refractory period 1 absolute refractory period as long as Na gates remain open

Refractory period 1 absolute refractory period as

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refractory period 1) absolute refractory period as long as Na + gates remain open an AP is being generated, no stimulus of any strength will trigger another AP lasts from the current AP to the next RMP
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The Refractory Period 2) relative refractory period only an especially strong stimulus will trigger new AP K + gates are still open and any affect of incoming Na + is opposed by the outgoing K + refractory period only occurs at a small patch of the neuron’s membrane other parts of the neuron/membrane can still be stimulated while the small patch is in the refractory period
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Signal Conduction in Unmyelinated Fibers for neural communication to occur, a nerve signal must travel to the end of an axon unmyelinated fibers have voltage-regulated ion gates along their entire length an AP from the trigger zone causes Na + to enter the axon and diffuse into adjacent regions just beneath the membrane the depolarization excites voltage-regulated gates immediately distal to the AP Na + and K + gates open and close producing new APs progressively distal down the axon by repetition, the membrane distal to that is excited this chain reaction continues all the way to the end of the axon The Nerve Impulse Video
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Nerve Signal Conduction of Unmyelinated Fibers
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Saltatory Conduction in Myelinated Fibers voltage-gated channels are needed for an AP to occur there are fewer than 25 voltage-gated channels per m 2 in the myelin-covered internodes BUT… there are up to 12,000 per m 2 in the nodes of Ranvier Na + diffuses very quickly on internodes even though the signal weakens under the myelin sheath, it is still just strong enough to produce an AP at the next node of Ranvier saltatory conduction – the nerve signal seems to jump/hop from node-to-node on its way down a nerve fiber/axon
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Saltatory Conduction saltatory conduction is much faster than conduction in unmyelinated fibers
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Synapses an AP can go no further once it reaches the end of the axon – So, what does it do? the AP triggers the release of a chemical neurotransmitter (NT) from the synaptic knobs of the axon NT diffuses across the synapse and produces a new AP in the next cell across the synapse in a synapse between two neurons the first neuron in the signal path is the presynaptic neuron that releases the chemical NT the second neuron is the postsynaptic neuron that binds and responds to the NT presynaptic neuron can synapse with the dendrite, soma, or axon of the postsynaptic neuron a neuron can also have an enormous number of synapses a spinal motor neuron is usually covered by about 10,000 synaptic knobs from other neurons in the cerebellum of the brain, one neuron can have as many as 100,000 synapses
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Synaptic Knobs
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Structure of a Chemical Synapse the synaptic knobs of a presynaptic neuron contain synaptic vesicles the synaptic vesicles contain chemical neurotransmitters (NT)
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  • Spring '13
  • ToddPfander
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