7 Synapses: CNS and NMJ Flashcards
synapse def
point of contact between the terminals of one neuron and the target neuron
release of a chemical transmitter from the terminals of the presynaptic neuron occurs in response to ____ by an ____
depolarization by an AP
the _____ signal in the presynaptic nerve is converted into a ______ one in the postsynaptic nerve
electrical, chemical
quantum of transmitter is stored in
synaptic vesicles of the presynaptic nerve
vesicles are anchored at the
active zone
after the nerve is depolarized, this happens (4 steps)
voltage gated Ca2+ channels open in the active zone
Ca2+ enters near the vesicles
vesicle fusion and excytosis
release of transmitter (quantum)
probability that vesicles at CNS synapses will fuse and release is low and depends on (2 things)
1/ number of vesicles in active zone
2/ increase in Ca2+ ions in the vicinity of the vesicles (due to AP frequency - higher frequency leaves a little Ca2+ behind and it builds up)
Ca2+ ions are removed by (3 things)
1/ Na+/Ca2+ exchange (secondary active transport)
2/ primary active transport across the PM or into the SR (Ca2+ ATPase)
3/ uptake by mitochondria
transmitter action terminates when it gets too low. this happens by two mechanisms:
1/ reuptake
2/ breakdown of the transmitter
postsynaptic receptors bind ____
ligands (chemical signaling molecules)
agonist
a ligand that produces a response in the target cell when it binds to the receptor
antagonist
a ligand that binds to the receptor but does NOT produce a response
transducer
convert chemical signals into cellular responses (all receptors are this)
this is how the post synaptic receptor works
- ligand (receptor) binds to the channel on the extracellular domain
- ion channel opens
- ions flow in, down their electrochemical gradient
- transmitter dissociates from receptor and channel closes
post synaptic potential (PSP)
- created by the ionic current that flows through open post synaptic channels
- graded, localized
- spreads passively
2 excitatory transmitters
acetylcholine
L-glutamate
main excitatory transmitter in the CNS
L-glutamate
excitatory transmitter at the NMJ
acetylcholine
excitatory post synaptic potential (EPSP)
produced by an inward positive ion concentration
depolarization
how many EPSPs must sum together to fire APs?
hundreds or thousands
the NMJ is the simplest synapse meaning
one to one relay
excitatory synapse at NMJ includes
single AP
acetylcholine released
nicotinic receptors (b/c ligand gated)
(open when they bind 2 Ach molecules, also permeable to Na+ and K+ ions)
2 inhibitory transmitters in CNS
GABA
glycine
inhibitory transmitters do this
open ion channels that are permeable to chloride ions
chlorine goes in, membrane is hyperpolarized (super negative)
IPSP (inhibitory postsynaptic potential) created
inhibitory synapses are located on
proximal dendrites or cell body of target neuron
AMPA receptor
L-glutamate
allow Na+ and K+ ions to pass and set up fast EPSPs
fast ionotropic signaling
NMDA receptor
blocked by magnesium ions at RMP
once open, Na+, K+, and Ca2+ can get in
Ca2+ coming in is special - has to do with long term potentiation, learning, and depression
transmitters involved in GPCR signaling (4)
norepi
serotonin
dopamine
L-glutamate
peptide transmitters are stored in
large dense cored vesicles (LDCV)
kinesin
a motor protein that moves macromolecules along microtubules. these macromolecules are involved in synthesis and storage of small transmitter molecules.
denervation supersensitivity
upregulation of postsynaptic receptors following loss of presynaptic nerve due to damage; its a pathological change
desensitization
when receptors are exposed to high conc of agonist (transmitter) for an extended period of time and they become unresponsive
long term potentiation (LTP)
- when central synapses are activated strongly and the number of receptors expressed in the postsynaptic membrane is increased/upregulated (can persist for hours/days)
- increase in # AMPA receptors (upregulation) + phosphorylation of these receptors
long term depression
- when weakly activated central synapses show a down regulation of receptors that persists for hours or days
- at glutamatergic synapses
- dephosphorylation of AMPA receptors
- triggered by diff levels of intracellular calcium
