205 L9 Flashcards
Cardiac electrical activity
What is arrhythmia?
When the heart doesn’t work at 100% efficiency.
What is trachycardia?
Heart is working faster than it should be so it gets less efficient because there isn’t enough time for the blood to fill up.
The heart pumps blood by a continuing cycle of ——– and ———-(SYSTOLE & DIASTOLE). In order for muscle to contract, it must first be ——— activated.
The heart pumps blood by a continuing cycle of contraction and relaxation (SYSTOLE & DIASTOLE). In order for muscle to contract, it must first be electrically activated.
The heart is not activated all at one instant. Its activated by a wave of ——– that spreads throughout the ——-in a co-ordinated manner. Therefore ——— each area at the appropriate ——–,
so that ——- is effective in ——– the blood forward into the circulation.
If this pattern of spread of electrical activation is upset then the heart will not act as an effective pump with results ranging from relatively minor such as limiting exercise capacity (eg. atrial fibrillation) to fatal (eg. ventricular fibrillation).
The heart is not activated all at one instant. Its activated by a wave of excitation that spreads throughout the myocardium in a co-ordinated manner. Therefore stimlating each area at the appropriate time,
so that systole is effective in propelling the blood forward into the circulation.
What are the myocyte electrical properties?
Excitability
Conductivity
Automaticity
Excitability - Fast response AP
—— response cells are found throughout the ——-, are the most ———- action potential that is seen, are part of the contracting/working cardiac muscle in the —— and ——–, the fast part of specialized conduction system
These specialised cells are very important at coordinating this rapid spread of —— activity throughout the ——- and ensure the ——– is tightly coordinated
This is a fast response action potential because the ———– (phase —) is very fast (same speed as nerve).
Fast response cells are found throughout the heart, are the most common action potential that is seen, are part of the contracting/working cardiac muscle in the atria and ventricle, the fast part of specialized conduction system
These specialised cells are very important at coordinating this rapid spread of electrical activity throughout the ventricles and ensure the contraction is tightly coordinated
This is a fast response action potential because the depolerization (phase 0) is very fast (same speed as nerve).
Fast response AP and ionic currents.
Phase 0: upstroke (rapid —— to —-mV from resting —-mV) very rapid increase in ——- permeability.
This occurs because the membrane potential is ——– externally which is usually due to a ——– passing through it by a neighboring —-.
The cell reaches a ——– potential and at this point it’s enough to trigger the opening of voltage gated —— channels which allows the rapid influx positively charged ——— ions
The ——– channels open and close very fast
Phase 1: early ———- (to near —- mV)
——– channels start closing (stopping influx of ——-) and chloride channels start opening (transcend outwards current - largely —-) brings the cell potential back a little bit
These channels close ——- as well
Phase 2: ——— i) slow inward ——- current (i—) ii) outward —— current (i—-)
Not much change in the membrane potential - the movement of ions is almost perfectly in ——– (doesn’t mean that the ions are not moving)
There is an inwards——— current (——— is needed to make the ——– contract not —-)
Outward ——- current opposes the inward current
Phase 3: ———–
——- and —— dependent channel is switched – by the initial ———- (phase –) but it takes time for the channel to actually —–
The ——– current is the ——- current which starts to —— the cell down towards the —— membrane potential
Phase 4: resting i— high ——- conductance defines ——- Potential
As the membrane potential —– more ——- channels (i—) will open and these are ——- sensitive and the i—- channels will begin to close.
At rest there is only one type of channel open the i— channels
Background activity
——— ——— - outward current
——— —— exchanger (3 — in for 1 —- out, net positive charge)
—— ——– ——— - (3 —out for 2 — in, maintains – gradient)
Phase 0: upstroke (rapid —— to —-mV) very rapid increase in ——- permeability.
This occurs because the membrane potential is ——– externally which is usually due to a ——– passing through it by a neighboring —-.
