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CVS Physiology > Electrical Activity Of The Heart > Flashcards

Electrical Activity Of The Heart Flashcards

1
Q

Mention the tertiary pacemaker of heart & its rhythm

A

Bundle of His & Purkinje fibers

20 bpm, idioventricular rhythm

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2
Q

Mention the rate of discharge of AVN & role of its autorhythmicity

A 
40-60 bpm
Secondary pacemaker (it is an alternative pacemaker in case of SAN destruction)
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3
Q

Mention effect of temperature on SAN firing rate

A

Decreases by cooling

Increases by heating

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4
Q

Mention the effect of drugs on SAN firing rate

A

Parasymoatholytics & sympathomimetics, inc heart rate & vice versa

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5
Q

Mention effect of autonomic nervous system on cardiac autorhythmicity

A

Sympathetic, acts by norepinepherine on B1 receptors,
1. Increase inward Na+ current
2. Increase cAMP which facilitates opening if L-Ca++ channels
3. Inactivates K+ channels
Parasympathetic, acts by acetylcholine of M2 receptos
Opposite effect to 1,2 & 3

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6
Q

GR: Normal heart rate is the less than firing rate of SAN

A

Due to inhibitory vagal tone

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7
Q

Define autorhythmicity

A

It is the ability of the heart to initiate its own regular repetitive bears independant of any external stimuli.

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8
Q

When do muscle fibers of heart regain auto-rhythmicity?

A

This is an imdication that such contractile cells are severely damaged.

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9
Q

GR: SAN is the natural pacemaker of the heart

A

Becuase its slow response action potential has:

  • RMP with the highest slope
  • RMP is nearer to threshold
  • Phase 0 of low amplitude
  • Repolarization is rapid
  • High repetitive rhythm of discharge
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10
Q

Define conductivity

A

The conduction of a cardiac impulse through the cardiac tissue.

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11
Q

What is the importance of slow conductivity of SAN

A

It prevents any ectopic focus from depolarizing it.

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12
Q

The zone of maximal delay is …., while zone of slowest conduction velocity is ….. .

A

A-N zone

N zone

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13
Q

N-H zone has …., it is not affected by ….

A

Typical slow response

TTX

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14
Q

Describe characteristic function of AVN

A
  1. A-V nodal delay
  2. A-V nodal block, refractoriness is both voltage and time dependant, it doesn’t allow except 180-200 bmp to pass from atria to ventricles
  3. Decrease chance of retrograde conduction, to protect SAN from ventricular ectopic focus
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15
Q

GR, Conduction though left wall is slower than Rt

A

Due to thickness of wall

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16
Q

The first part to be excited is …., while last part to be excited is …..

A

Left ventricular septum

Epicardial surface at the base of left ventricle

17
Q

Characteristics of slow and fast response action potentials and their site

A

S, unstable RMP, slow AP
SAN and AVN
F, stable RMP and fast AP
His bundle, bundle branches amd Purkinje fibers

18
Q

Mention value of RMP in fast respinse and reason.

A

-90 mV, stable

Due to outward K+ current which is equal to and compensating inward Na+ current

19
Q

Ustroke in fast response reaches …., due to ….. , though …. channels which all open at …. .

A

+30 mV, rapid Na+ entry acconding to electric and concentration gradients at depolarozation but conc grad alone in overshoot
Voltage gated Na+
-70 to -65 mV

20
Q

….. gate opens during depolarization.

A

Activation m gate

21
Q

H gate start to reopen at ….

A

Middle of repolarization (-50 mV)

22
Q

Early phase of repolarization in fast response is due to:

A
  1. Fall in membrane permeability to sodium

2. Opening of voltage gater K channels

23
Q

GR: Presence of plateau in fast response potential, mention its voltage

A

Due to Ca++ influx 2ry to opening od slow L-type Ca channels. Ca++ influx balances the increasing K+ efflux.
At 0 mV

24
Q

The unstable RMP is also called ….., its value is ….., theshold for firing is …… .

A

Pacemaker potential, prepotential diastolic depolarization

-50 mV to -60 mV

25
Q

GR, the RMP of nodal tissue is unstable

A

Due to imbalance between more Na and Ca inward currents, and weark inward K current.

26
Q

In prepotential, first inward current is by …. through …. . This starts during ….. .

A

Na+
Funny channels
Late part of repolarization phase of AP

27
Q

The second current of preoptential occurs through …. channels

A

Transient type Ca++

28
Q

During prepotential, there ia progressive ….. in outward K+ current

A

Decline

29
Q

Phase 0 of slow response AP is from …. to ….

A

-60 mV to (+1)-(+10) mV

30
Q

Deploarization in slow response is by …. channels

A

Slow L-type Ca++

31
Q

Repolarization in fast response is …., while in slow response is ….
Both are due to …..

A

Triphasic
Monophasic
K+ efflux

32
Q

Compare extension of absolute refractory period in fast and slow response AP

A

F, from phase 0 to middle of phase 3

S, from phase 0 to most of phase 3

33
Q

What is the significance of long ARP in fast response AP

A

The cardiac muscle cannot be re-stimulated during systole, tgis prevents tetanization of cardiac muscle which is fatal.

34
Q

Whta does RRR represent?

A

A state of partial recovery of fast Na channels due to opening of some not all of the h gates.

35
Q

Compare extension of RRR in slow and fast response AP

A

F, just after ARP till end of repolarization
S, from late phase 3 and extends particularly in AV node will beyond phase 3 even after complete repolarization (post-repolarization refractoriness)

36
Q

Drefin3 effective refractory period

A

A propagated AP cannot be elicited but a localized AP can be generated by strong stimulus.
ARP + first 10 mV of RRP

37
Q

Mention significance of ERP

A
  1. Prolongs the absolute refratoriness of the heart for another impulse originating from within the heart.
  2. It allows cardioversion in case of ventricular fibrillation by external defibrillating electric pulse.
    It induces localized AP in each cell which represents a real unified ARP for all cells thus give the SAN the chance to be the pacemaker again.

CVS Physiology (15 decks)

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