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<3 > Smooth Muscle Physiology > Flashcards

Smooth Muscle Physiology Flashcards

1
Q

How is the HISTOLOGY of Sk. M. Different from Sm. M?

A

Sk = large, multi nucleate striated cells

Sm = small, single nucleus, no striations

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2
Q

How is the SARCOPLASMIC RETICULUM of Sk. M. Different from Sm. M?

A

Sk: large, well developed, Sr w/ TRIADS, well developed t-tubules

Sm: poorly developed SR, T-tubules; membrane w/. Caveoli

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3
Q

How are the THIN FILAMENTS of Sk. M. Different from Sm. M?

A

Sk: actin, tropomyosin, troponin

Sm: actin & tropomyosin (calmodulin instead of Tropomyosin)

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4
Q

How is the THIN FILAMENT # of Sk. M. Different from Sm. M?

A

Sk. - lower than sm. Muscle

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5
Q

How is the THICK FILAMENT COMPOSITION of Sk. M. Different from Sm. M?

A

Sk: myosin, ATPase activity - faster

Sm: myosin, ATPase activity -slower; myosin light chain prominence

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6
Q

How is the THICK FILAMENT # of Sk. M. Different from Sm. M?

A

Sk: Greater than smooth muscle (thin was less)

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7
Q

How is the INNERVATION of Sk. M. Different from Sm. M?

A

Sk: alpha-motor neurons

Sm: multiple - including intrinsic and autonomic nervous system

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8
Q

How is the NTRs of Sk. M. Different from Sm. M?

A

Sk: ACh - excitatory

Sm: ACh, epi, NorE - excitatory/inhibitory

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9
Q

How is the TRANSMISSION SPECIALIZATION of Sk. M. Different from Sm. M?

A

Sk: NMJ

Sm: no NMJ - varicosities (pre-sun. Swelling), no end plate specialization

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10
Q

What are the other forms of activation for Sk. M. And Sm. M?

A

Sk: none others

Sm: blood-borne, paracrine, intrinsic

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11
Q

How is the ACTION POTENTIAL of Sk. M. Different from Sm. M?

A

Sk: required

Sm: no AP - pacemaker activity, hormonal

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12
Q

How is the SOURCE OF CALCIUM of Sk. M. Different from Sm. M?

A

Sk: release from Sr

Sm: release from SR but HUGE ECF influx

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13
Q

How is the ROLE OF CALCIUM of Sk. M. Different from Sm. M?

A

Sk: binds to troponin C

Sm: binds to Calmodulin, activates MLCK

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14
Q

How is the MECHANISM TO ALLOW ACTIN AND MYOSIN BINDING of Sk. M. Different from Sm. M?

A

Sk: tropomyosin moved by troponin

Sm: phosphorylation of myosin light chain

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15
Q

How is the RELAXATION of Sk. M. Different from Sm. M?

A

Sk: removal of Ca from troponin

Sm: activation of light chain phosphate seems, dephosphorylation

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16
Q

What are the 2 major types of Smooth M.?

A
  1. Multi unit smooth muscle

2. Unitary smooth muscle

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17
Q

What are the characteristics of

Multi unit smooth muscle?

Examples of it?

A

• Fibers operate individually
• Innervated by a single nerve
◦ I.e. ciliary muscles of eye, iris piloerector Ms.

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18
Q

What are the characteristics of

Unitary Smooth muscle?

Where is it found?

A
  • Visceral smooth muscle or syncytial
  • Works together as unit
  • Cell membranes adhere and contain gap junctions

◦ I.e. GI tract, bile ducts, uterus

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19
Q

How is the NTR Rs. of Sk. M. Different from Sm. M?

A

Sk: Nicotinic cholinergic

Sm: Muscarinic cholinergic; adrenergic; others

20
Q

What ar the 3 arrangements of Sm. M. Seen?

A
  1. Circumferential
  2. Circumferential & longitudinal
  3. Varied
21
Q

How is SM. M. Contraction slight different?

What does Actin attach to?

A

No true sarcomere structures

  1. Actin will attach to DENSE bodies/ADHERENS junctions
22
Q

What does the bi-directional arrangement of myosin heads help w/?

