The Action Potential.

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Presentation transcript:

The Action Potential

The Resting Potential of the Neuron results from difference in ion distribution inside and outside of cell (-70mV)

Forces Behind Resting Potential Selective Permeability- some molecules pass through membrane more freely than others; ion channels Sodium-Potassium Pump- transports 3 Na out of, 2 K into cell Result: Concentration Gradient Electrical Gradient

Forces Behind Resting Potential What would you do to generate electrical signal fast? RP takes work (Na/K Pump). Why do we bother?

Molecular Basis of Action Potential Sodium channels open once threshold is reached, influx of sodium Potassium channels open at AP peak; potassium flows out

http://faculty.washington.edu/chudler/ap.html http://www.blackwellscience.com/matthews/channel.html

The All-or-None Law The size, amplitude, and velocity of an action potential are independent of the intensity of the stimulus that initiated it. How then is stimulus intensity coded?

Figure 2.20 Saltatory conduction in a myelinated axon An action potential at the node triggers flow of current to the next node, where the membrane regenerates the action potential.

The Action Potential The RefractoryPeriod Absolute Refractory Period Sodium gates are firmly closed Membrane cannot produce AP, regardless of the stimulation. Relative Refractory Period Sodium gates in usual state, but the potassium gates remain open. Stronger than normal stimulus needed for action potential.

Propagation of the Action Potential From: Axon Hillock To: Terminal Buttons AP travels in one direction only. WHY?

The Myelin Sheath and Saltatory Conduction Myelin Sheaths increase the speed of neural transmission Nodes of Ranvier-Short area’s of the axon that are unmyelinated Saltatory Conduction-jumping action of actions potentials from node of Ranvier to node of Ranvier

Signaling Without Action Potentials Depolarizations and hyperpolarizations of dendrites and cell bodies Small Local neurons-produce graded potentials (membrane potentials that vary in magnitude and do not follow the all-or-none law)