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Echo 1 > C6: Cardiac Innervation > Flashcards

C6: Cardiac Innervation Flashcards

1
Q

What are the two MAIN types of cardiac cells? Do both cells work together to form a single contraction?

A

conduction cells
muscle/myocardial cells (most numerous)

yes

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2
Q

How are these two cells joined together?

A

by gap junctions

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3
Q

what are gap junctions and what do gap junctions allow?

A

they are electrical connection between cells

allows electrical impulse to pass from 1 cell to another

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4
Q

how are the branches of cardiac cells joined together?

A

by intercalated discs that contain gap junctions

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5
Q

describe the 4 types of cardiac cells and their functions.

A

myocardial/muscle cells: for contraction

conduction cells: thin tracks through the muscle cells that initiate or conduct electricity

avascular valvular tissue: composed of interstitial cells

Endocardial cells: line all of the blood/tissue interfaces (including valves) and allow blood to side easily over the surface of the endocardium

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6
Q

what must occur in order for myocardial cells to contract?

A

they must be stimulated by an electrical current (pacemaker) or an action potential

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7
Q

where specifically are myocardial cells located?

A

in the thin atrial walls and myocardial layer of the ventricles

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8
Q

describe the microscopic anatomy of myocardial cells

A

myocardial cells are made up of many myofibrils arranged in a row… myofibrils are the elements responsible for contraction

also contain sarcomeres which are a segment of a myofibril that are arranged in several layers on top of one another

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9
Q

what are the 2 components that make up the myofibrils and what are there functions?

A

Myosin and actin… they’re contractile proteins that slide over one another

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10
Q

describe the movement of myosin and actin during contraction and relaxation

A

contraction: actin and myosin slide past eachother and overlap
relax: actin and myosin side apart and are only overlapped at their ends

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11
Q

what are 2 things that can effect the amount of overlap of myosin and actin before and after contraction?

A

preload and afterload

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12
Q

How does increased preload effect over lap of M&A?

How does increased afterload effect M&A?

A

Preload: increased preload stretches M&A apart and the amount of contraction is increased

Afterload: increased afterload lease to less overlapping of M&A and contraction is decreased

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13
Q

how does an action potential stimulate contraction? (in general)

A

it causes a change in the ion levels in and outside the cell

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14
Q

can muscle cells stimulate themselves?

A

yes but it will result in a slower HR than if stimulated by conduction cells

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15
Q

how do impulses travel through conduction cells?

whats another name for conduction cells?

A

through gap junctions (from atria to ventricles)

auto-arrhythmic cells

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16
Q

are conduction cells completely independent of outside stimulation?

A

no

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17
Q

what is influx?

A

ions entering the cell through channels in the membrane

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18
Q

what is efflux?

A

ions exiting the cell through channels in the membrane

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19
Q

define stimulus

A

strong electrical signal that can be conducted through the heart

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20
Q

what is automaticity and what is it based on?

A

ability of a cell to produce its own impulse… based on the steepness of each cells phase 4 slope

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21
Q

define excitability

A

ability of a cell to accept an impulse and transmit it to surrounding cells

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22
Q

define refractory/refraction. what is it based on?

A

ability of a cell to respond to a stimulus

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

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23
Q

what is electrical mechanical coupling or excitation coupling?

A

a series of events that connected the elec. stimulation to a mechanical event

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24
Q

whats action potential (AP) and what does it include? what must occur in order for the AP to get through to the cell?

A

a wave of electrical discharge that travels along the outer membrane of a cell

it includes a cycle of elec. depolarization and repolarization thats repeated ever HB

it must reach a certain threshold

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25
Q

do muscle and conduction cells both have an AP?

A

yes

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26
Q

how is AP generated in conduction cells?

A

conduction/specialized cells are self stimulated or stimulated from an outside source

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27
Q

what are the 5 sequences of electrical events that every cell must go through for every HB?

A
  1. depolarization
  2. early repolarization
  3. plateau or contraction
  4. repolarization
  5. resting state
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28
Q

whats the value of the AP at resting state and at depolarization?

A

-90mV

+50mV

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29
Q

whats happens during depolarization?

A

the cell is stimulated and prepares for contraction… then the cell fires from threshold to its maximum + state and sodium enters the cell

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30
Q

is the cell refractory during depolarization?

A

yes

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31
Q

whats happens during early repolarization?

is the cell refractory during repolarization?

A

very short time interval where the cell moves to a slightly less positive state in preparation for plateau phase… K+ exits the cell

Yes

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32
Q

whats happens during plateau stage?

is the cell refractory during plateau?

A

excitation coupling occurs which leads to contraction and Ca2+ enters the cell while K+ leaves

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33
Q

which ion is responsible for contraction?

A

calcium (entering the cell)

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34
Q

whats happens during repolarization?

is the cell refractory during repolarization?

A

‘post contraction’ or the downward slop on the AP
the cell returns to a resting state and K+ leaves the cell

the cell can be stimulated with a strong stimulus

35
Q

whats happens during resting state?

A

cell is ‘waiting’ for another stimulus

36
Q

how does the steepness of the slope in the resting state effect HR?

A

steep: fast intrinsic HR
flat: slow HR

37
Q

do conduction cells have a plateau stage?

how do the graphs of the AP of these cells look?

A

No

they’re more rounded and have a steeper phase 4 slope

38
Q

when is a cell immune to stimulus?

A

during the refractory period

39
Q

what is the absolute refractory period?

when does this occur?

A

period where no external stimulus will make the HB

From phase 0 to the end of stage 2 and into stage 3

40
Q

what is the relative refractory period?

when does this occur?

