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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
Q

What initiated smooth muscle contraction?

A

Calcium from ECF and SR

26
Q

What happens when calcium enters cytoplasm?

A

Binds to calmodulin to form calcium-cadmodulin-MLCK complex

27
Q

What happens to the calcium complex?

A

Results in phosphorylation of myosin-light chain

Requires ATP

28
Q

What then happens to phosphorylated myosin?

A

Binds to actin

Power stroke

29
Q

What is required to release myosin head from actin?

A

ATP

30
Q

What must happen for smooth muscle relaxation?

A

Decrease in calcium concentration

31
Q

How is calcium concentration decreased?

A

Pumped out of cell

OR

Pumped into SR

32
Q

What does low calcium concentration cause?

A

Calmodulin releases calcium

33
Q

Why does low calcium concentration lead to relaxation?

A

Myosin light-chain phosphatase removes phosphate from MLC

Causes detachment of myosin head from actin filament

34
Q

3 mechanisms that increase calcium concentration:

A

Voltage-gated L-type calcium channels

Receptor-operated calcium channels

Store operated calcium channels

35
Q

Voltage-gated L-type calcium channels:

A

Result in calcium-induced calcium release

Activates ryanodine receptor on SR

36
Q

Receptor-operated calcium channels:

A

Results in IP3 receptor activation on SR

Releases calcium

37
Q

Store operated calcium channels:

A

Maintains calcium concentration in SR

38
Q

What must happen for smooth muscle to maintain high force for long periods?

A

Formation of latchbridges

Slow cycling rate - minimal ATP use

39
Q

What is a latch bridge?

A

Dephosphorylated myosin still attached to actin

40
Q

When can latchbridges only occur?

A

High intracellular calcium concentration

41
Q

What removes calcium?

A

Calcium ATPase pump (SERCA)

Socdium-calcium exchangers

42
Q

What refills SR stores of calcium?

A

Store-operated calcium channels

43
Q

What senses low calcium concentration in SR?

A

Stim1 - signals to Orai

Opens store operated calcium channels —-> influx of calcium

44
Q

WhatWhat regulates smooth muscle contraction?

A

Spontaneous electrical activity

Stretch

Neurotransmitters

Hormones

Locally induced changes in chemical composition in ECF

45
Q

How can smooth muscle cells generate action potentials?

A

By generation of pacemaker potential

46
Q

What happens if membrane potential drifts up and down in smooth muscle cells?

A

Slow waves of activity - result in action potential if excitatory stimulus applied

47
Q

Where are pacemaker cells found?

A

GI tract

48
Q

Why do smooth muscle cells have varicosities?

A

No motor end-plate region

49
Q

What do varicosities contain?

A

Neurotransmitters in vesicles

50
Q

Position of varicosities:

A

From single axon - located along several muscle cells

51
Q

What do varicosities originate from?

A

Postganglionic fibers of sympathetic and parasympathetic neurons

52
Q

Neurotransmitters and contractile activity:

A

Can both stimulate or decrease activity

53
Q

Why may neurotransmitter produce opposing effects in contractile activity?

A

Different interactions with G-proteins

54
Q

What can local factors include?

A

Paracrine signals

Acidity

Oxygen and carbon dioxide levels

55
Q

What can local factors cause?

A

Alteration of smooth muscle tension

Induce relaxation

Semester 2 Year 1 (12 decks)

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