary) smooth muscle

Answer 18

• arranged in sheets; sheets act as a single unit
• sparsely innervated
• electrically coupled via gap junctions

Question 19

pacemaker regions contain these special cells

Answer 19

Interstitial cells of Cajal (ICC)

Question 20

cross-bridges (for sliding filament mechanism) project from the ___ filaments

Answer 20

thick filaments

Question 21

myosin light chains must be ____

Answer 21

phosphorylated

Question 22

this enzyme is responsible for myosin phosphorylation

Answer 22

myosin light chain kinase (MLCK)

Question 23

myosin light chain kinase (MLCK) requires these two things for activity

Answer 23

calcium and calmodulin

Question 24

this initiates smooth muscle contraction

Answer 24

calcium-dependent phosphorylation of myosin light chain

Question 25

MLC dephosphorylation occurs via

Answer 25

myosin light chain phosphatase (MLCPase)

Question 26

for smooth muscle contraction, increase this, decrease that

Answer 26

increase MLC-p
increase MLCK
decrease MLCPase

Question 27

for smooth muscle relaxation, increase what decrease what

Answer 27

decrease MLCK
decrease MLC-p
increase MLCPase

Question 28

increased cytosolic ____ activates myosin light chain kinase (MLCK)

Answer 28

calcium

Question 29

electro-mechanical coupling is when

Answer 29

depolarization of the membrane leads to opening of voltage-gated Ca2+ channels, followed by increase in cytosolic Ca2+

Question 30

these receptors on the SR are stimulated to release more Ca2+ via calcium-induced-calcium release

Answer 30

ryanodine receptors (RyR)

Question 31

pharmaco-mechanical coupling of smooth muscle

Answer 31

binding of an agonist on the membrane leads to elevation in cytosolic Ca2+ without any change in membrane electrical potential

Question 32

pharmaco-mechanical pathway involves

Answer 32

G-q (heterotrimeric G protein)
PLC-B1
IP3
DAG

Question 33

in the pharmaco-mechanical pathway, IP3 binds to its receptor ____ on the SR which does this:

Answer 33

IP3R, to release calcium

Question 34

smooth mm relaxation results from reduction in cytosolic ____

Answer 34

calcium

Question 35

second messengers involved in smooth muscle relaxation

Answer 35

cAMP and cGMP

Question 36

For smooth muscle relaxation, cAMP is stimulated by

Answer 36

B-adrenergic activators (adrenalin)

Question 37

for smooth muscle relaxation, cGMP is stimulated by

Answer 37

NO