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Echo > Module 7 : Cardiac Innervation > Flashcards

Module 7 : Cardiac Innervation Flashcards

1
Q

Cardiac Innervation

A

How the heart stimulates itself

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2
Q

2 types of cardiac cells in relaxtion and contraction

A

Conduction cells

Muscle cells/ myocardial cells

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3
Q

Conduction cells

A
  • AKA auto-arrhythmic cells
  • capable of initiating impulse
  • not completely independent of outside stimulation
  • impulse travels via gap junction from cell to cell through heart
  • stim occurs and travels from atria to ventricles
  • DO NOT CONTAIN MYOFIBRILS
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4
Q

Muscle/myocardial cells

A

Do work
Contract (actin and myosin)
Must be stimulated in normal rhythm
Present in thinner atrial walls and myocardial layer of the ventricular walls

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5
Q

Cardiac cells function

A
  • work together to form one sequential contraction
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6
Q

Gap junctions

A
  • the conduction cells are joined together by gap junction

- allow passage of electrical impulse from one cell to the next

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7
Q

Anatomy of cardiac cells

A
  • cells have branches

- joined together by INTERCALATED DISCS which contain GAP JUNCTIONS

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8
Q

4 types of cardiac cells

A
  • myocardial/muscle/contractile cells
  • conduction cells
  • avascular valvular tissue
  • endocardial cells
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9
Q

Avascular valvular tissue

A
  • interstitial cells

- less water more collegen

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10
Q

Endocardial cells

A
  • line all of the blood tissue interface including valves fo the heart
  • allow blood to easily slide over the surface
  • 1mm or less in thickness
  • cover all other types of cardiac cells
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11
Q

Myofibril

A
  • make up contractile cells
  • contains contractile elements of muscle cells and contain many myofibrils lined up in a row
  • several lie on top of each other surround the heart in different directions
  • each layer contracts in different directions
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12
Q

Sacromere

A
  • segment of myofibril
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13
Q

Actin and myosin

A
  • within the sarcomeres
  • contractile protein
  • slide over each other
  • 20% more over lap in systole
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14
Q

Actin and myosin - contraction

A
  • actin and myosin slide together and overlap to a greater degree
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15
Q

Actin and myosin - relaxation

A
  • actin and myosin slide apart and overlap only at the ends
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16
Q

Preload effects on actin and myosin

A

-increased preload stretches the actin and myosin apart
- in normal hear amount of contraction is increased
+ diseased heart may go into failure

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17
Q

After load effects on actin and myosin

A
  • increased after load leads to less overlapping of actin and myosin during peak contraction
  • contraction is decreased
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18
Q

Muscle fiber contraction - 2 require stimulation

A

1) electrical current - pace maker or defibrillator

2) action potential (intrinsic electrical impulse transmitted from another cell or comes from cell itself)

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19
Q

Muscle cells stimulation

A
  • stimulates by impulses from the conduction cells

- can stimulate themselves but at slower heart rate 20-40bpm

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20
Q

Conduction cells contraction ?

A

Conduction cells DO NOTA contract

  • only conduct and generate pulses
  • their function is specialized to conducting impulses
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21
Q

Influx

A

Ions entering the cell through the channels in the membrane

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22
Q

Efflux

A

Opposite of influx

Exiting cells

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23
Q

Stimulus

A

Strong electrical signal capable of conducting through the heart (microvolts)

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24
Q

Automaticity

A

Ability of a cell to PRODUCE their own impulse

+ based on steepness of each cells phase 4 slope

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25
Q

Excitability

A
  • ability of cell to accept an impulse and transmit it to other surrounding cells
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26
Q

Refractory

A

Ability of a cell to RESPOND to a stimulus

+ based on which stage of action potential the cell is currently in

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27
Q

Electrical mechanical coupling

A
  • muscle fiber contraction requires electrical stimulation
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28
Q

Excitation coupling

A
  • series of events that connects the electrical stimulation to the subsequent mechanical event of contraction

ELECTRICAL BEFORE MECHANICAL ALWAYS

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29
Q

Electrical - action potential

A
  • a wave of electrical discharge (exchange of ions across a cell membranes) that travels along the outer membrane of a cell
  • cycle of depolarization/repolarization
  • repeated every heart beat
  • wave of electrical discharge sent to neighboring cells in heart
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30
Q

