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1
Q

how are cardiac and skeletal muscle similar

A

both have striations

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2
Q

how are cardiac and skeletal muscle different

A

skeletal: each fibre is separate and innervated by nerve from spinal cord
cardiac: fibres are connected
mechanically: intercalated discs
electrically: gap junctions in intercalated discs

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3
Q

what are some ribosomes found in the cardiac muscle fibre

A 
mitochondria
sarcoplasmic reticulum 
sarcomere
T tubules
bands
sarcolemma (PM)
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4
Q

what’s the sarcolemma

A

equivalent of plasma membrane but for muscle cells

barrier…

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5
Q

are there any intrinsic nerves in the heart

A

no

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6
Q

what vessel supplies the AV node

A

RCA, so if there’s MI there, no beat unless good enough anastomosis from LCA

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7
Q

where is the SA node found

A

right atrium near entry of SVC

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8
Q

are nodes nerves?

A

no, they’re modified cardiac cells

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9
Q

where is the AV node found

A

inter atrial septum near tricuspid valve

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10
Q

how are AP initiated=

A

by opening of sodium and calcium channels

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11
Q

what’s the funny current

A

mixed sodium–potassium current that activates upon hyperpolarization
after each AP, potassium channels close and Na channels open
it dictates pacemaker potential

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12
Q

when is a new AP generated

A

when there’s enough Na and Ca channels open (above threshold)

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13
Q

what ion Chanel maintains the resting potential enter -70 et -90 mv

A

K channels

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14
Q

what systems can alter the speed and rhythm of firing of SA node

A

sympathetic and parasympathetic NS

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15
Q

explain the effect of the PNS on the SA node

A

slows down pacemaker cells
vagus nerve actus via interneurones to inhibit closure of K channels via MUSCARINIC receptors
(depolarisation takes longer)

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16
Q

explain the effect of the SNS on the SA node

A

increase HR pacemaker cells
adrenaline increase rate of closure of K channels via beta adrenoreceptors
(depolarisation takes shorter)

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17
Q

explain the effect of the PNS SNS on the AV node

A

they have an effect bas weaker

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18
Q

what is sinus arrhythmia and why does it happen

A

decrease in HR during expiration (respiratory sinus arrhythmia is normal)
happens bc parasympathetic outflow to vagus nerve increases during expiration and decreases during inspiration

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19
Q

what drug blocks parasymp? what can it be used for

A

atropine blocks PNS and can be used to treat sinus arrhythmia.

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20
Q

how long after SA node stimulation does AP reach both atria and AV node

A

60ms

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21
Q

how long after SA node stimulation does AV node transmit AP to ventricles papillary muscle and bundle of his

