APK 2105C Lecture Notes - Lecture 30: Excitatory Synapse, Acetyl-Coa, Muscarinic Acetylcholine Receptor
5 Jun 2018
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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 recycled—put back
into the presynaptic axon terminal
▪ Does not get taken up again
▪ More remains in the synaptic cleft—more 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
find more resources at oneclass.com
find more resources at oneclass.com
