Synaptic Transmission Flashcards
Ways chemical synapses differ from electrical synapses (3)
1) no gap junctions
2) synaptic cleft is wider
3) use of vesicles
Site of transmitter release on a pre-synaptic axon
active zone
Enzyme responsible for breaking down ACh in cholinergic synapses (found in extracellular matrix)
AChE enzyme
The driving force of Ca2+ will be inward at any potential between what two equilibrium potentials
E(K) and E(Na)
What is another name for v-SNARE protein (vesicle)
synaptobrevin
The two t-SNARE (target) proteins
SNAP-25 and syntaxin
Neurotransmitter release is dependent on what
Ca2+
What does Ca2+ bind to which mediates neurotransmitter release?
synaptotagmin
Does the v-SNARE and synaptotagmin associate with the membrane before or after the action potential
before
Reserve vesicles are tehtered to the cytoskeleton by dephosphorylated _____
synapsin
Dephosphorylates synapsin has a high affinity for this protein
actin
How are reserve vesicles stimulated/mobilized?
A rise in free Ca2+ stimulates the phosphorylation of synapsin, which now has a low affinity for actin.
Kinase responsible for phosphorylation of synapsin
Ca2+/calmodulin-dependent protein kinase (CaMK)
Where is calcium primarily sequestered in the axon terminal?
the mitochondria
Two modes of transmitter action termination
1) diffusion and enzymatic degradation
2) diffusion and reuptake
Enzyme responsible for degrading acetylcholine
acetylcholinesterase
What is glutamate exported from post-synaptic neurons and reuptaken as?
glutamine
Key proteins in vesicle recycling (2)
dynamin and clathrin
What does dynamin need to function?
GTP
Dynamin’s function in vesicular retrieval
Uses GTP to pinch off membrane tube
Where are small molecule neurotransmitters synthesized and packaged?
in the axon terminal
Where are large molecule neurotransmitters synthesized and packaged?
soma. the completely filled vesicle is then transported to the axon terminal
Found in the axon terminal, this enzyme converts choline and acetyl CoA to Acetylcholine
choline acetyltransferase (ChAT)
Found in the synaptic junction, this enzyme breaks down acetylcholine in choline and acetyl CoA
acetylcholinesterase (AChE)
Group of small molecule neurotransmitters derived from tyrosine
catecholamines
List of catecholamines (3)
1) dopamine (DA)
2) norepinephrine (NE)
3) epinephrine (E)
Group of small molecule neurotransmitters derived from tryptophan
Indoleamine
The only indoleamine we learned
serotonin (5-HT)
Group of small molecule neurotransmitters derived from histidine
Imidazoline
The only imidazoline we learned
histamine (HA)
Enzyme responsible for conversion of histidine to histamine
histidine decarboxylase
Location of serotonin production in the brain
raphe nuclei
Location of histamine production in the brain
tuberomammillary nucleus of hypothalamus
Location of norepinephrine production in the brain
locus coeruleus
Locations of dopamine production in the brain
substantia nigra and ventral tegmental area
Enzyme responsible for conversion of glutamate to GABA
Glutamic acid decarboxylase (GAD)
Principle inhibitory neurotransmitter in the spinal cord
Glycine
Principle excitatory neurotransmitter in the central nervous system
Glutamate
Principle inhibitory neurotransmitter in the brain
GABA
Why is adenosine not technically a neurotransmitter?
It’s not loaded into vesicles
Adenosine’s function in the synaptic junction
extracellular signaling molecule
How is adenosine formed in the synaptic junction?
Formed by extracellular enzyme ecto-nucleotidases from released ATP
Function of adenosine as a signaling molecule
sleep signal promoting drowsiness (caffeine blocks receptor!)
Membrane soluble gas, synthesized directly in response to Ca2+
nitric oxide
Where does nitric oxide bind in postsynaptic cells and what does it activate?
Binds to intracellular receptors, activating cytosolic guanylyl cyclase
Simultaneous release of 2 neurotransmitters by a neuron, typically one small molecule and one peptide
Co-expression
Directly activated neurotransmitter receptor, where ligand binding opens a channel
ionotropic receptor
Indirectly activated neurotransmitter receptor, where ligand binding leads to intracellular messaging and second transmembrane protein becoming active
metabotropic receptor
Type of acetylcholine receptor which directly opens Na+/K+ channels
nicotinic acetylcholine receptor (ionotropic)
Acetylcholine receptor type/subtypes which stimulate phospholipase c (PLC) and close K+ channels
Muscarinic acetylcholine receptors (Subtypes: M1, M3, M5) [Metabotropic]
Acetylcholine receptor type/subtypes which inhibit adenylyl cyclase, open K+ channels, and inhibit Ca2+ channel opening
Muscarinic acetylcholine receptors (Subtypes: M2, M4) [Metabotropic]
Serotonin receptor type which directly opens Na+/K+ channels
5-HT3 (ionotropic)
Glutamate receptor types which directly open Na+/K+ (Na+/K+/Ca2+) channels
Kainate (KA), AMPA, and NMDA receptors (ionotropic)
GABA receptor type which directly opens Cl- channels
GABA(A) (ionotropic)
GABA receptor type which indirectly opens K+ channels and inhibits Ca2+ channel opening
GABA(B) (metabotropic)
Glycine receptor type which directly opens Cl- channels
GlyR (ionotropic)
Function of nicotinic acetylcholine receptors
directly open Na+/K+ channels
Function of M1, M3, M5 subtype muscarinic acetylcholine receptors
stimulate phospholipase C and close K+ channels
Function of M2, M4 subtype muscarinic acetylcholine receptors
inhibit adenylyl cyclase, open K+ channels, and inhibit Ca2+ channel opening
Function of 5-HT3 serotonin receptors
directly open Na+/K+ channels
Function of Kainate, AMPA, NMDA receptors
directly open Na+/K+ (Na+/K+/Ca2+) channels
Function of GABA(A) receptors
directly opens Cl- channels
Function of GABA(B) receptors
indirectly opens K+ channels and inhibits Ca2+ channel opening
Function of GlyR receptors
directly opens Cl- channels
Change in postsynaptic ion permeability caused by released neurotransmitter
postsynaptic potential
postsynaptic response which increases the probability that postsynaptic neuron will fire an action potential
Excitatory Postsynaptic Potential (EPSP)
postsynaptic response which decreases the probability that postsynaptic neuron will fire an action potential
Inhibitory Postsynaptic Potential (IPSP)
What determines the effectiveness of spatial summation of action potentials?
length constant (easier to sum if the length constant is “more forgiving”)
Temporal summation is more possible with a long or short time constant?
Long time constant since they’re more drawn out
Stellate neurons are relay cells with small surface area and often act as interneurons. What is there time constant like?
short time constant helps maintain timing information
Pyramidal neurons are integrating neurons which integrate information over time. What is there time constant like?
Long time constant helps with temporal summation
What is an axo-axonic synapse?
Where an axon terminal receives input from another axon
Most axo-axonic synapses are…
inhibitory
How does presynaptic inhibition usually work?
Activating of K+ channels inhibits voltage gated Ca2+ channels from opening (which in turn prevents vesicle exocytosis)
Presynaptic receptors activated by same transmitter released at the terminal
autoreceptor
Neurotransmitters affecting multiple postsynaptic cells
volume transmission
Three mechanisms of volume transmission
1) diffusion out of synaptic cleft (spillover)
2) release into non-synaptic extracellular space (diffuse release)
3) neurotransmitter diffuses through cell membranes
How does neuromodulation work without changing ion conductance?
Stimulates or inhibits second messenger pathways in postsynaptic cells