A

120 ms

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22
Q

how long is the delay at AV node

A

60ms

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23
Q

where does AV node transmit AP

A

to ventricles PAILLARY MUSCLE and bundle of His

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24
Q

why is there a delay at AV node

A

to allow atria to contract and fill ventricles

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25
are Purkinje fibres nerves
no they are fast conducting cardiac muscle
26
what two branches come off the bundle of his
right bundle branch and left bundle branch
27
what are the fibres that branch out from the bundle branches
Purkinje fibres
28
where do the right and left bundle branches connect
bundle of His
29
what's one unique feature of the AV node
Decremental conduction. the more its stimulated the slower it conducts, so that in atrial fibrillation the ventricles don't contract too quickly and still have time to fill
30
what part of the ventricle first contracts
papillary muscles
31
how long after SA stimulation is the base of the heart stimulated
180ms
32
how do valves close
papillary muscles pull on chordate tendinae
33
what pathologies result from poor conduction?
bundle branch blocks. can be a result of ischemia of septum (bc it causes poor conduction)
34
dos branch block necessarily mean CESSATION of conduction
no it can just be a decrease in conduction
35
in terms of AP, what is one key difference between cardiac and skeletal muscle
cardiac muscle needs to contract longer so there's a plateau with a prolonged Ca entry to cell.
36
explain the process of ventricular muscle action potential initiation
``` Na channels open. na influx. k and cl out prolonged and delayed ca entry (PLATEAU) k out k rectified ```
37
what channels do calcium enter from
L type calcium channels on cardiac cells
38
what drugs can be given to reduce strength of contraction and so work of the heart and o2 demand
calcium Chanel blockers.
39
strength of contraction of ventricular muscle depends on what
calcium concentration intracellylary
40
Na Chanel blockers (CLASS 1)
weak: lidocaine phenytoin moderate: quinidine proquanindaine strong flecavidine, propafenone
41
ca Chanel blockers (CLASS 4)
verapamil, dilfiazen
42
k Chanel blockers (CLASS 3)
amiodanone sotalol
43
beta blockers (CLASS 2)
BLOCK K rectifier propanolol metaprolol
44
why is a refractory period important
prevents premature muscle contraction and so allows everything to beat in synchonry
45
what tool can be used to override refractory period
defibrillator
46
what are the 6 limb leads and what area do they measure
``` lead 1: Left --> Right axillae lead 2: Right axillae --> leg lead 3: Left axillae --> leg aVL aVR aVF ```
47
what is one downside of limb leads
it only gives you an image on the frontal plane.
48
what leads make up eiahovens triangle
lead 1: Right --> Left axillae lead 2: Right axillae --> leg lead 3: Left axillae --> leg
49
standard ECG is recorded from which lead and why
lead 2 because it gives off the largest signal
50
PR interval normal duration
120-200ms
51
QRS complex normal duration
60-100ms
52
which wave on an ECG is not always visible
Q
53
P wave normal duration
100 ms
54
what does the P wave correspond to? | positive/negative?
START of atrial depolarisation | positive in leads 1, 2 and sometimes 3
55
what does the PR interval correspond to
delay at AV node
56
what does the QRS complex correspond to | positive/negative?
electrical activity in ventricles | polarity depends on lead, can be pos, neg, bipolar.
57
what does the R wave correspond to? | positive/negative?
ventricle depolarization ALWAYS POSITIVE present on leads 1,23
58
what does the ST segment correspond to? | what is one unique feature of the ST segment
the interval between ventricular depolarization and repolarization its isoelectric 0mV can be raised in MI
59
what does the T wave correspond to | positive/negative?
repolarisation of ventricles. base of ventricle depolarises depolarises before apex so upward wave pathological T wave for septum injuries normally same polarity as QRS
60
how many seconds in one big square?
0.2 seconds
61
how many seconds in one small square?
0.04s
62
how many small square for 1 mV
10
63
how many mm for 1 second
25
64
when is the ECG large
when depolarisation is changing
65
what does the Q wave correspond to | positive/negative?
earlier depolarisation of left side of intervenrticalr septum NEGATIVE lead 1, aVL, V5, V6
66
what does the S wave correspond to? | positive/negative?
spread to depolarisation to base of ventricle | negative ALAWYS
67
what are the 3 augmented leads
aVR from middle to right axillae aVL from middle to left axillae aVF from middle to groin
68
how are the augmented leads oriented
aVR upside down aVL v small aVF variable bas normally like lead 2
69
what is one benefit of augmented leads over the three standard ones
help better identify locus of abnormality
70
how many chest leads are there and what are their names
6 (V1-V6)
71
what is one benefit of chest leads over limb leads
gives you a 3D picture
72
what are pericardial leads
chest leads
73
location of V1
4th ICS left sternal edge
74
location of V2
4th ICS right sternal edge
75
location of V3
Rib 5 entre V2 and V4
76
location of V4
5th ICS midclavicular
77
location of V5
5th ICS anterior axillar
78
location of V6
5th ICS midaxilla
79
where an apex beat be heard
v4
80
chest leads measure from what
from an imaginary reference point in the heart to the position of electrode
81
``` what degree are the following in v1 v2 v3 v4 v5 v6 ```
``` v1 100 v2 80 v3 75 v4 60 v5 30 v6 0 ```
82
V leads can also be called
c leads
83
what is the normal polarity of leads v1 to v6
``` v1 negative (small R large S) v2 negative (small R large S) v3 bipolar v4 bipolar v5 positive (large R small S) v6 positive (large R small S) ```
84
``` what parts of the heart is each lead best at I II III aVL aVR aVF V1-V6 ```
``` v1 view septal v2 view septal v3 view anterior heart wall v4 view anterior heart wall v5 v6 I aVL lateral wall II III aVF inferior ```

Cardioresp (23 decks)

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