Phys 5

Question 1

What are the characteristics of multi-unit smooth muscle?

Answer 1

• the fibers operate individually (one nerve for multiple cells)
• examples: ciliary muscles of the eye, iris…

Question 2

What are the characteristics of unitary smooth muscle?

Answer 2

• visceral smooth muscle or syncytial
• work together as a unit
• cell membranes there and contain gap junctions
• the type we mainly see in CP
• examples: GI tract, bile ducts, uterus…

Question 3

Where does actin attach in smooth muscle?

Answer 3

dense bodies

Question 4

What is unique about the myosin heads in smooth muscle?

Answer 4

they are bidirectional

Question 5

Which has more actin: smooth or skeletal? myosin?

Answer 5

1. smooth

2. skeletal

Question 6

What is unique about the timing of smooth m. events?

Answer 6

1. the myosin cross bridge cycling is slower
2. the time myosin and actin are attached is longer (allows for greater contraction)

*this means that ATP demand is low (latch mechanism)

Question 7

What replaces troponin in smooth m.?

Answer 7

calmodulin (CaM)

Question 8

What can lead to increased Ca2+ in the cytosol?

Answer 8

1. Nerves
2. Hormones
3. Environmental factors
4. Stretch

Question 9

How does calcium enter the cell?

Answer 9

Ca2+ L type channels

Question 10

Calcium Entry Mxns

Answer 10

1. Sarcolemmal
   a. L type voltage gated Ca2+ channels
   b. Receptor activated Ca2+ channels (ligand gated)
2. SR
   a. InsP3 receptors
   b. RYRs

Question 11

Calcium Exit Mxns

Answer 11

1. SERCA
2. 3 Na/Ca antiporter
3. Sarcolemmal Ca2+ ATPase

Question 12

How does Calcium bind to CaM?

Answer 12

reversibly (it has 4 binding sites, and once Ca2+ binds it changes conformation and binds to actin/tropomysoin)

Question 13

What does CaM activate?

Answer 13

-Myosin light chain kinase, which phosphorylates light chain of myosin, and this leads to the heavy chain being more active

Question 14

What is contraction strength generally proportional to?

Answer 14

Ca2+ levels

Question 15

What two mxns allow for smooth m. relaxation?

Answer 15

1. Ca2+ pumps (remove the Ca2+)

2. Myosin light chain phosphatase (remove phosphate group from light chain)

Question 16

What is the difference between depolarization and hormones/NTs in Ca2+ entry? Similarity?

Answer 16

1. Depolarization uses voltage gated and H/NTs use ligand gated
2. They both induce Ca2+ release from the SR

Question 17

What two ways can hormones/NTs release Ca2+?

Answer 17

1. Ligand gated channels

2. IP3

Question 18

What are varicosities?

Answer 18

bulges on nerves that they serve as NT release sites (can release ACh and more)

Question 19

Control of Smooth M:

1. NE and Epi
2. ACh
3. Angiotensin II/vasopressin/endothelin I
4. Adenosine
5. NO
6. CCK/Oxytocin/Serotonin/Histamine

Answer 19

1. excitatory or inhibitory depending on receptors at target organ
2. excitatory or inhibitory depending on organ (contraction is direct effect; relaxation can be indirect)
3. contraction
4. relaxation
5. relaxation
6. just listed

Question 20

Environmental Controls of Smooth muscle

Answer 20

Hypoxia, excess CO2, increased H+, adenosine, LA, increased K+…—-> common vasodilators (common release is exercise)

Question 21

What is the sequence of events on a G protein coupled pathway?

Answer 21

GPCR–>PLCy1–>PIP3–>IP3–>release of Ca2+ from SR

Question 22

What is the RPM of smooth m?

Answer 22

-50 to -60 mV

Question 23

What type of smooth m. can have APs?

Answer 23

unitary

Question 24

What is a spiked potential?

Answer 24

• the spikes on top o the waves

- stimulated by hormones, NTs, stretch, spontaneous…

Question 25

What are slow waves stimulated by? Plateaus?

Answer 25

1. Oscillating Ca2+ influx (L type VGCCs) and K+ efflux (Ca2+ activated K+ channels) 2. Stimulated by NTs and stretch

Question 26

When do Ca2+ dependent K+ channels open?

Answer 26

with accumulation of Ca2+ (goal is to prepare for repolarization)

Question 27

What ion is most important in smooth m. APs?

Answer 27

Ca2+ (way bigger of a player than Na+)

Question 28

Latch mxn

Answer 28

- a way to increase tension while decreasing ATP usage - dephosphorylation of the light chain - attached cross bridges are still generating tension because they are still attached and have low affinity for ATP

Question 29

What thin filaments are in skeletal m? smooth?

Answer 29

1. Actin Tropomyosin, troponin | 2. Actin, Tropomyosin

Question 30

What's the innervation of skeletal m? smooth?

Answer 30

1. alpha motor neuron | 2. Multiple (intrinsic, extrinsic (ANS))

Question 31

What's the difference between NMJ in skeletal vs. smooth?

Answer 31

skeletal has one, and smooth does not (varicosities)

Question 32

NT receptors in skeletal? smooth?

Answer 32

1. Nicotinic cholinergic | 2. Muscarinic cholinergic, adrenergic...

Question 33

Are APs required for both skeletal and smooth m?

Answer 33

nope, only for skeletal *smooth can used pacemaker activity, IP3, hormonal

Question 34

Why do we want smooth muscle?

Answer 34

1. to maintain contraction 2. contract periodically 3. maintain organ shape 4. continue to generate active tensility 5. use relatively little ATP

Question 35

Other forms of activation for skeletal? smooth?

Answer 35

1. None | 2. Paracrine, blood born, intrinsic

Question 36

Steps of Smooth m. Contraction

Answer 36

1. Ca2+ enters cytosol through PM Ca2+ channels (a little from SR) 2. Ca2+ binds reversibly to CaM 3. CaM-Ca2+ complex activates myosin light chain kinase (MLCK) 4. Phosphorylated MLCK allows myosin and actin binding 5. Relaxation

Question 37

What is the key regulator for smooth m. relaxation?

Answer 37

myosin phosphatase because it removes phosphate from myosin (inactivates it)

Question 38

What's the difference between active and passive tension?

Answer 38

1. what the cross bridges do | 2. stretching of the muscle cell membrane

Question 39

What is another name for Dense bodies?

Answer 39

adheren junctions