The cell reaches a ——– potential and at this point it’s enough to trigger the opening of voltage gated —— channels which allows the rapid influx positively charged ——— ions
The ——– channels open and close very fast
Phase 1: early ———- (to near —- mV)
——– channels start closing (stopping influx of ——-) and chloride channels start opening (transcend outwards current - largely —-) brings the cell potential back a little bit
These channels close ——- as well
Phase 2: ——— i) slow inward ——- current (i—) ii) outward —— current (i—-)
Not much change in the membrane potential - the movement of ions is almost perfectly in ——– (doesn’t mean that the ions are not moving)
There is an inwards——— current (——— is needed to make the ——– contract not —-)
Outward ——- current opposes the inward current
Phase 3: ———–
——- and —— dependent channel is switched – by the initial ———- (phase –) but it takes time for the channel to actually —–
The ——– current is the ——- current which starts to —— the cell down towards the —— membrane potential
Phase 4: resting i— high ——- conductance defines ——- Potential
As the membrane potential —– more ——- channels (i—) will open and these are ——- sensitive and the i—- channels will begin to close.
At rest there is only one type of channel open the i— channels
Background activity
——— ——— - outward current
——— —— exchanger (3 — in for 1 —- out, net positive charge)
—— ——– ——— - (3 —out for 2 — in, maintains – gradient)
Slow response AP phases
Found in the ——- and ——- nodes.
The resting potential of the cells is —— than the fast response cells at about —-mV.
The upstroke (phase –) is —– because there is — current in these cells. It is produced by an influx of ———- via i—.
Phase 2 is a slight —–.
There are either no ——– channels, or there are inactive ——– channels. This is because the cells resting potential is ——, the —– channels become active by the rapid ———– so some of the channels that need to be turned on by the —— are not ———.
Found in the ——- and ——- nodes.
The resting potential of the cells is —— than the fast response cells at about —-mV.
The upstroke (phase –) is —– because there is — current in these cells. It is produced by an influx of ———- via i—.
Phase 2 is a slight —–.
There are either no ——– channels, or there are inactive ——– channels. This is because the cells resting potential is ——, the —– channels become active by the rapid ———– so some of the channels that need to be turned on by the —— are not ———.
Ischemia and AP
Sometimes in ischemia (part of the heart that’s not getting any blood) you have cells that become sick and the —— potentials of the —– response cells can ——- resulting in a change in action potential with a —— upstroke and —— conduction. This can lead to ——.
Sometimes in ischemia (part of the heart that’s not getting any blood) you have cells that become sick and the —— potentials of the —– response cells can ——- resulting in a change in action potential with a —— upstroke and —— conduction. This can lead to ——.
Cardiac AP - Excitability
In the —– —— period all the cells in the heart within this time period after ——– with an action potential are not able to be ——– again. This is because the ——- channels responsible for the ——— have certain properties which mean that after they have —— they cant —— again after a certain —— delay has gone by, so they can’t be —— during this period. Therefore if you hit the heart with another —— stimulation in the —— ——- period you would get —- response.
In the —- —– period you can ——— the cells but its ——- to do so you might need to inject more ——- to ——- the cells so that they are likely to be able to produce a ——-. This is because some of the —— channels have opened but others are still closed.
You get a normal action potential after the —– —– time.
Refractoriness over long periods prevents ——– of the heart
In the —– —— period all the cells in the heart within this time period after ——– with an action potential are not able to be ——– again. This is because the ——- channels responsible for the ——— have certain properties which mean that after they have —— they cant —— again after a certain —— delay has gone by, so they can’t be —— during this period. Therefore if you hit the heart with another —— stimulation in the —— ——- period you would get —- response.
In the —- —– period you can ——— the cells but its ——- to do so you might need to inject more ——- to ——- the cells so that they are likely to be able to produce a ——-. This is because some of the —— channels have opened but others are still closed.
You get a normal action potential after the —– —– time.
