The initiation and regulation of the heart beat L11 Flashcards Preview

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Flashcards in The initiation and regulation of the heart beat L11 Deck (100):
1

How is the rhythmic pulsation of heart maintained?

rhythmic pulsation of the heart is maintained by the excitatory signals generated within the heart itself.(auto-rhythmicity)
hence the heart will continue to beat tyhmically if removed from the heart in appropriste conditions

2

What does the heart need in order for it to be an effective pump?

the contractions of the myocardial cells of the atria and ventricles must be co-ordinated
which is achieved by specialised cardiac conducting tissue

3

What is on the vertical y axis of the cardiac action potential graph?

Membrane potential (mv)

4

Where is Membrane potential (mV) on the cardiac action potential graph?

Vertical y axis

5

What is on the horizontal x axis of the cardiac action potential graph?

Time (s)

6

Where is time (sec) on the cardiac action potential graph?

horizontal x axis

7

What is the duration of a Cardiac action potential?

300ms
with a refractory period which lasts nearly as long-where the 2nd contraction cannot be triggered

8

What membrane potential does the cardiac action potential begin at?

Resting Membrane Potential RMP
-90mV

9

What is the first stage of the cardiac action potential?

Fast initial upstroke
Rapid depolarisation
Due to sodium influx, as the voltage gated FAST sodium channels open, which overall causes contraction

10

What stage in the cardiac action potential is this?: Fast initial upstroke, Rapid depolarisation
Due to sodium influx, as the voltage gated FAST sodium channels open, which overall causes contraction

FIRST STAGE of cardiac AP

11

What is the second stage of the cardiac action potential?

Plateau phase of depolarisation
Maintained depolarisation is due to inward, sustained Ca2+ ion current of movement
This allows the AP to last ALMOST as long as the CONTRACTION of the myocardial cells
Because the muscle is in refractory during and shortly after the passage of the AP, the plateau phase ensures the UNIDIRECTIONAL EXCITATION of the myocardium
caused by the Ca2+ outflow by the SLOW voltage gated Ca2+ CHANNELS and some K+ outflow when some K= channels open (Ca2+ inflow = K+outflow)-to restore negative resting membrane potential

12

What does the second stage of the cardiac action potential ensure?

Plateau phase ensures the UNIDIRECTIONAL EXCITATION of the myocardium ,
-due to plateau phase of slow sustained Ca2+ movement, the refractory period occurring during and shortly after the passage of the AP
caused by the Ca2+ outflow by the SLOW voltage gated Ca2+ CHANNELS and some K+ outflow when some K= channels open (Ca2+ inflow = K+outflow)-to restore negative resting membrane potential

13

What ensures the unidirectional excitation of cardiac muscle/myocardium?

The second plateau phase with the long refractory period occurs during and shortly after the passage of the AP
caused by the Ca2+ outflow by the SLOW voltage gated Ca2+ CHANNELS and some K+ outflow when some K= channels open (Ca2+ inflow = K+outflow)-to restore negative resting membrane potential

14

What is the third stage of the cardiac action potential?

Repolarisation period
Occurs when the voltage gated slow Ca2+ channels INactivate
This inactivation causes the Repolarisation of the myocardial cells
The inactivation/close of the Ca2+ flow channels and opening of the voltage gated K+ channels activation and outflow, occurs increases when ADDITIONAL K+ channels open
Resets it back to negative RMP

15

What resets the cardiac action potential back to negative resting potential?

the opening of the voltage gated K+ channel's acitvation and outflow and additional K+ channels open- reseting membrane potential down to Resting Membrane Potential (RMP) resetting

16

What is maximum HR heart rate for humans?

180-200bpm

17

What does 180-200 bpm represent?

Maximum heart rate for humans

18

What is the maximum stroke volume SV for humans?

150mLbeat-1

19

What does 150 mLbeat-1 represent?

Maximum SV for humans

20

What lies close to the point of entry of the great veins?

SA node
where excitation is initiation, due to its specialised cells

21

What happens at the beginning of excitation in the myocardium?

a WAVE of depolarisation is conducted through the myocardium SWEEPING the heart, and therefore DIFFERENT parts of the heart CONTRACT BEFORE other parts
-the membrane potential between APs shows a PROGRESSIVE depolarisation and therefore progressive contraction of the myocytes

22

What sort of depolarisation occurs in the heart?

Progressive depolarisation and therefore a progressive wave on contraction of the myocytes, some occurring before others depending on when the AP hits it

23

Essentially what is the plateau phase?

Inward movement of Ca2+ calcium ions through SLOW voltage gates calcium channels

24

What does the Ca2+ influx ensure?

