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DEN 7101S Human Structure and Function II > 2/5 Britton Electrical and Mechanical Events of the Heart > Flashcards

2/5 Britton Electrical and Mechanical Events of the Heart Flashcards

1
Q

The prevalence of CV disease in adults over 20 years of age is:

A

48%

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2
Q

The function of the heart is essentially:

A

A pump for blood flow through the circulatory system

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3
Q

Human heart must beat ______ for one’s entire life

A

Regularly and continuously

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4
Q

Myocardium

A

Cardiac muscle tissue

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5
Q

Myocardium is composed of what types of cardiac muscle?

A
  • Atrial
  • Ventricular
  • Conductive muscle fibers
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6
Q

Together, muscle cell types produce the:

A

Organized contraction of the heart

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7
Q

_____ generate contractile force

A

Atrial and ventricular myocytes

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8
Q

Atrial and ventricular myocytes are also known as:

A
  • Contractile cells
  • Working myocardium
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9
Q

Atrial and ventricular myocytes contract _____ as skeletal muscle, except:

A

The same way; the duration of the contraction is much longer

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10
Q

Conductive muscle fibers are _____ that allow for:

A

specialized muscle fibers; generation of AP’s; rapid conduction of AP’s

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11
Q

_____ contract only feebly because it contains few contractile cells

A

Conductive muscle fibers

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12
Q

Cardiac muscle cells are ____ coupled via:

A

Electricaly; gap junctions

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13
Q

Gap junctions form a _____ synapse

A

Electrical

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14
Q

Gap junctions are positioned at regions called:

A

Intercalated discs

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15
Q

Intercalated discs are unique to:

A

Cardiac muscle

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16
Q

Gap junctions allow for:

A

flow of electrical current and AP propagation between adjacent cells

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17
Q

_____ are vital for the coordinated electrical activity of cardiac muscle cells

A

Gap junctions

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18
Q

The electrical activity of the heart originates:

A

Within the heart itself

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19
Q

The heart has its own:

A

Auto-rhythmicity

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20
Q

True or false: the heart requires neural input to generate action potentials

A

False - does not require

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21
Q

Auto-rhythmicity is due to ____ cells

A

Pacemaker cells

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22
Q

Pacemaker cells are ____

A

Modified cardiomyocytes

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23
Q

Where are pacemaker cells located?

A
  • SA node
  • AV node
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24
Q

____ is also called the sinus node

A

SA node

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25
Q

Cardiac muscle cells either:

A
  • exhibit automatic rhythmical electrical discharge of APs
  • conduct APs through the heart
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26
Q

Cardiac muscles have an _____ difference across the cell membrane, termed _____

A

Electrical potential; resting membrane potential

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27
Q

In a ventricular cell, resting membrane potential is:

A

-90 mV

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28
Q

RMP of cardiac cell is close to:

A

Ek (equilibrium potential for K+)

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29
Q

Resting membrane potential is determined by:

A
  • the concentration of ions across the cell membrane
  • relative permeability of the cell membrane to these ions (if selective ions are open or closed)
  • membrane pumps that transport ions across the cell membrane and maintain ionic gradients
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30
Q

Ion pumps and exchangers on the cardiac cell membrane maintain ____ for Na+, K+, Ca2+

A

ionic gradients

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31
Q

Ion pumps associated with cardiac cell electrophysiology

A
  • Na+/K+ ATPase (3:2)
  • PMCA (plasma membrane Ca2+ ATPase)
  • NCX (Na+/Ca2+ exchanger, 3:1)
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32
Q

During each cardiac cycle, what happens?

A

Na+, K+, Ca2+ ions move back and forth across the cardiomyocyte cell membrane (thereby changing Vm)

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33
Q

Cardiac APs occur when:

A

Membrane potential depolarizes and then repolarizes back to its resting state (similar to neuronal APs)

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34
Q

APs occur in ____ cardiac cell types, but the appearance ____ depending on the cell type

A

All; varies

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35
Q

What are the two types of cardiac APs?

