lecture 26. Introduction to Neurons . The resting membrane potential Flashcards
Which parts of the neuron conduct electrical/chemical signals
dendrites, cell body, axon- electrical potential
synapses- chemical
The experiment by Hodgkin and Huxley to determine RMP
done in a giant squid
a reference electrode(outside in in ECM) and a recording electrode(inside the squids axon)
measured a difference, inside of the cell being more negative
RMP
Resting membrane potential
-almost all cells in the body have a -ve RMP
-BUT only neurons and muscle are “excitable”- able to generate action potential
(suddenly respond with a transient change)
How are intracellular potentials measured today?
1) Microelectrode recording technique
2) Patch-clamp technique
What generates resting membrane potential?
1) unequal distribution of Na+ and K+ inside and outside the cell, which result in the electrochemical gradients driving the movement of ions
2) Unequal permeability of the cell membrane to these ions
K+ and Na+ concentrations inside and outside the cell
Na+ is higher outside the cell and lower inside( 15 mM to 150 mM)
K+ is higher inside the cell and lower outside( 100mM to 5mM)
how are the concentration gradients for K+ and Na+ maintained?
Na+/K+ pump( primary active transport)
3 Na+ pumped out, 2 K+ move in
-> some diffusion down conc. gradients is allowed
how are the concentration gradients for K+ and Na+ maintained?
Na+/K+ pump( primary active transport)
3 Na+ pumped out, 2 K+ move in
-> some diffusion down conc. gradients is allowed
Selective permeability to ions
1) Non-gated (‘leak’) channels
-open at rest
2) Gated channels( voltage-gated, ligand-gated, mechanically gated)
Closed at rest, only open when stimulated
In the cell membrane of neurons there are many leak K+ channels, but very few leak Na+ channels
At rest: PK+/PNa+= 40/1, P-membrane permeability
Selective permeability to ions
1) Non-gated (‘leak’) channels
-open at rest
2) Gated channels( voltage-gated, ligand-gated, mechanically gated)
Closed at rest, only open when stimulated
In the cell membrane of neurons there are many leak K+ channels, but very few leak Na+ channels
At rest: PK+/PNa+= 40/1, P-membrane permeability
Equilibrium potential
-An intracellular potential at which the net flow of ions is zero, in spite of a concentration gradient and permeability
a balance between chemical and electrical forces - electrochemical gradient
Eg the equilibrium potential for K+= 80 mV
equilibrium potential for K+ and Na+
-80 mV( K+)
+60mV(Na+)
Nernst equation
The equilibrium potential can be calculated for each ion by the ‘Nernst equation’
Eion = 2.3 x RT/zF x log [ion]o/[ion]i
Simplified:
Eion = 61.5 mV x log [ion]o/[ion]i
The Nernst equation applies only to a situation when a cell membrane is permeable only to one ion! (ie. has leak channels only for one specific ion).
what cells have only leak channels for K+
glial cells
RMP value
The higher the permeability of the cell membrane to a particular ion, the more this ion shifts the RMP towards its own equilibrium potential.
At rest in neurons, the membrane permeability is much higher to K+ than to Na+, therefore the RMP is closer to the equilibrium potential for K+(EK) than the equilibrium potential for Na+ (ENa).
• Thus, in comparison to glial cells, in neurons the RMP is less negative than EK
(about -65 mV). This is due to a small contribution of leak Na+ channels.
Goldman Equation
• A way of calculating the value of the RMP taking into account both
the concentration gradients AND the relative permeability of
the resting cell membrane to K+ and Na+ ions.