Action potential in muscle and conduction cells

A
  • both have action potential but look very different
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31
Q

Auto-rhythmic / conduction cell action potential

A
  • can be self stimulated or stimulated from nearby cells
  • impulse or action potential travels all the way to the ‘end’ of the electrical circuit (atria-ventricle)
  • heart keeps beating outside body because of this
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32
Q

Action potential ion flux

A

Stage 1 = sodium rushes into flee
Stage 2 = calcium rushes in
Stage 3/4 = potassium out of cell

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33
Q

Selective permeability

A
  • gate keeper of the cell

- allows certain ions in and out of the cell membrane

34
Q

The action potential - electrical stages

A 
- sequence of electrical events that must occur every heart beat
     \+ stage 0 = depolarization (cell)
     \+ stage 1 = early repolarization
     \+ stage 2 = plateau - contraction 
     \+ stage 3 = repolarization
     \+ stage 4 = resting state
35
Q

Phase 0

A
  • depolarization of the cell
  • DEPOLARIZATION IS NOT CONTRACTION
  • cell is stimulated and prepares to contract
  • cell fires from threshold to maximal positive state
  • cell becomes refractory to all stimulus (cannot respond to another stimulus)
  • sodium entering the cell quickly through sodium potassium pump
36
Q

voltage change in phase 0

A

(-)90 mV to (+) 40-50 mV

37
Q

phase 1

A
  • early depolarizing
  • very short time interval
  • call is refractory (cannot accept another stimulus)
  • moves toward a slightly less positive state
  • preparing for plateau phase
  • potassium chloride leaking out
38
Q

phase 2

A
  • plateau stage
  • EXCITATION COUPLING = actin and myosin reacting to electrical signal leading to contraction
  • contraction phase of cell
  • cell is still refractory
  • calcium is responsible for contraction of cell
39
Q

phase 3

A
  • repolarization = post contraction
  • cell returns to resting state
  • all ions return to initial state
  • downslope of action potential
40
Q

resting voltage of cells

A

(-) 90 mV

41
Q

phase 4

A
  • upward slope of the stage determines how fast the automaticity rate of the cell is
  • once the membrane potential reaches threshold it will depolarize again
42
Q

steep phase 4

A

fast intrinsic rate

43
Q

falt phase 4

A

slow intrinsic rate

44
Q

refractory period

A
  • when cell is immune to stimulus
  • from onset of depolarization to close to the end of depolarization
  • another impulse cannot normally be initiated or transmitted
45
Q

absolute refractory period

A
  • no external stimuli will make heart beat

- absolut refractory until end of stage 2

46
Q

relative refractory period

A
  • only a string external stimulus will make the heart beat

- after stage 3

47
Q

sequence of events (electrical - mechanical)

A
  • electrical events in the heart must occur before mechanical events
48
Q

cardiac conduction system

A
  • network of specialized cardiac fibres that provide a path for each cycle of cardiac excitation to move through the heart
49
Q

electrolytes

A
  • importance of electrolyte balance (sodium, calcium, potassium)
  • ions are responsible for the action potential and can alter the action potential when there are abnormal levels
50
Q

not enough electrolytes

A
  • poor function of heart
51
Q

too much electrolytes

A
  • hyper function of heart
52
Q

intrinsic innervation

A
  • controls the base heart rate

- controls rates of the individual components of the conduction system (heart rate within heart)

53
Q

extrinsic innervation

A
  • gives the heart signals to speed up or slow down
  • autonomic nervous system
  • through sympathetic and para sympathetic nervous system
54
Q

sympathetic nervous system

A
  • from medulla oblongata to thoracic spine level
  • fibres send impulse to heart
    + SA and AV nodes, myocardium
  • ACCELERATION
55
Q

parasympathetic nervous system

A
  • DECELERATION

- from medulla to heart via vagus nerve - SA and AV node

56
Q

sympathetic nervous system on heart

A
  • accelerator
  • stimulates in times of stress
    + physical or emotional
  • releases nor-epinephrine
  • increases ion exchange
  • increases BOTH HEART RATE AND FORCE OF CONTRACTION
57
Q

parasympathetic nervous system

A
  • innervates the SA node via vagus nerve
  • acts as brake - slows heart down
  • stimulated during times of rest
  • being fit or beta blockers
  • releases acetylcholine
  • carotid massage
58
Q

