Smooth muscle contraction Flashcards

1
Q

What innervates smooth muscle?

A

ANS

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2
Q

What neurotransmitter can be release from post-ganglionic nerves onto smooth muscles from the PNS?

A

Acetylcholine (Ach)

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3
Q

What neurotransmitter can be released from post-ganglionic nerves onto smooth muscles from the Sympathetic NS?

A

Noradrenaline

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4
Q

What neurotransmitter can be released from post-ganglionic nerves onto smooth muscles from NANC (non-NA-non-Ach) nerves?

A

Nitric oxide (NO)

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5
Q

What hormone can be released from post-ganglionic autonomic nerves onto smooth cells from the adrenal medulla?

A

Adrenaline

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6
Q

How is smooth muscle contraction initiated?

A

By an increase in cytosolic Ca2+

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7
Q

How is there an increase in cytosolic Ca2+ ?

A
  • By influx from extracellular medium
  • Release of Ca2+ from internal Ca2+ stores (from sarcoplasmic reticulum
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8
Q

What is calmodulin (CaM)?

A

A Ca binding protein

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9
Q

How does smooth muscle use a Ca2+- Calmodulin complex to generate a muscle contraction?

A
  • Ca2+ binds to to calmodulin
  • This Ca2+ and calmodulin complex activates the myosin light chain kinase (MLCK)
  • MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity
  • Actin myosin crossbridges slide along actin, creating muscle tension
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10
Q

In the absence of a rise in cytosolic Ca2+, what compound produces relaxation and how?

A
  • Myosin light chain phosphatase
  • Due to the myosin light chain being dephosphorylated, MLCP activity becomes dominant, leading to relaxation
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11
Q

How can cytosolic Ca2+ decrease?

A
  • Ca2+ can be untaken into the SR- via Ca2+ ATPase
  • Extrusion of Ca2+ from cell via Ca2+ ATPase and Na-Ca exchanger (1Ca+ moves out, 3Na+ move in)
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12
Q

How does stimulation of Gq mediated receptors produce a rise in intracellular Ca from voltage gated calcium channels?

A
  • When a neurotransmitter binds to Gq protein receptors, it stimulates Na channels (ion channels) to open, causing depolarisation of the cell
  • This creates an excitatory junctional depolarising potential, which, if reaches the threshold value of -40mV, activates the opening of VGCC
  • This causes an influx of Ca2+
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13
Q

How does stimulation of Gq protein receptors cause the release of Ca2+ from internal Ca2+ stores in smooth muscle?

A
  • Stimulation of Gq receptors causes Pip2 to be converted into IP3 and DAG via PLC.
  • IP3 binds to IP3 receptors (these are ligand gated receptors) on the sarcoplasmic reticulum, which opens the ion channel, leading to an influx of Ca2+ down a concentration gradient, due to there being low Ca2+ in cytosol, and high in the SR
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