Phys. II Test One: Smooth Muscle

Question 1

Nerves to smooth muscle are derived from what NS?

Answer 1

Autonomic

Question 2

What anchors actin to the cells plasma membrane and is analogous to Z discs in skeletal muscle?

Answer 2

Dense Bodies

Question 3

Describe Single unit/visceral muscle.

Answer 3

Entire group of muscle fibers responds to stimulation as a single unit due to gap junctions

Question 4

What happens to muscle fibers in a single unit that have pacemaker activity?

Answer 4

They spontaneously generate AP’s that can spread to other cells through gap junctions

Question 5

What affects the contractile activity of cells?

Answer 5

Nerves
Hormones
Local factors

Question 6

How can the entire single unit muscle be regulated?

Answer 6

By controlling the frequency that the pacemaker fires

Question 7

Describe multi-unit muscle.

Answer 7

Few to no gap junctions so each cell within the muscle responds independently of each other. Depends on the number of fibers that are activated and frequency of nerve stimulation

Question 8

Which muscle unit can respond to stretch?

Answer 8

Single Unit

Question 9

What regulates cross bridge binding and movement?

Answer 9

Calcium activating the enzyme myosin light chain kinase

Question 10

How is MLCK activated?

Answer 10

Concentration of Ca in cytoplasm is increased through opening of membrane calcium channels allowing extracellular calcium in, or through stimulation of SR to release intracellular calcium. Calcium then binds with Calmodulin to activate/bind with MLCK.

Question 11

What does calcium bind to since troponin is not in smooth muscle?

Answer 11

Calmodulin

Question 12

What does MLCK use ATP for?

Answer 12

To phosphorylate one of the light chains of each myosin head

Question 13

How does smooth muscle relax?

Answer 13

Myosin needs to be dephosphorylated. First the slow acting ATP requiring pump movews calcium back into the SR so MLCK is no longer activated. Then the dephosphorylating enzyme myosin light chain phosphatase, which is always active, outpaces MLCK and relaxation occurs.

Question 14

Which muscle type has faster rates of ATP splitting and cross bridge cycling during contraction?

Answer 14

Skeletal

Question 15

What is the “latch state”?

Answer 15

Smooth muscle develops a full contraction and tension generated is high and can be maintained nearly full level even with a decline in energy.

Question 16

What inputs can increase a cells cytosolic Ca concentration?

Answer 16

1. Transmitters from ANS
2. Hormones
3. Local factors, acididty, osmolarity, O2 or CO2 and paracrines
4. Stretch of fibers
5. spontaneous electrical activity in fibers PM

Question 17

How can a smooth muscle cell contract in the absence of a membrane potential change?

Answer 17

An internal second messenger molecule such as IP3 is generated in response to external chemical messenger binding which will trigger the release of calcium from the SR.

Question 18

What cation causes action potentials in smooth muscle?

Answer 18

calcium not Na

Question 19

Where are slow waves typically found?

Answer 19

Single unit smooth muscle. When the AP is produced the AP will spread over the entire unit.

Question 20

What does smooth muscle have instead of a motor end plate region?

Answer 20

Axons of post ganglionic auto.neurons have swollen regions called varicosities which contain NT and when the AP reaches the varicosity it releases it NT.

Question 21

What happens if a Norepinephrine binds to alpha adrenergic receptors?

Answer 21

Most blood vessel smooth muscle contraction is enhanced.

Question 22

What happens if Norepinephrine binds to beta2 adrenergic receptors?

Answer 22

It relaxes bronchiole smooth muscles