L5 - AP and AIS Flashcards
At slow frequencies, what type of NT used?
Amino acid type
At increasing frequencies, what vesicles are used?
Large dense core vesicles have peptides and modulators in them
Burster
- Slight depolarises after each AP hence intracellular Ca2+ builds up where it acts as a ligand at a Ca2+/K+ channel allowing more K+ to enter the cell -> hyperpolarise cell
Metronome
- No build up as it is slow and Ca2+ gets taken back up each time
IN THE ABSENCE OF ANY CHANNELS:
Length constant/potential of the axon? Determined by?
- A potential difference will dissipate over time (e.g. inject current in axonal membrane and record at different points of the axon, as it moves away from the point of activation – the AP gets smaller and smaller.
- Determined by the resistance intra, extra and across the membrane
THERE IS NO DELAY IN THE OPENING OF VOLTAGE GATED K+ CHANNELS – The same voltage (around 20 – 40 mV) opens both Na+ and K+ at the same time. K+ have slower kinetics hence opening speed is slower. At rest, there is no drive for K+ to move through the channel so it appears delayed.
THERE IS NO DELAY IN THE OPENING OF VOLTAGE GATED K+ CHANNELS – The same voltage (around 20 – 40 mV) opens both Na+ and K+ at the same time. K+ have slower kinetics hence opening speed is slower. At rest, there is no drive for K+ to move through the channel so it appears delayed.
Voltage gated K+ Channel
Within one of these transmembrane loops, it has positively charged Amino Acids in the paddles which twist in response to changes in polarity across the membrane, changing the conformation of the gate (opening/closing) (e.g. if the inside of the membrane was +ve, the +ve amino acids would repel it and close, if it was –ve then the +ve amino acids would be attracted and open)
Voltage gated K+ Channel
Within one of these transmembrane loops, it has positively charged Amino Acids in the paddles which twist in response to changes in polarity across the membrane, changing the conformation of the gate (opening/closing) (e.g. if the inside of the membrane was +ve, the +ve amino acids would repel it and close, if it was –ve then the +ve amino acids would be attracted and open)
Is there a specific site of AP activation?
AIS
What is a bleb?
A bleb forms after you cut processes on a neuron and the membrane closes over to seal itself, this point of closure is known as a bleb. Now we are able to place a patch clamp recording electrode on it as it is big enough.
Bleb or Soma reaches AP first?
Bleb
AIS sometimes have axon inputs (blue bits on AIS in diagram on the right) on it. What does this mean?
Not just integration, generation of AP but also regulation as axon inputs have a role in inhibit/exciting the cell
What special properties determine that AIS is where AP is initiated?
More sensitive voltage gated Na+ channels, needs less depolarisation to open. Smaller structure, hence would be activated more easily.
Voltage Gated Na+ Channel Config.
- Alpha: 4 subunits (each one has 6 membrane spanning domains)
- Beta: trafficking and kinetics (but not actually part of the channel)
- Re-entered loop for pore selectivity
Voltage Gated K+ Channel Config.
- 4/5 Subunits (6 transmembrane voltage paddle)
- Re-entered loop for pore selectivity
Nav1.1, Nav1.2, Nav1.3. Nav1.6 – which are found in brain, AIS, most neurons? What is special about 2
Brain – 1236
AIS – 126(2 is found predominantly at the nerve terminal)
Predominates in most neurons – 6
