Lecture 2- Conduction System Flashcards
Resting state
The activation gates on Na+ and K+ channels are closed and the membrane’s resting potential is maintained constant
Depolarisation
A stimulus opens the activation gates on some Na+ channel Na+ influx through those channels depolarise the membrane If depolarisation reaches the threshold, it triggers an action potential
Rising phase of action potential
Depolarisation opens activation gate on most Na+ channel, while K+ channel activation gate remain closed. Na+ influx make inside of membrane positive with respect to outside
Falling phase of action potential
The inactivation gates on most Na+ channels close, blocking Na+ influx. The activation gates on most K+ channel open, permitting K+ effluent which again make the inside of cell negative
Undershoot
Both gates of the Na+ channel are closed, but the activation gates on some K+ channel are still open. As these gates close on most K+ channel, and the inactivation gate opens on Na+ channel, the membrane returns to resting state
What are primary pacemaker site within the heart?
Cells within sinoatrial node
Cells within sinoatrial node
No true resting potential Generate regular, spontaneous AP
What is the depolarising current carried into cell by?
Relatively slow ca++ current
What is funny current?
At end of repolarization, when the membrane potential is very negative, ion channel open that conduct slow, inward current
When does T-type ca++ channel open and what does it do?
As the membrane potential reaches -50mv Ca++ enters the cell Further depolarises the cell
When does L-type ca++ channel open?
When the membrane depolarises to about -40mv More ca++ enters the cell Further depolarises the cell until action potential threshold is reached
What are funny channels and T-type calcium channel?
Voltage gated but also opened by CAMP Sodium and calcium ions enter the cell
Since there are no ‘regular’ fast Na+ channel, what is the Na+ influx due to?
F channels
L-type calcium channel
Long term ca++ influx
What does funny channel allow?
Allow Na+ to enter
What does T-type allow?
Allow Ca2+ to enter transiently
How does neurotransmitters and drugs often work?
Indirectly through G protein
Chemical synaptic transmission within neutron
AP reaches axon terminal of presynaptic neuron Ca2+ enter synaptic Knob in the presynaptic terminal This causes the vesicles containing ACH to fuse with the membrane and be released into synaptic cleft via exocytosis ACH diffuses through synaptic cleft and bind to post-synaptic receptors This binding leads to opening of Na+ voltage gated channels that generate an excitatory post-synaptic response ACH is then broken down in the synaptic cleft by acetylcholinesterase into choline and acetate. These compounds are re-uptaken by transport proteins into the pre-synaptic terminal to be stored
How can heart beat without neural stimulation?
They are myotonic due to heart muscle in SAN
What does cardiac cells display ?
Pacemaker potentials
What does cardiac AP describe?
Molecular basis of electrical activity within heart cardiomyocyte
What is the resting potential of cardiomyocte?
-90Mv and depolarisation reaches to +20mV
What are the functions of cardiac skeleton?
Structural Guides and insulated electrical conduction down the specialised muscle cells within Causing electrical waves passing through the heart muscle to pause between atria and ventricles
What are the cardiac cell features ?
Found in the heart Cardiac muscle cells are conductive Uninucleated Have striations Many mitochondria and myoglobin Extensively branches and are connected by intercalated discs
What does intercalated disc allow?
Cardiac muscle cells to contract in a wave-like pattern so that the heart can work as a pump
What are 2 types of membrane junction?
Desmosomes - hold cardiac cells together so don’t pull apart during stress of individual fibres contracting Gap junctions - form channels between adjacent cardiac cells(links cell)
What are fluorescent labelling used for?
Connexin (the protein that makes gap junction)
Why are gap junctions important?
To keep AP flowing into neighbouring cells
What are the features of skeletal muscles?
Striated Voluntary muscle Multinucleated cells Attached to bones of skeleton Cyclindrical in shape
What does one myofibril divide into?
Segments: sarcomere
What are sarcomere?
Contractile units of a muscle
What are sarcomere composed of?
Thick filaments (myosin) and thin filaments (actin)
What are associated with actin filament?
Filamentous protein - tropomyosin Regulatory protein - troponin
What does tropomyosin do?
Extend the length of actin filament in a spiral
What is changes in length of sarcomere caused by?
Sliding intercalation of the two sets of filaments
what is phase 4?
ventricular myocyte
the cell is at rest - diastole
the voltage during this phase is -90mV
what is phase 0?
rapid, positive change in voltage across cell membrane in SAN cell
produced by action of funny Na+ channel - incrrease membrane conductance of Na+
channel activated when action potential arrives from neighbouring cell through gap junction
the voltage within cell increases slightly
if increased voltage reaches a certain value - Na+ channel to open
Larger influx of Na+ ionto cell
T type channel open
What is phase 1?
rapid inactivation of Na+ channel - reduce the movement of Na+ ions into celll
at same time potassium channels open and close rapidly
allow for brief flow of potassium ions out of cell
make membrane potential slightly more negative
what is phase 2?
plateu phase
membrane potential remain almost constant
the membrane very slowly begins to repolarise
L type channel open allow Ca2+ to enter
what is phase 3?
L type ca2+ channel close
slow delayed rectifier K+ channel remain open
more potassium leak channels open
what are the two types of refractory period of cardiac cells?
absolute refractory period
relative refractory period
how are these 2 refractory period causes?
changes in the states of sodium and potassium channel
what is absolute refractory period?
as the membrane potential becomes more psotive, the sodium channel close and lock - inactivated state
the channels cannot be opened regardless of the strength of excitatory stimulus
what is relative refractory period?
leaking of potassium channel
membrane potential is more negative
resets the sodium channels stronger stumulus than normal is required
what is Gap junction?
allows action potential to be transferred from one cell to the next
made from connexin family of proteins
form a pore through which ions can pass
what is the difference in membrane potential for pacemaker AP and the ventricular AP dude to?
different Na+ permeability
Transient channel (TT) + Long term channel (LT)
a gradual spike in the pacemaker AP
ventricular AP has a sharp increase in what?
sodium influx
followed by a LT channel influx of calcium
why does pacemaker AP have a lower permeability to Na+?
due to funny channel
calcium has a gradual rise due to combination of T+L channels
