1. Action & Resting Potentials

2.  Create the electrical impulses needed for communication in the nervous system  They occur in the axons of all neurones  They are maintained and created by changing the membrane permeability Action & Resting Potentials

3.  Resting potentials occur when the nuerone is at rest and not transmitting an impulse  The membrane of the neurones is polarised, so The inside of the membrane is more negatively charged than the outside of the membrane  The difference in these charges is the resting potential  The resting potential is normally -60mV Resting Potentials = The potential difference (voltage) across the neurone membrane, whilst the neurone is at rest.

4.  The membrane of the neurones contain gated sodium and potassium channels, as well as sodium/potassium pumps  The sodium/potassium pump actively transports three sodium ions out of the axon and two potassium ions in.  These are both positively charged ions and therefore by pumping more positive ions out of the axon the negative charge will be maintained. Generating & Maintaining The Resting Potential

5. Sodium/ Potassium pump http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio03.swf::Sodium-Potassium%20Exchange%20Pump

6.  When receptor cells respond to a stimulus, gated sodium channels on the neurone membrane will open.  The larger the stimulus the more channels will open  When the channels open, sodium ions will diffuse into the axon down their concentration gradient  The change in potential by one or two channels opening is a generator potential  If many open then the change in potential will initiate an action potential Generator Potentials

7.  Action potentials are the impulses and must be stimulated.  The potential of the membrane changes from -60mV to +40mV  When an action potential occurs the axon is said to be depolarised, and when the resting potential is re- established it’s said to be repolarised. Action Potentials

8.  Action potentials are generated by opening many sodium channels, allowing sodium ions to move into the axon  The action potential moves along the axon because the positive charge of the sodium ions is attracted to the negative charge of the resting potential in the rest of the membrane.  This excites the next part of the membrane, and as a result more sodium channels open. Generating Action Potentials

9.  Allow the action potential to travel faster down the axon.  The nodes of ranvier are created by the gaps between the schwann cells that make up the myelinated sheath that insulates the axon.  The electrical impulses jump from node to node in a process called saltatory conduction Nodes of Ranvier

10.  Happens because the sodium ions cannot pass through the myelinated sheath  As a result depolarisation can only occur at the nodes of Ranvier where there is a gap in the myelinated sheath. Saltatory Conduction

11.  Depolarisation= sodium channels open  Repolarisation=sodium channels close and potassium channels open, causing potassium ions to rush out of the axon by diffusion.  Too many ions diffuse out of the axon, causing the refractory period  The sodium/potassium pump brings the charge back up to resting potential Oscilloscope Display

12.  Resting potential is maintained by the sodium/potassium pump; three sodium ions out & two potassium ions in.  Action potential is created by the opening of the sodium channels  Axon is repolarised by the opening of the potassium channels and the closing of the sodium channels Conclusion...