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Anatomy and Physiology 1 > 3. Smooth Muscles > Flashcards

3. Smooth Muscles Flashcards

1
Q

What two proteins do smooth muscle contain?

A

Actin and myosin

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2
Q

Describe the arrangement of the proteins in smooth muscle.

A

Not in a striated arrangement

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3
Q

To what structure are actin filaments attached in smooth muscle?

A

Dense bodies

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4
Q

What is the function of dense bodies in smooth muscle?

A
  • Serve the same function as Z discs in skeletal muscle
  • Some are attached to cell membranes, some are dispersed in the cell, some are bonded together to adjacent cells (force of contraction is transferred from one cell to another)
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5
Q

What protein complex is not present in smooth muscle? What is there instead?

A

The troponin complex

  • Instead it has myosin filaments that have side polar cross-bridges
  • Arranged so that the bridges on each side hinge in opposite directions
  • Allows smooth muscle to contract as much as 80% of their length
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6
Q

What are the two major types of smooth muscle contraction?

A

Multi-unit and single-unit (also known as unitary, syncytial, or visceral)

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7
Q

Describe the structure of multi-unit smooth muscle.

A

Composed of discrete, separate fibers that operate independently of each other. - the fibers are insulated from each other like skeletal muscle and innervated by a single nerve ending

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8
Q

Provide examples of multi-unit smooth muscles. (3)

A

Ciliary muscle of the eye, iris muscle of the eye, and piloerector muscles.

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9
Q

How does depolarization occur in multi-unit smooth muscle?

A
  • No action potential
    The fibers are too small to generate action potentials, so local depolarization caused by nerve transmitter substance spreads ELECTRONICALLY, causing muscle contraction.
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10
Q

Describe the structure of single-unit smooth muscle.

A

A mass of hundreds to thousands of smooth muscle fibers that contract as a single unit.
- Fibers are arranged in sheets or bundles with adherent cell membranes and gap junctions.

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11
Q

What do gap junctions allow in single-unit smooth muscle?

A

Ions to flow freely through.

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12
Q

Where are single-unit smooth muscles found in the body?

A

In the walls of most viscera (soft internal organs).

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13
Q

What is the normal resting potential of unitary smooth muscle?

A

-50 to -60 millivolts.

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14
Q

What types of action potentials occur in unitary smooth muscle?

A

Spike potentials and action potentials with plateaus.

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15
Q

Describe spike potentials in unitary smooth muscle.

A

Similar to those seen in skeletal muscle.

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16
Q

Describe action potentials with plateaus in unitary smooth muscle. Where is it found

A

Characterized by slow repolarization and are found in the uterus under certain conditions and some vascular smooth muscle.

17
Q

What is the difference between the ion channels in smooth muscle membranes compared to skeletal muscle membranes?

A

Smooth muscle membranes have few voltage-gated sodium channels and more voltage-gated calcium channels.

18
Q

Calcium vs sodium channels in smooth muscles

A

Calcium channels open more slowly and remain open longer than sodium channels.
- for prolonged action potentials
- calcium acts directly on smooth muscle contractile mechanism

19
Q

What does it mean for some smooth muscle to be self-excitatory? and what causes this

A

a basic slow wave rhythm causing an ap

Waxing and waning of the pumping of positive ions and changes in the conductance of ion channels.

20
Q

What is each graph

A
  1. spike potentials
  2. action potentials with plateus
  3. smooth muscle self-excitatory
21
Q

SMOOTH MUSCLE CONTRACTION 1. Describe the cycling of myosin cross-bridges in smooth muscle.

A

It is slow, and the fraction of time that the cross-bridges remain attached to the actin filament is GREATLY INCREASED, leading to increased force of contraction.

22
Q

SMOOTH MUSCLE CONTRACTION 1. Why is the cycling of myosin cross-bridges slow in smooth muscle?

A

The myosin head cross-bridges have far less ATPase activity, so ATP degradation, which energizes the movement of the cross-bridge heads, is reduced.

23
Q

SMOOTH MUSCLE CONTRACTION 2. How much energy is required to sustain smooth muscle contraction compared to skeletal muscle contraction? Why?

A

1/10th to 1/300th.

Only one ATP is needed per cross-bridge per cycle, and fewer cycles mean less energy is required.

24
Q

SMOOTH MUSCLE CONTRACTION 3. What regulates the concentration of intracellular calcium ions in smooth muscle?

A

INCREASE IN CALCIUM ION
Nerve stimulation, hormonal stimulation, stretch of the fiber, and changes in the chemical environment.

25
Q

CONTRACTION OF SMOOTH MUSCLE 4. What happens when calcium ions bind to calmodulin in smooth muscle?

A

The calmodulin-calcium complex joins with and activates myosin kinase, a phosphorylating enzyme.

26
Q

CONTRACTION OF SMOOTH MUSCLE 4. What is the role of myosin kinase in smooth muscle contraction?

A

It phosphorylates the myosin heads, allowing them to bind repetitively with the actin filament and initiate contraction.

27
Q

Step by step of smooth muscle contraction/relaxing

A
28
Q

How does smooth muscle contraction cease?

A

When the calcium ion concentration lowers, myosin kinase is inactivated.
Myosin phosphotase splits the phosphate from myosin and cycles stops

29
Q

Where does the calcium go when contraction ceases?

A

Back into SR or pumped into ECF

30
Q

What is the source of calcium ions for smooth muscle contraction?

A

Extracellular fluid, as smooth muscle has only a few, slightly developed sarcoplasmic reticula.

31
Q

What happens if extracellular fluid calcium concentration drops significantly?

A

Smooth muscle contractions cease.

32
Q

How are calcium ions removed from smooth muscle cells?

A

A calcium pump pumps calcium ions out of the smooth muscle into the extracellular fluid.

33
Q

Why do smooth muscle contractions often last for seconds?

A

The calcium pump in smooth muscle is slow-acting compared to the fast-acting sarcoplasmic reticulum calcium pump.

34
Q

What is the latch-bridge phenomenon?

A

The muscle maintains full force of contraction with little use of energy.

35
Q

When does the latch-bridge phenomenon occur?

A

When myosin kinase and myosin phosphatase are strongly activated, the cycling frequency of myosin heads and the velocity of contraction are great.

36
Q

How is energy conserved during the latch-bridge phenomenon?

A

Deactivation of the enzymes allows myosin heads to remain attached to the actin filament, and little energy is used because ATP is not degraded until the myosin head detaches.

37
Q

What is stress-relaxation in smooth muscle?

A

The ability of smooth muscle to return to its original force of contraction seconds or minutes after it has been elongated or shortened.

38
Q

What is the significance of stress-relaxation?

A

It allows a hollow organ to maintain the same amount of pressure inside its lumen despite long-term large changes in volume.

Anatomy and Physiology 1 (15 decks)

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