04 -- synaptic physiology 1

04 -- synaptic physiology 1 - Intercellular Communication...

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Intercellular Communication by Neurons
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Definition SYNAPSE SYNAPSE Specialized junction where one part of a neuron contacts and communicates with another neuron or other cell type (muscle, gland, etc).
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Types of Synapses 2 types: Electrical Electrical direct physical contact between cells Chemical Chemical indirect (no physical contact) communication between cells using various molecules (neurotransmitters) to pass signals Pre Pre synaptic synaptic Cell Cell Post Post synaptic synaptic Cell Cell
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Electrical Synapses Direct passage of current from pre- to post-synaptic cell post-synaptic potential post-synaptic potential (PSP) (PSP) * a change in the membrane potential of the post synaptic cell 1 mV
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Electrical Synapses Direct passage of current from pre- to post-synaptic cell • occurs at GAP JUNCTIONS – formed by CONNEXIN MOLECULES 6 connexins = 1 connexon 2 connexons = 1 gap junction
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Electrical Synapses Allow rapid transmission of a “signal” among a network of interconnected neurons Good if want quick action of organism Good if want to SYNCHRONIZE activity of a group of neurons Examples: • Crayfish sensory-motor connections quick getaway • Human hypothalamus circadian rhythms • Human thalamus and brainstem synchronicity of neurons controlling breathing Downside = static, non-adaptable
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Chemical Synapses More dynamic, adaptable More complicated Much more numerous in mammalian nervous system
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Chemical Synapse Vesicle Neurotransmitter Voltage-Gated Calcium Channel Receptor Synaptic Cleft Pre-synaptic Cell (“sender”) (“sender”) Post-synaptic Cell (“receiver”) (“receiver”) Axon Terminal Axon Terminal (or Synaptic Terminal or Synaptic knob) NT-degrading enzyme (optional) NT pump (optional) POST SYNAPTIC SYNAPTIC DENSITY ACTIVE ZONE
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Chemical Synapse The real thing PSD Active Zone
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Chemical Synapses On the cellular level, synapses occur in 3 places on a neuron (see below) Also note that each presynaptic cell may make multiple synapses with one postsynaptic cell any given CNS neuron may have as many as 1K-10K synapses to it from other neurons 10 billion neurons in cortex alone X a bunch of synapses per neuron 60-240 TRILLION synapses 60-240 TRILLION synapses in the human cortex
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Chemical Synapses Physical layout of chemical synapses can vary also Post Synaptic Densities
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Chemical Synapse Basic overview of activity at a chemical synapse
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Chemical Synapse Basic overview of activity at a chemical synapse Click image to be taken to animation
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Synaptic Activity Let’s break it down like this: What is going on in the presynaptic neuron: Neurotransmitter overview • Synthesis and packaging of neurotransmitters • Vesicular Activity in the axon terminal – Release of neurotransmitter Fate of vesicle after release – Role of calcium in release of neurotransmitter What is going on in the postsynaptic neuron: Overview of postsynaptic receptors
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04 -- synaptic physiology 1 - Intercellular Communication...

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