M1-C2-L18 --> Smooth Muscle

Front 1

What are the two types of smooth muscles and which one is predominant?

Back 1

1. Multiunit Smooth muscle
2. Unitary Smooth muscle (predominant)

Front 2

Describe the composition of multiunit smooth muscles.

Back 2

Discrete smooth muscle fibers

Front 3

Describe the composition of unitary smooth muscles.

Back 3

Large conglomerate of smooth muscle fibers.

Front 4

Describe the innervation of multiunit smooth muscle.

Back 4

Each muscle fiber is individually innervated, thus FINE control.

Front 5

Describe the innervation of unitary smooth muscle.

Back 5

A single neuromuscular junction serves the entire bundle/sheet of smooth muscles. The (outer) cells that receive stimulus will transmit it to other cells via gap junction.

Front 6

Unitary smooth muscle is also known as what?

Back 6

Syncitial smooth muscle.

Front 7

Examples of where you might find multiunit smooth muscle.

Back 7

Ciliary muscle of eye
Iris of eye
Piloerector

Front 8

Examples of where you might find unitary smooth muscle.

Back 8

Blood vessels
GI tract
Uterine wall

Front 9

What is the ratio of actin to myosin in smooth muscles?

Back 9

15 actin to 1 myosin

Front 10

Describe the organizational structure of actin and myosin in smooth muscles.

Back 10

Irregular structure

Front 11

In smooth muscle, what is analogous to the Z disc in skeletal muscle?

Back 11

Dense bodies

Front 12

Describe the sarcoplasmic reticulum in smooth muscle in comparison to skeletal muscles.

Back 12

Much reduced in smooth muscles

Front 13

Where does the calcium predominantly come from in smooth muscles?

Back 13

Outside the cell (ECF)

Front 14

Upon depolarization of smooth muscle cell membrane, the calcium comes in (from outside) and does what?

Back 14

Binds to calmodulin

Front 15

What activates the light chain kinase to phosphorylate myosin?

Back 15

Calcium / calmodulin complex

Front 16

What needs to happen to myosin so that contraction can occur?

Back 16

Needs to be phosphorylated by light chain kinase and needs the presence of actin.

Front 17

Why does smooth muscle stay contracted involuntarily?

Back 17

Because an enzyme is needed for relaxation to occur.

Front 18

Describe the four steps of contraction termination in smooth muscles.

Back 18

1. Calcium channels close
2. Cytosolic Ca levels fall below "critical level"
3. Myosin light chain is dephosphorylated by myosin phosphatase.
4. Cross-bridge cycling stops.

Front 19

Compare speed of cross-bridge cycling in smooth muscle to skeletal muscle.

Back 19

Slower in smooth muscle

Front 20

Compare onset of contraction and relaxation after stimulus in smooth muscle vs. skeletal muscle

Back 20

Slower in smooth muscle

Front 21

Compare energy of sustained contraction in smooth muscle vs. skeletal muscle.

Back 21

Less energy required in smooth muscle.

Front 22

Compare maximum force of contraction in smooth muscle vs. skeletal muscle.

Back 22

Greater in smooth muscle.

Front 23

Compare degree of shortening in smooth muscle vs. skeletal muscle.

Back 23

Greater degree in smooth muscle.

Front 24

Compare the quantitative energy of sustained contraction between smooth muscle and skeletal muscle.

Back 24

Smooth muscle uses 1/300th the energy of skeletal muscle to sustain a contraction

Front 25

Describe the "Latch" mechanism.

Back 25

Once smooth muscle in fully contracted, it will sustain it at 1/300 the energy of skeletal muscle.

Front 26

What occurs slower in smooth muscle than in skeletal muscle?

Back 26

1. Cycling of cross bridges
2. Relaxation
3. Contraction

Front 27

What are the two mechanisms of control in smooth muscle contraction?

Back 27

Neural and hormonal mechanism.

Front 28

Describe the receptors of muscle contraction in smooth muscles in comparison to skeletal muscles.

Back 28

1. Smooth muscle membrane has many different receptor types (rather than just Na+/K+).
2. Smooth muscles also have receptors that can inhibit contraction (not seen in skeletal muscles)

Front 29

Do smooth muscles have discrete neuromuscular junctions?

Back 29

No. Nerves terminate over muscle fibers, not in them.

Front 30

Describe the actions of diffuse junction in smooth muscles.

Back 30

Secretes transmitters into fluid surrounding muscle fibers.

Front 31

What are the transmitting substances of autonomic nerves?

Back 31

Acetylcholine and Norepinepherine

Front 32

T/F - Acetylcholine and norepinephrine are released by the same nerve.

Back 32

False - released by different nerves, where one is stimulatory and the other is inhibitory.

Front 33

What is the general rule of ACh/NE effects on organs.

Back 33

Action varies with organ type, but in general: if ACh excites, NE inhibits. and vise versa.

Front 34

What is the resting potential in smooth muscles?

Back 34

-50 mV.

Front 35

Action potentials are seen in what type of smooth muscles?

Back 35

In unitary smooth muscles, but not much in multiunit smooth muscles.

Front 36

What are the two types of action potential seen in unitary smooth muscles?

Back 36

1. Spike potential
2. Action potential with plateaus

Front 37

Describe the duration of spike potentials

Back 37

10 - 50 milliseconds

Front 38

Describe the polarization character of spike potentials with plateaus.

Back 38

Very slow repolarization.

Front 39

Where would you find spike potentials?

Back 39

Places of peristalsis (approx. 8 contractions per minute)

Front 40

Where would you find action potentials with plateaus.

Back 40

In muscles requiring extended period of contraction usch as ureter, uterus, and vascular smooth muscle.

Front 41

Describe the number of calcium channels in smooth muscle cells.

Back 41

Calcium channels far exceed sodium channels in smooth muscle cells.

Front 42

The flow of what is responsible for Action potential in smooth muscles.

Back 42

Calcium

Front 43

Describe the opening of calcium channels.

Back 43

Opening is much slower.

Front 44

What are the characters of these slow waves? X 3

Back 44

1. Self excitatory
2. No extrinsic stimulus needed
3. Source of slow waves unknown

Front 45

What are the possible reasons for explaining slow waves?

Back 45

1. Changes in Na pumping
2. Ion conductance changes
3. Leak of ions (either Na or Ca)

Front 46

Action potential is directly COUPLED with what in smooth muscles?

Back 46

Contraction

Front 47

What causes excitation by stretch in smooth muscles? X 2

Back 47

1. Normal slow waves
2. Increase in membrane potential (less negative)

Front 48

Half of smooth muscle contraction is caused by what two factors?

Back 48

1. Local tissue factors
2. Hormones

Front 49

What are the five local tissue factors?

Back 49

1. Lactic acid
2. Acidity
3. Carbon Dioxide
4. Oxygen
5. Prostanoids

Front 50

How does hormones effect smooth muscle contraction?

Back 50

Alters the ion conductance

Front 51

T/F - Troponin - Tropomyosin complex seen in smooth muscles.

Back 51

False

Front 52

What are three major factors of contraction stimulation in smooth muscles.

Back 52

1. Stretch
2. Hormones
3. Local factors

Front 53

What exhibits intrinsic contraction without external stimuli?

Back 53

Slow waves