What is an action potential?
The nerve impulse that overcomes biological constraints that allows axonal membranes to conduct signals.
What is the resting membrane potential?
In the resting neuron, the cytosol along the inside surface of the membrane has a negative electrical charge compared to the outside. This difference in electrical charge across the membrane is called the resting potential
What are the most important ions for cellular neuro physiology?
The monovalent cations sodium and potassium, the divalent cation calcium, and the monovalent anion chloride
What is the average Resting Membrane potential (Vm)?
~65 millivolts (mV)
What effects on RMP would result from injecting positive or negative ions into a neuron?
What is depolarization?
When the membrane voltage becomes more positive
What is hyperpolization?
When the membrane voltage becomes more negative
Positive ion influx results in:
Positive ion efflux results in:
Negative ion influx results in:
Negative ion efflux results in:
depolarization
hyperpolarization
hyperpolarization
depolarization
What mechanisms produce/maintain the charge separation?
The neuronal membrane is a lipid bilayer composed of phospholipids
- The polar phosphate heads are hydrophilic.
- The nonpolar lipid tails are hydrophobic.
- Charged ions are hydrated (surrounded by water molecules). Therefore they are attracted to hydrophilic regions and repelled by hydrophobic regions. Thus ions cannot pass through the neuronal membrane and this is what maintains the separation of charges that is essential to the RMP.
What is an ion channel?
a protein with a pore through which ions can flow.
What are the types of ion channels?
- Ligand-gated (a.k.a. neurotransmitter-gated) ion channels (a.k.a. neurotransmitter receptors).
a. The binding of the ligand (the neurotransmitter) to the receptor causes the ion channel pore to open.
b. Each type of receptor specifically binds only one type of neurotransmitter. Note for future reference: There are also chemical receptors that are not ion channels. - Voltage-gated ion channels.
a. These channels are opened and closed by changes in the voltage across the membrane. The opening and closing of these channels is dependent upon the amplitude and direction of the voltage change. - Another type of ion channels are the leak channels.
a. These channels are not gated by either voltage changes or neurotransmitters. b. An example of a leak channel is the K+ leak channel.
c. The default state of a leak channel is open! (opposite to the other types of
channels) .
What is the default state of the K+ leak channel?
Open
It is neither ligand-gated nor voltage-gated
What zone(s) does the K+ leak channel exist in?
All four zones of the neuronal membrane
What does the K+ leak channel result in?
A high resting permeability to K+, which is a major factor in determining the RMP.
Show the outward diffusion force on K+ caused by its concentration gradient:
Show four examples of how membrane voltage affects flux of K+ through the K+ leak channels and how this K+ flux in turn changes the membrane voltage
What is the driving force, and what does it determine?
The driving force determines the rate of flux. It is the sum of the diffusion and electrostatic forces. It is calculated by Vm-Eion
What is the equilibrium potential of K+ (EK)?
-80 mV
What is a mechanism of recovery after perturbation that makes the membrane potential resistant to change?
Any change in the membrane potential (Vm) away from the equilibrium potential value of K+ (EK) will produce a flux of ions which tends to drive the Vm back towards the EK.
What is the functional significance of the K+ equilibrium potential?
it acts like a voltage clamp, because the membrane is highly permeable to K+ at rest due to the default open state of the K+ leak channel.
Which ions are the most important in determining the membrane potential, and why?
If the membrane is impermeable to an ion, then it doesn’t matter (for that ion) what the membrane potential is, or the driving force acting on that ion. Therefore, the ion with the greatest permeability is the most important in determining the membrane potential (permeability isn’t constant).
EK=
61.54mV log [K+]o/[K+]i
ENa=
61.54 mV log [Na+]o/[Na+]i
ECl=
-61.54 mV log [Cl-]o/[Cl-]i
