Chapter 1: chemical neurotransmission Flashcards
axodendritic synapse
signals from the axon of one neuron to the dendrite of another
axosomatic synapse
signal sent from the axon of one neuron to the soma of another
axoaxonic synapse
signal from the axon of one neuron to the axon of another
anterograde communication
trasmission of thesignal fromthe axon of one neuron to the axon, dendrite, or soma of the next neuron
neurons
cells of chemical communcation in the brain
chemically addressed nervous system
how signals are coded, decoded, transduced, and sent along the way
neurotransmitters
serotonin
norepinephrine
dopamine
acetylcholine
glutamate
GABA
b-endorphin (body’s morphine)
endocannabinoids (body’s pot
what is involved in neuron input
can involve many different neurotransmitters coming from many different neuronal circuits
types of neurotransmission
classic, retrograde, volume
classic neurotransmission
electrical impulses are sent through neuron until it is changed to chemical signal. then chemical messenger is hurled from one neuron to the next where it is either converted back to an electrical impulse or triggers a cascade of chemical messages to change the neurons molecular and genetic functioning
excitation-secretion coupling
process of converting the electrical impulse in a neuron to the chemical signal at the synapse between neurons
retrograde neurotransmission
when postsynaptic neuron talks back to presynaptic neuron
chemical produced specifically as retrograde neurotransmitters at some synapses
endocannabinoids (EC)
nitric oxide (NO)
nerve growth factor (NGF)
retrograde neurotransmission of endocannabinoids (EC)
interacts with CB1 (cannabinoid receptor 1) in presynaptic neuron
retrograde neurotransmission of nitric acid
interacts with cGMP in presynaptic neuron
retrograde neurotransmission of nerve growth factor (NGF)
taken up in presynaptic neuron vesicles to travel back to cell nucleus to interact with the genome there
volume neurotransmission
do not require synapses
when chemical messengers are sent into the synapse they may spill over to distant sites with compatible receptors through diffusion
excitation-secretion coupling
process of electrical impulse being converted to chemical signal
basic description of excitation-secretion coupling
electrical impulse enters axon terminal of presynaptic neuron and stimulates release of chemical neurotransmitter
electrical impulse opens ion channel by changing charge across the neuronal membrane
How does a VSSC work
sodium flows into the presynaptic nerve through the axonal membrane causing the electrical charge there to move along the axon to the presynaptic nerve terminal where it opens up calcium channels
How does a VSCC work
after receiving signal from VSSC, calcium flows into the presynaptic nerve terminal causing the synaptic vesicles to spill their chemical contents into the synapse
what makes it possible for the genome of one neuron to communicate with the genome of another
signal transduction cascades
basic description of signal transduction cascades
A first messenger neurotransmitter activates the production of a second chemical messenger that then activates a third messenger enzyme (known as a kinase) that adds phosphate groups to a fourth messenger protein to create phosphoproteins
what are the two main targets of signal transduction
phosphoproteins and genes
how is signal transduction reversed for retrograde communication between neurons
The first messenger neurotransmitter opens an ion channel that allows calcium to enter the neuron and act as the second messenger which then activates a third messenger (enzyme known as a phosphatase) which removes the phosphate groups from the fourth messenger phosphoproteins and thus reverses the action of the third messenger
what is determined by the balance of kinase and phosphatase in signal transduction cascades
the degree of chemical activity that gets translated into the active fourth messenger
what does the active fourth messenger trigger
diverse biological responses such as gene expression and synaptogenesis
what are the four signal transduction cascades
g-protein linked systems
ion-channel linked systems
hormone linked systems
neurotrophins
how is a second messenger formed in g-protein linked signal transduction cascade
neurotransmitter (first messenger) binds to receptor site to change it so it can bind with the G protein. Once G protein is bound it changes shape so it can bind to an enzyme that can synthesize the second messenger
what is the second messenger in G-protein linked signal transduction cascades
a chemical
what is the second messenger in ion-channel linked signal transduction cascades
