NSCI 110 1st Edition Lecture 13 Outline of Last Lecture I Temporal and spatial summation may lead to either hyperpolarization or depolarization of a neuron II There are several crucial differences between an action potential and synaptic potential III Synapses can be classified according to where on a neuron the release of neurotransmitters occurs IV Synaptic transmission a Docking and priming b Action potential reaches axon terminal i Gated calcium channels open c Transmitter is released and travels to post synaptic membrane Outline of Current Lecture I Metabotropic receptors and ionotropic receptors differ in their mechanisms of opening an ion channel II Acetylcholine is synthesized in the pre synaptic terminal in a specific sequence of steps a Eventually is broken down and taken back up by pre synaptic terminal III Catcholamines are all derived from tyrosine a The subsequent transmitter used by the neuron depends on the enzymes present at each step of the pathway IV Amino acids include glutamate and GABA V A superfamily of receptors is involved in transporting glutamate across the membrane a NMDA and AMPA receptors Current Lecture I II A metabotropic receptor is not directly attached to the channel unlike an ion channel a Coupled with the phosphorylation of G proteins that induce conformational changes in the channels Synthesis of Ach by the presynaptic terminal a Acetyl CoA carries acetate to the transmitter synthesis site b ChAT enzyme transfers acetate to the choline to form Ach and coenzyme A c Once in the synaptic cleft ACh is broken down by acetylcholinesterase i Forms acetic acid and choline ii These products go through reuptake and travel back into the presynaptic terminal iii Choline transporter allows this transportation across the membrane These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III IV Other common neurotransmitters a Catecholamines i Tyrosine from diet L dopa dopamine norepinephrine epinephrine 1 Tyrosine hydroxylase is the rate limiting factor in this pathway 2 If the third enzyme is not present in that synapse dopamine will be the neurotransmitter used 3 Forms a feedback system b Amino acids i Glutamate excitatory and GABA inhibitory are structurally very similar 1 GABA is missing one carboxyl group ii Glutamic acid decarboxylase GAD can turn glutamate into GABA iii If the concentration is increased from 5 mM to about 20 mM of glutamate in a presynaptic terminal glutamate will be used as the neurotransmitter More on glutamate a Glutamate superfamily of receptors i NMDA ionotropic exogenous 1 Specific receptors for glutamate and NMDA ii AMPA ionotropic exogenous 1 Specific receptors for glutamate and AMPA iii mGluR metabotropic b NMDA i Na K Ca 2 NMDA is a non selective cation channel 1 Don t normally have a current because a magnesium usually sits in the pore and prevents ions from flowing through ii NMDA receptors also have AMPA receptors nearby as partners 1 Kainate receptors may also be involved iii When glutamate binds to the AMPA receptor ions influx through the channel 1 Positive charge repolarizes the membrane in the immediate area and causes the magnesium ion to move and allow ions through the NMDA channel 2 Causes a summation and allows a longer action potential a Important in learning and memory 3 This is why the ionic current is voltage dependent iv At around 0 mV potassium starts flowing outward trying to reach equilibrium potential c Glutamate is not broken down in the synaptic cleft i Either goes through reuptake or absorbed by an adjacent astrocyte where it is stored at glutamine ii Astrocyte then releases the molecule as glutaminase back into the presynaptic terminal so glutamate levels may be restored iii GABA goes through the same process but is stored as glutamine and taken back up by the presynaptic terminal as glutamate then converted into GABA
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