Sanders: Smooth muscle

Question 1

Regions such as sphincters and the fundus of the stomach produce this type of contraction

Answer 1

Tonic contraction (sustained contractions or periods of sustained relaxation)

Question 2

Other regions, such as the distal stomach or small intestine, produce this type of contraction

Answer 2

Phasic contraction (periods of relaxation between contractions)

Question 3

A third type of contraction with phasic contractions superimposed upon tonic contractions

Answer 3

Mixed contractions

Question 4

Smooth muscle can become activated spontaneously in the absence of exogenous stimuli. This is considered a…

Answer 4

myogenic mechanism

Question 5

Smooth muscles are also regulated by (blank) and (blank)

Answer 5

motor neurons; hormones

Question 6

Another mechanism of activation of smooth muscles

Answer 6

humoral or paracrine (substances produced in the immediate environment of GI smooth muscle cells)

Question 7

Analogous to the Z lines in skeletal muscles

Answer 7

Dense bodies

Question 8

These are pockets found around the edges of smooth muscle cells that bind calmodulin

Answer 8

caveolae

Question 9

These couple smooth muscle cells into an electrical syncytium

Answer 9

gap junctions

Question 10

Discuss the biochemical mechanism behind smooth muscle contraction.

Answer 10

Ca+ rises in the cytoplasm, binds to calmodulin, activates MLCK, which phosphorylates the light chain of myosin allowing it to bind and form a cross-bridge with actin.

Question 11

What is the major player that reduces cross-bridge cycling and leads to smooth muscle relaxation?

Answer 11

Myosin light chain phosphatase (MLCP)

Question 12

So when the light chain of myosin is phosphorylated, what occurs? When it is dephosphorylated, what occurs?

Answer 12

contraction; relaxation

Question 13

How does much of the Ca+ required for contraction of smooth muscle cells enter the cell?

Answer 13

voltage dependent calcium channels

Question 14

Ca+ can also enter smooth muscle cells through these two mechanisms

Answer 14

GPCRs

Release of intracellular stores from the SR

Question 15

What activates Ca+ channels in the G protein coupled receptor pathway?

Answer 15

IP3

Question 16

Some GPCRs can lead to Ca+ desensitization. Discuss this pathway.

Answer 16

GPCR activates adenylate cyclase, produces cAMP, which activates PKA, which increases the activity of myosin light chain phosphatase. This causes relaxation.

Question 17

Guanylate cyclase can also cause relaxation when bound by (blank)

Answer 17

NO

Question 18

Another way to inhibit EC coupling and smooth muscle contraction is through activation of these channels, which decreases the opening of voltage gated Ca+ channels

Answer 18

K+ channels

Question 19

Major excitatory neural receptors in smooth muscle

Answer 19

muscarinic receptors

neurokinin receptors

Question 20

One inhibitory neural receptor in smooth muscle

Answer 20

Guanylate cyclase

Question 21

Excitatory hormone receptors in smooth muscle

Answer 21

Gastrin receptors

CCK receptors

Question 22

Inhibitory hormone receptor in smooth muscle

Answer 22

Secretin receptors

Question 23

How is resting membrane potential set in GI smooth muscle cells?

Answer 23

The dominant resting permeability in smooth muscle cells is due to K+ channels.

Question 24

This increases open probability of Ca+ channels

Answer 24

Slow wave depolarization

Question 25

Slow waves are depolarizations that increase the open probability of (blank) channels in smooth muscle cells

Answer 25

Ca+

Question 26

Pacemaker cells of the gut; these cells form a network through the GI tract to generate rhythmical electrical activity of the gut

Answer 26

Interstitial cells of Cajal

Question 27

There are at least (blank) classes of ICCs. Some lie between the circular and longitudinal muscle layers are are called (blank). Others lie between muscle bundles and are called (blank).

Answer 27

3; ICC-MY; ICC-IM

Question 28

If there is a loss of ICC-IM cells, what happens following motor nerve activation? What does this suggest about these cells?

Answer 28

a reduced response; ICC cells are innervated and play a role in the response to neural stimulation

Question 29

What cells make up the SIP syncytium?

