APK 2105C Lecture Notes - Lecture 30: Excitatory Synapse, Acetyl-Coa, Muscarinic Acetylcholine Receptor

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Chapter 8, All Lectures
Synaptic Transmission
Lecture 1
Chapter 8, Lecture 1
Synaptic Transmission
Synapses in the nervous system
o Electrical synapses
Gap junctions
Electrical coupling of cells with similar function
Less common
o Chemical synapses
Neurotransmitters to communicate with
Neurons
Muscles
Glands
Most common
Parts of synapse are acting together to create site of communication
Presynaptic neuron contains mitochondria
o Mitochondria needed to exocytose neurotransmitters
Synaptic cleft = space between pre and postsynaptic neurons
o Very small
o Neurotransmitters cross this and then bind to ligand gated
receptors on the postsynaptic neurons
Postsynaptic neuron
Functional anatomy of chemical synapses
o Presynaptic neuron
o Postsynaptic neuron
o Most common with multipolar neurons
o Synaptic cleft
Full of interstitial fluid
o Axo-dendritic synapse
o Axo-somatic synapse
o Axo-axonic synapse
Usually closer to end of axon on postsynaptic neuron
Synaptic transmission
o The more Ca allowed into the axon terminal the more neurotransmitter is
released
How can we get more Ca in?
Higher firing frequency of APs
Ca channel stays open for a longer period of time
More neurotransmitter = more response from target cell
o Steps
AP comes down
Ca is absorbed through voltage gated Ca channels
Voltage change from AP coming down
Initiates exocytosis
Neurotransmitter binds to receptor site on postsynaptic neuron
Degretory enzymes on membrane of pre and post synaptic neurons
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Break down ligands so they can be reused
Reuptake enzymes on presynaptic neurons
o Helps recycle ligands
o May break down and only some parts are recycled
Clinical correlation = SSRIs = selective serotonin reuptake inhibitors
o Patients with clinical depression display low levels of serotonin production and
release in the brain
o SSRIs prevent the serotonin that is exocytosed from being recycledput back
into the presynaptic axon terminal
Does not get taken up again
More remains in the synaptic cleftmore goes to postsynaptic neuron
Longer in synaptic cleft = more of a response from target cell
o Examples
Prozac
Lexapro
Paxil
Zoloft
Signal transduction at chemical synapses
o Fast response
Typically results in a change in Vm = post-synaptic potential (PSP)
Graded by amt of neurortransmitter bound to receptors
Ionotropic receptors = directly impact the movement of an ion
Contributes to change in membrane potential
Ligand binds and opens
Na comes in = depolarization = makes it more positive
K goes out = hyperpolarization = makes it more negative
o Slow response direct coupling
Metabotropic receptor
G protein regulated
Neurotransmitter binds
Activates G protein
G protein goes over and activated ion
channel
o G protein goes directly to ion
channel
Gets PSP as the results
Membrane potential changes
o Slow response 2nd messenger
Metabotropic receptor
Neurotransmitter binds
Activates G protein
Activates or inhibits enzyme
o Gi protein or Gs protein are ones
that go on to activate/inhibit
enzymes
Produces 2nd messenger
o cAMP
o cGMP
o Opens or closes ion channels
o Produces other cell responses
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