extrinsic controls - affect what

A
  • heart rate = chronotropy
  • contractility = inotropy
  • ventricular filling volumes = pre load
  • afterload = arterial pressures controlled by baroreceptors in the carotids and aorta
59
Q

baroreceptors

A
  • pressure sensors in carotid bulb and aortic arch regulate the pressure to protect the brain
  • massaging carotid bulb increases pressure to brain to slow HR down
60
Q

intrinsic conduction pathway

A
  • SA node > LA/RA (internodal tracts) > AV node > bundle of His > right and left bundle branches > purkinjie fibres (LV)
61
Q

Sinoatrial Node (SA node)

A
  • located near superior wall of RA - near entry of SVC
  • pace maker fo heart
  • generates pulses 100 times per minute but parasympathetic tone reduces to 60 - 100 bpm
  • fastest phase 4 in the heart in action potential
  • ability to create pacemaking stimuli is automaticity
62
Q

SA node > LA/RA internodal pathway > AV node

A
  • impulse travels from SA node through right and left internodal pathway to AV node
  • once RA and LA are stimulated they will contract to push blood to ventricles (atrial kick)
63
Q

AV node location

A
  • located in right side interatrial septum
  • above annulus of TV
  • near opening of coronary sinus
64
Q

atrioventricular node (AV node) funtion

A
  • AV groove
  • insulates pulse so that it only travels in the pathway of specialized cells
  • impulse is delayed to allow for atrial contraction and ventricular filling to occur
  • if this sequence malfunctions arrhythmias happen
65
Q

AV node pulses

A
  • can generate pulses at 40-60 times for second
  • ONLY NEEDS TO GENERATE IMPULSES IF SA NODE FAILS
  • impulse then travels to AV bundle/bundle of His
66
Q

junctional rhythm

A
  • the rhythm created when the AV node takes over as pace maker
67
Q

Bundle of His (AV bundle)

A
  • slightly distal to AV node
  • only electrical pathway between atria and ventricles
  • sends impulse forward to left and right bundle branches
68
Q

bundle branches (right and left)

A
  • speed up impulses
  • travel along interventricular septum toward apex then turn superiorly toward base on lateral sides of heart
  • sometimes path can be blocked LBBB RBBB
  • RV septum stimulated first than the Lv septum
  • as wave of pulse travels ventricular myocytes depolarize
69
Q

LBBB or RBBB

A
  • slows conduction through the ventricles and QRS is lengthened
70
Q

purkinjie fiber location

A
  • branch off of bundle branches
  • more elaborate on left side due to thicker muscle
  • ## tiny spider webs
71
Q

purkinjie fibers

A
  • deliver impulse to the individual muscle cell
  • long strands of cells
  • complete the pathway through the IVS to the apex
  • as pathway is completed contraction is completed and ventricle starts to regroup or repolaraize
72
Q

purkinjie fibres helping AV valves

A
  • aid in the valves function by pulling down on MV and TV when pap muscles are stimulated before rest of the muscle
73
Q

purkinjie fiber pulse rate

A
  • only generate pulses every 30-40 times per minute

- would need a pacemaker

74
Q

contraction of ventricles

A
  • ventricular contraction folllows ventricular depolarization
  • contraction begins at apex and mover superiorly through base
  • post contraction depolarization begins
  • REPOLARIZATION CAUSES T WAVE ON ECG
75
Q

time from impulse formation to repolarization

A

200 ms

76
Q

atria and ventricle polarization relationship

A

as atria are repolarizing the ventricles are depolarizing and vice versa

77
Q

depolarization wave

A
  • wave of depolarization passes from cell to cell causes all of the cells to depolarize and contract in sequence
  • ## atria > ventricles
78
Q

SA node intrinsic rate

A

60-100bpm

PACEMAKER NUMBER 1

79
Q

AV node intrinsic rate

A

40-60 bpm

PACEMAKER NUMBER 3 BUT ACTIVATES WHEN SA NODE FAILS

80
Q

bundle of His intrinsic rate

A

40-60bpm

PACE MAKER NUMBER 4

81
Q

LV/RV muscle cells

A

20-30bpm

PACE MAKER NUMBER 6

Echo (19 decks)

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