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Neurotransmission
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How neurons communicate
Neurons communicate through an electrical signal called the Action Potential
Action Potentials may be triggered by sense organs or by other neurons
An action potential is an all-or-nothing event
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When does a neuron fire?
Neurons receive neurotransmitter signals through dendrites
Some signals are excitatory (accelerator), some are inhibitory (brake)
If the combined signals reach the “threshold”, it will trigger the action potential
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Action Potentials
The neuron is electrically charged with positive and negative ions both inside and surrounding the cell
If the threshold is reached, the neuron “fires”, moving ions in and out of the cell and generating an electric impulse which travels down the axon
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Action Potentials
When an Action Potential occurs, a molecular message is sent to neighboring neurons Neurotransmitters leave the Terminal
Buttons and are collected by neighboring dendrites
After this happens, the ions and neurotransmitters move back to their starting positions, and the neuron is at rest again
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Myelin Sheath & Nodes of Ranvier
If an axon is myelinated (has a myelin sheath), the action potential will jump directly from node to node, without having to actually travel the whole axon.
Myelin Sheath
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Neuron to Neuron
Axons branch out and end in buttons near dendrites of neighboring cells
A gap separates the terminal buttons from dendrites
Gap is the “Synapse”
CellBody
Dendrite
Axon
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Synapse
axon buttons contain small storage sacs called synaptic vesicles
vesicles contain neurotransmitters
SendingNeuron
SynapseAxonTerminal
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Neurotransmitter Release
Action Potential causes vesicle to openNeurotransmitter released into synapseLocks onto receptor molecule in dendrite of
adjacent neuronNormal psychological (and physiological)
functioning is dependent on neurotransmitter activity
Can be affected by factors such as disease and drugs
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Locks and Keys
Neurotransmitter molecules have specific shapes
Receptor molecules have binding sites of the same shape
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Some Drugs work on receptors
Some drugs are shaped like neurotransmitters
Antagonists : fit the receptor but poorly and block the NT e.g. beta blockers
Agonists : fit receptor well and act like the NT e.g. nicotine.
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Further research
We have covered a lot of material already in this unit and there is more to come!
Make sure you understand what we are doing as we go along!
You can come in for tutoring after school M-Th, I am here most days until at least 3:30.
For this material, check http://www.worthpublishers.com/bloom/content/psychsim/index.htm (site is listed in your packet) – Quiz next class!