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Physiology 1 > Muscle Physiology Part 5 > Flashcards

Muscle Physiology Part 5 Flashcards

1
Q

What are the two types of smooth muscle?

A
  1. Multi-unit

2. Single-unit (visceral)

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2
Q

Which type of smooth muscle is visceral?

A

Single unit

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3
Q

What are the properties of multi-unit smooth muscle:

A
  1. Discrete, and separate muscle fibers
  2. Each fiber contracts INDEPENDENTLY
  3. Inervated by a single nerve ending (each fiber)
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4
Q

What are the locations of multi unit smooth muscle?

A
  • walls of blood vessels
  • Base of hair follicles
  • iris
  • ciliary muscle of the eyes
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5
Q

Properties of single unit smooth muscle:

A
  1. Also called visceral, syncytial, or unitary smooth muscle
  2. Fibers are arranged in sheets and bundles
  3. Contract as a single unit
  4. Cells joined by “gap junctions”
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6
Q

What are the locations of single unit smooth muscle?

A
  1. GI tract
  2. Bile ducts
  3. Ureters
  4. Uterus
  5. Blood vessels
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7
Q

What type of ions can pass through gap junctions?

A

Water-soluble molecules

Ex: ions, glucose

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8
Q

How big is the gap between gap junctions?

A

2-4 nm

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9
Q

In what type of cells are gap junctions important for?

A

Electrically excitable cells

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10
Q

Where can you find gap junctions?

A
  • Connective tissue
  • Smooth Muscle
  • Cardiac muscle
  • Neurons
  • epithelial tissue
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11
Q

Does smooth muscle have the same striations arrangement of actin and myosin filaments?

A

NO

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12
Q

In skeletal muscle,actin is bound to zdisks. What is actin bound to in smooth muscle?

A

Actin is bound to DENSE BODIES in smooth muscle

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13
Q

Is there troponin-tropomyosin complex in smooth muscle?

A

No there is no troponin-tropomyosin complex

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14
Q

Smooth muscle myosin filaments form cross bridges like skeletal muscle. What kind?

A

Side-polar cross-bridges

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15
Q

What are side-polar cross-bridges?

A

The bridges on one side of the cross-bridge go one direction and the bridges on the other side go the OPPOSITE DIRCETION

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16
Q

Why are side-polar cross bridges important?

A
  • the configuration allows myosin to pull actin in two directions simultaneously
  • smooth muscle can contract up to 80% of their length
    - skeletal muscle only 30%
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17
Q

In the smooth muscle, is the SR more or less developed?

A

less developed

18
Q

Where is the major source of calcium for smooth muscle? Skeletal?

A

Smooth- ECF

Skeletal-SR

19
Q

What is a caveolae?

A

Caveolae are found in Smooth muscle SR and are:

-small invaginations that excite calcium release from the SR

20
Q

What 3 factors stimulate smooth muscle contraction?

A
  1. Nervous system (ANS) (Skeletal-CNS)
  2. Hormones
  3. Local tissue chemical factors
21
Q

Which nervous system is the ANS (Autonomic Nervous system) a part of? What are the branches? What does it control?

A
  1. Peripheral Nervous System (PNS)
  2. 2 Branches: Sympathetic & Parasympathetic nervous system
  3. The ANS controls organ function
Sympathetic= "fight or flight"
Parasympathetic= "rest and digest"
22
Q

What type of fibers inervate smooth muscle fibers?

A

Autonomic Nerve fibers

23
Q

Do the autonomic nerve fibers make direct contact with the smooth muscle cell?

A

In most cases the fibers do not make direct contact with the smooth muscle cell

24
Q

How are neurotransmitters released in smooth muscle if not through direct contact?

A
  • The nerve forms “diffuse junctions” that secrete the neurotransmitters into the matrix of smooth muscle.
  • Neurotransmitters then diffuse to the smooth muscle cells
25
Q

What neurotransmitters (2) do smooth muscles secrete?