A

period where only a strong external stimulus will make the HB

stage 3

41
Q

whats the cardiac conduction system?

A

network specialized cardiac fibres that provide a path for each cycle of cardiac excitation

42
Q

whats the importance of electrolytes in the body?

A

they’re responsible for the AP…. (Na, K and Ca)
not enough= poor function of heart

too much= hyper function

43
Q

whats the function of intrinsic innervation and where it it located?

A

controls the base HR and the HR of individual parts of the conduction system

found inside the heart

44
Q

whats the function of extrinsic innervation and where it it located?

A

give the heart signals to change rhythm

located in the sympathetic and parasympathetic nervous system

45
Q

wheres the cardiac centre in the brain?

A

medulla oblongata

46
Q

where the Symp sys. located? how does it stimulate the heart and what does it stimulate?

how does it effect HR?

A

from medulla to thoracic spine

stimulates through fibres which send impulses to the SA and AV nodes and myocardium

increases it

47
Q

where the parasymp sys. located? how does it stimulate the heart and what does it stimulate?

how does it effect HR?

A

from medulla to heart

stimulated through the vague nerve which stimulate the SA and AV nodes only

decreases it

48
Q

when is the symp sys. activated? what does it release and what does it increase?

A

in times of stress…. releases nor-epinephrine

increases ion exchange, increases HR and force of contraction

49
Q

when is the parasymp sys. activated? what does it release and what does it decrease?

A

in times of rest… releases acetylcholine

HR

50
Q

what type of controls are the symp. and parasympathetic NS?

A

extrinsic

51
Q

the symp. and parasympathetic NS are capable of effecting what 4 things?

A

chronotropy/HR
inotropy/contractility
preload/ventricle filling volume
afterload

52
Q

what controls arterial pressure?

A

baroreceptors in the carotid bulb and AO arch

53
Q

what happens with carotid bulb massage?

A

increases press to brain which slows HR

54
Q

what are the 6 parts of the intrinsic conduction pathway?

A
  1. SA node
  2. LA/RA (intermodal tracts)
  3. AV node
  4. bundle of His
  5. R & L bundle branches
  6. purkinje fibers in LV
55
Q

describe the location and function of the SA node

A

located near the superior wall of the RA, near entry of SVC

pacemaker of the heart, HB starts in the SA node

56
Q

how many pulses per min does the SA node generate? what mechanism slows it down?

A

100 pulses per min

parasympathetic tone reduces it to 60-100

57
Q

what demographic has high parasympathetic tone?

A

athletes

58
Q

how does stimulation in the atria travel?

A

from the SA node along the internal atrial conduction paths and ends at the AV node

59
Q

whats the location of the AV node?

A

found in the right side of the IAS above the annulus of the TV and near the opening of the coronary sinuses

60
Q

whats the function of the AV node?

A

delays the impulses to allow for atrial contraction and ventricle filling… also so that the atria can contract before the ventricles

61
Q

what is the AV groove?

A

insulates the pulses so that they only travel in the pathway of specialized cells

62
Q

how many pulses per min can the Av node generate? and when would it generate pulses?

A

40-60… called a junctional rhythm

only if the SA node fails

63
Q

where is the Av bundle located? what is its main function?

A

sightly distal to the AV node

only electrical pathway between the atria and ventricles (like a ‘major highway’) and protects the ventricles from fast atrial rhythms

64
Q

what occurs to the impulse when it travels through the bundle branches?

A

it speeds up again

65
Q

Through what pathway does the impulse travel along the bundle branches?

A

they travel along the IVS towards the apex of the heart and then turn superiorly towards the base on the lateral sides of the heart

66
Q

what happens to the impulse in a left bundle branch block?

A

it will slow the conduction through the ventricles and lead to the longer QRS complex

67
Q

which septum is stimulated first from the bundle branches?

A

RV septum, then L

68
Q

when does ventricular depolarization occur?

A

as the wave of stimulation travels along the bundle branch pathway

69
Q

whats causes the QRS complex on the EKG?

A

ventricle depolarization.

70
Q

where are the purkinje fibres located? describe their appearance

A

through the IVS and into the ventricles/apex

they’re more elaborate on the left side due to thicken muscle (like small roads going through neighbourhoods)

71
Q

whats the function of the purkinjie fibres?

A

deliver impulses to the individual muscle cells

help the AV valves function by stimulating the pap muscles before the rest of the cells

72
Q

what happens as the stimulation is going through the purkinjie fibres?

A

contraction is completed and the ventricle start to repolarize

73
Q

how many pulses per min and the perkinjies produce?

A

30-40 (would require a pacemaker)

74
Q

where does contraction being?

A

apex, helps with the ejection of blood

75
Q

whats responsible for the t wave of the ECG

A

Repolarization of ventri

76
Q

how long does it take for repolarization to occur in the SA node?

A

200 ms

77
Q

when the atria are repolarizing, what are the ventricles doing?

A

depolarizing… they will always be opposite

78
Q

like which conducting pathways will take over if the SA node fails

A

AV node
bundle of his
LV/RV muscle cells

79
Q

How many pulses per minute can the LV and RV produce?

A

20-30

80
Q

What part of the conduction path way is malfunctioning when a person has a heart arrhythmia?

A

The AV node

81
Q

what is the HR generated by the AV node called?

A

junctional rhythm

82
Q

What’s another term for electrical mechanical coupling?

A

Excitation coupling

83
Q

How long should the AP last from phase 0 to the beginning of phase 4?

A

200ms

84
Q

What are the 3 ions are most responsible for AP and depolarization?

A

Sodium, calcium, potassium

Echo 1 (17 decks)

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