3. Synaptic Transmission Part 1 Flashcards
type of synapse where current flows directly from one cell to another through connexons
electrical synapse
type of synapse with secretion of a specific chemical by a nerve terminal and its interaction with specific postsynaptic receptors
chemical synapse
at an electrical synapse, the distance between pre and post synaptic cell membranes is:
~3.5nm
at electrical synapses, the agent of information transmission is:
ionic current
is there synaptic delay between electrical synapses?
no
is signal transmission unidirectional or bidirectional in electrical synapses?
usually bidirectional
at electrical synapses, there is _____ between the cells
cytoplasmic continuity
composed of 6 connexins and form the gap junction
connexon
gap junctions and connexons are more common during:
embryonic development
if current injection into either cell A or cell B results in the depolarization in both cells, the cells are:
electrically coupled
at chemical synapses, the distance between pre and post synaptic cell membranes is:
20-40nm
is there cytoplasmic continuity between cells at chemical synapses?
no
at chemical synapses, current flows via:
activation of receptors and the consequent opening of postsynaptic ion channels
at chemical synapses, the agent of information transmission is a:
chemical transmitter
is there synaptic delay at chemical synapses?
yes (~1-5ms)
is signal transmission unidirectional or bidirectional in chemical synapses?
unidirectional
many synapses occur on dendrites and dendritic spines, and these are usually:
excitatory synapses
some synapses occur on dendrites closer to the cell body, and on the cell body itself, these are usually:
inhibitory synapses
true or false: synapses occur randomly
false
where is the postsynaptic density found?
at both excitatory and inhibitory synapses
provides a structural matrix which clusters ion channels and anchors signalling molecules such as kinases and phosphatases
the post synaptic density (PSD)
the post-synaptic density is a general organizer of the:
postsynaptic signal transduction machinery
links regulatory molecules to their targets, and coordinates developmental and activity-dependent changes in postsynaptic structures
the postsynaptic density (PSD)
one of the earliest models to examine muscle function
neuromuscular junction (NMJ)
action potentials at the neuromuscular junction (NMJ) are dependent on the release of:
acetylcholine (ACh)
located inside the nerve terminal of neuromuscular junctions and contains vesicles of neurotransmitters
active zones
synapses in the peripheral nervous system (PNS) are found at the:
neuromuscular junction (NMJ)
a plant alkyloid that binds to and blocks nicotinic ACh receptors; it prevents nerve transmission at the neuromuscular junction
curare (or tubocurarine)
tubocurarine is a _____ that binds to the same site as ACh
reversible competitive antagonist
curare blocks neuromuscular transmission by blocking the activation of:
ACh receptors at the neuromuscular synapse
go review slide 154
wahooooo
the process of passing a weak electrical current through the synapse
ionophoresis
as ACh is ionophoresed further from the synapse, the post synaptic potential (PSP) becomes:
weaker
mapping the distribution of ACh sensitivity using ionophoresis suggests that:
the ACh receptors are very close to, if not directly at the neuromuscular synapse
found at very high concentrations at the folds of the cleft of the neuromuscular junction (~10 000 per um^2)
ACh receptors
found at the base of the folds of the neuromuscular junction
voltage gated Na+ channels
at the neuromuscular junction, ACh binds to and activates the:
nicotinic acetylcholine receptor (nAChR)
once the nicotinic acetylcholine receptor (nAChR) is activated, the receptor allows ____ to flow into the cell and ____ to flow out of the cell
Na+ ions, K+ ions
why does the synpatic current at the neuromuscular junction have a reversal potential of ~0mV?
because the nicotinic receptor channels (nAChRs) allow both Na+ and K+ ions to flow
the current at the neuromuscular junction is a summation of:
the individual currents through each nAChR channel
the current at the neuromuscular junction is also known as the:
endplate current (it has a very sharp onset which is followed by an exponential decay)
what causes the sharp onset of the endplate current?
all of the channels are activated nearly simultaneously
what causes the exponential decay of the endplate potential?
the channels close in a stochastic (random) function: some close quickly and the others take longer
what are the three major neurotransmitters found in the CNS?
glutamate, glycine, GABA
what is the difference between ionotropic vs metabotropic receptors?
ionotropic receptors are ligand gated, and metabotropic receptors are GPCRs
what are the three major types of glutamate receptors?
- NMDA
- AMPA
- kainate
true or false: several types of glutamate receptors may be found at a single synapse
true
the subunits of ionotropic receptors may have _____ each, and usually _____ subunits assemble to form a functional receptor
3-4 transmembrane regions, five
how many glutamate molecules are needed to activate the AMPA receptor?
2 (but can bind up to 4)
how many AMPA receptor subunits are there?
