Cardiology 2: Electrical and Mechanical Activity Flashcards
cells of the heart, like neurons, are excitable and generate ___
AP
rate of AP generation determines _____ and initiates ___
heart rate; muscle contractionn
AP is a result of changes in ___
membrane potential
membrane potential is determined by the balance in inward ___ ions and outward ___ ios
na and Ca; K
changes in membrane potentia are reliant and what type of ion channels?
voltage-gated
what are the 5 phases of cardiac ap?
Phase 0: upstroke Phase 1: early repol Phase 2: plateau Phase 3: repol Phase 4: resting
describe what is happening in the upstroke phase 0
there is rapid influx of Na through fast Na channels which are quick to open but also quick to inactivate
describe what is happening in early repolarization (phase 1)
there is a brief efflux of K through transient outward K channels
describe what is happening in the plateau phase and the ion channels involved
influx of Ca through long-lasting (L-type) ca channels, this is counterbalanced by the efflux of K through delayed rectifier K channels (reason for plateau)
t/f long-lasting Ca channels open and inactivate slower than Na channels
true
describe what is happening in the repolarization (phase 3)
there is increased opening of delayed K rectifier channels and the Ca channels inactivate, so the efflux of + is greater than influx and cell repolarizes
describe what is happening during rest (phase4) What membrane potential is held? What happens to residual Na/ca ions during this time>
inward rectifying K channels open, making cells almost exclusively permeable to K, so membrane potential is held close to K’s equilibrium value ~90mV. residual Na and ca are removed
in what three ways can Na and Ca be removed from the cell during the resting phase? What are the ratios of exchange and which of these methods requires ATP?
Na removed by Na/K pump (3Na out : 2K in) ATP
Ca removed by Na/Ca exchanger (3 Na in : 1ca out) No ATP
Ca removed by Ca pump (ATP)
what are 4 important difference between AP of the sinoatrial node compared to the atria and ventricles?
- slower upstroke
- smaller amplitude
- no early repolarization
- no resting potential
why does the sinoatrial AP have a slower uptake and smaller amplitude?
the lack of fast Na channels (driven by slow L-type Ca channels)
the upstroke of sinoatrial node ap is driven by what type of channels?
slow L-type ca channels
why does the sinoatrial ap not have early repolarization?
lacks transient outward k channels
why does the sinoatrial ap not have a resting potential?
it has automaticity (self-excitation) due to diastolic depolarization
what causes the diastolic depolarization in SA Ap? 2 channels involved
- Na influx through inward hyperpolarization-activated “funny channels”
- Ca influx through transient T-type ca channels
inward hyperpolarisation-activated funny channels and transiet T type Ca channels are olnly found in the ___
SA node
are there inward rectifying K channels in the SA node?
no
what makes funny channels funny?
as cell becomes more - causes more depol (?)
differences in pacemaker cells results in diastolic depolarization which is essential for cell ___
automaticity
excitation of the heart is initiated in the ___
SA node
excitation travels cell-cell across the atria through ____
gap juntion
excitation is delayed at the ___
AV node
why is excitation delayed at they AV node?
want ventricles to fill with blood before excited
excitation continues through fast conduction system composed of ____ cells, resulting in rapid excitation of the ventricles
Purkinje
Purkinje fibers reach into all parts of the ventricles, what is the point of this?
allows heart to contract as one
the is a ring of fibrous tissue between the A and V that electrically ____ that atria from ventricle
isolates
what does an ECG measure?
the projection of the heart’s electrical activity onto surface of the body
in an ECG, recording electrodes or “leads” are connected at specific locations on the body to measure the _____ between 2 points
potential difference
what 2 points are most commonly used for ECG?
right arm and left leg
the Q-T interval is a measure of
how rapidly ventricle is excited and how long it takes to repolarize
what does the P wave represent?
atrial excitation
what does q represent?
exciation enters purkinje, beginning of ventricle excitation
what does p-R interval represent?
AV delay
what does the QRS represent?
ventricle excitation
what does the S-T interval represent?
AP plateau
what does the T wave represnt>?
ventricular repolarization
what is the path of normal excitation of the heart?
SA –> A –> AV node –> [Delay] –> Purkinje –> ventricle
t/f each part of the heart has a unique shaped curve of activity
true
excitation triggers highly efficient contraction of the heart muscle which is dependent on the ___ of the cardiac cell
structure
cardiac muscle is striated due to ___
regular arrangement of contractile proteins (actin and myosin) in the sarcomere
the actin and myosin generate force for contraction through ___
cross-bridge cycling
Z line
site of actin attachment
M line
site of myosin attachment
I band
actin filaments
A band
myosin filament s
titin
tethers myosin to Z line
filament buldles called ____ are surrounded by the ____ which stores Ca
myofibrils; SR
the SR is closely associated with ____ which are invaginations of the membrane at the Z bands
T tubules
T tubules are filled with ____ fluid
extracellular
mitchondria make up ____% of the heart’s volume
30
the abundance of mitochondria in the heart cells provide cells with high ____ capacity
oxidative
when calcium enters _____ receptors in the SR it riggers large efflux of Ca from SR to allow for cross bridge cycling
ryanodine
relaxation of muscle occurs when Ca is removed from cytosol in what 3 ways?
- SECRA takes back into SR (most)
- Na Ca exchanger
- ca pump
