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Cardiovascular > Conduction and force generation of the heart > Flashcards

Conduction and force generation of the heart Flashcards

1
Q

Define audtorhythmicity?

A
  • heart is capable of beating rhythmatically in the abscence of an external stimuli
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2
Q

Where does normal excitation of the heart occur

A
  • Sinoatrial node (SA)
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3
Q

Define sinus rhythm

A
  • a heart that beats from the electrical impulses from the SA node only
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4
Q

How does the SA node generate an action potential?

A
  • SA node has no stable resting potential
  • generates regular spontanous pacemaker potentials
  • if they met threshold they produce an action potential
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5
Q

Explain the membrane potential graph in SA and AV nodes?

A
  • Pacemaker potential generated by funny current and small eflux of K+
  • CA2+ L-type channels open = depolarisation
    = closure of CA2+ channels and K+ efflux = repolarisation
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6
Q

How does an action potential travel from the SA to AV node?

A
  • cell-to-cell conduction

- through gap junction

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7
Q

Explain the movement of action potentials through the heart

A
  • SA
  • AV
  • Bundle of His
  • Right and left bundle branches
  • purkinje fibres
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8
Q

Why does the AV node have a slower velocity?

A
  • to allow atrial systole before ventricular systole
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9
Q

What is the ONLY point of electrical contact between the atria and ventricles?

A
  • AV node
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10
Q

Explain depolarisation in myocytes

A
  • Na+ channels open = influx
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11
Q

Explain phase 1 in myocytes

A
  • Na+ channels close

- K+ efflux

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12
Q

Explain phase 2 in myocytes

A
  • Ca2+ influx and K+ efflux in balance
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13
Q

Explain phase 3 in myocytes

A
  • closure of Ca2+ channels

- K+ efflux

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14
Q

Explain phase4 in myocytes

A
  • resting potential
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15
Q

What is the sympathetic effect on the heart

A

+ve chronotropic

- increase HR

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16
Q

What is the vagus (parasympathetic) effect on the heart?

A
  • ve chronotropic

- decreases HR

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17
Q

Explain the parasymathetic coupling on the HR

A
  • Ach –> M2 –> Gi –> decreases HR
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18
Q

Explain the sympathetic coupling on the HR

A
  • NA –> B1 –> GS –> Increases HR
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19
Q

What does the sympathetic nerves supply in the heart?

A
  • SA and AV nodes

- myocytes

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20
Q

What is the numerical value for bradycardia

A

<60bpm

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21
Q

What is the intrinsic HR and what reduces it?

A
  • intrtinsic HR = 100bpm

- the vagal tone reduces it to - 70bmp

22
Q

What does cardiac muscle look like?

A
  • stritated
  • branched
  • intercalated disks
  • centrally located nucleus
23
Q

What electrically couples cardiac cells?

A
  • gap junctions
24
Q

What provides mechanical adhesion to ensure tension developed by one cardiac cell is passed onto the next?

A
  • desmosomes
25
Q

What are myofibrils

A
  • contractile units of muscle
26
Q

What is the thick and thin parts of the sacromere?

A
  • thin = actin

- thick = myosin

27
Q

Explain the actin and myosin cycle

A
  • ATP given energises the myosin head to break ATP –> ADP + Pi
  • this allows binding of the myosin head to the actin filament
  • ADP + Pi is released and powerstroke generated
  • ATP given again detaches the head
28
Q

What is required for mysoin binding to actin?

A
  • Ca2+

- Moves the tropomysoin complex out of the way, exposing the myosin binding sites

29
Q

Where is Ca2+ released from that allows muscle contraction and what is it dependant on?

A
  • released from sacroplasmic reticulum

- dependant on extracellular Ca2+ levels

30
Q

Define the refractory period?

A
  • ther period after an action potential which prevents the generation of a new action potential
  • prevents against tetanic contractions
31
Q

Define stroke volume?

A
  • the volume of blood pumped by each ventricle per heart beat
32
Q

Equation for stroke volume?

A

SV = EDV - ESV

33
Q

What determins preload?

A
  • EDV
34
Q

Define preload

A
  • the ventricular wall stress at the end of diastole
35
Q

Define afterload?

A
  • the resistance to which the heart is pumping
36
Q

What does the frank-starling curve illustrate?

A
  • how as end diastolic volume increases, stroke volume increases
37
Q

What happens to the position of the frank-starling curve due to sympathetic stimulation?

A
  • shifted to the left
38
Q

What happens to the position of the frank-starling curve due to parasympatetic stimulation

A
  • shifted to the right
39
Q

What health condition may shift the frank-starling curve to the right?

A
  • heart failure
40
Q

Define inotropic?

A
  • force of the heart

- sympathetic inervation, little parasympathetic

41
Q

Define cardiac output?

A
  • the volume of blood pumped by each ventricle per minute
42
Q

What is the equation for cardiac output?

A

CO = HR X SV

43
Q

What is a normal cardiac output value?

A

5l

44
Q

What is the cardiac cycle defined as?

A
  • all events that occur from the beginning of one heart beat to the beginning of the next
45
Q

What are the 5 stages of the cardiac cycle?

A
  • passive filling
  • atrial contraction
  • isovolumetric ventricular contraction
  • ventricular ejection
  • isovolumetric ventricular relaxation
46
Q

When is the first heart sound heard?

A
  • the closure of the AV valves

- beginng of systole

47
Q

When is the 2nd heart sound heard?

A
  • the closure of the Aortic/pulmonary valves

- end of systole/begining of diastole

48
Q

Explain passive filling

A
  • 80% of ventricular filling is achieved by passive filling
49
Q

When does atrial contraction occur on an ECG?

A
  • Between P wave and the QRS complex
50
Q

When does ventricular contraction occur on an ECG?

A
  • After QRS complex
51
Q

What occurs if ventricular pressure falls below atrial pressure?

A
  • AV valves open

Cardiovascular (26 decks)

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