Signaling Within Neurons

I.        The Nerve Impulse

         A.     The Resting Potential

                  1.        electrical properties

                  2.        ionic concentration gradients

                             a.        potassium ~20:1

                             b.        sodium ~1:10

                             c.        chloride ~1:11.5

                             d.        calcium ~1:10,000

                             e.        anions

          B.    Maintenance of the Resting Potential

                  1.        opposing forces

                             a.        diffusion

                             b.        electrostatic pressure

                  2.        semi-permeable membrane

                             a.        membrane proteins

                                        i.     pumps

                                        ii.    channels

                                        iii.   receptors

                                        iv.   enzymes

                                        v.    structural proteins

                            b.    sodium-potassium adenosine triphosphate pump (Na-K pump)

                  3.        potassium spatial buffering

         C.     The Action Potential

                  1.      depolarization vs. hyperpolarization

                  2.      all-or-none law

II.       Events During the Action Potential

         A.      Ionic Flow

                  1.        threshold met (voltage-gated sodium channels open)

                  2.        rising phase (influx of sodium)

                  3.        overshoot (Na+ gates close, K+ gates open)

                  4.        falling phase (potassium efflux)

                  5.        undershoot

                  6.        refractory period

                            a.        absolute

                            b.        relative

       B.       Propagation of the Action Potential

                 1.        unmyelinated axons (active conductance)

                 2.        myelinated axons

                            a.        saltatory conduction

                            b.        passive cable conductance

III.    Dendrites, Soma, and Short Axons

        A.    graded potentials (NOT propagated)

        B.    EPSPs and IPSPs

                1.        summation

                            a.        temporal

                            b.        spatial