A
  1. Acetylcholine
  2. Norepinephrine

-can inhibit or stimulate muscle contraction

26
Q

How do action potentials differ in smooth muscle (single vs multi-unit)?

A

Single-unit= action potentials are the SAME as SKELETAL

Multi-unit= the neurotransmitters themselves cause depolarization of
the membrane and contraction
-they do this WITHOUT ACTION POTENTIAL
-uses “JUNCTIONAL POTENIAL” instead
-fibers are TOO Small so stimuli spreads over the entire fiber

27
Q

In small blood vessels, are there a lot of nerve supply?

A

No, in small blood vessels there is little to no nerve supply

  • so in these areas CONTRACTION is HIGH
28
Q

Many hormones in the blood affect smooth muscle contraction: true or false?

A

True! Target tissues must have a specific hormone receptor for them

29
Q

What are some examples of smooth muscle hormones that affect contraction?

A

Norepinephrine, Epinephrine, Angiotensin II, Endothelin, Vasopressin, Oxytocin, Serotonin, Histamine

30
Q

What are some other ions that can stimulate smooth muscle contraction?

A

Na+ and Ca+ by the opening of their channels

  • they depolarize the membrane the same way nerve stimulation does
    • can inhibit them by closing the channels
31
Q

Some hormones can activate membrane receptors that use second messengers! What are 3 second messengers used?

A
  1. Calcium
  2. cAMP
  3. cGMP
32
Q

What is the actual stimulus for smooth muscle contraction?

A

The increase in intracellular calcium ions

33
Q

Some properties of calcium as a second messenger:

A
  • Ca 2+ in the cytosol is initially low
  • Ca 2+ in the ECF, ER, and SR (muscles) is HIGH
  • there is a large gradient that drives Ca 2+ to cross membranes into the CYTOSOL
  • increases in calcium are easily detected and activates responsive proteins in the cell
34
Q

In smooth muscle cells calcium ions do not bind with troponin on actin filaments. What does calcium bind to instead to activate cross bridges?

A

Calmodulin

35
Q

What is calmodulin?

A

Calmodulin is a regulatory protein and functions as an “intracellular receptor”
-when “calcium” binds to it undergoes a conformational change and then binds to activate other proteins

36
Q

What are the 5 steps of the actual activation of myosin and contraction in smooth muscle? (This is after action/junctional potential depolarizes the membrane)

A
  1. Calcium concentration increases in the cytosol
    -remember, this is mainly from Ca channels on cell membrane!!!! Some are from SR release
  2. Calcium ions bind with “calmodulin”
  3. The calcium-calmodulin complex joins /activates:
    MYOSIN LIGHT CHAIN KINASE
  4. The “regulatory chain” of each myosin head is phosphorylated (ATP) by Myosin Light Chain Kinase
    -opens Actin-binding sites on myosin heads (Active state)
  5. Smooth Muscle contracts
    -depending on extracellular calcium concentration
37
Q

How do you return smooth muscle to a resting state?

A
  1. a calcium pump is required
    • moves Calcium back to ECF or SR
    • requires ATP
    • slow acting so contraction lasts longer
  2. Myosin Phosphatase
38
Q

Are contractions in smooth muscle slower or faster than skeletal, why?

A

Slower because the Ca pump is slow acting

39
Q

Once calcium concentration decreases, what enzyme is activated, where is it located, and what does it do?

A

Myosin Phosphatase

- located in the cytosol of smooth muscle
- splits the phosphate from the light chain of the myosin heads
- cycle stops and contraction ceases
40
Q

What are some particular things about smooth muscle contraction?

A
  1. Slow attachement release and re attachment of contraction than skeletal muscle
    • force of contraction is greater
  2. Low energy required to sustain contraction
    • myosin heads stay active till shut of, in skeletal ATP is needed for every pull
    • important for organs like intestines, gallbladder, bladder

Physiology 1 (10 decks)

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