Refractoriness over long periods prevents ——– of the heart
Cardiac AP - Excitability
In the —– —— period all the cells in the heart within this time period after ——– with an action potential are not able to be ——– again. This is because the ——- channels responsible for the ——— have certain properties which mean that after they have —— they cant —— again after a certain —— delay has gone by, so they can’t be —— during this period. Therefore if you hit the heart with another —— stimulation in the —— ——- period you would get —- response.
In the —- —– period you can ——— the cells but its ——- to do so you might need to inject more ——- to ——- the cells so that they are likely to be able to produce a ——-. This is because some of the —— channels have opened but others are still closed.
You get a normal action potential after the —– —– time.
Refractoriness over long periods prevents ——– of the heart
In the —– —— period all the cells in the heart within this time period after ——– with an action potential are not able to be ——– again. This is because the ——- channels responsible for the ——— have certain properties which mean that after they have —— they cant —— again after a certain —— delay has gone by, so they can’t be —— during this period. Therefore if you hit the heart with another —— stimulation in the —— ——- period you would get —- response.
In the —- —– period you can ——— the cells but its ——- to do so you might need to inject more ——- to ——- the cells so that they are likely to be able to produce a ——-. This is because some of the —— channels have opened but others are still closed.
You get a normal action potential after the —– —– time.
Refractoriness over long periods prevents ——– of the heart
Conductivity
Cardiac muscle cells do not contract in response to a ——- signal. They are ———.
The signal begins within the heart itself in the —– node.
——– activation spreads throughout ——— from cell to cell.
This occurs because each cell is electrically coupled to several other cells via ——- ——, so as one cell ———-, current spreads to ——— cells allowing coordinated ——-.
Cardiac muscle cells do not contract in response to a ——- signal. They are ———.
The signal begins within the heart itself in the —– node.
——– activation spreads throughout ——— from cell to cell.
This occurs because each cell is electrically coupled to several other cells via ——- ——, so as one cell ———-, current spreads to ——— cells allowing coordinated ——-.
Automaticity
Ability of cells to initiate an —- impulse through their own ——- activity, or diastolic ——– (AP)
These cells are found in the —— node in the ——. Some are found around the —– node and the __ ___-___ network
Ability of cells to initiate an —- impulse through their own ——- activity, or diastolic ——– (AP)
These cells are found in the —— node in the ——. Some are found around the —– node and the __ ___-___ network
Pacemaker AP phases (automaticity)
The ——— membrane potential is never flat because there is a —– rate of —– in membrane potential which is responsible for the spontaneous firing.
The ———- of these cells is either due to the influx of —– via i—- or ——–.
The ——— current is slightly out doing the ——– current such that the balance of the net current movement is in favour of ——— resulting in the slow ——– membrane potential.
The outward current is due to ———- via i—- and i—- channels which are on most of the time but it varies in strength throughout the action potential.
The inward current is due to i— channels that switches on and then off and the i— current that is largely a —— current that is activated by hyperpolerisation.
The ——— membrane potential is never flat because there is a —– rate of —– in membrane potential which is responsible for the spontaneous firing.
The ———- of these cells is either due to the influx of —– via i—- or ——–.
The ——— current is slightly out doing the ——– current such that the balance of the net current movement is in favour of ——— resulting in the slow ——– membrane potential.
The outward current is due to ———- via i—- and i—- channels which are on most of the time but it varies in strength throughout the action potential.
The inward current is due to i— channels that switches on and then off and the i— current that is largely a —— current that is activated by hyperpolerisation.
Mechanisms for altering the intrinsic rate of pacemaker discharge to increase HR;
Alter rate of ——— by ——- inward current (open the i— more) or ——- outward current (close i—- channels)
Alter ——— potential - —— to increase HR
Alter maximum ——- potential resulting in a decreased ——- membrane potential (opening i— channels more)
Alter rate of ——— by ——- inward current (open the i— more) or ——- outward current (close i—- channels)
Alter ——— potential - —— to increase HR
Alter maximum ——- potential resulting in a decreased ——- membrane potential (opening i— channels more)