A
  • Myocardium (non-pacemaker AP)
  • SA node (pacemaker AP)
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36
Q

Non-pacemaker AP is triggered by:

A

Depolarizing current from adjacent muscle cells

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37
Q

Pacemaker cells are capable of:

A

Spontaneous AP generation

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38
Q

An AP is a recording of:

A

Cell’s membrane potential versus time

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39
Q

What are the 5 phases of myocardium action potentials?

A
  1. Depolarization
  2. Brief repolarization
  3. Plateau
  4. Rapid repolarization
  5. RMP
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40
Q

What is the duration of a myocardium action potential?

A

200-400 msec (roughly how long the contraction lasts)

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41
Q

Cardiac AP is largely dominated by the movement of:

A

Na+, Ca2+, K+ ions

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42
Q

Myocardium action potentials

Phase 0

A
  • Upstroke/rapid depolarization
  • Na+ channels open
  • Membrane potential shifts into positive voltage range
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43
Q

Myocardium action potentials

Phase 1

A
  • early repolarization
  • K+ channels open
  • sets the potential for phase 2
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44
Q

Myocardium action potentials

Phase 2

A
  • Ca2+ channels open
  • K+ channels are still open
  • long phase marks the entry of Ca2+ into the cell
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45
Q

Myocardium action potentials

Phase 3

A
  • rapid repolarization
  • Additional K+ channels open
  • Membrane potential returning to its resting value
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46
Q

Myocardium action potentials

Phase 4

A

Stable at -90 mV in myocardium

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47
Q

How do ion channels make the cardiac cell membrane permeable to ions?

A
  • selective for particular ions
  • open and closed states
  • exhibit gating properties (voltage/ligand gated)
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48
Q

The phases of the AP are the result of:

A

Ion movement down their electrochemical gradients (established by active pumps and exchangers)

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49
Q

The cardiac AP reflects the ____ behavior of numerous individual ____ and their ____

A

Integrated; ion channels; ionic currents

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50
Q

____ always precedes muscle contraction

A

AP

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51
Q

Long AP duration allows:

A
  • cardiac muscle to contract for this same long period
  • heart chambers to fully contract and eject blood
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52
Q

Features of APs in cardiac myocytes

A
  • Cardiac AP has a long duration
  • Cardiac AP has a plateau
  • have refractory periods
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53
Q

____ are largely responsible for the plateau portion

A

Voltage-gated Ca2+ channels

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54
Q

Voltage gated K+ channels in cardiac myocyte membranes are ____ to open

A

Slower than usual (delayed repolarization of membrane potential)

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55
Q

Interval of time during which cardiac cells are unexcitable to the initiation of a new AP

A

Refractory period

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56
Q

Cardiac cells are refractory during AP phases ____, termed the ____

A

0, 1, 2, part of 3; effective refractory period (ERP)

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57
Q

ERP of ventricular AP is ___ msec

A

200 (approximately the duration of the AP)

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58
Q

ERP occurs due to:

A

Na+ channels remain inactivated following channel closing during phase 1

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59
Q

____ is a protective mechanism in the heart, prevents multiple APs from occurring

A

ERP

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60
Q

Relative refractory period

A

Interval of time during which a 2nd AP can be initiated with a greater stimulus than before

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61
Q

What are afterdepolarizations?

A

Depolarizations of muscle cells during the AP

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62
Q

When do afterdepolarizations occur?

A

Can occur in the relative refractory period if amplitude of depolarization is large enough to reach threshold

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63
Q

Afterdepolarizations must be preceded by at least ____, thus the term _____ is used

A

One AP; Triggered activity

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64
Q

True or false: afterdepolarizations occur spontaneously

A

False - they are triggered by prior activation of the heart (previous AP)

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65
Q

Early afterdepolarizations may occur spontaneously in patients with ______

A

Congenital long QT syndrome (LQTS) due to defective K+ channels

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66
Q

Early afterdepolarizations (EAD’s) occur during what phase?

