Lecture 2 - myocardial cells and fast type AP

Question 1

___ has unique caracteristics that enable the whole heart to synchronously and spontaneously depolarize

Answer 1

myocardium

Question 2

main difference between cardiomyocyte and skeletal muscle cell?

Answer 2

cardiomyocytes have gap junctions (electrically coupled) = faster communication than skeletal m cells

Question 3

cardiac muscle cells have increased __ and __

Answer 3

glycogen storage and higher # of mitochondria

Question 4

rapid spontaneous sequential depolarization occurs in special myocardial cells called __ that results in the synchronized rhythmic contractions of the heart known as __

Answer 4

pacemaker cells, systole

Question 5

changes in pressure within ventricles resulting from systole results in __ providing unidicretional flow followed by relaxation known as __

Answer 5

passive open/close of the heart valves, diastole

Question 6

myofibers end with specialized region called the ___ which contains gap juntions. This allows for ___ between cells = rapid impulse conduction and depolarization across the myocardium

Answer 6

intercalated disk, direct elelctrical coupling

Question 7

Depolarization is initiated by specialized myocardial cells called __ located in the __ node.

Answer 7

pacemaker cells, SA node

Question 8

__ nodal cells and ___ also have pacemaker qualitites but are referred to as auxiliary pacemakers

Answer 8

AV, purkinje fibers

Question 9

Pacemaker cells of the SA node produce __ APs allowing them to __ depolarize which eliminates need for input from external controls (why the heart beats when it is removed from the body)

Answer 9

self generating, spontaneously

Question 10

The 2 most important characteristics of all excitable membranes

Answer 10

1. maintain ion concentration gradients

2. respond to electrical depolarization

Question 11

Resting membrane potential (RMP) is determined by

Answer 11

high permeability to K+ and low permeability to Na+ and Ca++ (K+ concentration is greater inside cell at rest)

Question 12

Why is the K+ concentration greater inside a cell at rest

Answer 12

1. membrane is permeable to K+
2. negative proteins inside cell draw K+ in
3. Na+/K+ ATPase pump pulls K+ inside

Question 13

Increases in EXTRAcellular K+ cause __ of RMP of cardiac muscle fibers. Changes in extracellular concentrations of Na+ and Ca++ have __ effect on RMP (!)

Answer 13

increase/depolarize, little to no

Question 14

Due to the RMP of neurons (-65mV) they are 5x more permeable to __ than myocardiac cells (-90mV RMP)

Answer 14

Na+

Question 15

True or False: AP of myocardial cells are longer in duration than skeletal muscle cells or neuron APs.

Answer 15

True, increase duration of AP in cardiac cells is due to large influx of Ca++ during depolarization (along with normal Na+ influx)

Question 16

What causes the longer duration of mycardiocyte AP

Answer 16

large influx of Ca++ along with Na+ during depolarization

Question 17

What are the 2 types of AP that can be recorded from myocardiocytes

Answer 17

fast type AP and slow type AP

Question 18

___ AP is observed in most myocardiocytes, recorded from the atrial and ventricular myocytes and in the specialized conducting fibers, the __

Answer 18

fast response AP, purkinje fibers

Question 19

___ AP is observed in pacemaker cells of the SA and AV nodes

Answer 19

slow response AP

Question 20

List the phases of the fast response cardiac APs

Answer 20

1. Phase 0 = rapid depolarization
2. Phase 1 = transient repolarization
3. phase 2 = plateau phase
4. phase 3 = rapid repolarization
5. phase 4 = RMP

Question 21

Phase 0 (rapid depolarization) depends on rapid influx of __ causes by __ channels

Answer 21

Na+, “fast” type Na+ channels

Question 22

Phase 1 (transient repolarization) the Na channels __ and outward __ current is activated by depolarization

Answer 22

inactivate, K+

Question 23

phase 2 (plateau) __ channels begin to open slowly at -35mV threshold and flow via concentration gradient before slowly spontaneously closing at the end

Answer 23

Ca++ (also, K+ conductance is low which contributes to plateau)

Question 24

In phase 2 the __ influx from extracellular space is very important in depolarization and is also referred to as the __

Answer 24

Ca++, “excitation-contraction coupling” process

Question 25

in phase 3 (rapid repolarization) __ conductance increases via ___ channel that is activated by depolarization during phase 2 plateau which drives __ out of the cell. All other channels are closed/closing.

Answer 25

K+, voltage sensitive K+ channel, K+

Question 26

Phase 4 (RMP) Is dependent upon ___ K+ conductance and low __ conductance. After the AP __ balance the Na+:K+ and Ca++ is balance via ___ and __.

