4. Physiology II - Conducting System Flashcards
what BEGINS the CARDIAC CYCLE (at end of diastole) what causes ATRIA to CONTRACT after passive filling
SINO-ATRIAL NODE FIRES (DEPOLARISES)
spreads wave of depolarisation through right atrium and to left atrium
-> ATRIA CONTRACT
(15% ventricular filling)
what happens as the CONDUCTION / wave of DEPOLARISATION PASSES through the AV NODE
DELAYS it - slows down before reaching Bundle of His, Bundle Branches, Purkinje Fibres
allows time for atria to move blood out through valves before the ventricles contract (so atria and ventricles don’t contract simultaneously)
how are IMPULSES in SYSTOLE (ventricular contraction)
RAPID TRANSMISSION through VENTRICLES
- COORDINATED VENTRICULAR CONTRACTION
(radially, longitudinally and twisting motion)
SPECIFIC ACTIVATION SEQUENCE to OPTIMISE EJECTON of blood
(bundle branch block is dangerous)
in what direction are VENTRICULAR CONTRACTIONS to OPTIMISE ejection of blood
RADIALLY (side to side)
LONGITUDINALLY (from apex to base)
and TWISTING MOTION
what is POLARISATION
a DIFFERENCE in CHARGE between sides of a MEMBRANE
if something is POLARISED what does it mean
INSIDE MORE NEGATIVE
if something is DEPOLARISED what does it mean
INSIDE MORE POSITIVE
what is VOLTAGE
the DIFFERENCE in POSITIVE CHARGES from one side of a membrane to the other
(-80mV in myocytes, resting)
what is a CURRENT
the FLOW of CHARGED PARTICLES ACROSS a MEMBRANE
how are CARDIAC MYOCYTES at REST (resting potential)
POLARISED (inside Negative)
at - 80mV
due to K+ EFFLUX (out of cells)
how do CURRENTS PASS BETWEEN MYOCYTES (excite each other)
via GAP JUNCTIONS
when can MYOCYTES REGAIN EXCITABILITY
ONLY when FULLY REPOLARISED
what is REFRACTORY PERIOD
period of TIME during which a second STIMULUS will FAIL to GENERATE a 2ND ACTION POTENTIAL in a myocyte
- as cannot generate 2nd action potential unless fully repolarised
how do PARTICLES travel into cells (by what gradients)
DOWN ELECTRO-CHEMICAL GRADIENT
- CHEMICAL gradient
- ELECTRICAL gradient for CHARGED particles
What is a REVERSAL POTENTIAL
when ELECTROCHEMICAL GRADIENT is BALANCED
(inward and outward forces are equal / eventually reach equilibrium)
name of the EQUATION that PREDICTS WHERE the REVERSAL POTENTIAL will lie / where the ELECTROCHEMICAL GRADIENT WILL BALANCE
NERNST EQUATION
what CHANNELS should we OPEN if we want to make MEMBRANE REVERSAL POTENTIAL LOWER / MORE NEGATIVE, as they have really negative reversal potential
K+ CHANNELS
(-95mV reversal potential)
what CHANNELS should we OPEN if we want to make MEMBRANE REVERSAL POTENTIAL HIGHER / MORE POSITIVE, as they have high reversal potential
Na+ CHANNELS
(+55mV reversal potential)
types of ION CHANNELS in cardiomyocytes
VOLTAGE GATED
- activation gate opens when membrane potential becomes more positive
- are TIME DEPENDENT
LIGAND GATED
by chemical (ie Ach) or mechanical (stretch)
what channel uses ATP in cardiomyocytes
NA/K PUMP
3 Na+ OUT
2 K+ IN
(restore balance)
(electrogenic, creates current)
what TRANSPORTER is used in cardiomyocytes
NA/CA EXCHANGER
1 Ca2+ OUT (CALCIUM EFFLUX)
exchanged for
3 Na+ IN
- PASSIVE, no ATP
can also work in reverse for Calcium Influx
- electrogenic, creates current
what is the RESTING POTENTIAL and how is this GENERATED
-80 mV
- K+ EFFLUS as K+ CHANNELS OPEN in resting state
stages of an ACTION POTENTIAL GENERATION that make the SPIKE AND DOME MORPHOLOGY
- RAPID Na+ INFLUX as Na+ channels OPEN
(exceeds threshold) - K+ CHANNELS OPEN, K+ EFFLUX
- Ca2+ CHANNELS OPEN, Ca2+ INFLUX (makes plateau as balances K+ efflux)
- Ca2+ CHANNELS CLOSE
- REPOLARISATION (flat)
ACTION POTENTIAL CREATED by the FLOW of which ION(S)
-
CHANNELS used to CREATE ACTION POTENTIALS
- Na+ CHANNEL (Na+ in)
- K+ CHANNEL (K+ out)
- Ca2+ CHANNEL (Ca2+ in)
- NA/K ATPase (Na+ out, K+ in)
- NA/Ca EXCHANGER (Na+ in, Ca2+ out)
