Smooth Muscle

Question 1

What does myosin light chanin Phosphotase (MLCP) do ?

Answer 1

removes phosphates from myosin necks inhibiting its action

Question 2

When Ca++ binds with Calmodulin making a Ca++/CAM complex it then:

Answer 2

*#1: Inhibits calponin and caldesmen which moves tropomyosin out of the way exposing the G sites and allows cleavage of ATP by the myosin head

*#2: Activates MLCK (myosin light chain kinase) which adds a phosphate to the myosin neck activating ATPase cleaving ATP and cocking the head

Question 3

What does Myosin light chain kinase (MLCK) do?

Answer 3

Once activated by the Ca++ calmodulin complex it phosphorylates the light chain of myosin thus activating myosin

Question 4

What does Myosin light chain phosphatase (MLCP) do?

Answer 4

dephosphorylates myosin initiating relaxation

Question 5

What does the Gq (GPCR) receptor do in smooth muscle?

Answer 5

*#1: Activates IP3 which acts as a second messenger to release stored calcium

*#2: activates Rho-kinase which inactivates MLCP inhibiting relaxation

Question 6

What does the Gs (GPCR) receptor do in smooth muscle?

Answer 6

stimulates cAMP release which decreases activation of MLCK inhibiting contraction

Question 7

What does the Gi (GPCR) receptor do in smooth muscle?

Answer 7

inhibits cAMP release which decreases activation of MLCK. less inhibition means more contraction!

Question 8

Nitric oxide increases cGMP. What does this do?

Answer 8

Activates MLCP which initiates muscle relaxation

Question 9

How many calcium are needed to activate Calcium calmodulin complex?

Answer 9

4

Question 10

Smooth Muscle size:

Answer 10

1 - 5 mocrometers in diameter
20 - 500 mocrometers in length

Question 11

Multi-Unit smooth muscle:

Answer 11

“fine control”
fibers seperated from eachother by basement membrane (cilliary, iris of eye, piloerector, tunica media?, large airways?)

Question 12

Unitary smooth muscle:

Answer 12

MANY fibers contract as ONE
sheet/bundles
gap junctions
(GI, Bile ducts, Ureters, uterus, blood vessels)

Question 13

What are Dense Bodies?

Answer 13

“the Z disks of smooth muscle”
actin attachments
attach to cell membrane
inter-cellular protein bridges

Question 14

Smooth mucle nerves:

Answer 14

Autonomic neruon varicosity
diffuse junctions
secret NTs diffusely into cell
no direct innervation
(ACh & Norepinephrine)

Question 15

The regulatory chain (one of the lght chains) of myosin is phosphorylated in response to what?

Answer 15

Activation of myosin light chain kinase (MLCK)

Question 16

What are Caveolae?

Answer 16

Possibly underedveloped version of a T-tubule
(invaginations on cell membrane)

Question 17

What is the mitigating factor in smooth mucle contraction?

Answer 17

Calcium concentration in the ECF

Question 18

What happens when Ca++ levels drop in the cytosol?

Answer 18

*1: Ca++ is released from calmodulin
*2: Myosin phosphatase removes phosphate from myosin light chain (rendering in inactive) causing detachemtn of mysoin head from actin

Question 19

What controls smooth muscle contraction

Answer 19

Nervous signals
Hormonal stimulation
muslce stretch
chemiclas

Question 20

Latch Mechanism

Answer 20

Prolongs contraction with little energy use (can be hours)

Question 21

Stress-Relaxation Mechanism

Answer 21

hollow organs maintain same amount of pressure despite large volume changes

Question 22

Smooth muscle membrane potential:

Answer 22

usually -50 to -60mV

Question 23

What is smooth muscle latent period?

Answer 23

time requried for diffusion oc CA++ from ECF to ICF (200-300 miliseconds) (50x longer than in skeletal muscle)

Question 24

How much less energy is needed than in skeletal muscle:

Answer 24

1/10 - 1/300 of energy needed to sustain tension of contraction

Question 25

Total time of contraction

Answer 25

1-3 seconds (30x skeletal muscle)

Question 26

Is force of contraction less or greater than in skeletal muscle

Answer 26

Greater force of contraction

Question 27

Action potentials in unitary muscle are usually:

Answer 27

Spiked or plateau

Question 28

What % of smooth mucle contraction is not caused by APs?

Answer 28

50%

Question 29

Local feedback mechanisms that will cause VASODILATION

Answer 29

Lack of O2
Excess CO2
Increased H+