Transcript MEMBRANE POTENTIALS

Neuronal Potentials
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Resting membrane pot. ~ -70 mV
Action pot. (“spike”) ~ +40 mV (all-or-none)
Threshold ~ -60 mV
Graded pot. :
Excitatory post-synaptic pot. (EPSP)
Inhibitory post-synaptic pot. (IPSP)
Polarization, depolarization, hyperpolarization
Absolute and relative refractory periods
MEMBRANE POTENTIALS
V
~ -70 mV
Ions: cation : +V ; anion : -V
Sodium - Na+ ( higher outside )
Potassium - K+ ( higher inside )
Chloride - Cl- ( higher outside )
Amino acids - A- ( higher inside )
(protein)
Resting membrane
potential
1. Concentration gradients: ( high to low)
2. Electrical gradients - electrostatic
pressure ( +/- attract ; equal repel )
3. Na+ and K+ “pumps”
Resting Level (~ -70mV ):
Na+
--- (a) hi concentration outside > driven into cell (concent.
gradient)
(b) inside negative > Na+ attracted (electrical gradient)
BUT: (a) membrane channels closed (voltage gated)
(b) Na+ pumps to outside
K+
-- (a) driven out by hi inside concentration (concent. grad.)
BUT: (a) stopped by inside negative charge ( attract; elect. grad)
(b) K+ pumps to inside
Resting Potential
Cl-
Na+
Sodium channels ar
closed (voltage gate
Sodium cannot
move into the cell a
readily
A-
“Pumps”
Na+ - out
K+ - in
mV
Axonal Propagation of Action
Potential: Electrotonic Current
Electrotonic current
Spread of Na+ to adjacent polarized region, slightly
depolarizing it ( -60mV = Threshold); removes voltage gate on
Na+ channels, action potential (“spike”) occurs. Electrotonic
current becomes smaller as distance from spike increases
(decremental conduction)