Ca2+ influx in the SLOW voltage gated calcium channels occurs during the Plateau phase, and ensures that the AP lasts almost as long as the contraction of the cell
-becuase the muscle is refracotry period is both during and shortly after the passage of the actionpotentials
-the long plateau phase ensures the unidirectional excitation of myocardium

25

What phase can vary in the cardiac cycle?

REpolarisation
repoloaristion caries, and occurs in the myocardiacl cells when the Voltage gaates/dependant calcium channels inacitivate?

26

Why is repolarisation really the only phase in the cardiac cycle susceptible to the most variation?

As it is dependant on WHEN the voltage gated CA2+ CHANNELS INACTIVATE

27

Is the 3rd repolarisation period of the cardiac cycle non-variable of variable?

the Third repolarisation period in the cardiac cycle IS variable
-this is due to its Dependance on WHEN the Ca2+ voltage gated ion CHANNELS INACTIVATE

28

How do changes in blood ion composition of Na+, K+ and Ca2+ effect the heart?

Sensitive to change is potassium K+, sodium Na+ and calcium Ca2+
This can effect their potential to generate AP
-therefore they need to maintain 1. Osmolarity
2. Ionic gradient
-as both these things effect blood composition of ion and water

29

What can cause changes in the heart's ability to generate AP and how can this be controlled?

changes in ionic composition in the blood
-the heart is very sensitive to changes in potassium, sodium and calcium
-these ionic compositions can affect the heart's ability to generate action potentials
-therefore they need to be tightly controlled and regulated
-by maintaining : Osmolarity and Ionic gradient

30

How can osmolarity and ionic gradients affect the heart's ability to generate AP action potentials?

Maintains ionic compositions in the blood

31

What happens to your heart when it is contracting?

It twists and rings

32

Does your heart contract symmetrically?

No,
When the heart contracts, it twists and rings

33

What is the best way to increase somebody's survival rate?

early treatment

34

What make's it possible for electrodes on the Skin of the chest wall to be able to measure the electrical activity?

Water
-the body is composed of 70% water
-water is a good conductor
-allows electrical activity to spread out to your fingertips

35

What proportion of the body is composed of water?

70%
-water is a good conductor
-therefore allows the electrical activity to spread out to your fingertips

36

What does the electrical activity of the heart do?

Co-ordinates muscle activity
-needs to spread over the SURFACE of the heart

37

Does the heart's electrical activity spread deep into the muscle or over the surface of the muscle?

Electrical activity spreads over the Surface of the heart
-allows this electrical activity to co-ordinate muscle activity

38

What happens if the firing of the heart Isnt at the correct time?

Ventricles don't contract at the same tim
Don't pump blood at the right time
System goes haywire
Causes ventricular Arrhythmia (pt. death)

39

What is Ventricular Arrhythmia?

"arrhythmia" = lack of rhythm
=lack of rhythm of the ventricle
= severe when LV is no longer pumping blood at all (due to this lack of rhythm)
=leads to death
=Need a AED (automatic Electrical Defibrillator) shock in order to Reset
-Require an Electrical Shock in order to RESET the Rhythm of the ventricular contraction in the heart - allowing the ventricle to start pumping blood again

40

What does "arrhythmia" mean?

"Lack of rhythm"
can be severe ventricular arrhythmia
or the daily liveable atrial arrhythmia

41

Is Ventricular Arrhythmia severe of liveable?

Severe, can cause death due to the LV not pumping any blood out (due to the lack of rhythm)

42

How can ventricular arrhythmia cause death?

LV stops pumping blood altogether
-due to the severe lack of rhythm

43

What is the treatment for ventricular arrhythmia?

AED
Automatic Electrical Defibrillator
- require an Electrical shock in order to reset the Ventricular rhythm- allow the ventricle to start pumping blood again

44

When is AED automatic electrical defibrillator a solution?

When an electrical shock is required in order to Reset the lost ventricular rhythm in ventricular arrhythmia, allowing the LV to pump blood again

45

How does the wave of depolarisation initiated by the SA node spread throughout the heart?

As a wave of depolarisation SWEEPING over the SURFACE of our heart through the CONDUCTION fibres

46

What is meant by the "intrinsic ability of the heart"?

Pacemaker like activity
is the heart's ability to Co-ordinate and contract (its activity of the heart)
-alone is at 90-100
-with vagal nerve, HR is set at 60-70 bpm

47

What is the heart's intrinsic heart rate?

90-100 bpm
-due to the AP firing of the SA node's integral ability (60-100)
-however actual HR is lower, due to vagal parasympathetic activity

48

What is our heart rate at rest?

60-70 bpm

49

Why is out HR at rest lower than out heart's intrinsic heart rate?

