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Human Physiology and Pharmacology > Week 15: Physiology of Smooth muscle > Flashcards

Week 15: Physiology of Smooth muscle Flashcards

1
Q

what muscle types are voluntary?

A

skeletal

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2
Q

What muscle types are striated?

A

skeletal and cardiac

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3
Q

What muscles types are part of the autonomic innervatio?

A

smooth and cardiac

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4
Q

What are striations due to?

A

organisation of a contractile proteins in individual muscle fibres
actin and myosin proteins= orderly

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5
Q

What are the key features of skeletal muscle?

A

Individual muscle fibres are large, elongated, cylindrical and possess multiple nuclei

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6
Q

What are the key features of cardiac muscle?

A

Individual muscle fibres are large, cylindrical and possess multiple nuclei

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7
Q

What are the key features of smooth muscle?

A

Individual muscle fibres are relatively small, spindle shaped, and possess one nucleus

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8
Q

What neurones are involved in skeletal muscle?

A

alpha and gamma neurone

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9
Q

What fibres are involved in cardiac and smooth muscle?

A

sympathetic and parasympathetic postganglioic fibres

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10
Q

Where is smooth muscle mostly found?

A

walls of hollow organs and tubes

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11
Q

What does smooth muscle mediate?

A

propulsive movements and exerting pressure

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12
Q

What are the 2 classes of smooth muscle?

A

phasic & tonic

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13
Q

What is phasic smooth muscle?

A

muscle exhibits rhythmic or intermittent activity

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14
Q

What is tonic smooth muscle?

A

muscle that is continuously active

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15
Q

What is an example of a phasic smooth muscle that is phasically active?

A

phasically active

stomach intestines underlies peristalsis

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16
Q

What is an example of a tonic smooth muscle usually in contracted state?

A

normally contracted
sphincter
prevent faeses from rectum to anal canal

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17
Q

What is an example of a phasic muscle normally in the relaxed state?

A

normally relaxed

oesophagus, urinary bladder

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18
Q

What is an example of tonic smooth muscle?

A

normally partially contracted

blood vessels, airways

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19
Q

What can smooth muscles also be classified as?

A
  • Single unit (connected by gap junctions)

- Multiunit ( muscle cells are not electrically coupled, activity in one cell does. not results in activity in another)

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20
Q

What does the single unit smooth muscle stimulate?

A

wave contraction across a muscle sheet

only stimulated by one type of neurone

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21
Q

What does the multiunit smooth muscle stimulate?

A

individual muscle fibres

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22
Q

What allows finer control of smooth muscle, multiunit or single unit?

A

multiunit

stimulated by parasympathetic and sympathetic post ganglionic neurones

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23
Q

What are the muscles which a single unit smooth muscle will stimulate?

A

stomach, intestines, urinary bladder, airway smooth muscle

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24
Q

What are the muscles which a multiunit smooth muscle will stimulate?

A

iris, vas deferens

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25
Q

What type of filament does smooth muscle contain?

A

myosin, actin & intermediate

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26
Q

What proteins form most of the intermediate filament in smooth muscle?

A

desmin and vimentin

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27
Q

What does the actin of smooth muscle lack?

A

contains tropomyosin but lacking troponin

Where does Ca2+ bind

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28
Q

What structure is important in maintaining the shape of the cell?

A

intermediate filaments

29
Q

What direction do actin filaments run?

A

parallel to the long axis of the cell

30
Q

Why is the smooth muscle unorderly and unstriated?

A

filaments do not form myofibrils

no sarcomere patternNo Z line

31
Q

With no Z line in. smooth muscle, where do actin filaments bind to?

A

attach to dense bodies in the cytoplasm and dense bands at the inner surface of the plasmalemma

32
Q

What contains more actin skeletal or smooth?

A

smooth

33
Q

How does contraction occur in smooth musc;e?

A

very similar to skeletal (cross bridge + Ca2+ dependent)

Apart from the contraction is over dense band to dense body to the other dense band

34
Q

What does Ca2+ bind to?

A

calmodulin in the cytoplasm

35
Q

What is the change in Ca2+ conc. from a maximal contraction to occur?

A

100nM to 1 microM

up 10 fold

36
Q

what does Ca2+-calmodulin activate?

A

MLCK enzyme

37
Q

What does active MLK permit?

A

the transfer of organic phosphate to the myosin head

38
Q

What is required for actin to myosin binding?

A

ATP

39
Q

Why is additional ATP required in contraction?

