Part 5: Smooth Muscle Flashcards Preview

SF1.12 Muscle Physiology (ZACHOW) > Part 5: Smooth Muscle > Flashcards

Flashcards in Part 5: Smooth Muscle Deck (27)
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1

Visceral smooth muscle is what kind of smooth muscle?

  • single unit smooth muscle

2

Single unit smooth muscle:

  • sheets or bundles of smooth muscle fibers that function/contract as a single unit 
  • connected via gap junctions
  • innervation of only a few muscle fibers results in excitation or inhibition of all muscle fibers in a given region

3

The two types of action potentials in visceral smooth muscle:

  • spike potentials (slow wave followed by spike)
    • responsible for basal rhythm and peristalsis
  • plateau potentials

4

Spike potentials:

  • slow wave induced by calcium channel opening
  • threshold reached, spiked AP occurs
  • potassium channels open, hyperpolarization

5

Visceral smooth muscle is innervated by ANS efferents. What type of synaptic junctions are formed between these efferents and visceral smooth muscle cells?

  • diffuse
    • neurotransmitter released and bathes all cells simulataneously

6

What motor neuron efferents cause contraction of visceral smooth muscle?

parasympathetic

7

What motor neuron efferents cause relaxation of visceral smooth muscle?

sympathetic

8

Dimensions of contraction in smooth muscle versus skeletal muscle:

  • Smooth muscle contracts in 3D
  • Skeletal muscle contracts in 2D

9

How does smooth muscle contract in 3D?
 

  • very high actin:myosin ratio (15:1) when compared to skeletal muscle (2:1).
  • actin filaments arranged obliquely instead of longitudinally. 

10

Three ways to activate smooth muscle: 

  1. action potentials: activate type-l calcium channels
  2. neurohormonal: activate voltage-independent calcium channels
  3. stretch: activate stretch activated calcium channels

11

What differentiates smooth muscle contraction from skeletal muscle contraction?

  • Smooth muscle has:
    • calmodulin dependent protein kinases (CaMKs)
    • myosin light-chain kinases (MLKCs)

12

Steps in the activation of smooth muscle contraction:

  1. stimulus causes calcium influx
  2. calcium activates kinases and/or calcium pumps
  3. calcium binds to calmodulin (CaM)
  4. calmodulin-dependent kinases (CaMKs) activated 
  5. CaMKs activate myosin-light chain kinase (MLCK)
  6. MLCK activates phosphomysin
  7. cross-bridge cycling and contraction

13

Steps in smooth muscle relaxation:

  1. MLCK phosphatase inhibits phosphomyosin.
    • primary cause of relaxation; interferes with CBC.
  2. pumps on the saroplasmic membrane pump out calcium from the sarcolemma.

14

The sympathetic nervous system causes vasoconstriction of arterioles (smooth muscle) via:

  • epinephrine and norepinephrine.
  • type alpha-1 adrenoreceptors. 

15

Vascular smooth muscle controls:

blood pressure 

16

What can effect vascular smooth muscle (and, therefore, blood pressure)?

  • arterial tree
  • sympathetic nervous system
  • vasoactive metabolites
  • hormones

17

What regulates capillary flow in vascular smooth muscle/arterioles?

precapillary sphincters

18

Steps in sympathetic nervous system causing vasoconstriction:

  1. norepinephrine/epinephrine binds to alpha-1 adrenoreceptors on vascular smooth muscle.
  2. G-protein cascade leads to influx of calcium and inhibition of calcium efflux via SERCA channels.
  3. sarcoplasmic calcium levels increase
  4. vascular smooth muscle contracts (vasoconstriction).

19

Vasodilatory drugs target:

  • alpha adrogenic receptors or calcium channel blockers.

20

Steps in vascular smooth muscle relaxation:

  1. nitric oxide synthase/nitric oxide activate cGMP.
  2. cGMP activates kinases that activate membrane calcium pumps and SERCA pumps.
  3. sarcoplasmic calcium levels decrease
  4. vascular smooth muscle relaxes

21

Nitric oxide is a potent:

  • Vasodilator
  • Activates cGMP, which activates SERCA channels and causes calcium efflux from sarcoplasm of smooth muscle.

22

What enzymes block vasodilation?

  • phosphodiesterases via inhibition of cGMP
    • cGMP activates kinases that cause SERCA channel opening, calcium efflux, and vascular smooth muscle relaxation

23

Phosphodiesterase (PDE) inhibitors:
 

  • Viagra
  • promotes vasodilation
    • inhibits cGMP, which causes activation of SERCA channels

24

Blood pressure = 

BP = CO + TPR

  • CO = cardiac output
  • TPR = total peripheral resistance

25

Law of Laplace:

P = T/r

  • increase radius, decrease pressure

26

Smooth muscle with a high stress relaxation:

  • bladder smooth muscle
  • expands to lower pressure
  • less resistance to renal urine output

27

Smooth muscle with a low stress relaxation:

  • vascular smooth muscle
  • high pressure enables propulsion of blood/perfusion