Two layers of linked fatty molecules within which specialized proteins float

Important membrane spanning protien = Ion Channel

Selectively Permeable

• the property or a membrane to allow some substances to pass through, but not others.
• Some ion channels are gated and can open and close in response to changes in voltage.  This kind of opening and closing is passive process (does not require energy)

The inside of the cell is more negative than the outside.

Typically, the electrical-potential difference across the membran is -70 mV

• the steady membrane potential is about -70mV
• Potential inside the neuron is about 70mV less than that outside the neuron
• In this state it is polarized 

Four Factors Establishing

the Resting Membrane Potential

1. Concetration Gradients:  particales tend to move from area of high concentration to low concentraion
2. Electrostatic Presures:  oppisite charges attract, same charges repel
3. Permeability of the Membrane to Ions:  the ion channels contributing to the membrane potential are voltage-gated
4. Active Ion Transport (Na+/K+ Pump):  a transporter that uses energy provided by mitochondria to pump 3 Na+ out of the neuron for every 2 K+ into the neuron

Excitatory Postsynaptic Potentials

EPSP's

postsynaptic depolarization

make the inside of the cell more positive relative to the oustide

Increase the likelihood that the neuron will fire

Inhibitory Postsynaptic Potentials 

IPSP's

Postsynaptic hyperpolarization

make the inside of the cell more negative relative to the outside

decrease the likelihoodthat the neuron will fire

(Initial Segment)

high in voltage-gated Na+ channels

highly sensitive to ionic flux

where the action potential is generated

a massive momentary (1 msec) reversal of the membrane potential (from -70mV to +50 mV)

Its ALL-or-None

a depolarization of about 5 to 20 mV

causes Actoin Potential to generate