SA node integral rate of AP generation/depolarisation is 90-100 bpm, but due to vagal/parasympathetic nerve activity, HR at rest lower to 60-70 bpm (ACh release which suppresses rate of spontaneous depolarisation of SA node)

50

What is atrial arrhythmia?

arrhythmia = "loss of rhythm"
Loss of rhythm of the atria
Atria is not contracting in a co-ordination manner
Atria's are less important than the ventricles
-it would just result in the loss of the 20% top up of blood by the atria
Liveable/survivable = many people live their daily lives with it and are perfectly fine, living in oblivion of have this arrythmia

51

What causes arrhythmia ?

Lack of co-ordinated conduction/contraction of the heart. i.e. loss of rhythm.
-contraction is not in a co-ordinated manner
Causes the heart to stop pumping blood from the respective area if severely out of rhythm

52

Is atrial arrhythmia lethal?

No.
Loss of rhythm in the atria/the contraction of the atria (the top up contraction) is no co-ordinated/in rhythm
Atria's are less important than the ventricles
-it would just result in the loss of the 20% top up of blood by the atria
Liveable/survivable = many people live their daily lives with it and are perfectly fine, living in oblivion of have this arrhythmia

53

Where are the 3x places in the body where Pacemaker cells are located?

1. Brain
2. CNS
3. Heart

54

Which conduction fibre is found in the Heart, CNS and Brain?

Pacemaker cells
-auto-rhythmic cells
-depolarisation and re-polarise at an automatic intrinsic rate

55

What sort of regulation is the autonomic system considered to be?

Extrinsic regulation

56

Is the Autonomic Nervous System and example of Intrinsic or Extrinsic regulation?

Extrinsic
Intrinsic is ionic concentrations and contractility (inotropy/inotropic agents effecting strength/forcefullness of contraction)

57

What is the main features of autonomic Nervous system regulation over the body?

is a method of EXTRINSIC regulation
Is more Automatic control
Don't have it under conscious control
-Receives input from Higher centres (limbic, cerebral cortex and hypothalamus) + sensory receptors such as Room temperature, Dehydration (chemo-, proprio- and baroreceptors)
the adjustments in HR is important to the Short term control of CO cardiac output and BP blood pressure
the CVC cardiovascular centre in the Medulla is responsible for the Regulation of HR and SV

58

Is the autonomic system under voluntary or automatic control?

Automatic
-inferred by the "auto" in autonomic

59

From which 3x higher centres does the Autonomic Nervous system receive input?

1. Cerebral Cortex
2. Limbic system
3. Hypothalamus

60

Where does the Cerebral cortex, Limbic system and Cardiovascular system collectively act as input into?

Autonomic Nervous system

61

Outside of higher centres, where else does the Autonomic system receive input from?

Proprio receptors (joint receptors/movement)
Chemo receptors (monitors blood chemistry)
Baro receptors (blood pressure)

62

Which receptors monitor blood pressure?

Baroreceptors

63

What is the function of baroreceptors?

Blood pressure receptors
Located in the carotid sinus and Aortic arches

64

Where is the Cardiovascular centre located?

In the Medulla

65

What essential area of organisation is located in the Medulla?

the CVC cardiovascular centre

66

What 2x systems of the body does the medulla have essential control over?

1. cardiovascular control
2. Respiratory control

67

Where is the Respiratory system controlled?

In the medulla

68

Where is the cardiovascular system controlled?

In the CVC cardiovascular centre in the MEDULLA

69

What are the key features of the Parasympathetic Nervous System?

1. Efferent effector Vagus nerve (goes to SA/AV pacemaker nerves). part of the Autonomic (automatic) Nervous system of Extrinsic regulation
2. ONLY effects HR - therefore doesn't effect CONTRACTILITY, as that is only a feature of SV
3. Medulla --> down 10th Cranial nerve/Carotid Artery (4-5mm thick)
4.Slow Heart rate down
5. Its neurotransmitter is ACh
6. ACh release SLOW HR via decreasing the rate of spontaneous depolarisation of the SA node-this decreases the intrinsic ability of the SA node's specialised auto rhythmic cells AP firing at 90-100 bpm --> down to 60-70 bpm
7.Tonic activity is the baseline/resting level of activity
8. Faster acting on HR

70

What is the pathway of the Vagus nerve?

from the Medulla --> down the 10th Cranial/Carotid artery (4-5mm thick)

71

What is another name for the 10th cranial nerve?

Carotid artery (sinus is just when exiting the aorta/heart) (4-5mm thick)
-pathway of the vagus nerve

72

What is another name for the carotid artery?

10th (X) Cranial nerve (4-5mm thick)
- pathway of the Vagus nerve

73

How thick is the carotid artery?

4-5 mm thick

74

What are the dimensions 4-5mm referring to?

the thickness of the 10th cranial nerve/Carotid Artery - the path of the vagal nerve

75

What sit eh neurotransmitter of the Para-sympathetic system?