Answer 26

high K+, low Na+ and Ca++, Na+/K+ ATPase pump, Na+/Ca++ exchanger on sarcolemma and reuptake of Ca++ into sarcoplasmic reticulum

Question 27

associated with the extremely long cardiac AP is an extremely long ___ which allows for __

Answer 27

refractory period = time between heart beats for adequate cardiac filling and Ca++ reuptake

Question 28

The refractory period length depends on the number of __ that have recovered from their inactive state

Answer 28

Na+ channels

Question 29

the ___ occurs during phases 1-3, where in phase 1-2 the cell is completely __ to new input and at phase 3 the cell can produce local AP but there is no propagation

Answer 29

absolute or effective refractory period (EFP)

Question 30

The __ period occurs during phase 3 repolarization. At this point the cell can be stimulated, an AP can be triggered but the conduction is slow and may not depolarize the rest of the heart and thus will not generate a heart beat

Answer 30

relative refractory period

Question 31

__ node contains true pacemaker cells which can depolarize spontaneously and maintain a normal HR

Answer 31

SA

Question 32

__ node is located in the atrium where the cranial vena cava empties and __ node is located between the supraventricular/ventricular area

Answer 32

SA, AV

Question 33

Does the contraction happen at the same time as an electrical event?

Answer 33

no, happens shortly after

Question 34

AV node is separated into __ and __ branches/bundles

Answer 34

left and right

Question 35

___ AV node branch divides into anterior and posterior bundles

Answer 35

left

Question 36

__ AV node branch goes to the apex of the heart

Answer 36

right

Question 37

__ AV node branch goes to the septum and gives rise to purkinje fibers in the ventricle walls

Answer 37

both (right and left AV node branches)

Question 38

If something happens to the SA node the AV node takes over at a ___ rate

Answer 38

slower

Question 39

SA and AV nodes undergo __ type AP = slow depolarization

Answer 39

slow

Question 40

___ is important for cardiac cell returning to RMP and produces a net outward movement of positive charge

Answer 40

Na+/K+ ATPase pump (3 Na+ : 2K+)

Question 41

resting cardiomyocyte has large amounts of __ inside cell

Answer 41

K+

Question 42

while neurons and cardiac cells ahve similar equilibium potentials for K (~-95mV) their RMP drastically differ (neuron = -65mV, cardiac = -90mV), why is this?

Answer 42

at rest, cardiomyocytes are relatively impermeable to Na+ , K+ influx determines the RMP

Question 43

changes in extracellular K+ levels can quickly alter myocardial RMP; increase in K+ outside cell = __ where decrease in K+ outside cell = __

Answer 43

depolarization (increase AP) of cardiac cell, hyperpolarization of cardiac cells

Question 44

Cat with urinary obstruction becomes hyperkalemic (high K) - how does this affect the heart?

Answer 44

predisposes to severe arrhythmia, must address

Question 45

high __ levels can lower the K levels (via excretion by kindeys) and predispose p to arrhythmia

Answer 45

aldosterone

Question 46

unlike extracellular changes in K (greatly affect RMP), changes in extracellular __ and __ have little to no effect on cardiac cell RMP

Answer 46

Na+ and Ca++

Question 47

Cardiomyocyte plateau in fast AP is important for

Answer 47

squeezing blood out of heart

Question 48

phase __ of fast type AP is K+ dependent and NO Na or Ca conduction occurs

Answer 48

4 (RMP)

Question 49

phase __ is critical for heart contraction. Ca++ slowly flows into cells and K conductance decreases

Answer 49

2 (plateau)

Question 50

phase __ is where repolarization is completed and Ca conductnace decreases (Ca channels slowly close) and K conductance ___ via rectifier channel

Answer 50

3 (final repolarization), increases (driving force for K to exit cell)

Question 51

Phase 4 (RMP) K conductance is __, __ pumps regulate Na levels and __ exchanger regulates internal Ca++

Answer 51

high, Na+/K+ ATPase pump, Na+/Ca++ exchanger

Question 52

___ are protection mechanisms that prevent tetanus and arrythmias and allows for ___ and ___

Answer 52

Refractory periods, maximum stroke volume, diastolic filling

Question 53

__ in phases 1-2 the cells will not respond to impulses and the cell is contracting

Answer 53

effective or absolute refractory period

Question 54

__ in phase 3 cells can respond to impulse but need a much higher than normal impulse to cause an AP propogation (drugs or disease)

Answer 54

relative refractory period

Question 55

__ period ensures that cels finish contractions before restimulation allowing for max stroke volume and sufficient diastolic filling

Answer 55

absolute/effective refractory period

Question 56

__ period there are APs with reduced amplitudes due to the low driving force for Na channels to open

Answer 56

relative refractory period

Question 57

myocardial cells are ___ allowing the whole heart to synchronously and spontaneously depolarize

Answer 57

electrically coupled

Question 58

long AP and refractory periods are associated with cycles of changing

Answer 58

ions (Na, Ca, K)

Question 59

Cardiomyocytes have a RMP of __, highly permeable to __ at rest, and are relatively impermeable to __ and __ at rest

Answer 59

-90mV, K+, Na+, Ca++