Muscle Pt. 3 Flashcards

1
Q

How is smooth muscle activated?

A

Involuntarily.

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2
Q

What are the 2 types of smooth muscle?

A
  1. Single unit/unitary/visceral.
  2. Multiunit.
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3
Q

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

A
  1. Smaller.
  2. Much shorter.
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4
Q

How are multiunit smooth muscle fibers described?

A

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

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5
Q

What happens when multiunit smooth muscle fibers are stimulated?

A

Only that fiber is stimulated.

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6
Q

Where are multiunit smooth muscle fiber found?

A
  1. Airways to lungs.
  2. Ciliary body.
  3. Muscles of iris.
  4. Pilo-erector muscles.
  5. Walls of large arteries.
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7
Q

How are visceral smooth muscle fibers described?

A

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

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8
Q

How are visceral smooth muscle fibers arranged?

A

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

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9
Q

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

A

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

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9
Q

Where are visceral smooth muscle fibers found?

A
  1. Hollow organs.
  2. Walls of small arteries.
  3. Walls of veins.
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10
Q

What does an individual smooth muscle fiber look like?

A
  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.
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11
Q

What are dense bodies?

A

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

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11
Q

What are caveolae?

A

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

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12
Q

Where are dense bodies found?

A
  1. Sarcolemma.
  2. Sarcoplasm.
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13
Q

How does the smooth muscle contract?

A

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.

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14
Q

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

A
  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.
15
Q

What initiates the contraction?

A

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

16
Q

What is calmodulin and what is its function?

A

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.

17
Q

What rate does myosin light chain kinase function at?

A

Slowly, contributing to the slower rate of contraction.

18
Q

What rate does Ca2+ move out of smooth muscle?

A

Slowly, delaying relaxation.

19
Q

What does the prolonged presence of Ca2+ contribute to?

A
  1. Smooth muscle tone.
  2. The state of continued partial contraction.
20
Q

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

A

Maintenance of steady pressure on contents in GIT.

21
Q

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

A

Maintenance of steady blood pressure.

22
Q

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

A
  1. Action potentials from the ANS.
  2. Hormones.
  3. Ion concentrations.
  4. pH change.
  5. Stretching.
  6. Temperature change.
23
Q

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

A

Undergo great length fluctuations and still contract effectively.

24
Q

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

A

It changes very little.