A

Help w/ length tension relationship

23
Q

How is the cycling of myosin cross bridges in SK. M. Compared to Sm. M.?

What does this cause?

A

Slower in Smooth m. Than SK. M.

= greater time together = greater force in smooth muscle

24
Q

What is the MECHANISM of contraction in Sm.M.?

A
  1. Calcium entry into cytosol thru PM
  2. 4 Ca binds reversible to CaM
  3. Calmodulin-Ca complex activates myosin light chain kinase
  4. Kinase phosphorylates myosin light chains = contraction
  5. Relaxation due to myosin light chain phosphotase
25
Q

How does Calcium enter the cytosol to help initiate Sm. M. Contraction?

A
  • from SR (but only very small amount)

- Much from Extracellular

26
Q

What receptors are found in the Sarcoplasmic reticulum?

A

IP3-gated Ca release channel rs.

Ryanidine Rs.

27
Q

What are the channels that allow calcium to enter via Sarcolemmal?

A

L-type voltage gated calcium channels

Receptor activated Ca channels

28
Q

How does calcium exit during the sm. M. Contraction ?

A
  • serca
  • 3 Na/Ca antiporter
  • Sarcolemmal Calcium ATPase
29
Q

How many calcium’s bind calmodulin?

What happens upon their binding?

A

4 calcium’s

  • calmodulin will change conformation, resulting in an active complex
  • the 2 globular heads of complex wrap around binding site on target protein
30
Q

What is the contraction strength of Sm.M. Generally proportional to?

A

Proportional to Calcium levels

31
Q

Does phosphorylation or dephosphorylation of myosin light chain produce contraction?

A

Phosphorylation

-allows myosin and actin binding

32
Q

What 2 things do you need for relaxation to occur in Sm. M.?

A
  1. Calcium pumps removes calcium
  2. Myosin light chain phosphotase - removes P group on myosin light chain (inactivates it)

= relaxation

33
Q

What 4 things can activate Sm. M.?

A
  1. Nerve stimulation
  2. Hormones
  3. Stretch
  4. Environmental ques
34
Q

What are the NTR release sites in sm. M.?

A

Varicosities

35
Q

What are the hormones released by nerves to stimulate Sm. M. ?

A

ACh

Ne/E
(To alpha-1 = constriction; beta-2 = relaxation)

Angiotensin II, vasopressin, endothelin = contraction

Adenosine = relaxation

NO = relaxation

36
Q

What are the hormones used to stimulate Sm. m.?

A

Cholecystokinin

Oxytocin

Serotonin

Histamine

37
Q

How do hormones “stimulate” sm. M.?

A

Actions thru their own receptors influence Ca channels

38
Q

What are environmental ques that stimulate sm. M.?

What do they each cause?

A
  1. Hypoxia - dilation
  2. Excess CO2 - dilation
  3. Increased H+ = dilation
  4. Adenosine, LA, increased K etc.
39
Q

What is ATP’s role in the contraction of Sm. M>

A

latch mechanism

40
Q

What is the latch mechanism?

A

Allows for binding w/ slow to fatigue - slow myosin ATPase

41
Q

What does the latch mechanism allow for?

A

‣ Way to increasing tension while decreasing ATP usage

42
Q

How does the latch mechanism work?

A

‣ Dephosphorylation of light chain
‣ Cycle proceeds slowly
‣ Attached cross bridges are still generating tension (20-30%)

Due to slow myosin ATPase

43
Q

In which SM. m. Type do APs occur?

A

Only occur in Unitary smooth muscle

44
Q

What are the 2 forms of APs in sm. Ms.?

A
  1. Plateaus

2. Spike potentials

45
Q

What are spike potential stimulated by?

What do they indicate?

A

Stimulated by: hormones, NTRs, stretch, spontaneous

More spike potential present = greater force

46
Q

What causes the slow wave of APs in sm. Ms.?

A

Oscillating Ca influx (L-type VGCCs)

K+ efflux (ca-activated K channels)

47
Q

What are the plateaus in Sm. M. Contraction stimulated by?

A

NTRs, stretch

<3 (26 decks)

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