67
Q

Early afterdepolarizations (EAD’s) are usually caused by:

A
  • hypokalemia
  • K+ channel blockade
  • drugs
68
Q

Delayed afterdepolarizations are facilitated by ____

A

Intracellular Ca2+ overload

69
Q

Delayed afterdepolarizations are usually caused by:

A
  • Ischemia
  • Catecholamines (NE, Epi)
  • Drugs (digitalis)
70
Q

Delayed afterdepolarizations occur during what phase?

71
Q

Pacemaker potentials are generated in the ____ and are different from _____

A

SA node and AV node; working myocardium APs

72
Q

The resting membrane potential is _____ in the SA node

A

Less negative (-50 to -65 mV)

73
Q

In the SA node, the resting membrane potential is unstable and exhibits a ____

A

slow diastolic depolarization

74
Q

The slope of the upstroke in a pacemaker potential during phase _____ is ____ steep

A

Phase 0 depolarization; less (slower rate of depolarization)

75
Q

What are the phases of a pacemaker action potential?

76
Q

What happens during phase 4 of a SA node potential?

A
  • Diastolic depolarization
  • Slow Na+ influx (HCN channels)
77
Q

Diastolic depolarization during phase 4 of SA node potential is also known as:

A
  • Funny current
  • Pacemaker potential
78
Q

What happens during phase 0 of a SA node potential?

A
  • Rapid depolarization
  • Ca2+ channels that open when Vm reaches threshold and depolarization occurs (-40 mV)
79
Q

SA node pacemaker potentials

2 types of Ca2+ channels

A
  • T-type (open transiently)
  • L-type (long lasting)
80
Q

What happens during phase 3 of a SA node potential?

A

Repolarization via K+ channels

81
Q

The leaking of _____ during the resting phase is called the pacemaker potential

82
Q

Why is the pacemaker potential called the funny current (lf)?

A

It displays unusual properties

83
Q

The funny current is a ____ current with a 3-fold higher selectivity for ____ than for ____

A

Mixed Na+-K+; Na+; K+

84
Q

The funny current conducts an ____ current that generates the _____ in pacemaker cells

A

Inward; slow membrane depolarization

85
Q

True or false: the funny current is activated by membrane depolarization

A

False: it is activated by hyperpolarization rather than depolarization

86
Q

The funny current has dual modulation by:

A

Voltage and cAMP

87
Q

What channels are responsible for the pacemaker current?

A

HCN ion channel

Hyperpolarization-activated Cyclic Nucleotide gated channels

88
Q

HCN channels are preferentially present in:

A

SA node and AV node

89
Q

HCN channels are more permeable to:

A

Na+ ions (over K+ ions)

90
Q

HCN channels are gated by both:

A

Voltage and cyclic nucleotides (cAMP)

91
Q

Key to automaticity in SA node potentials

A

Slow depolarizing baseline drift of the membrane potential

92
Q

How is the automaticity of SA node cells explained?

A

SA nodal cells start leaking Na+ into the cell as soon as they return to their resting state

93
Q

The rate of APs initiated in the SA node is determined by:

A

How fast Na+ moves inward through HCN channels

94
Q

If more HCN channels open, ____ moves inward faster, reaching the threshold for _____ faster and ____ the time/duration between APs

A

Na+; the activation of voltage-gated Ca2+ channels; shortens

95
Q

The heart is innervated by the ___. The network of nerves supplying the heart is the ____

A

ANS; cardiac plexus

96
Q

In the SA and AV node, what nerve terminals end on the SA node and AV node to modulate heart rate?

A
  • Sympathetic adrenergic
  • Parasympathetic cholinergic
97
Q

In ventricular muscle, _____ fibers innervate to modulate heart contractility

A

Sympathetic adrenergic

98
Q

In addition to sympathetic nerve innervation, what else can modulate heart contractility?

