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cardiac biology > cardiac AP 1: ventricular muscle > Flashcards

cardiac AP 1: ventricular muscle Flashcards

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1
Q

what is cardiac muscle contraction triggered by

A

action potential at the membrane plasma (sarcolemma)

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2
Q

where does electrical excitation originate from

A

SAN and spreads throigh atria and ventricles

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3
Q

what separates electrical charge

A

plasma membrane of cells

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4
Q

what sets up a membrane potential

A

an uneven distribution of ions

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5
Q

what determines the uneven distribution of ion

A

fx of ions pumps

ion exchangers

ion channels

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6
Q

what are the main ions in the modulation of membrane potential

A

calcium

potassium

sodium

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7
Q

at rest what channels are closed

A

sodium

calcium

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8
Q

how does potassium leak out durin rest

A

through inward rectifier k+ channels

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9
Q

what does the inward rectifier k+ channels generate

A

it generates -90mV current

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10
Q

how long is an AP duration

A

~250-300msec

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11
Q

what occurs during upstroke of graph

A

sodium influx

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12
Q

what happens during plateau

A

calcium influx

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13
Q

what occurs doing repolarisation

A

potassium efflux

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14
Q

what is refractory period

A

electrically inexcitable period

  • no summation of contractions
  • no tetanic contractions
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15
Q

what occurs during refractory period

A

permits filling of the ventricles between contractions

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16
Q

ventricular AP has how many phases

A

5 phases

0-4

17
Q

what happens at phase 0 (4)

A

action potential reaches adjacent myocyte

depolarisation begins

fast sodium channels open beyond their threshold of -65mV but inactivates rapidly

*channels are voltage dependent & tome dependent

sodium drive the mb potential in a positive direction, generates overshoot

18
Q

when fast sodium channels are in inactivated confoguration, what occurs

A

refractory period

*AP cannot be triggered in inactive state

19
Q

what occurs during phase 1

A

brief period of repolarisation caused by transient outward current

20
Q

how are currrnt in phase 1 carried

A

thru voltage gated potassium chanels

they are activated by depolarisation and inactivate quickly

21
Q

what occurs during phase 2

A

a plateau period with inward current thru voltage gated calcium channels called L type calcium channels

L= long opening

inward current counterbalanced the small K+ efflux that occurs throughout the AP

22
Q

what occurs during phase 3

A

plateau period progresses K+ efflux increases due to opening of voltage dependent K+ chanels

known as delayed rectifier or slow K+ channels (Kv or Ks)

when repolarisation occurs Kir reopen to complete repolarisation and Kv (or Ks) are closed when resting Vm is reached

23
Q

what occurs in phase 4

A

75-90% of rasied calcium in the cytosol is pumped to SR via calcium ATPase

remainder is extruded from the cel mainly by 3Na+/Ca2+ exchangers with a small contribution from sarcolemmal Ca2+ ATPase

inward background current reduces Vm

24
Q

what does removal of ca2+ from ECF do

A

prevent contraction

25
Q

why removal of ca2+ prevent contraction

A

because no calcium entry to trigger calcium-induced calcium release from the sarcoplasmic reticulum

no long plateau phase in AP

26
Q

adrenergic stimulation of cardiac myocytes leads to increase in i(Ca). what does this do

A

increases contractility

27
Q

L type calcium are blocked by antagonist such as

A

verapamil

diltiazem

28
Q

what do L type ca2+ antagonist do

A

reduce plateau duration and cardiac contractility

29
Q

restong membrane potential is established by

A

k+ efflux

small background of na+ influx

30
Q

what determines the form of AP

A

magnitude

direction

time

of na+ ca2+ and k+

31
Q

what does prolonged AP provide

A

extended refractory period

32
Q

what does extended refractory period do

A

avoids tetanic contraction

33
Q

AP is influenced bu

A

autonomic nerves

34
Q

what does shorter duration of AP do

A

allows more AP to occur per minute

35
Q

brief current of repolarisation in phase 1 has contribution from

A

Cl- influx thru Cl- channels

cardiac biology (6 decks)

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