task 3 - neurotransmitters Flashcards
synapse
; 3 components, junctions between the terminal buttons at the end of axonal branches of 1 neuron and the membrane of another
presynaptic membrane
axon terminal of the presynaptic neuron
synaptic cleft
gap of 20-40 nanometers that separates the presynaptic and post synaptic neurons
postsynaptic membrane
on the surface of the dendrite or the cell body of the post of the postsynaptic neuron
postsynaptic potentials
; brief depolarizations or hyperpolarization that increase or decrease the rate of firing of the axon of the postsynaptic neuron
directed synapses
synapses at which the site of neurotransmitter release and the site of neurotransmitter receptors are in close proximity
non-directed synapses
site of release is at some distance from the site of reception
ligand
→ the chemical that attaches to the binding site (neurotransmitters are types of ligands)
- only bind to receptors
- cannot enter into a neuron through a binding site, can open ion channels tho
endogenous ligand
any substance that is produced within the body and selectively binds to a receptor
exogenous ligand
any substance that originates outside the body and selectively binds to a receptor
binding site
the area that neurotransmitters attach to in order to exert their effects on cells
release zone
the region where the neurotransmitter is released
docking
→ a cluster of protein molecules in the vesicles membrane attach to other protein molecules located in the presynaptic membrane (docking the vesicle against the presynaptic membrane)
synaptic vesicles
→ small rounded structures made of membrane and filled with molecules
transport protein
; fills vesicles with neurotransmitter molecules
trafficking proteins
; involved in true release of neurotransmitters and recycling of vesicles
small vesicles
; (found in all terminal buttons) contain molecules of the neurotransmitter. produced in the soma (golgi apparatus) and are carried by fast axoplasmic transport to the terminal button
large vesicles
; contain 1 or more neuropeptides (short protein composed of 3-36 amino acids) only produced in the soma and transported through the axoplasm to the terminal buttons
axodendritic synapses
→ synapses of axon terminal buttons on dendrites or dendritic spines
axosomatic synapses
→ synapses of axon terminal buttons
axoaxonic synapses
synapses that occur between 2 terminal buttons
presynaptic inhibition
; axoaxonic synapse decreases the release of neurotransmitter
presynaptic facilitation
; axoaxonic synapse increases the release of neurotransmitter
dendrodentritic synapses
→ synapses between dendrites
exocytosis
(cell secretes molecules of neurotransmitter) the membrane wrapped product migrates to the outer membrane of the cell, fuses with the membrane, and bursts, spilling its contents into the fluid surrounding the cell
- with action potentials the small synaptic vesicles located just inside the presynaptic membrane fuse with the membrane and break open spilling their contents into the synaptic cleft
EPSP
occur because neurotransmitter opens sodium channels (increases flow of Na+ ions into the neuron, causing depolarization of the neuron)
IPSP
occur because neurotransmitter opens potassium channels or chloride channels (increase flow of K+ ions out of the neuron or the flow of CL- ions into it, respectively causing hyperpolarization of the neuron)
voltage-dependent calcium channels
(in the release zone) calcium flows into the channels (when open) by the force of diffusion and electrostatic pressure [calcium transporters later remove the intracellular Ca]
some of the calcium ions bind with the clusters of protein molecules that join the membrane of the synaptic vesicles with the presynaptic membrane produces fusion pore
release-ready vesicles
docked against the inside of the presynaptic membrane, ready to release their contents when an action potential arrives (less than1% of the ones found in the terminal)
recycling pool
; (10-15% of the total pool)
reserve pool
; (the rest, 85-90%)
depends on the axon rate.. if the rate is LOW
only vesicles from the release-ready will be used
depends on the axon rate.. if the rate INCREASES
vesicles from the recycling pool and then the reserve pool will release their contents
kiss and run
; release most or all of their neurotransmitter, the fusion pot closes and the vesicle breaks away and gets filled again with neurotransmitter
merge and recycle
; (lose their identity) merge with the presynaptic membrane. small buds of membrane later pinch off into the cytoplasm and become new synaptic vesicles, proper proteins are inserted into the new vesicles membranes and the vesicles are filled with neurotransmitter
bulk endocytosis
; the vesicles in the reserve pool are recycled- large pieces of terminal membrane fold inward, break off and enter the cytoplasm. new vesicles are formed from small buds that break off of these pieces of membrane
ionotropic receptors (direct neurotransmission)
ion channels open when a molecule of a neurotransmitter attaches to the binding site
- direct gating
- fast, chemical synaptic transmission
- short-lasting effects (EPSP and IPSP)
metabotropic receptors (indirect neurotransmission)
ligand binding to some receptors does not open ion channels but instead expenditure of metabolic energy
- indirect gating
- slow transmission
- long-lasting effects
glutamate
main excitatory neurotransmitter in the CNS, synthesized from a precursor by the enzyme glutaminase. stored in vesicles after synthesis
produces EPSPs, excitatory
types of glutamate receptors
NMDA, AMPA, and kainite receptors
GABA
most prevalent inhibitory neurotransmitter in the CNS, excitatory effects at some of the synapses
several GABAA receptors, many drugs interact with it
produces IPSPs inhibitory
monoamines
dopamine, epinephrine, norepinephrine, serotonin
monoamine neurotransmitters
produced by systems of cell bodies in the brain stem, whose axon branch repeatedly and give rise to a huge number of terminal buttons distributed throughout many regions of the brain (modulate the function of many brain regions, increase or decrease the activities of particular brain functions)
agonists
drugs that facilitate the effects of a particular neurotransmitter
inverse agonist
; a substance that binds to a receptor and cause it to do the opposite of what the naturally occurring neurotransmitter does
antagonists
; drugs that inhibit the effects of a particular neurotransmitter
precursor
most neurotransmitters are produced by precursors), increase the amount of neurotransmitter synthesized and then released into the synapse
direct agonist
; a drug that mimics the effect of a neurotransmitter
direct antagonist/receptor blocker
; a drug that binds with the postsynaptic receptor but blocks it from being activated, occupy the binding site and block the neurotransmitter from activating the receptor
