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MED 310 > muscle 2 > Flashcards

muscle 2 Flashcards

1
Q

how does smooth muscle differ from cardiac and skeletal muscle

A

-lacks striated pattern
-contains sense bodies throughout cytoplasm and plasma membrane. analogous to Z lines in skeletal muscle
-dense bodies, actin, myosin network connects to cytoskeletal network of non- contracting intermediate dilaments- house frame- that connects to plasma membrane
-contracts via sliding filament mechanism like cardiac and skeletal muscle

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2
Q

what innervates smooth muscle

A

sympathetic and parasympathetic nerves

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3
Q

autonomic nerves and smooth muscle

A

acon divides into multiple acons to form fish net like plexus that surrounds SM

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4
Q

what do the axons of the plexus form

A

structures called varicosities which are the sites of transmitter release

multiple varicosities along each axon. one AP stimulates many varicosities like a sprinkler system

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5
Q

varicosities and junctions

A

dont form distinct motor junctions like. smooth muscle cell can recieve transmitters from multiple varicosities including varicosities from sympathetic and parasympathetic nerves

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6
Q

what causes contraction

A

elevation in Ca

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7
Q

what augments contraction

A

enhancement of actin/ myosin cross bridging

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8
Q

SM and relaxing mechanisms

A

has unique mechanisms that inhibit cross bridging

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9
Q

the type of response (contraction vs relaxation) within a smooth muscle depends on

A

-type and predominance of ANS innervation. symp vs. parasymp
-predominance and subtype of receptor which is being stimulated by acetylcholine or noradrenaline
Ability of transmitter to access a given receptor

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10
Q

a1

A

contract SM
predominantly via pharmacomechanical contraction through SR ca release and PKC activation

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11
Q

b2

A

relax SM via pharmacomechanical relaxation by increasing intracellular CAMP

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12
Q

M2 +M3

A

increase pacemaker cell activity in the gut, enhancing gut contraction and peristaltic movement via electromechanical coupling

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13
Q

M3

A

contract SM via pharmacomechanical contraction through SR Ca release and PKC activation like a1 receptors

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14
Q

what activates muscranic receptors

A

acetylcholine released by parasympathetic nerves

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15
Q

what receptors most often contract SM

A

muscranic receptors

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16
Q

what do muscranic receptors do in the blood cessels

A

act on endothelium to produce SM relaxation

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17
Q

what do M3 receptors do in the endothelium of blood vessels

A

either release NO and or produce the transmission of hyperpolarization to the SM via gap junctions between the endothelium and SM . both mechanisms relax SM

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18
Q

pharmacomechanical coupling

A

contraction or relaxation not mediated by a change in SM cell membrane potential
produced via a biochemical event within SM cell with no movement of ions across membrane
cell membrane potential does not alter during contraction or relaxation

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19
Q

electromechanical coupling

A

contraction or relaxation mediated by a change in SM membrane potential. produced by opening of Ca channel (L type Ca channel) in response to depolarization- contraction- or closing of the same channel in response to hyperpolarization- relaxation-

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20
Q

skeletal and cardiac muscle contraction

A

soley mediated via electromechanical coupling- AP formation

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21
Q

pheamomechanical contraction is produced through

A

intracellular release of Ca from sarcoplasmic reticiulum via IP3 receptors and/or activation of protein kinase C which enhances myosin actin cross bridging. in many cases this mechanism combines with electromechanical contraction

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22
Q

every smooth muscle can contract using this mechanism

A

intracellular release of Ca from sarcoplasmic reticiulum via IP3 receptors and/or activation of protein kinase C which enhances myosin actin cross bridging. in many cases this mechanism combines with electromechanical contraction

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23
Q

pharmacomechanical relaxation

A

virtually always produced by an intracellular elevation in CAMP of CGMP which respectively activates CAMP OR CGMP dependant protein kinases that inhibit myosin/actin cross bridging

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24
Q

what is electromechanical contraction mediated by

A

SM membrane depolarization

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25
Q

what is electromechanical relazation mediated by

A

SM membrane hyperpolarization

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26
Q

what does SM membrane depolarization lead to

A

opens voltage gated ca channels in all SM in in some it initiates Ca ac tion potentials via the same gated ca channel. this promotes contraction

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27
Q

what does SM hyperpolarization lead to

A

the closing of ca channels and inhibition of ca APs and this leads to relxation

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28
Q

how do SM cells increase intracellular Ca

A
  1. generation AP which are produced by ca not na influx in SM
  2. depolarization but no AP

both mediated by L type ca channel

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29
Q

what causes electromechanical coupling and pharmacomechanical coupling to occur together

A

sympathetic or parasympathetic nerve stimulation via ATP co release with noradrenaline or acetylcholine

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30
Q

what produces excitatory junction potentials

A

sympathetic or parasympathetic nerve stimultaion in some SM tissue

31
Q

what can ejps do if they are large enough

A

eleicit ca APs

32
Q

what produces ejps

A

the co release of ATP from the nerves

33
Q

multiunit SM cells

A

not electrically connected with gap junctions

depo or hyperpolarization can no spread from cell to cell via gap junction

system similar to skeletal muscle- individual contraction

34
Q

unitary SM cells

A

are electrically connected with gap junctions

cell depolarization can spread via gap junction bw cells

system similar to cardiac muscle

35
Q

what must unitary cells exhibit

A

electromechanical coupling bc they have to be able to depolarize and hyperpolarize

36
Q

what do parasyptathetic nerves and acetylcholine increase

A

slow wave frequency, peristalsis and SMC contraction via M3 receptors

37
Q

what do sympathetic nerves and noradrenaline lead to

A

reduction of SW frequency, peristalsis and relax the SMC via B receptors

38
Q

setup of stomach and intestines

A

composed of SMC that are connected with gap junctions that allow transmission of depolarization from cell to cell

