Action Potential Notes

1. Action Potential Notes

2. Why do animals need a nervous system? • What characteristics do animals need in a nervous system? • fast • accurate • reset quickly Remember…think aboutthe bunny… Poor bunny!

3. Fun facts about neurons • Most specialized cell in animals • Longest cell • blue whale neuron • 10-30 meters • giraffe axon • 5 meters • human neuron • 1-2 meters Nervous system allows for 1 millisecond response time

8. Resting Potential

9. Transmission of a nerve signal • protein channels are set up along cell membrane • once first one is opened; rest openin succession • all or nothing response • “wave” action travels along neuron • have to re-set channels so neuron can react again

10. Measuring cell voltage unstimulated neuron = resting potential of -70mV

11. Gate + + – + channel closed channel open

13. Sodium Potassium Pump

16. action potential saltatory conduction Na+ myelin + – axon + + + – + Na+ Multiple Sclerosis • immune system (T cells) attack myelin sheath • loss of signal

18. Neurotransmitters • Acetylcholine • transmit signal to skeletal muscle • Epinephrine (adrenaline) & norepinephrine • fight-or-flight response • Dopamine • widespread in brain • affects sleep, mood, attention & learning • lack of dopamine in brain associated with Parkinson’s disease • excessive dopamine linked to schizophrenia • Serotonin • widespread in brain • affects sleep, mood, attention & learning

19. Neurotransmitters • Weak point of nervous system • any substance that affects neurotransmitters or mimics them affects nerve function • gases: nitrous oxide, carbon monoxide • mood altering drugs: • stimulants • amphetamines, caffeine, nicotine • depressants • qualudes, barbiturates • hallucinogenic drugs: LSD, peyote • SSRIs: Prozac, Zoloft, Paxil • poisons

20. Acetylcholinesterase • Enzyme which breaks downacetylcholine neurotransmitter • acetylcholinesterase inhibitors = neurotoxins • snake venom, sarin, insecticides neurotoxin in green active site in red snake toxin blockingacetylcholinesterase active site acetylcholinesterase

21. Generation of Postsynaptic Potentials • Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell • Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential

22. Postsynaptic potentials fall into 2 categories • Excitatorypostsynaptic potentials (EPSPs) • depolarizations that bring membrane potential toward threshold • Inhibitorypostsynaptic potentials (IPSPs) • hyperpolarizations that move membrane potential farther from threshold

23. Summation of Postsynaptic Potentials • many synapses on dendrites and cell body • Single EPSP is usually too small to trigger action potential in a postsynaptic neuron • Two EPSPs produced in rapid succession • Causes temporal summation • EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together • Produces spatial summation • combination of EPSPs through spatial and temporal summation can trigger an action potential

24. Figure 48.17 (a) Spatial summationof EPSP and IPSP Subthreshold, nosummation (d) Terminal branchof presynapticneuron E1 E1 E1 E1 E2 E2 E2 E2 Axonhillock Postsynapticneuron I I I I 0 Actionpotential Actionpotential Threshold of axon ofpostsynaptic neuron Membrane potential (mV) Restingpotential 70 E1 E1 E1 E1 E2 I E1 E1I E1 (b) Temporal summation (c) Spatial summation