Nerve Impulse Conduction Neuron Function Nerve Impulse Conduction http://www.youtube.com/watch?v=dSkxlpNs3tU

Cell Membrane Potential A resting neuron’s cell membrane is polarized Polarized = electrically charged Charge inside the cell is different than the charge outside the cell Potential difference is the measure of the difference in the electrical charge

Question to think about: What does depolarized mean?

Resting Membrane Potential Normal distribution of ions across the resting membrane results the outside of the membrane being more positively charged : K+ is high inside Na+ is high outside Cl- is high outside

Resting Membrane Potential Ions concentrations are maintained by active transport Channel proteins pump ions across the cell membrane

Action Potential: aka Nerve Impulse Normal resting membrane has a potential difference of -70 mV When a significant stimulus is applied the membrane potential will change the potential difference to +30 mV Threshold stimulus is the amount of a stimulus needed to begin the change along the cell membrane

Action Potential Depolarization occurs when the Na+ channels open and Na+ moves into the cell. The result is a more positive ion concentration on the inside Thus the membrane surface is more negatively charged compared to the inside of the axon.

Repolarization Behind the action potential the K+ channels will open The exit of K+ causes the membrane to once again become more positively charged

Re-setting the membrane If another action potential is to be conducted ……the Na+ must be pumped back across the membrane….( must re-set the “game board” to play again) http://www.youtube.com/watch?v=GTHWig1vOnY

Polarized once again Because 3 Na+ will be pumped out for every 2 K+ that are pumped in……the result is a more positive charge on the outside of the axon

Takes only about 1/1000 of a second The Entire Process……. Takes only about 1/1000 of a second http://www.youtube.com/watch?v=dSkxlpNs3tU

All-or-None Response If a neuron responds to a stimulus it responds completely…..there is no partial nerve impulse All impulses carried on an axon will be the same strength If the intensity of the stimulus increases, it causes more impulses per second…….but does not increase the strength of the individual impulse

Refractory Period Time following a nerve impulse when another impulse can not occur regardless of the strength of the stimulus Time when the membrane is being repolarized and is returning to the original conditions of the resting membrane

Speed of the impulse Affected by: Myelin – myelin speeds up the conduction….. Saltatory conduction caused by myelin – impulse “jumps” from node to node Axon Diameter – larger diameter = faster Speed of the impulse

Neuron to Neuron Chemicals called neurotransmitters convey the impulse from the presynaptic neuron across the synaptic cleft to the postsynaptic neuron. Same thing occurs when impulse is being conveyed to an effector (muscle, gland, etc….)

Neuron to Neuron Release of neurotransmitters is by exocytosis Action potential causes Calcium to enter the synaptic knob. Calcium is entering the synaptic knob triggers the release of the neurotransmitter

Neurotransmitters Over 30 different neurotransmitters Cell membranes contain receptors which specifically match with each individual neurotransmitter See pages 376-377 for tables with info on neurotransmitters http://www.youtube.com/watch?v=dSkxlpNs3tU