Neurons are electrically active; They have a resting voltage, and can undergo electrical changes

1. Neurons are electrically active; • They have a resting voltage, and can • undergo electrical changes 2. Neurons can “fire”; They generate Action Potentials that move along the axon 3. When the action potential reaches the terminals, it causes a chemical signal (neurotransmitter) to be released, which moves across the synapse to affect a second neuron. Fig. 1.6.1

2. Membrane Proteins and the Movement of Ions Na+ pump (Na+/K+ pump) Actively pumps Na+ out of cell Na+ Na+ Na+ Receptor K+ K+ enzyme Chloride channels are open Second Messenger production Fig. 1.6.2

3. EPSP, IPSP AND ACTION POTENTIAL ACTION POTENTIAL Larger EPSP EPSP threshold Resting Membrane Potential IPSP Fig. 1.6.3

4. TRANSMITTER BINDING TO A RECEPTOR outside inside WHEN THE TRANSMITTER AND RECEPTOR ARE BOUND TO EACH OTHER, IT STIMULATES BIOLOGICAL ACTIVITY RECEPTOR Chemically Gated Channel Opens: Ions Move Into Cell (can be EPSP or IPSP depending on the channel NEUROTRANSMITTER membrane Fig. 1.6.4

5. Action Potential is Generated Na+ moves in- Voltage moves more positive (ascending limb) K+ Na+ Na+ Na+ Na+ K+ K+ moves out- restores resting Potential (i.e., descending limb) AXON Towards terminals Towards soma Fig. 1.6.5

6. INFORMATION PROCESSING BY NEURONS Each neuron is like a tiny computer; it receives many inputs, both excitatory and inhibitory, and adds them together (i.e. summation) over time and space. If the summed excitatory input at the initial part of the axon exceeds the threshold, an action potential is fired. Fig. 1.6.6

7. INFORMATION PROCESSING BY NEURONS: THE ACTION POTENTIAL LOW FREQUENCY LIGHT OFF HIGH FREQUENCY LIGHT ON VISUAL SYSTEM NEURON Fig. 1.6.7

8. Chemical Transmission Synthesis Storage Release Calcium flowing into the terminal, which is caused by the action potential, stimulates transmitter release. Fig. 1.6.8

9. Postsynaptic Action (a) and Inactivation (b, c) Fig. 1.6.9