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Foundation > Physiology of smooth muscle > Flashcards

Physiology of smooth muscle Flashcards

1
Q

Where can you find smooth muscles?

A

walls of hollow visceral organs eg stomach, airways, bv’s, uterus etc.

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2
Q

In smmu whats the function of desmosomes and gap junctions

A

gap junctions allow movement of AP between cells.

desmosomes allow mechnical coupling of adjacent cells - passing of ions

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3
Q

Sarcoplasmic reticulum located very close to the

A

caveolae.

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4
Q

Interaction between the _________ and __________ are responsible for the contraction and relaxation of smooth muscle cells.

A

thick (myosin) and thin (actin) filaments

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5
Q

Structure of smmu

A
  • no striations
  • spindle shaped with single nucleus
  • usually arranged in sheets
  • have dense bodies
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6
Q

dense bodies

A

anchoring the actin filaments as there is no z line.

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7
Q

smmu cells have 3 types of filaments

A
  1. myosin thick
  2. actin thin
  3. intermediate - do not directly participate in muscle contraction
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8
Q

What is caveolae?

A

Caveolae is the invagination of the cell membrane so as to increase the total surface area for controlling Ca2+ influx via the voltage-gated Ca2+ channels (VGCC).
The equivalent of caveolae in skeletal muscles is the T-tubule.

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9
Q

What is the SR?

A

SR is a specialized endoplasmic reticulum that serves as a storage for Ca2+ but it is not as important in the smooth muscles as it is in the skeletal muscles and cardiac muscles.

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10
Q

The _____________ on the SR contribute only slightly to the Ca2+ needed for contraction.

A

voltage-independent calcium channels (VICC)

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11
Q

VGCC on caveolae
VICC on SR

functions?

A

Two ways to bring in Ca2+ into the cell.

  1. less by SR
  2. extracellularly
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12
Q

calmoduline

A

protein used to bind ca2+ in the cytosol

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13
Q

how is smmu organized? explain the two ways.

A
  1. MULTIUNIT (as a multi unit, singles)
    fast but lesser power, PHASIC. fast contraction and relaxation, high fast myosin content. stimulation of one fibre contracts that one fibre only. electrically isolated - allows finer motor control.
  2. UNITARY (as a whole unit)
    slow but more powereful, sustained contraction, TONIC.
    Low fast myosin content. Stimulation of one unitary fibre causes contraction of adjacent fibre.
    coordinated contraction due to gap junctions.
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14
Q

smmu vs skmu
calmoduline =
caveolae =
dense bodies =

A

troponin
t tubules
z line

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15
Q

where are multiunit and unitary fibres found?

A

Multiunit: Example: vasculature, epididymis, vas deferens, iris, piloerector muscle

Unitary: Example: GIT, uterus, ureter, urinary bladder, respiratory tract

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16
Q

Mu and Su organization both have different varicosity organization. explain what are varicosities

A

The varicosities are formed from the autonomic nerve fibres and contain neurotransmitters.

17
Q

Whats the procedure of smooth muscle contraction and relaxation?

A
  1. Depolarization - ca enters from VGCC and VICC
  2. Ca2+ binds to calmoduline –> activated = ca2+-calmoduline complex
  3. activation of MLCK (myosin light chain kinase) by CCC.
  4. MLCK catalyze transfer of P from ATP to myosin –> activated myosin ATPases
  5. MLCP (phosphatase) dephosphorylates myosin head so it cannot form cross bridges with the actin
  6. Ca2+ pumps on the cell membrane and SR remove intracellular Ca2+ and normalize the levels intracellularly.
18
Q

Three things that are slow in smmu compared to skmu. significance?

A

A. Three things are slow in smooth muscles compared to skeletal muscles:
1. Ca2+ influx
2. Activity of MLCK
3. Ca2+ removal
Significance: Contraction of smooth muscles starts slowly but sustained for longer time, generating the smooth muscle tone.

19
Q

Smooth muscles are __________ more than skeletal muscles.

significance?

A

stretchable

Smooth muscles will first contract and relax within a minute when it is stretched (called stress-relaxation response).

Significance: Allows the organs to expand (which stretches the smooth muscles around it) while retaining its ability to contract.

20
Q

Regulation of smooth muscle contraction by:

  1. ANS
  2. Hormones
A
  1. ANS
    Vascular smmu - constriction or dilation - only sympathetic response no parasympathetic response.

Lungs - airways, in PSR: bronchoconstriction. SR: bronchodilation

  1. HORMONES
    - oxytocin: Stimulate contraction of uterus
    - progesterone: Inhibit contraction of uterus
    - angiotensin II:Stimulate vasoconstriction
    - epinephrine: Stimulate vasoconstriction but inhibit bronchoconstriction
21
Q

Remember: it all depends on the location of the smooth muscles!!

A

The visceral smooth muscles contract upon parasympathetic stimulation whereas the vascular smooth muscles contract upon sympathetic stimulation.

22
Q

compare

A

No cross striation

Calmodulin as the Ca2+ sensor

Dense body instead of Z-line

Foundation (26 decks)

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