4 (GluR1-GluR4)
which subunit of the AMPA receptor confers Ca++ impermeability
GluR2
the GluR2 subunits make the AMPA receptors impermeable to:
Ca++
which site of the GluR2 subunit is responsible for Ca++ permeability?
the Q/R site (this is an arginine in GluR2 but a glutamine in GluR1, 3, and 4)
Ca++ permeable AMPA receptors are involved in:
epilepsy, ALS, pain and addiction (reward centres)
GluR2 subunits have a(n) ____ residue at the Q/R site
arginine
NMDA receptors are composed of:
2 NR1 subunits and 2 NR2 subunits
glutamate binds to the _____ subunits of the NMDA receptors
NR2
glycine binds to the _____ subunits of the NMDA receptors
NR1
how many molecules of glutamate and glycine are needed to required for activation of the NMDA receptor?
two molecules of glutamate and two molecules of glycine
at resting potentials, NMDA receptors are blocked by:
external Mg++
NMDA receptors act as _____ because they require both neurotransmitters and cell depolarization to be activated
coincidence detectors
true or false: the properties of the various NMDA receptor subtypes can very significantly
true
inhibitory fast synaptic transmission is mediated through the activation of:
glycine and GABA receptors
glycine and GABA receptors allow ____ to flow across the cell membrane
Cl- ions
all known glycine receptors are:
ionotropic
glycine receptors are composed of:
five subunits
native glycine receptors (GlyRs) are complexes of different combinations of:
alpha subunits, beta subunits, and a scaffolding protein known as gephyrin
homomeric glycine receptors are composed of:
five alpha subunits
heteromeric glycine receptors are composed of:
two alpha subunits and three beta subunits
how many types of alpha subunits for the glycine receptor are there?
four
how many types of beta subunits for the glycine receptor are there?
one
neonatal animals express the ____ subunit on their glycine receptors, but this changes throughout development such that older animals express the ____ subunit
alpha two, alpha one
how does glycine activate the glycine receptors (GlyRs)?
glycine binds to the interface between the alpha and beta subunits
how many molecules of glycine are required for activation of glycine receptors (GlyRs)?
at least 2
a potent antagonist of glycine receptors (GlyRs) is:
strychnine (rat poison)
what is the difference between glycine receptors containing alpha two subunits and glycine receptors containing alpha one subunits?
alpha two subunits have a longer mean open time
what are the two major kinds of GABA receptors?
1) ionotropic (GABAa and GABAc)
2) metabotropic (GABAb)
list two GABAa antagonists that bind to and reduce GABA IPSPs
picrotoxin and bicuculline
picrotoxin is a:
GABAa pore blocker
bicuculline is a:
GABAa competitive antagonist
both picrotoxin and bicuculline cause:
convulsions
addictive drugs which lengthen the open time of GABAa receptor channels
barbituates
non-addictive drugs that increase the number of GABAa receptor channels opening
benzodiazepines (diazepam/valium)
drug which binds to GABAa receptors and potentiates IPSPs and leads to calming and sedation
alcohol
activation of neonatal GABA receptors depolarize the cell membrane and leads to the unblocking of:
NMDA receptors
true or false: equilibrium potential for Cl- changes during development
true
GABA is _____ in neonates and _____ in adults
excitatory, inhibitory
in neonates, high levels of _____ ensures that Cl- concentrations are high inside the cell
the NKCC1 transporter
in more mature organisms, _____ levels are low and _____ becomes highly expressed to ensure that Cl- concentrations inside the cell are low
NKCC1, KCC2
the equilibrium potential of Cl- in neonates is:
-40mV
go review slides 184-186
you can do it!
inhibitory synapses are usually located closer to the cell body, while excitatory synapses are located further away from the cell body along more distal dendrites, this ensures that:
EPSPs can be reduced or shunted before they get to the AP initiation zone
what are the two mechanisms of inhibition?
1) maintaining the membrane potential away from threshold via increasing the Cl- or K+ conductance
2) shunting inhibition, where the EPSP is ‘reduced’ and is not strong enough to depolarize the cell to threshold
consists of two large axons that form a chemical synapse
stellate ganglion of the squid
there must be some presynaptic depolarization if we are to get a:
postsynaptic potential change
a big molecule that cages Ca++ so that is cannot interact with cell components
nitrophen
an increase in _____ is all that is needed to cause neurotransmitter release
Ca++
we only need _____ to open voltage-gated Ca++ channels
presynaptic depolarization
the minimum amount of neurotransmitter that can be released
one quanta (one vesicle)
is it possible for there to be release of neurotransmitters into the synaptic cleft in the absence of a presynaptic AP?
yes (called spontaneous release)
spontaneous release of neurotransmitters leads to:
miniature PSPs (or miniature endplate potentials at the NMJ)
transmitter release occurs through the fusion of vesicles with the:
presynaptic membrane
veiscle recycling near the active zone occurs with the aid of:
clathrin-coated pits
what are the major proteins involved in vesicle fusion to the cell membrane?
SNARES (snap receptors)
- v-SNAREs (vesicle snares)
- t-SNAREs (membrane proteins)
vesicle docking, fusion, and release of neurotransmitters involves the:
SNARE complex
Ca++ binds to synaptotagmin (v-SNARE) and triggers:
membrane fusion
how do SNAREs work?
interaction of the SNARE proteins brings the vesicle and presynaptic membrane closer together
go review slide 199
I’m just too lazy to write it all down