39
Q

what is imbedded bw the SMC in the stomach and intestines

A

non SMC pacemaker cells that produce slow waves of depolarization that are transmitted to the SMC which intiate ca AP fomratio within the SMC causing coordinated phasic contraction resultnig in peristalsis that moves food through the gut

ELECTROMECHANICALLY COUPLED SYSTEM

40
Q

example of non SMC cells

A

intersitital cells of cajal

41
Q

does SM have toponin

A

no

42
Q

what does ca bind to in SM

A

molecule called calmodulin fomring complex that activates an enxyme MLCK

43
Q

what si MLCK

A

myosin light chain kinase

44
Q

what does MLCK do

A

phosphorylates myosin which activates myosin ATPase activity which initiates myosin cross-bridging with actin to produce contraction

45
Q

sacromere structure in cardiac muscle compared to skeletal muscle

A

organiation of all the parts is similar

46
Q

mechanism of contraction in heart vs skseletal muscle

A

identical

47
Q

what is the difference between heart and skeletal muscle

A
  1. heart is spontaneously active. no direct motor nerve connection to CNS
    contraction initiated and maintained by rhythmically by intrinsic pacemaker cells producing action potentials within SA node
  2. AP transmitted bw cells thru gap junctions within intercalated discs forming tunnels bw cells
48
Q

volume fraction of mitochondria of heart compared to skeletal

A

20x

49
Q

capilary density of cardiac vs skeletal muscle

A

7.5x

50
Q

o2 extraction heart vs skeletal

A

more o2 extraction

51
Q

myoglobin content of heart vs skeletal

A

high in heart

52
Q

phosphorylation method of heart vs skeletal

A

almost exclusively oxidative phosphorylation in heart as opposed to glycolysis

53
Q

heart muscle twitch characteristic resemblence

A

fast twitch but its characteristics are of the slow twitch muscle

54
Q

sequential contraction of atria

A

a- atria and ventricles fill when heart is relaxed

b- atrai contract forcing more blood into centricles

c- after a delay, ventricles contract simultaneously pushing bood into lungs and body

55
Q

what forms a conduction system

A

modified cardiac cells

56
Q

where does the conduction system start and propagate to

A

in the SA node and propagates AP to the atrai then to the venticles initiating contrcation in the cardiac muscle cell within both areas

57
Q

what is the hearts pacemaker

A

the sa node

58
Q

what does the sa node produce

A

spontaneous repetitive unique ca not na driven AP

59
Q

AP process of SA node

A
  1. resting at -60 mv and leaky to na and ca and influx of both slowly depolarizes the cell
  2. at threshold of -40mv ap is produced via a fast influx of ca and platueaus at 0mv
  3. depolarization to 0 triggers a rapid efflu of k which hyperpolarizes the cell back to -60mv

repeat about 70 times per min which is average heart rate in humans

60
Q

what are gap junctions

A

protein tunnesl that connnect cytoplasm of adjacent cells and transmits depolarization

61
Q

where do AP in the SA node spread to

A

spread thru conduction system and depolarize atrial and ventricular cardiac muscle cells causing them to evoke AP and contract

62
Q

what can every cardiac cell do when it is depolarized ot threshold

A

evoke a AP

63
Q

what is a fact about the cell siwthin the conducting system

A

cant contract byt they transmit depolarixationt othe cells in the atria and vetricles which can contract

64
Q

difference bw ca driven AP in sa node and atrial and ventricullar cells

A

atrial and ventricular cells are driven by na influx which leads to depolarization which leads to ca influx thru special voltage gated channels

ca small influx is important bc it triggers large release of ca from the sarcoplasmic reticulum resulting in contraction

65
Q

sequence of depolarization and subsequent contraction in the heart

A
  1. SA node spontaneously fires AP and depolarization spreads through the atria producing APs in the atrial muscle cells
  2. atrial contraction results pushing blood into ventricles
  3. 0.13 delay and then depolarization and AP transmitted down conducting system to the apex of the ventricle
  4. depol and AP sread from apex/ bottom up thru the ventricle cells producing contraction and squeezing blood into lungs and body
66
Q

AP travelling in skeletal muscle

A

travels thru T tubule system and activates DHP receptor which mechanically releases ca from sarcoplasmic reticulum

67
Q

cardiac muscle AP travelling

A

thru plasma membrane and T tubule system and opens voltage gated ca channels and ca enters inducing release of ca from sarcoplasmic reticulum

68
Q

what controls heart rate and strength of ventricular contraction

A

PNS AND SNS

69
Q

SNS and heart rate and strength of ventricular contraction

A

releases noradrenaline and adrenaline from adrenal gland- bind to B1 receptor- depolarizes SA- inc heart rate- enhance ca release- inc force of contraction- more blood from ventricles

70
Q

another name for PNS

A

vagal

71
Q

PNS heart rate and strength of ventricular contraction

A

releases acetylcholine which binds to muscranic M2 receptors- hyperpolarization of SA and conducting system- reduces SA node fiding and slowing heart rate

72
Q

what happens when heart ventircles fill with blood

A

cardiac cells stretch

73
Q

what does stretching of cardiac cells and skeletal muscle produce

A

more optimal orientation of actin and myosin allowing greater contrcatile force to be generated

74
Q

whta does more blood pushed into heart lead to

A

greater contractility of heart cells and larger ejection fraction of blood pumped out of heart named STARLINGS LAW OF THE HEART

MED 310 (47 decks)

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