A

ATP is required for cross bridge cycling to continue via hydrolysis

40
Q

What is calmodulin? Where is it found in a cell?

A

multifunctional Ca2+ binding protein

present in the cytoplasm of all eukaryotic cells

41
Q

What happens when 2 or more Ca2+ molecules bind to calmodulin?

A

undergoes a large confo change

the strand under the 2 lobes to become an alpha helix

42
Q

Where does Ca2+ bind to on calmodulin?

A

2 Ca2+ binds to EF hand motifs
4Ca2+ per calmodulin
called CaM

43
Q

What can CaM bind to?

A

vast range of kinase peptides

e.g. CaM kinase

44
Q

What does CaM activate?

A

MLCK

45
Q

Is calcium calmodulin an enzyme?

A

NO

46
Q

What is activated in smooth muscle contraction?

A

myosin

47
Q

What can smooth muscle contraction be called?

A

myosin based contraction

48
Q

How does contraction occur in smooth muscle?

A

phosphorylation of the regulatory myosin light chain (MLC) in the presence of elevated intracellular Ca2+ (and ATP)

49
Q

How does relaxation occur of smooth muscle?

A

dephosphorylation of MLC by myosin phosphatase which has constitutive activity, but is also regulated

50
Q

What chain in phosphorylated in myosin?

A

light chain

51
Q

What is the differnece between MLCK and MP?

A

MLCK phosphorylates MLC

MP de-phosphorylates MLC

52
Q

What autonomic innervation do arteries primarily receive?

A

sympathetic (NA) adrenoR

53
Q

What autonomic innervation do other tissue receive?

A

symp and para innervation(ACh, muscarinic)

54
Q

What autonomic innervation occurs in the G.I tract?

A

enteric/ANS

55
Q

What tissue have no autonomic innervation?

A

uterus

56
Q

Where does chemical transmission between autonomic neurones and smooth muscle take place? The junction between postganglionic fibre

A

neuroeffector junctions

57
Q

What are varicosities?

A

where the transmitter is released from. many of them along nerve fibre

58
Q

What factors can increase/decrease smooth muscle activity?

A
  • Hormones
  • Autonomic neurotransmitter
  • Pacemaker activity of smooth muscle itself
  • Many therapeutically important drugs
59
Q

What can increase [Ca2+]?

A
  • Ca2+ influx from the extracellular fluid by cell-surface voltage-activated Ca2+ channels opened by membrane depolarisation
  • Release of Ca2+ from intracellular stores, typically as a result of the activation of cell surface G protein-coupled receptors (GPCRs)
60
Q

What is pharmacomechanical coupling?

A

-Processes by which an agent causes a change in smooth muscle tone without a change in membrane potential

61
Q

What does a secondary messenger do in pharmacomechanical coupling?

A

-That either contract, or relax, the muscle

62
Q

What are the important secondary messengers in pharmacomechanical coupling?

A
  • Inositol trisphosphate (IP3) causing contraction

- (cGMP) and cyclic adenosine monophosphate (cAMP), both causing relaxation

63
Q

What processes can E-C coupling be described as?

A 
Pharmacomechanical coupling
Electromechanical coupling
(in reality the 2 overlap to some extent)
64
Q

What us electromechanical coupling?

A

opening of plasma membrane voltage-activated L-type Ca2+ channels in response to depolarization with, or without, action potential generation

65
Q

In pharmacomechanical coupling in smooth muscle how is Ca2+ released into the SR?

A

IP3 – generated by activation of PLC opens IP3 receptors in the SR membrane releasing Ca2+

66
Q

In electromechanical coupling what does the released Ca2+ bind to?

A

-Opening of Ca2+-activated chloride channels (CaCC)
-Ca2+ in to cell causing depolarisation
OR// binds to CaM= contraction

67
Q

What does DAG bind to and activate/ inhibit?

A

Inhibit K+ channel directly or activate PKC to then inhibit the channel (keep positive charge in)
-Na/Ca channel, Ca2+ in to cell

68
Q

What does the depolarisation in electromechanical coupling lead to?

A

Opens voltage-activated L-type Ca2+ channels, further increasing [Ca2+]i and contraction (4)

69
Q

What 2 mechanisms decreases Ca2+ levels and cause relaxation?

A

pumped back into SR via a Ca2+ ATPase (SERCA)

Pumped out of cell via Na/Ca exchanger or Ca2+ ATPase

Human Physiology and Pharmacology (31 decks)

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