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
