Action Potential Propagation

Interneuronal Communication pre-class video

Sue Keirstead, Ph.D. Assistant Professor Dept. of Integrative Biology and Physiology Stem Cell Institute

Tel: 612 626 2290 Class 6: Action Potentials – Learning Objectives 1. Explain how a receptor potential in a sensory neuron can lead to the initiation of an action potential at the trigger zone of the sensory axon. 2. Compare and contrast the properties of mechanically-gated channels and voltage- gated channels (consider what causes them to open and close, where they are located, what kind of membrane potentials they mediate). 3. Compare and contrast the properties of voltage-gated Na+ and voltage-gated K+ channels, and understand how voltage influences their activation and inactivation (do they both have inactivation gates?). 4. Understand how the activity of voltage-gated Na+ and K+ channels generates an action potential and the roles of these channels in each phase of the action potential (i.e. depolarization/rising phase, overshoot, repolarization, afterhyperpolarization/undershoot). 5. Explain how action potentials are propagated along an axon and compare this to the passive conduction like the local current flow in dendrites. 6. Compare the distribution of ion channels along unmyelinated versus myelinated axons and explain how this accounts for the difference in conduction velocity between these two types of axons. Predict the effects on action potential propagation of demyelinating diseases, such as multiple sclerosis. 7. Understand how stimulus intensity is encoded by neurons. Why do we need Right side of brain Left side of brain to have action Cerebral cortex potentials? 1 Brain Interneuron

Upper motor neuron 2 Thalamus

Interneuron

Sensory neuron 3

Spinal cord

4 Key: Graded potential Sensory Axon action potential receptor 6 5

ECF

ICF

ECF Propagation of the Action Potential

Plasma Membrane Key:

ECF Resting membrane potential Depolarizing phase of AP Plasma membrane Repolarizing phase of AP After-hyperpolarization phase of AP Na+ ICF

K+ ECF Time

Na+ ICF

K+ K+ ECF

Cell body Time Na+ 1 msec Na+ Current flow due to Trigger zone opening of Na+ channels Na+ 5 msec

Na+

Na+ 10 msec Na+

Leading edge of action potential Saltatory conduction (myelinated axons)

Cell body Time Nodes of Ranvier Na+ 1 msec Na+ Current flow due to opening of Na+ Trigger zone channels Na+ 5 msec Na+

Na+ 10 msec Na+

Leading edge of action potential Continuous vs Saltatory Conduction CT 3.2 The purpose of propagating action potentials down the axon is to trigger neurotransmitter release from the axon terminal

1 Presynaptic axon Action potential

2+ 2 Ca Voltage-gated Ca2+ Ca2+ 2 channel

Synaptic vesicles 8

Synaptic cleft Ca2+ Neurotransmitter 3 Na+ Neurotransmitter receptor: 4 Neurotransmitter binding site Ion channel 5

7 Local current flow Postsynaptic neuron 6 Postsynaptic potential