Elec Activity Of The Heart, Regulation Of CO 🫀 Flashcards
What is a cardiac muscle cell called?
myocyte
What is meant by autorhythmic?
myogenic/ self-excitable - cells generate an APl throughout myocardium causing heart to contract as a single unit
What do APs/ current pass through to be conducted to the next myocytes?
gap junctions
What are the key organelles within a cardiomyocyte? (7)
- contractile myofilaments
- T-tubules containing:
- Na/Ca exchanger
- L-type Ca2+ channel
- RyR receptors
- SERCA pump
- sarcoplasmic reticulum
role of gap junctions in cardiac myocyte?
help generate elec activity of heart = 1 contraction/heart beat
impulses between myocytes
role of calcium stored in the cardiac muscle cell- sarcoplasmic reticulum (SR)?
helps contraction of the myofilament
What is an action potential?
transient depolarisation as a result of ion channels
What are the 3 broad cardiac action potential patterns?
- SA and AV node AP
- Atrial muscle AP
- Purkinje fibres & ventricular muscle AP
Through what 3 characteristics do the 3 broad cardiac action potential patterns differ by?
- duration
- shape
- ionic basis
What are the 5 phases of ventricular action potential?
1) phase 0: depolarisation
up
2) phase 1: partial repolarisation
3) phase 2: plateau
4) phase 3: repolarisation
down
5) phase 4: resting membrane potential
In phase 0 of ventricular action potentials, what occurs in terms of ion movement? (hint: Na)
depolarisation: rapid influx of Na due to opening of Na ion channels
In phase 1 of ventricular action potentials, what occurs in terms of ion movement? (hint: Na, K)
repolarisation: closure of Na+ channels, small efflux of K+
In phase 2 of ventricular action potentials, what occurs in terms of ion movement? (hint: Ca, K)
plateau phase sustained by :
- influx of Ca into myocyte
- efflux of K
In phase 4 of ventricular action potentials, what occurs in terms of ion movement?
nothing - this is a stable state with no alteration
resting membrane potential
In phase 3 of ventricular action potentials, what occurs in terms of ion movement? (hint: Ca, K)
rapid repolarisation: fast efflux of K, due to closure of Ca channels
how does SA node fiber AP graph differ to ventricular muscle fiber graph?
SA: only has 0, 3, 4 phase
learnt in year 1
Ventricular has 0,1,2,3
In phase 0 of SA node action potentials, what occurs in terms of ion movement? (hint: Ca)
depolarisation:
VG Ca channels open, fast VG Na are inactivated due to less negative resting potential of these cells = slow conduction velocity used by SA node
In phase 3 of SA node action potentials, what occurs in terms of ion movement? (hint: Ca, K)
repolarisation:
inactivation of Ca channels but increase activation of K channels so increase K efflux
In phase 4 of SA node action potentials, what occurs in terms of ion movement? (hint: Ca, K)
slow, spontaneous depolarisation due to ‘funny current’ channels: responsible for slow K and Na inward current, different from Na in phase 0 in ventricular AP
fall below threshold
What phase of what type of action potential determines the heart rate?
phase 4 of SA node action potentials
slope of repolarisation.
catecholamines more = higher HR
how does atrial muscle depolarisation compare with SA and AV nodes depol?
atrial muscle: fastest depol
SA and AV: slow depol
what happens to VG K+ channels in SA node AP when resting potential = -.
become permanently inactivated. slow velocity conduction by SA nodes
upstroke in SAN compared with ventricular?
upstroke in SAN much slower.
what is rhythm of heart determined by and what is this?
pacemaker cell:
excitable cells that generate electrical impulses (autorhythmic) to set the heart rhythm
where are pacemaker cells mainly found?
in SA node.
have natural automacity = can gen impulses themselves
Pacemaker cells have an unstable what potential, and what is this also known as?
have an unstable resting potential, AKA pacemaker potential
= slow depol towards threshold
The rate of decay of resting potential determines what?
Rate of decay of the SA node resting potential determines the rate of AP, and hence HR
heart rate.
When does the pacemaker potential occur?
at the end of 1 AP and before the start of the next one - this is the slow depolarisation of pacemaker cells (e.g. SA cells) towards the threshold
What is “cardiac muscle excitation-contraction coupling?”
the process whereby AP triggers myocyte to contract
how does AP travel through cardiac myocyte?
AP conducted through gap junctions of cardiac myocyte - each has filament for contraction
1st step in cardiac muscle excitation-contraction coupling? (3)
- Na enters into cytosol via channel (red dots)
- increase in AP
- Initiates beginning of depolarisation phase
2nd step in cardiac muscle excitation-contraction coupling? (5)
- Depolarisation phase= Ca enters myocyte through L-type channels, stimulating RyR receptor on SR
- Ca released from SR via RyR into cytosol =plateau phase of ventricular AP
- Also increase of [Ca], then binds to myofilament
3rd step in cardiac muscle excitation-contraction coupling?
contractions take place, Ca released from myofilament after it binds
4th step in cardiac muscle excitation-contraction coupling?
repolarisation
decreased Ca and contractions. (relaxation)
Ca leaves via:
- goes to SR - via SERCA//PLB
- Na-K (Na-CaX) exchanger. 3 Na come in for 1 Ca out
5th step/ ending summary in cardiac muscle excitation-contraction coupling?
cell wants to return to normal AP.
using the ATP on surface,
3Na leave, 2K enter.
helps resting MP.
contract, relax = 1 HR/beat :)
