Muscle Pt. 3

Question 1

How is smooth muscle activated?

Answer 1

Involuntarily.

Question 2

What are the 2 types of smooth muscle?

Answer 2

1. Single unit/unitary/visceral.
2. Multiunit.

Question 3

How does smooth muscle compare to skeletal muscle fiber in size? Length?

Answer 3

1. Smaller.
2. Much shorter.

Question 4

How are multiunit smooth muscle fibers described?

Answer 4

Individual fiber that each have their own motor neuron terminals w/ few gap junctions between neighboring fibers.

Question 5

What happens when multiunit smooth muscle fibers are stimulated?

Answer 5

Only that fiber is stimulated.

Question 6

Where are multiunit smooth muscle fiber found?

Answer 6

1. Airways to lungs.
2. Ciliary body.
3. Muscles of iris.
4. Pilo-erector muscles.
5. Walls of large arteries.

Question 7

How are visceral smooth muscle fibers described?

Answer 7

Auto-rhythmic fibers connected by gap junctions that allow for the communication of an action potential to permit contraction in unison.

Question 8

How are visceral smooth muscle fibers arranged?

Answer 8

A tubular fashion in the form of either circular or longitudinal sheets.

Question 9

What happens when a signal (autorhythmic, hormone, neurotransmitter) stimulates one fiber?

Answer 9

The muscle action potential would be transmitted to neighboring fibers, leading them to contract in unison.

Question 9

Where are visceral smooth muscle fibers found?

Answer 9

1. Hollow organs.
2. Walls of small arteries.
3. Walls of veins.

Question 10

What does an individual smooth muscle fiber look like?

Answer 10

1. Contains dense bodies.
2. Contains intermediate filaments.
3. Lacks T-tubules.
4. Less organized sarcomere.
5. Single, centrally located nucleus.
6. Small amount of SR, caveolae instead.

Question 11

What are dense bodies?

Answer 11

Structures that thin and intermediate filaments are attached to that are similar to Z-discs.

Question 11

What are caveolae?

Answer 11

Small pouch-like plasma membrane invaginations that contain extracellular Ca2+.

Question 12

Where are dense bodies found?

Answer 12

1. Sarcolemma.
2. Sarcoplasm.

Question 13

How does the smooth muscle contract?

Answer 13

The sliding filament mechanism generates tension that is transmitted to intermediate filaments that pull on the dense bodies to cause a lengthwise shortening of the muscle fiber. This shortening causes a corkscrew rotation of the muscle as the fibers twist in a helix pattern.

Question 14

How does the contraction of smooth muscle differ from that of skeletal muscle?

Answer 14

1. Contracts more slowly (due to Ca2+ taking longer to reach the filaments) and lasts much longer.
2. Can shorten and stretch to a greater extent.

Question 15

What initiates the contraction?

Answer 15

Increased Ca2+ in the cytosol that flows in from the interstitial fluid, SR, and caveolae.

Question 16

What is calmodulin and what is its function?

Answer 16

A regulatory protein that binds to Ca2+ in the cytosol and activates myosin light chain kinase to phosphorylate the myosin head and allow for binding to actin.

Question 17

What rate does myosin light chain kinase function at?

Answer 17

Slowly, contributing to the slower rate of contraction.

Question 18

What rate does Ca2+ move out of smooth muscle?

Answer 18

Slowly, delaying relaxation.

Question 19

What does the prolonged presence of Ca2+ contribute to?

Answer 19

1. Smooth muscle tone.
2. The state of continued partial contraction.

Question 20

What does the prolonged presence of Ca2+ in the smooth muscle aid with in the GIT?

Answer 20

Maintenance of steady pressure on contents in GIT.

Question 21

What does the prolonged presence of Ca2+ in the smooth muscle aid with in the arterioles?

Answer 21

Maintenance of steady blood pressure.

Question 22

What do the smooth muscles contract/relax in response to?

Answer 22

1. Action potentials from the ANS.
2. Hormones.
3. Ion concentrations.
4. pH change.
5. Stretching.
6. Temperature change.

Question 23

What does the excellent contractile property allow smooth muscle to do?

Answer 23

Undergo great length fluctuations and still contract effectively.

Question 24

What happens to the pressure on the contents inside the hollow tubes/organs as the muscle stretch and contract?

Answer 24

It changes very little.