Hole’s Human A&P Hole’s Text : pp Chapter 10 - The Nervous System, Part II  Resting Membrane Potential  Graded Potentials  Action Potential Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4-1

Resting Membrane Potential membrane is polarized in a resting neuron charge difference on either side of membrane Inside cell Outside cell

Resting potential:  chp44/4401s.swf chp44/4401s.swf

Resting Membrane Potential Inside cell Outside cell K + ; high concentration inside the cell Na + ; high concentration outside the cell (-) charged proteins are inside the cell Which way is K+ leaking? Which side of the membrane is more (-)? Inside or outside Outside cell

Potential Changes polarized resting membrane potential = -70mV depolarization event that makes the interior less negative repolarization return to -70mV (can hyperpolarize) Predict what could make the interior more positive.

Gated Channels Different types of gates… some open due to: - binding of chemicals - sensory changes (temperature, light, pressure) - voltage

Local Potential Changes chemical gates “chemical” that opens the gate = neurotransmitter (nt) opens Na + channels  depolarization Na + ions flow into cell  inside of cell becomes more positive enough (+) change in charge  opens voltage gates See animation of a chemical gated channel: Into or out of ? ( + or -?)

Local Potential Changes chemical gate opening leads to graded depolarization more nt  more Na + channels open  more depolarization summation combined effect of nt  greater depolarization until it reaches threshold  action potential 10-16

chemical gates -local potential changes- graded response voltage gates – action potential

1.Compare location of chemical gates and voltage gates. 2.What opens chemical gates? Voltage gates? 3. To open voltage gates the interior of the neuron must reach “threshold”. Explain. 4. When threshold is reached there is an _____ potential.

Action Potentials – continues down entire axon 10-17

Axon Returns to Resting State Repolarization  Na + channels close  K + channels open Is K + flowing into or out of the cell?  Are ions now in their proper place?  Na + /K + pump restores: ion balance resting membrane potential.

Action potential  chp44/4402s.swf chp44/4402s.swf

Action Potential and Refractory Period all-or-none – AP continue along the entire length of axon after AP brief refractory period  absolute – new stimulus can’t start another AP  relative – new, stronger stimulus can start another AP

Conduction along Axons unmyelinated axons  AP depolarizes axon segment by segment  depolarization of 1 st segment causes voltage changes that depolarize the adjoining segment and so on myelinated axons  saltatory conduction  much faster  AP jumps from node to node

Saltatory Conduction Along Myelinated Fibers Rate depends on:  myelination  axon diameter (wider the axon, the faster) 10-20

Animations – conduction along unmyelinated and myelinated axons t.htm t.htm hews/actionp.html hews/actionp.html