ACh
ACh release SLOW HR via decreasing the rate of spontaneous depolarisation of the SA node -this decreases the intrinsic ability of the SA node's specialised auto rhythmic cells AP firing at 90-100 bpm --> down to 60-70 bpm

76

What is the function of Acetylcholine?

ACh release, SLOWS HR via decreasing the rate of spontaneous depolarisation of the SA node
-this decreases the intrinsic ability of the SA node's specialised auto rhythmic cells AP firing at 90-100 bpm --> down to 60-70 bpm

77

Is the Parasympathetic system fast or slow acting on HR?

Fast acting

78

Is the sympathetic system fast or slow acting on HR?

slow acting

79

Which is faster the sympathetic or parasympathetic system?

Parasympathetic system
-the parasympathetic system is fast acting than the sympathetic system

80

Does the parasympathetic system effect SV?

No
-it doesn't innervate myocytes
-therefore doesn't effect contractility, as that is starlings law, and an intrinisc factor/property of SV

81

Does the parasympathetic system effect contractility?

No
-it doesn't innervate myocytes
-therefore is does effect SV
as contractility is also an intrinsitic factor of SV

82

How is SV affected by the autonomic nervous system?

by the SYMPATHETIC system ONLY

83

How is HR affected by the autonomic nervous system?

by the PARA and SYMPATHETIC system BOTH

84

What are the main features of the Sympathetic nervous system?

1. Efferent nerve: Cardiac Accelerator Effector nerve (to SA/Av node pacemaker cells AND cardiac myocytes). part of the Autonomic (automatic) Nervous system of Extrinsic regulation
2. effects BOTH HR and SV - therefore does effect CONTRACTILITY, as that is a feature of SV
3. Medulla --> DOWN SPINAL CORD
4.Increases Heart rate up. Increases SV. Results in an increase in CO.
5. Its neurotransmitter is NE
6. NE release INCREASE HR (promotes Ca2+ entry) via increasing the rate of spontaneous depolarisation of the SA node-this levels HR closer to the intrinsic ability of the SA node's specialised auto rhythmic cells AP firing at 90-100 bpm --> NOT down to 60-70 bpm
7. Regulates inotropy : intrinsic regulation of contractility - force of contraction (SV)
Regulates chronotropy (HR)
8. Slower acting on HR

85

What does the sympathetic nervous system effect?

SV AND HR BOTH
therefore regulates inotropy - intrinsic regulation of contractility of Sv
therefore also regulates chronotropy - time - HR

86

Does the sympathetic nervous system regulate chronotropy?

yes
chrono = time
Sympathetic effects HR

87

Does the sympathetic nervous system regulate inotropy?

Yes
intrinsic regulation of contractility - force of contraction (SV)
Sympathetic is the ONLY area of the autonomic nervous system which effect SV - as it innervates mycocytes

88

Which part(s) of the autonomic nervous system innervates myocytes?

SYMPATHETIC autonomic extrinsic regulatory nerves
-therefore sympathetic effects SV
-therefore Parasympathetic doesn't effect SV

89

What is the sympathetic autonomic nervous system's Neurotransmitter?

NE

90

Which autonomic nervous system used NE as it's neurotransmitter?

Sympathetic nervous system

91

What is the function of Nor Epinephrine NE?

NE release INCREASE HR (promotes Ca2+ entry) via increasing the rate of spontaneous depolarisation of the SA node-this levels HR closer to the intrinsic ability of the SA node's specialised auto rhythmic cells AP firing at 90-100 bpm --> NOT down to 60-70 bpm

92

What is the pathway of the Cardiac Accelerator sympathetic nerves?

Medulla --> SPINAL CORD

93

Which system involves Cardiac accelerator nerves?

sympathetic
cardiac accelerator nerves innervates both the SA and AV node + the myocytes of cardiac muscle

94

What is the effector neuron of the sympathetic system?

Cardiac Accelerator nerve

95

What is the cardiac accelerator nerve?

the efferent effector neuron in the Sympathetic autonomic extrinsic regulatory nervous system
innervates both the SA and AV node + the myocytes of cardiac muscle

96

What is the Vagal nerve?

the efferent effector neuron in the parasympathetic autonomic extrinsic regulator nervous system
innervates ONLY the SA and AV node + NOT the myocytes of cardiac muscle-as it doesn't regulate SV, contractility or inotropy

97

What is the effector neuron of the para sympathetic system?

vagal nerve

98

Which 4x areas does the cardiac accelerator nerves of the sympathetic autonomic extrinsic regulatory nervous system innervate?

1. SA node pacemaker cells
2. AV node pacemaker cells
3. Myocardium
4. Coronary Arteries

99

Which part of the autonomic extrinsic regulatory nervous system innervates Coronary arteries?

Sympathetic nervous system

100

Does the cardiac accelerator nerves of the sympathetic autonomic extrinsic regulatory nervous system innervates the coronary arteries?

yes! :)