what is the fluid that neurons are bathed in?
extracellular fluid
What are the two types of ion channels:
- Non gated - are continually open and offer no resistance to the passage of ions
- gated - can close and prevent the flow of ions
What are the two types of gated channels?
- Voltage gated channel
- chemically gated channel.
Voltage gate channel:
open when there is an electrical current (stream of ions)
Chemically gated channel:
will only open when a specific type of molecule binds to a binding site on the channel molecule
How is charge generated?
Resting potential & action potential
What are the two factors that resting potential depends on?
Ion distributions or concentrations, inside and outside the membrane, and the state of the gates on the ion channels
What are the two forces that cause ions in a solution to move?
- Diffusion
- electrostatic force
Diffusion
ions move from an area with high concentration to an area of low concentration (no energy is needed)
electrostatic force
ions move due to their electrical charge
- opposite charges attract each other
- like charges repel each other
(no energy is needed)
What does DNP do?
it is a metabolic inhibitor
the Sodium potassium pump
- pumps 3 sodium out of the cell and brings in 2 potassium ions during each cycle
- because it removes 3 positive ions and replaces only two inside the membrane, every cycle makes the inside more negative by one ion
- the pump is electrogenic
Where is TTX obtained from?
Puffer fish
What does TTX do?
- blocks sodium channels, but has no effect on potassium channels.
- allows researchers to study how the membrane changes when only potassium channels are open
What are the properties of Na+ channels?
- 2 gating mechanism
- activation gate opens
- Na+ flows briefly
- inactivation gate closes
What are the properties of voltage gated K+ channels?
- delayed in opening
- one gating mechanism
- it won’t open until the sodium channel has opened and closed
What happens when K+ ions leave?
membrane potential will hyperpolarize
Na+ channel opening produces what?
Depolarization
absolute refractory period
fixed period of time when the ball and chain gate closes before sodium channels can rest and the hinge gate can open again.
relative refractory period
time it takes until resting potential is re-established
how is the action potential generated?
initiated when the voltage gated sodium channels open and sodium rushes into the cell. if the threshold is reached, all remaining sodium channels in the area open and the rapid depolarization known as an action potential occurs.
