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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
How does Calcium enter the cytosol to help initiate Sm. M. Contraction?
- from SR (but only very small amount) | - Much from Extracellular
26
What receptors are found in the Sarcoplasmic reticulum?
IP3-gated Ca release channel rs. Ryanidine Rs.
27
What are the channels that allow calcium to enter via Sarcolemmal?
L-type voltage gated calcium channels Receptor activated Ca channels
28
How does calcium exit during the sm. M. Contraction ?
- serca - 3 Na/Ca antiporter - Sarcolemmal Calcium ATPase
29
How many calcium’s bind calmodulin? What happens upon their binding?
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
What is the contraction strength of Sm.M. Generally proportional to?
Proportional to Calcium levels
31
Does phosphorylation or dephosphorylation of myosin light chain produce contraction?
Phosphorylation -allows myosin and actin binding
32
What 2 things do you need for relaxation to occur in Sm. M.?
1. Calcium pumps removes calcium 2. Myosin light chain phosphotase - removes P group on myosin light chain (inactivates it) = relaxation
33
What 4 things can activate Sm. M.?
1. Nerve stimulation 2. Hormones 3. Stretch 4. Environmental ques
34
What are the NTR release sites in sm. M.?
Varicosities
35
What are the hormones released by nerves to stimulate Sm. M. ?
ACh Ne/E (To alpha-1 = constriction; beta-2 = relaxation) Angiotensin II, vasopressin, endothelin = contraction Adenosine = relaxation NO = relaxation
36
What are the hormones used to stimulate Sm. m.?
Cholecystokinin Oxytocin Serotonin Histamine
37
How do hormones “stimulate” sm. M.?
Actions thru their own receptors influence Ca channels
38
What are environmental ques that stimulate sm. M.? What do they each cause?
1. Hypoxia - dilation 2. Excess CO2 - dilation 3. Increased H+ = dilation 4. Adenosine, LA, increased K etc.
39
What is ATP’s role in the contraction of Sm. M>
latch mechanism
40
What is the latch mechanism?
Allows for binding w/ slow to fatigue - slow myosin ATPase
41
What does the latch mechanism allow for?
‣ Way to increasing tension while decreasing ATP usage
42
How does the latch mechanism work?
‣ Dephosphorylation of light chain ‣ Cycle proceeds slowly ‣ Attached cross bridges are still generating tension (20-30%) Due to slow myosin ATPase
43
In which SM. m. Type do APs occur?
Only occur in Unitary smooth muscle
44
What are the 2 forms of APs in sm. Ms.?
1. Plateaus | 2. Spike potentials
45
What are spike potential stimulated by? What do they indicate?
Stimulated by: hormones, NTRs, stretch, spontaneous More spike potential present = greater force
46
What causes the slow wave of APs in sm. Ms.?
Oscillating Ca influx (L-type VGCCs) K+ efflux (ca-activated K channels)
47
What are the plateaus in Sm. M. Contraction stimulated by?
NTRs, stretch

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