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Lecture 4

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University of Toronto Scarborough

Lecture 4 Neurotransmitters - when action potential goes past the threshold, Na channels open and lots of sodium enters the neuron and neuron fires Action potential: large positive charge across the neural membrane, caused by sodium influx - info travels down the axon until the synaptic terminal button – which meets w a dendrite of the next neuron - presynaptic => axon - postsynaptic => dendrite - junction = synapse; space in between is the synaptic cleft - synaptic vesicles get released from presynaptic axon when action potential hits – fuse w the membrane and empty transmitter substance contents into synaptic cleft - transmitter interacts w receptors on the postsynaptic membrane of dendrite => cause channels to open, allow Na to enter and continues the action potential - in order to transmit information transmitter needs to interact, but needs to be quickly inactivated so that a different signal can come in - chemicals in the synaptic cleft exist to breakdown transmitters Life cycle of transmitter: 1. synthesis – from basic ingredients 2. storage – critical bc can be broken down by enzymes if not stored properly 3. vesicle release – usually when there’s an action potential 4. interaction w receptor – transmission to the next cell 5. inactivation – reuptake or degradation/breakdown 2 ways to alter a system – can increase or decrease functional activity => can do this in each step of the life cycle Increase functional activity Decrease functional activity 1. Synthesis Production of more transmitter Reduction of transmitter increases functional activity production - eg in parkinson’s disease give - eg in sch decrease dopamine more L-dopa to increase synthesis of dopamine 2. Packaging - decrease packaging allows - - - transmitter to get destroyed => very little left for release 3. Release - more release leads to more - decrease release neuron firing 4. Receptor activation - administer mimicker - administer blocker 5. Inactivation - decrease breakdown - increase breakdown, before the => keeps stimulation on transmitter can reach the receptor postsynaptic receptor longer Mimicker: chemicals that can mimic the activity of a neurotransmitter; very similar to the transmitter in molecular shape => activates the receptor of the transmitter Blocker: fits perfectly in the receptor site, but no activation – blocks channel from opening 1 Classic Neurotransmitters 1. Monoamines (biogenic amines): A) Catecholamines => dopamine (DA), norepinephrine (NE) - synthesized from tyrosine => dopa => dopamine => NE - most effective way of treating Parkinsons is by increasing synthesis; taking L-dopa B) Serotonin (5HT) - synthesized from tryptophan => (5-hydroxy tryptophan) 5OHT -> (5-hydroxy tryptomine) 5HT - all monoamines are inactivated by re-uptake 2. Acetylcholine: - synthesized from choline + acetyl CoA => Ach - degraded by acetylcholinesterase (AchE) Epilepsy - one of the biggest physiological abnormalities in the brain Epilepsy: repetitive discharge of a hyperexcitable aggregate/collection of neurons - not always but often results of convulsions => jerking of the body - group of neurons starts doing the same thing at the same time, unlike normal brain activity, where all neurons do their own thing => exciting the motor strip – person starts convulsing => entire section of the brain repetitively firing in synchrony Causes: - can be genetic; increase in occurrence of disease in certain families => not the us
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