13. Physiology of Smooth Muscle

Question 1

What is the same among skeletal and smooth muscle regarding muscle contraction?

Answer 1

Elevation in intracellular [Ca2+] for excitation-contraction coupling

Question 2

The first major type of smooth muscle is multi-unit smooth muscle. The fibers operate individually and muscles are innervated by a single nerve. What are some examples of muscles that are this type?

Answer 2

Fine tuning muscles: ciliary muscles of the eye, iris and piloerector muscles

Question 3

90% of muscle falls under unitary smooth muscle which is visceral smooth muscle which works as a unit. Cell membranes adhere and contain ________. What are some examples?

Answer 3

Contain gap junctions!

GI tract, bile ducts, uterus

Question 4

There are no true sarcomere structures in smooth muscle. Where does actin attach and what arrangement do myosin heads have?

Answer 4

Actin attaches to dense bodies via adheren junctions

Myosin head have bidirectional arrangement

Question 5

What is more in smooth muscle… actin or myosin?

Answer 5

Actin filaments are much more prevelant in smooth muscle and myosin is much more in skeletal M

Question 6

Although the cycling of myosin cross-bridges are slower during contraction in smooth muscle because the ATPase is slower (less ATP used), the force is?

Answer 6

greater; The time myosin and actin are attached is greater = greater force

This is known as the latch mechanism

Question 7

Caveolae are underdeveloped T tubule-like system. Step one of contraction in smooth muscle is Ca enters through the plasma membrane calcium channels. What is a difference regarding the SR?

Answer 7

Ca from SR is minor in smooth muscle (in skeletal muscle this is the major source). Calcium that does come from the SR is by IP3 gated release channels and ryanodine receptors

Question 8

Calcium mainly enters from the sarcolemma via L type voltage gated Ca2+ channels and ?

Answer 8

Receptor activated Ca2+ channels (ligand gated) via hormones or NTs

Question 9

How does calcium exit the cell? 2

Answer 9

SERCA (ca/atpase exchanger)

3Na/2Ca antiporter

Question 10

Step two of contraction- after calcium is transported inside the cell- calcium will REVERSIBLY bind?

Answer 10

Calmodulin (which takes 4 Ca+) and changes confirmation into active form

Question 11

Step 3 of contraction: Calmodulin-clacium complex will activate myosin light chains via? What happens?

Answer 11

MLCK (kinase) phosphorylates myosin, which activates it, allowing binding to actin (step 4)

Question 12

When there is a high concentration of Ca2+ in the cell, there has to be a high amount of phosphorylation, which means?

Answer 12

the strength of contraction is stronger due to more myosin binding to actin to contract

Question 13

Step 5 of contraction is relaxation, how does this step occur?

Answer 13

1. calcium pumps remove calcium
2. MLCP (phosphatase) removes phosphate group on myosin light chain.

** even if Ca2+ is gone, it doesnt relax until MLCP removes phophates**

Question 14

What are the four major ways smooth muscle can be stimulated to contract?

Answer 14

1. Nerves
2. hormones
3. Stretch
4. Environment

Question 15

Varicosities serve as NT release sites also called diffused junctions which can release acetylcholine as well as?

Answer 15

Norepinephrine/Epinerphrine

Question 16

B2 adrenergic receptors cause dialation while Alpha 1 adrenergic receptors cause?

Answer 16

constriction

Question 17

Adenosine and nitric oxide (NO) are inhibitory effectors and result in?

Answer 17

relaxation

Question 18

What are the four main environmental ques that control smooth muscle?

Answer 18

1. Hypoxia/Decrease O2
2. Excess CO2
3. Increased H+
4. Adenosine, Lactic Acid, Increased K+ (etc)

ALL VASODIALTORS

Question 19

Angiontensin II, vaspressin, and endothelin 1 all do what to smooth muscle?

Answer 19

Contraction

Question 20

What are the two main pathways that increase intracellular Ca2+?

Answer 20

Voltage gated calcium channels, and ligand gated channels which respond to hormones and NTs
GPCR activated via hormones and NTs, activates pathways that influence voltage gated Ca/Na+ as well as activates PLC, which activates PIP2 which generates IP3, which binds to IP3R on the Sarcoplasmic reticulum and releases Ca2+

Question 21

What are the two forms that action potentials occur in unitary smooth muscle?

Answer 21

Action potentials with plateaus

Spike potentials

Question 22

Spike potentials are stimulated by hormones, neurotransmitters, stretch receptors. What are plateuas stimulated by?

Answer 22

NTs and stretch.

Question 23

The latch mechanism is a way to increase tension while decreasing ATP usage. How does this work?

Answer 23

In latch mechanism… there is sustained stimulation, which keeps some Ca increased, allowing 20-30% contraction because the cycle proceeds slowly

Question 24

Smooth muscle is able to continuously rearrange itself to reduce passive tension so it is able to stretch more. What is the difference in active tension between skeletal and smooth muscle?

Answer 24

Skeletal muscle has one optimal area where tension and length are best.

Smooth muscle due to actin rearrangment and aligning allows more stretch while also keeping tension relatively higher, where as in skeletal muscle we would see a drop once we pass a certain stretch length.

Question 25

The thin filaments in smooth muscle lack ______ compared to skeletal muscle

Answer 25

troponin

Question 26

ATPase activity is faster in skeletal muscle than smooth muscle due to?

Answer 26

myosin light chain prominence, ATPas activity is slow

Question 27

Skeletal muscle uses nicotinic cholinergic receptors while smooth muscle uses?

Answer 27

muscarinic and adrenergic

Question 28

Is an action potential required to activate smooth muscle?

Answer 28

No, IP3 or hormones

Question 29

In skeletal muscle, calcium binds to troponin while in smooth muscle it does?

Answer 29

Binds to calmodulin and activates MLCK

Question 30

Latch mechanism works because of smooth muscle. When MLCP removes the phosphate from the myosin, the actin and myosin are still bound becuase they have a low affinity for ATP, which allows it to continue to generate active tension. What does this allow?

Answer 30

smooth muscle to generate contractions for a long period of time without tiring