Electrochemical Gradient Causing an Action Potential Understand the basic processes in the transmission of an action potential.

What is an Action Potential? Nerve impulse or “signal” Signal that is passed from one neuron to another

Videos of Action Potential 1. Resources/Movies/vasynapt.mov 2. Resources/Movies/vaaction.mov

Important Ions Cation = positive ion Ex: K+, Na+, Ca++ Anion = negative ion Ex: Cl- K+ = Potassium Na+ = Sodium Ca++ = Calcium Cl- = chloride

Membrane Potential Caused when opposite charges are separated by a cell membrane and want to move to balance each other out. More cations on outside of cell than inside of cell so you have a membrane potential

Electrode measures membrane potential of a nueron Axon

Phases of Membrane Potential 1. Resting potential: –70mV (inside of axon more negative than outside) 2. Depolarization: 0 to +30 mV (inside of axon more negative than outside) 3. Repolarization: +30 back to –70mV (inside of axon becoming more negative than outside) 4. Hyperpolarization: -70 mV to –100mV (inside axon way more negative than outside)

Phases of Membrane Potential Hyperpolar-ization

Basic Steps to an Excitatory Action Potential 1. Neuron is at resting potential (-70 mV) 2. Neurotransmitters bind to receptors on dendrites 3. Causes Na+ to rush into cell body 4. Membrane potential becomes more positive +30mV 5. Na+ channels close 6. K+ rushes out of cell to balance out differences in membrane potential

Basic Steps to an Excitatory Action Potential (continued) 7. Membrane potential goes back to -90mV but then goes back to -70mV 8. Continues along length of axon 9. Action Potential reaches axon terminal and Ca2+ channel open 10. Ca2+ enters axon terminal and binds to vesicles 11. Vesicles with NT inside travel to end of axon terminal 12. Vesicles release NTs into synaptic cleft 13. NT’s travel through synaptic cleft and bind to next neuron

Copyright Pearson Prentice Hall The Nerve Impulse An impulse begins when a neuron is stimulated by another neuron. At the leading edge of an action potential, gates in the sodium channels open, allowing Na+ ions to flow into the cell. This flow of ions causes the action potential to move. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Nerve Impulse An impulse begins when a neuron is stimulated by another neuron. At the leading edge of an action potential, gates in the sodium channels open, allowing Na+ ions to flow into the cell. This flow of ions causes the action potential to move. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Nerve Impulse At the trailing edge of an action potential, gates in the potassium channels open, allowing positive ions to flow out and restoring the resting potential of the neuron. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Synapse Synaptic cleft Copyright Pearson Prentice Hall