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Chapter 3: Membrane Potential (Neurons (receive signals (dendrites),…
Chapter 3: Membrane Potential
Neurons
receive signals (dendrites)
generate signals (axon hillock)
conduct signals (axon)
lipid bilayer is an insulator
inside of membrane is non-polar and charged ions CAN'T pass through it unless there is some kind of pore
ion channels
cation channels
non-specific: any + ion
specific: pass only Na+ or K+ or Ca++
anion channels: negative ions
how are they gated
leak channels: passive, open all the time
channels that give rise to the resting potential
gated channels: active channels can be opened or closed by changes in
voltage
ligand
phosphorylation
mechanical forces
light
Resting membrane potential
when a neuron is AT REST, there is an excess of + charge OUTSIDE the cell and excess of - charge INSIDE it
Action potentials: changes in the resting potential, which travels from soma --> axon --> terminals (anterograde)
basis of resting potential
concentration gradient: diffusion
electric force
Current: movement of charged particles (direction of movement of positive charge)
Conductance: movement of ions through channels
if conductance is ZERO, no current will flow even when potential different is very large
if potential difference is ZERO, no current will flow even when conductance is very large
Voltage: electrical force
Equilibrium potentials
Equilibrium: When electrical force is equal and opposite to chemical force
Driving force: Vm - Eion
if cell membrane is NOT at the Nernst potential, driving force will move ions across the membrane to push Vm toward its Nernst potential
Nernst potential (Equilibrium potential): Vm that would balance ion's concentration gradient so there's NO NET CURRENT
if membrane voltage = Nernst potential for an ion, there will be NO NET CURRENT
What if membrane is permeable to more than one ion?
each will tend to pull the membrane toward its Nernst potential
the higher the permeability of the membrane to an ion, the greater the effect of that ion on the Vm
At rest, membrane is more permeable to K+ and resting membrane potential is closer to Ek than ENa
Regulation of extracellular K+
important because at rest, neuron is mostly permeable to K+
Increasing extracellular K+ depolarizes neurons, interferes with normal signaling
Na/K pump: pumps 3 Na+ out and 2 K+ in (requires ATP)
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blood-brain barrier prevents excess K+ from entering CNS