A

Catecholamines circulating in the blood following sympathetic stimulation of adrenal glands

99
Q

The sympathetic and parasympathetic branches have ____ effects on heart rate by modulating the opening and closing of ____

A

Opposite; HCN channels

100
Q

Describe the mechanism of sympathetic ANS modulation of the SA node

101
Q

Describe the mechanism of parasympathetic ANS modulation of the SA node

102
Q

ANS neurotransmitters change the rate of diastolic depolarization in the SA node via:

A

Lf (HCN channels)

103
Q

Sympathetic innervation at the SA node leads to _____ depolarization rate via the funny current

A

Faster (steeper slope)

104
Q

Parasympathetic innervation at the SA node leads to _____ depolarization rate via the funny current

A

Slower (less steep slope)

105
Q

What are the components of the cardiac conduction system?

A
  • SA node
  • AV node
  • AV bundle
  • Right and left bundle branches
  • Purkinje fibers

these are all specialized muscle cells

106
Q

The normal rhythmical electrical impulse (AP) is generated in the ____. Then the AP travels to the ____ through ____ cells and to the right and left ventricle through the _____ and _____. This stimulates _____

A

SA node; right and left atria; myocardial cells; AV node and His-Purkinje fibers; myocardial cells to contract

107
Q

Trace the conduction system of the heart

108
Q

The _____ of the cardiac AP varies in different regions of the heart

A

Conduction velocity

109
Q

AP conduction in the AV node is ______ more than ____ msec before appearing in the AV bundle, which allows for:

A

delayed; 100; time for the atria to contract and empty blood into the ventricles before ventricular contraction begins

110
Q

What is another name for the SA node?

A

Sinus node

111
Q

What is another name for the AV bundle

A

Bundle of His

112
Q

____ node has the slowest conduction

A

AV (0.05 m/sec)

113
Q

____ have the fastest conduction velocity

A

Purkinje fibers (4 m/sec)

114
Q

Using surface electrodes, the spread of electrical current within the heart can be recorded with:

115
Q

Recording ECG employs what technique?

A

Einthoven’s triangle

116
Q

What is Einthoven’s triangle?

A

Imaginary triangle that surrounds the heart at right arm, left arm, left leg

117
Q

Pairs of electrodes are called:

118
Q

Lead I

A

RA (-) to LA (+)

119
Q

Lead II

A

RA (-) to LL (+)

120
Q

Lead III

A

LA (-) to LL (+)

121
Q

The _____ is more common for viewing the electrical activity of the heart

A

12 lead ECG

122
Q

In addition to the 3 standard limb leads, there are:

A
  • 3 augmented limb leads (Lead aVR, aVL, aVF)
  • 6 precordial (V1-V6) chest leads
123
Q

The ECG shows the pattern of depolarization/repolarization that is produced by APs generated by:

A

A population of cardiac muscle cells

124
Q

The ECG is measurable because the electrical activity of cardiac cells is _____ during the cardiac cycle

A

Synchronized

125
Q

True or false: the ECG provides information about electrical and mechanical activity of the heart

A

False - only electrical (spread of excitation)

126
Q

Mechanical activity of the heart is portrayed in:

A

Echocardiogram

127
Q

What are the normal ECG waveforms?

A

P, Q, R, S, T

128
Q

The complete PQRST makes up a:

A

Depolarization-repolarization cycle

129
Q

P wave represents:

A

Atrial depolarization

130
Q

QRS complex portrays ____ and hides _____

A

Ventricular depolarization; atrial repolarization

131
Q

T wave represents:

A

Ventricular repolarization

132
Q

What information does the ECG provide?

A
  • Heart rate
  • Site of pacemaker origination
  • Rate of AV node conduction
  • Pathway of ventricular activation
133
Q

What is the RR interval?

A

Time between heart beats

134
Q

What is the PR interval?

