Lecture 4-8 Flashcards
Voltage
Seperation of charges
Current
Movement of charges
Resistance
Reduction of Movement
Ohms law
Talk about resistance and membranes (2)
What it does + membrane
- Resistance prevents or slow down movement of charge.
- Membrane with no ion channels, resistance is infinite (blackage of current), adding channels causes lower resistance and more current (infinite -> non-infinite)
Capacitance (F)
- C= q/v (charge over voltage)
- Ability to hold a charge aka voltage (seperation of charges)
- 3 components to it:
1. 2 Conductive plates: slabs of metal that charge can move around)
2. Insulator: space/air between the 2 plates that prevents charges from moving from one plate to the other
How do you charge up a capacitance (seperate charge?)
Apply a voltage
- Hooking up a battery and applying tyhe voltage will cause positive charge move away from cathod to conductive plate. Once they reach it, they will spread out on the plate. As you get more and more + charge building up, it will cause + on the other plate to repel. Those + charge on the pther plate will be repel back to the anode side of battery (- side). We will have - charges spread out instead on the seocnd plate bc we push + charge away.
Pull the battery out of a capacitance circuit what will happen?
Charges will still remain on capacitor until something comes around and discharges it.
Capacitor properties : hold charge that is…
equal to the input voltage (voltage of the battery)
Charging delay
Time needs to be taken for + to spread on plate and repel + on other plate.
When we apply voltage across a capacitor, it takes a while before the capacitor voltage is equal to the voltage we entered in the system.
How do current microelectrode introduce positive charges is like adding a battery to the capacitor: change in voltage across the membrane like change in capacitor. Amount of positive change put in determines maximium membrane potential. Explain how this works (3):
+ the parallel components
- Current microelectrode is put in membrane.
- Introduced + charge. The + charge builds up charge inse the membrane and repels + charge in the ECM fluid.The outside is left with a negative charge. The circuit is closed with positive charges leaving to the anode.
- Membrane acts as the insultor, extracellular and intracellular space act as capacitors and charges can move freely.
Tau (3) + formula
- The time constant to how quickly membrane potential changes to reach 63% of max voltage
- It takes time for membrane to charge up as it repulses the negative charges as well. Introducing a + current pulse will not cause instant change to reach the max voltage.
What happens when you input charges in the membrane interms of movement:
- Charges dont just sit, they spread out and can affect membrane potential further away from the site
- It affects the membrane potential less, the farther the charge move (max change in voltage is less)
Length constant
- Distance where change in voltage is 37% of max (origin)
- Dependent on Rm (membrane resistance) and Ri (axial resistance: things getting in the way of charge moving inside the axon such as organelles, cytoskeleton and diameter etc)
It is hard to get charge down the axon when length constant is —– because —–
- short
- more charges leak out to ECM (small Rm) as there will be less charge to change membrane potential farther down.
What happens when membrne resistance is low? (3)
what + length constant + Mp
- Theres alot of channels for leak
- length constant is short
- Not much charge in cell, membrane potential change at distant is small
If Ri is high:
- Lots of resistance, charge has hard time moving down the axon, length constant is short
Change in membrane potential becomes —– farther away from where the charge is being introduced
less
What would a distance vs membrane potential graph look like if you put charge in constanstly or a pulse
What is a difference between temporal and spatial summation?
Temporal summation occurs when a single neuron fires signals quickly enough that their effects accumulate over time, triggering an action potential in the receiving neuron.
Spatial summation, on the other hand, happens when multiple neurons simultaneously fire signals whose combined effects are enough to trigger an action potential in the receiving neuron.
End result with temporal summation (2):
MP + what
- Resultant change in membrane potential is even greater than original ones.
- Quick pulses, give stimulus before charge can dissipate fully causing summation, adds on whatever ion is left causing greater total change in voltage.
End result from spatial summation (3)
what + dependent + Mp
- Close enought that each can detech the other stimulus, not at same spot.
- Dependent on Ri, Rm, magnitude of stimulant, distance
- Stimulus A+B causes greater change in MP than A or B alone as giving at the same time, you are putting + charge due to A then due to B (summation).
Spatial and temperal subtraction:
- Introducing negative chage
- In temporal summation, more times in quick sucession causes greater - charge change and hyperpolarizaion
- In spatial summation, (physically diff sports) there is also greater hyperpolarization
Dendrite properties: Subtraction (2)
- Charges + and - can cancel out, stopping info from travelling down the dendrite
Voltage gated Na+ channels (3)
structure + when closed/open
- Has 4 domains, each domain has yellow 4 which is voltage sensor and what makes the channel voltage gated. It is known as part of protein that change and open up inside of protein to allow Na+ to flow through
- Mostly hydrophobic but yellow 4 is charged
- If inside of cell is - then the pore is closed as yellow 4 is pulled to inside of channel
Voltage gated K+ channel
- Typically composed of four separate α-subunits, each of which contributes to one-fourth of the ion-conducting pore.
Each α-subunit has six transmembrane segments (S1-S6), similar to Na⁺ channels.
How does ion channel selectivity work (2 +3)?
2 factrs + explain second factor
- Physical size
- Water of hydration (charged particles like Na+ and K+ will have water attached to it)
- How channel select for Na+ and K+ is dependent on where amino acid residue are in channel because of how they are placed will allow the H2O to be stripped.
- There are charged amino acid residues on central pore and the locations are distinct. As water moves in, charged amino acid pull water molecules off, replacing H2O. H2O is attracted to the ion via EMF forces, the charged amino acids replaces the water molecule attaching to the ion instead and knocking the water off. Unhydrated ion moves up and out and get rehydrated.
- This process doesnt use energy
Action potential graph measuring membrane potential on a patch:
Action potential is all or none!
What does the experiment used to determine this look like?
- Same amplitide but different duration, AP looks the same. As long as it rach threshold, looks the same
Action potential does not degrade with distance! Whats the experiment that explained this?
- Measured voltage at 3 different places, AP is still the same. Measure 1 point in membrane, the rest of cell membrane will look the same.
Depolarization
- Membrane potential starts to get less - due to + charge getting inside of cell
Rising phase
- If enough + charge gets into the cell and reach threshold, voltage-gated Na+ channels open
- Big influx of sodium (DF/EMF for Na+ is inside to the cell)
How does saltatory conduction work?
- Positive charge travel down to the next node causing membrane potential to change and making 2nd AP
Explain the 3 fundamentals of the action potential that causes refractory periods:
- Inactivation of Na+ channels
- Increased K+ permeability: we need membrane to be + and depolarized to activate VG na+ channels but the permeability push membrane to opposite direction.
- Decreased membrane resistance: Harder to get membrane depolarized beacuase lots of channels are open, maybe even VG Na+ so putting charge in the system is going to dissipate back out across the membrane very rapidly.
