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Lecture 4

PSYC 2P35 Lecture Notes - Lecture 4: Nernst Equation, Amyloid, Dynamic Equilibrium

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Dawn Good

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PSYC 2P35 Lecture 4: Membrane Potentials: Forces and the Nerve Impulse
Membrane Potentials
-the bases of how the neuron accomplishes communication or its action
-refers to the electrical charge of the membrane of the neuron
-neurons are not electrically neutral (tonically active) allows the neuron to respond rapidly
The Plasma membrane of a neuron (8nm thick)
-protein channels allow specially charged molecules to pass
-sodium, potassium, chloride (Cl-)
-embedded in the membrane are protein channels that permit certain ions to cross through the
membrane at a controlled rate
-one of the problems in SDAT (type of alzheimers) = leaky membranes due to amyloid plaques
The Resting Potential
-the membrane of a neuron maintains an electrical gradient (a difference in electrical charge)
between the inside and outside of the cell
-the inside is negatively charged
-the outside is positively charged
-the difference is negative (-70 milliV)
-this is called Polarization
Important ions in the neuron:
-Sodium Na+, Potassium K+, Chloride Cl-, +Proteins (A-)
-balancing these molecules across the neuronal membrane produces the “action potential”
Forces that Maintain the Resting Potential
1. Electrical (electrostatic) Gradient – difference in the electrical charge across the membrane
-electriccal pressure: results from the process of balancing ionic charges
-opposite charge attract and same charges repel eachother
2. Concentration (Osmotic) Gradient – difference in the number of ions on the inside and
outside the membrane
-Osmotic pressure: results from the process of diffusion; even distribution of ionic
concentrations; through a semi permeable membrane
Dynamic Equilibrium
-an active balance reached as a result of 2 equal and opposing disequilibriums
-neurons are at this dynamic equilibrium
Ex. 6 K+ and 6 acetate (AC-) on one side and 2 K+ and 2 acetate (AC-) on other side;
membrane semi permeable to K+
-net charge is zero on both sides (electrical static membrane)
-so results in concentration disequilibrium (6 potassium on one side and 2 on the other)
-causes an osmotic/gradient pressure which makes potassium equal on each side
-this messes up electrostatic gradient (negative charge on one side with more acetate than
other) which results in electrical gradient/pressure and potassium moves back to the other side
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