A

Time taken for impulse to spread over atrium, AV node, Bundle of His

135
Q

____ determines whether impulse conduction is normal

A

PR interval

136
Q

____ reflects the slow impulse conduction through the AV node

A

PR segment

137
Q

The PR ____ is an isoelectric point with no change in electrical activity

138
Q

What is the QT interval?

A

The time taken for depolarization and repolarization of the ventricles

139
Q

_____ reflects the time from ventricular depolarization ends until ventricular repolarization begins

A

ST segment

140
Q

_____ corresponds to the plateau phase 2 of the AP and is an isoelectric point

A

ST segment

141
Q

What 3 criteria are needed to qualify as normal sinus rhythm?

A
  • AP must originate in SA node
  • SA node impulses occur regularly at a rate of 60-100 impulses/min
  • Electrical activation of the myocardium must occur in the correct sequence and with correct timing and delays
142
Q

By examining the ____ for a couple of cycles, you can determine whether the rate and rhythm is steady or irregular

A

R-R interval

143
Q

_____ are disorders of AP generation or impulse conduction

A

Arrhythmias

144
Q
  • In a normal scenario, ___ is the primary pacemaker and controls rate of AP regulation.
  • In a pathological scenario, ____ can take over AP generation, causing ____ electrical activity and cardiac contraction. Foci can include:
A
  • SA node
  • Foci other than the SA node; disorganized; AV node, His-Purkinje fibers, atria
145
Q

Arrhythmias can be caused by:

A
  • Ischemia
  • Structural changes in the conduction system
  • Mutations on ion channels
146
Q

Bradycardia

A

Slow heart rate; fewer than 60 beats/min

147
Q

Tachycardia

A

Fast heart rate; more than 100 beats/min

148
Q

What would make the heart beat faster or slower?

A

Input from the ANS

149
Q

1st, 2nd, and 3rd degree atrioventricular blocks are examples of:

A

Bradyarrhythmias

150
Q

What is a 1st degree AV block?

A

PR interval is extended

151
Q

What is a 2nd degree AV block?

A

Not every QRS complex is followed by a P wave

152
Q

What is a 3rd degree AV block?

A

P waves and QRS complex appear independently but regularly from each other

153
Q

Atrial fibrillation

A

A quivering or irregular heart beat

154
Q

Atrial fibrillation can lead to:

A

Blood clots, stroke, heart failure, other heart-related complications

155
Q

Myocardial infarction shows a characteristic alteration in the ____, termed a ______

A

ST segment; STEMI (ST Elevation in MI)

156
Q
  • Ca2+ entering the cardiac cell during phase ____ of the AP triggers the release of Ca2+ from the SR
  • Ca2+ binds to ____, inhibiting the TnI allowing myosin to bind to actin
  • Ca2+ is returned to the ___
  • At the end of phase 2 of the AP, uncoupling (relaxation) begins to occur when ____
A

2; TnC; SR; concentration of Ca2+ falls

157
Q

AP always precedes:

A

Contraction

158
Q

Contraction is the force generated by interaction of:

A

Actin and myosin

159
Q

Contraction requires the _____ of intracellular Ca2+

A

Transient elevation

160
Q

Calcium is elevated by:

A
  • increasing Ca2+ influx via Ca2+ channels
  • Increasing release of Ca2+ by the SR
  • Sensitizing TnC to Ca2+
161
Q

Cardiac contractility can be modulated by:

A

SNS and catecholamines

162
Q

___ released by sympathetic nerves that innervate cardiac muscle

163
Q

____ in blood following SNS stimulation of the adrenals

164
Q

Cardiac Muscle Contractility

E and NE bind to ____ receptors. This increases ____ and ____ which phosphorylate multiple proteins that modulate ____. This results in ____ and ____

A
  • Beta 1 adrenergic
  • cAMP and protein kinases
  • Ca2+ uptake and release
  • elevated Ca2+ levels and increases heart contractility

DEN 7101S Human Structure and Function II (21 decks)

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