Smooth Muscle Physiology

Question 1

Multiunit smooth muscle

Answer 1

One nerve ending goes to a single smooth muscle fiber.

Ex: ciliary muscles, iris, piloerector muscles.

Question 2

Unitary smooth muscle

Answer 2

One nerve to a population of cells, and electrical component is transmitted through gap junctions.
Works as a unit.
Vast majority of smooth muscle.
Ex: GI tract, bile ducts, uterus.

Question 3

Dense bodies/adherens junctions

Answer 3

Where actin binds (actin is much more populous in smooth muscle). Equivalent to Z disks.

Question 4

What is the general rate of cycling of myosin cross-bridges?

Answer 4

Slower than skeletal muscle.

Question 5

What is the general timeline that myosin and actin are attached?

Answer 5

They are attached longer and have a grater force.

Question 6

Latch mechanism

Answer 6

When excitation slows, but contraction remains.
ATP demand is less.
A way to increase tension while decreasing ATP usage.
Dephosphorylation of light chain.

Question 7

Ca 2+ concentration in the muscle cell can be controlled by:

Answer 7

Nerves, hormones, stretch, environmental ques.

Question 8

Calcium can enter the cell via which ways across a sarcolemma? (2)

Answer 8

L-type VG Ca 2+ channels

Receptor activated Ca 2+ channels (ligand gated)

Question 9

Calcium can enter the cell via which ways across from the SR? (2)

Answer 9

InsP3 receptors

Ryanodine receptors

Question 10

The diversity of Ca 2+ channels functions how?

Answer 10

To fine-tune the needs of the cell.

Question 11

Mechanisms of Ca 2+ exiting (3)

Answer 11

SERCA
3Na/Ca antiporter
Sarcolemmal Ca ATPase

Question 12

Once Ca is release, it binds to ______, which activates _______ and allows for _______.

Answer 12

Calmodulin (CaM)
Myosin light chain kinase
Myosin and actin to bind

Question 13

Relaxation of smooth muscle

Answer 13

Ca pumps remove the Ca from cytosol.

Myosin light chain phosphatase removes phosphate group

Question 14

Summary of contraction of smooth muscle (8)

Answer 14

Increased Ca
Binds CaM
Increased myosin light chain kinase
Phosphorylation of myosin light chains
Increased myosin ATPase
Myosin-P and actin bind
Cross bridging
Tension

Question 15

Varicosities

Answer 15

Serve as NT release sites.
Release ACh among others.
Distance between varicosities and targets can be variable.

Question 16

NE/Epi cause:

Answer 16

Adrenergic

Excitatory or inhibitory depending on organ.

Question 17

ACh causes:

Answer 17

Cholinergic

Excitatory or inhibitory depending on organ.

Question 18

Angiotensin II, vasopressin, endothelin-1 causes:

Answer 18

Contraction

Question 19

Adenosine causes:

Answer 19

Relaxation

Question 20

NO causes:

Answer 20

Relaxation

Question 21

Environmental ques that control smooth muscle (4)

Answer 21

Hypoxia
Excess CO2
Increased H+
Increased K+

Question 22

How is IP3 generated?

Answer 22

GPCR activated –> activates PLC –> generates IP3 which activates Ca release.

Question 23

VDCC is a:

Answer 23

Membrane channel allowing Ca to enter cytosol and cause contraction.

Question 24

Spiked potentials

Answer 24

Eventually enough potential to cause a spike.

Similar the phase 4.

Question 25

Spike potentials are stimulated by:

Answer 25

Hormones, NTs, stretch.

Question 26

Slow waves of smooth muscle activity

Answer 26

Oscillating Ca influx and K efflux.

Has pacemaker capabilities.

Question 27

Plateaus are stimulated by:

Answer 27

NTs, stretch.

Question 28

Calcium’s role in APs in smooth muscle

Answer 28

Ca is responsible for generating the AP instead of Na.

Fewer VG Na channels and more VG Ca channels.

Question 29

Overall histology of smooth muscle:

Answer 29

Small, single nucleus, no striations.

Question 30

SR in the smooth muscle:

Answer 30

Poorly developed SR, t-tubules.

Question 31

Thin filaments in smooth muscle:

Answer 31

Actin and tropomyosin.

Question 32

Thick filament composition in smooth muscle:

Answer 32

Myosin and ATPase activity is slow.