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smooth and cardiac muscle Flashcards

1
Q

what is the main function of smooth muscle?

A

mechanical control of organ systems

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2
Q

describe the shape and structure of a smooth muscle fibre

A

spindle shaped

single central nucleus

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3
Q

is smooth muscle voluntary or involuntary?

A

involuntary

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4
Q

is smooth muscle striated or non-striated?

A

non-striated

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5
Q

what is the function of cardiac muscle?

A

intrinsic myogenic activity that’s responsible for heart beat

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6
Q

how are cardiac myocytes organised?

A

in a branched network that runs in different directions

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7
Q

is skeletal muscle voluntary or involuntary?

A

voluntary

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8
Q

what kind of movements is skeletal muscle responsible for?

A

locomotion
maintenance of posture
breathing via contraction of the diaphragm

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9
Q

is skeletal muscle striated or not?

A

striated

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10
Q

how many nuclei are found in skeletal muscle cells and how are they arranged?

A

multiple

peripherally-located

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11
Q

what cellular junctions are found in cardiac muscle?

A

intercalated discs

gap junctions

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12
Q

what cellular junctions are found in smooth muscle?

A

gap junctions

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13
Q

what calcium binding mechanisms do skeletal, smooth and cardiac muscle have?

A

skeletal - troponin
cardiac - troponin
smooth - calmodulin

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14
Q

what are A bands in cardiac muscle fibres?

A

thick bands

dark bands

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15
Q

what are I bands in cardiac muscle fibres?

A

thin bands

light bands

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16
Q

what is the sarcolemma?

A

the plasma membrane of the muscle

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17
Q

what are intercalated discs?

A

sites of thickening of the sarcolemma

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18
Q

what are intercalated discs made up of and what are their functions?

A

gap junctions - allow ions to pass from cell to cell so the AP can move between cells in a coordinated fashion

desmosomes - anchor ends of the cells together

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19
Q

define automaticity

A

the ability to spontaneously depolarise

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20
Q

define rhythmicity

A

the ability to depolarise in a regular and repetitive way

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21
Q

what is an electrical syncytium?

A

where myocardium functions as a single contractile unit

22
Q

which ions form repolarising currents?

A

K+

23
Q

which ions form depolarising currents?

A

Na+ and Ca2+

24
Q

which type of cardiac cells show automaticity?

A

pacemaker cells

atrial and ventricular cells in disease

25
Q

what is the refractory period?

A

the period of time during which the ion channels are inactivated and the muscle is unresponsive

26
Q

what is the advantage of long refractory periods in ventricular cells?

A

individual contractions don’t fuse together like in skeletal muscle

27
Q

explain the process of calcium signalling in cardiac muscle contraction

A

membrane depolarises
sodium influx
causes calcium to enter through LTCC
triggers calcium release from SR via ryanodine receptor
calcium associates with troponin C to initiate contraction
contraction ends when calcium dissociates from troponin c and goes back to SR

28
Q

how does the sympathetic NS affect cardiac muscle?

A

increases HR and force of contraction

29
Q

what receptors does noradrenaline act on in cardiac muscle?

A

beta1 adrenoreceptors

30
Q

what receptors does acetylcholine act on?

A

M2 muscarinic receptors

31
Q

describe the structure of smooth muscle

A

loose lattice of thick and thin filaments held together by dense bodies

32
Q

what do intermediate filaments do in smooth muscle?

A

help in the transmission of force generated by contraction

33
Q

what are the 2 types of attachment in smooth muscle?

A

mechanical attachment between cells

gap junction - pathway for electrical signals between cells

34
Q

gives examples of where smooth muscle is found in the body

A 
bladder
gut
uterus
blood vessels
bronchi
urethra, bladder
erector pili in the skin
35
Q

what are the functions of smooth muscle?

A

Regulation of the diameter of blood vessels

Regulating diameter of airways

Propulsion of food through GI tract

Contraction of the uterus delivery of baby

36
Q

what are the types of action potential that can be seen in smooth muscle action potentials?

A

simple repetitive spiking of action potential
spike followed by plateau (seen in ventricular APs)
spikes on top of slow waves (pacemaker cells)

37
Q

why are smooth muscle APs longer than skeletal muscle Abs?

A

Ca2+ channels open more slowly than Na+ channels

38
Q

what are varicosities?

A

structures which release neurotransmitters into the space surrounding muscles

39
Q

what are the types of smooth muscle organisation?

A

multi-unit smooth muscle

single-unit smooth muscle

40
Q

describe the innervation of cells in multiunit smooth muscle

A

each cell receives their own synaptic input
little electrical coupling
can contract independently of their neighbour

41
Q

give examples of where multiunit smooth muscle is found

A

iris of the eye

larger blood vessels

42
Q

describe the innervation of cells in single unit smooth muscle

A

ANS innervates one cell within a sheet/bundle
gap junctions propagate APs to neighbouring cells
whole sheet contracts as a single functional syncytium

43
Q

give examples of where single unit smooth muscle is found

A

walls of all visceral organs apart from the heart

44
Q

what kind of contractions are produced by visceral smooth muscles

A

slow and steady contractions to allow movement of substances through the body

45
Q

what are the two ways in which calcium can enter smooth muscle cells

A

depolarisation of the membrane opens VG calcium channels

agonist induced release of calcium via IP3

46
Q

explain the process of agonist induced release of calcium in smooth muscle

A 
agonist binds to receptor
G protein complex activated
binds to phospholipase C (PLC)
PLC generates IP3
IP3 triggers calcium release from SR
47
Q

explain the process of excitation-contraction coupling in smooth muscle

A

calcium is released
binds to calmodulin
activates enzyme myosin light-chain kinase (MLCK)
MLCK phosphorylates regulatory region on myosin light chains
increases ATPase activity
myosin head groups bind actin and undergo cross-bridge cycling
leads to contraction

48
Q

how do thick and thin filaments work in smooth muscle cells to cause contraction?

A

thin filaments slide past thick filaments to pull on dense bodies
dense bodies pull on intermediate fibres
muscle fibres contract
ends are pulled to the centre, causing mid-section to bulge

49
Q

what triggers smooth muscle contraction?

A

hormones
neural stimulation by the ans
local factors
stretching the muscle (walls of visceral organs)

50
Q

what type of smooth muscle is found in blood vessels and where is it found?

A

vascular smooth muscle

under the endothelium

51
Q

what type of blood vessels have vascular smooth muscle mainly?

A

arteries

52
Q

how is smooth muscle found in airways?

A

in bands surrounding the airway

c (25 decks)

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