BGYB30H3 Lecture 5 Notes Chemical Synapse 1-Sep 24

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11 Aug 2010
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BGYB30H3 Lecture 5 Notes
-graded potentials occur in the cell body and dendrites
-action potentials occur in the axon (particularly the axon hillock)
-chemical neurotransmission occur in the synapse of the neuron
-neurotransmission is the conversion of the action potential into a chemical signal, which induces a
response in the target
-chemical signal could be a neurotransmitter
-pre-synaptic bouton is located near the post-synaptic junction (synaptic cleft in between)
-post-synaptic junction contains voltage gated channels of sodium and potassium
-pre-synaptic bouton contains calcium channels
-before a synapse, the action potential depolarizes the axon terminal by opening calcium channels and
calcium enters the bouton
-calcium triggers exocytosis of synaptic vesicles that release neurotransmitter
-neurotransmitter binds with receptor on post-Çv]oovZdownstream response[oo
signal transduction
-neurotransmitter remains outside the post-synaptic cell
-signaling cascades are activated by different types of receptors which are ionotropic receptors and G-
protein coupled receptors
-ionotropic receptors (ligand gated) are coupled to an ion channel
-ionotropic receptors cause movement of ions across membrane through ion channel when
neurotransmitter binds to them (creates a fast response)
-in G-protein coupled receptors, neurotransmitter causes activation of receptor, which activates G-
protein (creates a slow response)
-signal is amplified once receptor is activated because G-protein signals amplifying enzymes that signal
secondary messengers
-secondary messengers are the initiators of responses in the cell
-ionotropic and G-protein coupled receptors alter the open state of voltage gated channels by closing
the channel to alter membrane potential
-less sodium inside the cell causes IPSP, less potassium outside the cell causes an EPSP
-secondary messengers modify existing proteins and synthesize new proteins, which are referred to as
co-ordinated cellular responses
-after synapsis, neurotransmitters are transported back to presynaptic cell where they are packed into
vesicles again and transported to a reserve pool of synaptic vesicles
-the active zone is the region where the exocytosis of neurotransmitters occurs
-calcium binds to calcium sensitive proteins on vesicles before exocytosis occursn
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