1. COGNITIVE SCIENCE 17 The Electric Brain Part 1 Jaime A. Pineda, Ph.D.

2. INPUT INTEGRATION OUTPUT Law of Dynamic Polarization Dendrites generally receive synaptic input (i.e. are postsynaptic) and axons generally send synaptic output (i.e., are presynaptic)

3. Resting Membrane Potential (Vm) is ~ -70 mV in mammals Vm is the voltage difference between the inside and outside of the cell

4. 50 440 400 20 40 560 many few Different concentrations of ions inside and outside the cell

5. Unequal distribution of ions across cell membrane creates two major forces osmotic pressure electrostatic pressure

6. Other important factors -Specific protein channels -Na +, K +, Cl -, Ca ++ -Selective permeability of channels -leaky channels -K + > Cl - > Na + -Sodium-potassium pump

7. Na+ / K+ Pump Restores equilibrium

8. Graded and Action Potentials Graded –A–Are small changes in membrane potential –A–Are conducted passively –L–Lose energy as they travel down dendrite/axon Action –A–Are large changes in membrane potential –A–Are conducted actively (regenerated) –D–Do not lose energy as they travel down the axon

9. Graded Potentials Depolarization (EPSP) –Vm becomes more positive (Na+ flows in) and the neuron is more likely to produce an action potential Hyperpolarization (IPSP) –Vm becomes more negative (K+ flows out) and the neuron is less like to produce an action potential

10. Graded Potentials AM signals Degrade with distance (decremental conduction) Short distance signaling V Distance from source

11. Action Potentials FM signals Do not degrade with distance (non decremental conduction) Long distance signaling

12. Phases of the Action Potential Firing threshold is the point at which the number of activated Na+ channels > inactivated Na+ channels Absolute refractory period Relative refractory period