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Semester 2 Year 1 > Smooth Muscle Contraction > Flashcards

Smooth Muscle Contraction Flashcards

1
Q

Types if smooth muscle:

A

Unitary

Multiunit

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2
Q

Unitary smooth muscle:

A

Sheets of cells which act in unison - syncytium

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3
Q

Where is unitary smooth muscle usually found?

A

Gut

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4
Q

Multiunit smooth muscle:

A

Bundle of cells

Electrical isolation of cells

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5
Q

Where is multiunit smooth muscle found?

A

Finer tissues - vas deferens

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6
Q

How are unitary and multiunit smooth muscle different?

A

Unitary have gap junctions

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7
Q

What’s obviously different between smooth muscle structure and skeletal muscle?

A

No visible striations - filaments not aligned by Z discs

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8
Q

How are actin and myosin filaments arranged on smooth muscle?

A

Diagonally

Attached at dense bodies (a-actinin-rich) throughout sarcoplasm

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9
Q

What other types of filaments does smooth muscle have?

A

Contractile arrays - fixed by intermediate filaments (vimentin and desmin)

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10
Q

How are contractile arrays anchored?

A

By dense plaques to sarcolemma

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11
Q

How are smooth muscle cells connected to eachother?

A

By focal adhesions (adherens junctions)

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12
Q

Thick myosin filaments in smooth muscle compared to skeletal:

A

Same tertiary structure

Different amino acid sequence

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13
Q

What chains do myosin filaments contain?

A

2 myosin heavy chains and 2 myosin light chains

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14
Q

How are thin actin filaments in smooth muscle different to skeletal?

A

Slightly different structure - have two smooth muscle actin isoforms

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15
Q

The two isoforms of smooth muscle actin:

A

Alpha and gamma

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16
Q

What do smooth muscle thin filaments contain?

A

Tropomyosin

NO troponin

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17
Q

What do thin filaments have instead of troponin?

A

2 regulatory proteins - caldesmon and calponin

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18
Q

How are actin sites exposed?

A

Calcium-calmodulin complex

OR

Phosphorylation of regulatory proteins by calcium-calmodulin dependent protein kinase

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19
Q

Difference in sarcolemma of smooth muscle to skeletal:

A

No T-tubules

Have Caveolae

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20
Q

Difference in SR with smooth muscle and skeletal:

A

Not as extensive

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21
Q

What form must myosin be in to bind to actin?

A

Phosphorylated form - allows cross-bridge cycling

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22
Q

How is myosin phosphorylated?

A

Myosin light chain kinase (MLCK)

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23
Q

What must happen to myosin to allow relaxation?

A

Dephosphorylated - no longer able to bind

24
Q

How is myosin dephosphorylated?

A

Myosin light chain phosphatase (MLCP)

25
What initiated smooth muscle contraction?
Calcium from ECF and SR
26
What happens when calcium enters cytoplasm?
Binds to calmodulin to form calcium-cadmodulin-MLCK complex
27
What happens to the calcium complex?
Results in phosphorylation of myosin-light chain Requires ATP
28
What then happens to phosphorylated myosin?
Binds to actin Power stroke
29
What is required to release myosin head from actin?
ATP
30
What must happen for smooth muscle relaxation?
Decrease in calcium concentration
31
How is calcium concentration decreased?
Pumped out of cell OR Pumped into SR
32
What does low calcium concentration cause?
Calmodulin releases calcium
33
Why does low calcium concentration lead to relaxation?
Myosin light-chain phosphatase removes phosphate from MLC Causes detachment of myosin head from actin filament
34
3 mechanisms that increase calcium concentration:
Voltage-gated L-type calcium channels Receptor-operated calcium channels Store operated calcium channels
35
Voltage-gated L-type calcium channels:
Result in calcium-induced calcium release Activates ryanodine receptor on SR
36
Receptor-operated calcium channels:
Results in IP3 receptor activation on SR Releases calcium
37
Store operated calcium channels:
Maintains calcium concentration in SR
38
What must happen for smooth muscle to maintain high force for long periods?
Formation of latchbridges Slow cycling rate - minimal ATP use
39
What is a latch bridge?
Dephosphorylated myosin still attached to actin
40
When can latchbridges only occur?
High intracellular calcium concentration
41
What removes calcium?
Calcium ATPase pump (SERCA) Socdium-calcium exchangers
42
What refills SR stores of calcium?
Store-operated calcium channels
43
What senses low calcium concentration in SR?
Stim1 - signals to Orai Opens store operated calcium channels —-> influx of calcium
44
WhatWhat regulates smooth muscle contraction?
Spontaneous electrical activity Stretch Neurotransmitters Hormones Locally induced changes in chemical composition in ECF
45
How can smooth muscle cells generate action potentials?
By generation of pacemaker potential
46
What happens if membrane potential drifts up and down in smooth muscle cells?
Slow waves of activity - result in action potential if excitatory stimulus applied
47
Where are pacemaker cells found?
GI tract
48
Why do smooth muscle cells have varicosities?
No motor end-plate region
49
What do varicosities contain?
Neurotransmitters in vesicles
50
Position of varicosities:
From single axon - located along several muscle cells
51
What do varicosities originate from?
Postganglionic fibers of sympathetic and parasympathetic neurons
52
Neurotransmitters and contractile activity:
Can both stimulate or decrease activity
53
Why may neurotransmitter produce opposing effects in contractile activity?
Different interactions with G-proteins
54
What can local factors include?
Paracrine signals Acidity Oxygen and carbon dioxide levels
55
What can local factors cause?
Alteration of smooth muscle tension Induce relaxation

Semester 2 Year 1 (12 decks)

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