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Lecture 4 The Action Potential

Allows generation of ap hillock conduction of ap axon

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allows generation of AP (hillock) conduction of AP (axon) ions channels and “microgradients” channel closed (at rest) channel opens (ions rush in) channel closes (ions diffuses)
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why does AP go in one direction? Refractory period (?) AP goes in one direcction due to inactivation gate on proximal (toward soma) side of axon conduction speed –> speed is determined by conductance which is proportional to volume, larger is faster and less leakage (i.e. surface are vs volume) larger axon → faster conduction, and less leakage myelination : speeds up electrical signal conduction : “jumping” of electrical signal from node to node nodes of ranvier – AP propagates skips gap to gap myelin serves to insulate axon: reduces leakage → stronger repulsion down axon → faster conduction. Disorder affecting myelination: characterized by degeneration of myelin, resulting in neuronal death and the formation of plaques (hardenings) in brain and spinal cord disruption is fast, saltatory conductance; sometimes loss of conductance altogether results in weakness, paralysis or spams, impaired coordination, visual problems etc white = myelin = axons an autoimmune disease where your body is attacking it's own myelin Chapter 4 Notes The Generation of an Action Potential AP's studied with oscilloscope. Graph of membrane potential vs. time rising phase (peak of 40 mV), overshoot (inside positively charged relative to outside), falling phase (rapid repolarization), undershoot/after-hyperpolarization, gradual restoration of resting potential action potentials are caused by depolarization of the membrane beyond threshold said to be “all or none” The Generation of Multiple Action Potentials if we pass continuous depolarizing current into a neuron through a microelectrode, we will generate not one, but many action potentials in succession. The firing frequency of action potentials reflects the magnitued of the depolarizing current
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