Biology Final Notes

Biology Final Notes - Biology Final Notes Action potential...

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Biology Final Notes Action potential o If a depolarization is great enough (threshold) it will stimulate an action potential o This involves voltage-gated channels Voltage Gated Channels o Na+ channels: 2 gates Activation gate (opens) Inactivation gate (closes) o K+: 1 gate Opens slow o Differ in the ions that are allowed through, and number of gates that they have Action Potential o Is the result of the Na+ gate opening causing a rapid delpolariztion of the membrane (na+gate open) o Followed by the closing of the Na+ inactivation gate and the opening of the K+ gate, causing a repolarization of the membrane This is then propagated The formation of an action potential in one location cause a depolarization in the surrounding areas triggering an action potential there Speed of Propagation o Large Diameter=faster propagation o Myelin shealth=faster propagation Speed of Action Potential Propagation o Non-myelinated axons 5-25 m/sec o Myelin Directionality of propagein
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o Normally from cell body to axon terminus. o Begins at axon hillock Synapses with another neuron of effto Refractory period of the membrane Chemical Synapses o Slower transmission o Action potentials can only flow in one direction o Action potential opens ca+ channels in pre synaptic axon terminus o Ca++ cause fusion of vesicles of neurotransmitter to fuse to presnaptic membrane o Neurotransmitter diffuses across the synaptic cleft o Binds to receptors on postsynaptic membrane o Opens gated ion channels o Enzymes secreted by post synaptic membrane destroy neurotransmitters o Enzymes secreted by postsynaptic membrane destroy neurotransmitters or neurotransmitters pumped back into presynaptic cell Opening the gated channels causes: o EPSP: excitatory postsynaptic potential o IPSP: inhibitory postsynaptic potential Clicker An EPSP is the result of ……………….. Gates opening and results in a ……………… Answer: Na+, depolarization Integration of Signals o Since many neurons may synapse with one it is the combination of EPSPs and IPSPs that determine whether or not an action potential fires in the post synaptic neuron Clicker: If the combination of EPSPs and IPSPs does not reach the threshold level in the post-synaptic neuron, what happens?
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