Neurotransmission Flashcards
What are some criteria to classify neurotransmitters?
The presynaptic cell contains the chemical and the mechanism to make it
There is a mechanism for inactivating the chemical
The chemical is released from the axon terminal when neuron is stimulated
Receptors for chemical are present on postsynaptic cells
What is the monoamine synthesis of epinephrine?
Tyrosine to dopa to dopamine to norepinephrine to epinephrine
What is the monoamine synthesis of serotonin?
Tryptophan to 5-hydroxytryptophan to serotonin
What are the enzymes involved in the monoamine synthesis of epinephrine?
Tyrosine hydroxylase
Aromatic amino acid decarboxylase
Dopamine beta-hydroxylase
Phenylethanoamine N-methyltransferase
What are the enzymes involved in the monoamine synthesis of serotonin?
Tryptophan hydroxylase Aromatic amino acid decarboxylase
How is glutamate made?
Using glutamate synthase from glutamine or the citric acid cycle
How is GABA made?
Using glutamate decarboxylase from glutamate
How is glutamate recycled?
GABA is made into succinate semialdehyde using 4-aminobutyrate transaminase
Succinate semialdehyde enters the CAC by succinate semialdehyde dehydrogenase
The CAC uses glutamate synthase to make glutamate
How is acetylcholine made?
Choline acyltransferase uses AcetylCoA to and choline to make acetylcholine
What is a classical neurotransmitter?
In punctated
Release the impulse for each AP
Synthesized in the cytoplasm and Golgi apparatus of terminals
Released into synaptic cleft with depolarization of axon terminal
How do monoamines work?
Vesicles stuffed with precursor amino acid and synthesizing enzymes en route to terminal
How are neuropeptides synthesized?
Gene transcription and translation into amino acid chains that can act as signalling molecules
What do peptide neurotransmitters do?
Release gradually in response to increases in AP
Has widespread effects as they are released into ECF, ventricles, or bloodstream as an undirected synapse
Act as neuromodulators
Where are peptide neurotransmitters synthesized?
In the cell body, processed and packaged into Golgi into large vesicles and then transported to the terminal
Can take a long time to replenish the releasable pool in the terminal
What are neurotransmitters packaged into?
Secretory vesicles
How are neurotransmitters packaged?
Proteins are synthesized in the RER and transported to the golgi
Bud off golgi to form the vesicle with the propeptide and proteolytic enzymes
Transporter proteins actively pump neurotransmitters into vesicles
What are small clear core vesicles?
Contain classical NT
40-60 nm diameter
What are large dense-core vesicles?
Contain monoamine and neuropeptides
90-250 nm diameter
Why might you not be able to find large vesicles?
Because the neuropeptides have been depleted and waiting for replenishment
What does the coexistence of neurotransmitters refer to?
More than one type of neurotransmitter is synthesized and released in a neuron
-a mix of classical and neuropeptide
How are neurotransmitters transported to the axon terminal?
Anterograde to the axon terminal by motor proteins like kinesin
Requires energy
What are the steps of neurotransmitter release?
- AP in the axon terminal
- Open voltage-gated Ca2+ channels
- Increase calcium influx
- Activates proteins responsible for mobilizing vesicles and fusing vesicles with synaptic membrane
- Vesicles move to the active zone
- Vesicles dock onto the synaptic membrane
- Fuse with synaptic membrane and release NTs into the cleft
What happens when neurotransmitters are in the synapse?
They bind to receptors
Receptors are:
Specific for neurotransmitter
What are ionotropic receptors?
Ligand-gated ion channels NT can open or close ion channel Fast-acting Generate EPSP or IPSP Found postsynaptically
What are metabotropic receptors?
G protein-coupled - second messenger signalling Slow acting Long-lasting changes More prevalent than ionotropic Found pre and postsynaptically
What receptors do neuropeptide receptors bind to?
Metabotropic
What happens when neurotransmitter activates receptors?
EPSP or IPSP (ionotropic)
Activate second messenger systems (metabotropic)
What are two mechanisms for terminating neurotransmitter action?
Reuptake
Enzymatic degradation
What are autoreceptors?
Metabotropic Bind to own neurons NTs Presynaptic Provide feedback -reduce when NT is high -increase when NT is low
What happens during neurotransmitter reuptake?
Transporters on presynaptic cell and/or glia pick up NT from the synaptic cleft
In the cell they are either repackaged into vesicles for future release or are degraded by enzymes
What happens during neurotransmitter degradation?
Some NTs do not have transporters for reuptake
-enzymes are degraded in the cleft (like acetylcholinesterase for Ach)
Some NTs are taken buck up into the cell but degraded in cytosol
What do astrocytes do in synaptic transmission?
Modulate neuronal activity
Tripartite synapse
Uptake glutamate
How do glial cells communicate via gap junctions?
Made up of connexin
Connect cytoplasm of 2 adjacent cells to share second messengers and electrical signals
Electrical synapse that is faster than a chemical synapse
Function to synchronize activities of similar cells