Answer 29

smooth muscle cells interstitial cells of Cajal PDGFRa cells

Question 30

What does activation of inhibitory nerves cause in smooth muscle cells?

Answer 30

hyperpolarization; inhibition of phasic contraction for a few cycles

Question 31

Regions of the GI tract undergo this type of contraction to adjust organ volume and compliance and to maintain sphincter function

Answer 31

Tonic contraction

Question 32

Ring of contraction moving in the aborad (anal) direction

Answer 32

Peristaltic wave

Question 33

Ring of contraction that is stationary; pinches off a region separating it into two sections

Answer 33

Segmental contraction

Question 34

To make propulsion effective, there is contraction toward the (blank) end, and relaxation toward the (blank) end.

Answer 34

oral; anal

Question 35

Swallowing induces receptive relaxation in the (blank) and proximal (blank)

Answer 35

LES; stomach

Question 36

Region of the stomach that functions as a reservoir

Answer 36

proximal stomach

Question 37

region of the stomach that functions to grind solids

Answer 37

distal stomach

Question 38

This increases the compliance of the stomach, allowing it to store large volumes with little change in pressure

Answer 38

gastric accomodation; adaptive relaxation

Question 39

NO dependent inhibition of muscle

Answer 39

gastric accomodation; adaptive relaxation

Question 40

3 mechanisms regulate gastric accomodation

Answer 40

Adaptive relaxation Receptive relaxation Feedback relaxation

Question 41

The fundus (proximal stomach) gradually contracts so that a bit of food is passed along at a time. The tonic contractions that occur are stimulated by what?

Answer 41

ACh

Question 42

Which region of the stomach has the greatest frequency of contraction?

Answer 42

Body (corpus)

Question 43

Where is the dominant pacemaker located in the stomach?

Answer 43

in the orad corpus (body)

Question 44

Slow waves propagate in two directions across the stomach. Which direction is faster?

Answer 44

Around the stomach and down the stomach more slowly.

Question 45

Slow waves move toward the pylorus as smooth muscle cells (blank)

Answer 45

depolarize

Question 46

The frequency of the entire stomach runs at the frequency of the (blank)

Answer 46

dominant pacemaker in the body

Question 47

Also called adaptive relaxation; allows the stomach to accomodate and increase compliance in the fed state

Answer 47

Gastric accomodation

Question 48

3 mechanisms to regulate gastric reservoir function

Answer 48

1. Feedback relaxation (from gut to vagal centers) 2. Receptive relaxation (from vagal centers to gut) 3. Adaptive relaxation

Question 49

Dominant pacemaker of the stomach is found in the (blank). Where is a "secondary" pacemaker located, which produces more infrequent contractions?

Answer 49

body; antral

Question 50

3 parts of motility in antrum and pylorus

Answer 50

1. propulsion 2. emptying 3. repulsion (of larger particles) back into stomach

Question 51

Activated in response to nutrients, osmolarity, and pH of the stomach

Answer 51

vagal afferents

Question 52

Do liquid or solid meals empty first? Do isotonic/hypotonic/hypertonic meals empty first? Calorie dense or low calorie?

Answer 52

liquid; isotonic (hypertonic = slowest to empty); low calorie

Question 53

Lipids in the stomach cause this phenomenon (slow gastric emptying)

Answer 53

ileal break

Question 54

Excitation-contraction coupling in the small intestine occurs in a (blank) wave and is dependent on (blank)

Answer 54

slow; Ca+

Question 55

Segmentation involves both (blank) and (blank) inputs

Answer 55

stimulatory; inhibitory

Question 56

There is a cyclic contraction pattern overnight that occurs in III phases. What is the purpose of this? What phase is the most forceful?

Answer 56

To sweep all undigested material in the anal direction to prevent bacteria from building up; phase III is the most powerful

Question 57

Innervation to the colon

Answer 57

Right colon innervated by vagus nerve | The rest of the colon innervated by the pelvic nerves

Question 58

Which nerve controls the external anal sphincter?

Answer 58

poo-dendal

Question 59

3 contractile patterns of the colon

Answer 59

1. mixing movement 2. haustral migration 3. mass movement