an ion (like calcium or sodium)
how is the second messenger formed in hormone-linked signal transduction cascades
hormone binds to its receptor in the cytoplasm to form a hormone-nuclear receptor complex
how is the second messenger formed in neurotrophin signal transduction cascades
there is a complex set of various second messengers that trigger each other
structure of inactive protein kinase exist
a dimer made of 2 copies of the enzyme protein kinase, each with a regulatory unit
how does inactive protein kinase become an active third messenger
2 copies of the second messenger cAMP cause the regulatory unit to detach from each inactive enzyme in the dimer. Once the regulatory units detach the enzymes split apart and are now active 3rd messengers
what is phosphorylation and how does it happen
active third messenger kinases shoot phosphate groups into proteins to create 4th messenger phosphoproteins
how is active third messenger protein phosphatase synthesized
neurotransmitter (1st messenger) opens ion channel that allows calcium (second messenger) to enter and activate third messenger protein phosphatase
what is dephosphorylation
when third messenger protein phosphatase rips phosphate groups off of phosphoproteins
how are phosphoproteins activates
some by phosphorylation (uses kinase)
some by dephosphorylation (uses phosphatase)
what are the things that activation of phosphoproteins can do
change the synthesis of neurotransmitters
alter neurotransmitter release
change the conductance of ions
maintain chemical neurotransmission apparatus in a state or dormancy
what is the ultimate cellular function of neurotransmission
to turn a gene on or off (all 4 signal transduction pathways end with this goal)
what is the difference between a signal transduction cascade and a signal transduction pathway
there are 4 cascades that end with generation of a phosphoprotein.
there are 2 pathways from the third messenger to the fourth messenger in the signal transduction cascade
which 2 signal transduction cascades are triggered by neurotransmitters
G-protein linked receptor cascades
Ion channel linked receptor cascades
what system do the 2 neurotransmitter signal transduction cascades act on
CREB system (responds to protein phosphorylation)
how do g-protein linked receptors act on CREB
the g-protein linked receptor activates protein kinase A
THEN
the activated receptor goes into the cell nucleus to stick a phosphate group to CREB
THEN
this activates the transcription factor that causes nearby genes to be expressed
how do ion channel linked receptors act on CREB
they enhance intracellular calcium (second messeger) levels which interact with calmodulin protein to activate certain kinases
THEN
these kinases translocate into the cell nucleus to add a phosphate group to CREB
what can activate both kinases and phosphatases
calcium
how does hormone signal transduction cascade target genes
hormones bind cytoplasmic receptors to produce a hormone-nuclear receptor complex that can translocate into the cell nucleus
THEN
the complex finds elements in the gene it can influence (HREs)
THEN
it acts as a transcription factor to trigger activation of genes
how do neurotrophin cascades trigger gene expression
first messengers (neurotrophins) activate one kinase after another until one finally phosphorylates a transcription factor in the nucleus to start transcribing genes
how does neurotransmission trigger gene expression
chemical info message is passed along “pony express” from molecular rider to molecular rider until it reaches the right phosphoprotein mailbox in the postsynaptic neuron
how much DNA is occupied by genes
only a few %
2 regions of a gene
regulating region
encoding region
regulating region of genes
transcription factor is activated by phosphorylation of protein kinase
THEN
the activated transcription factor can bind to the regulatory region of the gene
THEN
RNA polymerase is activated
coding region of gene
enzyme RNA polymerase transcribes DNA into its mRNA
THEN
mRNA translates itself into the corresponding protein that will activate the gene
what does an early immediate gene do
functions as a rapid responder to neurotransmitter input
cJun and cFos
nuclear proteins (leucine zippers) team up to form the zipper transcription factor that activates later onset genes
what happens when the product of two early genes is a transcription factor (like with leucine zippers)
it returns to the genome to activate late genes
what are the products of late genes
any protein the neuron needs:
enzyme
transporter factors
growth factors
what determines which late genes get activated
which neurotransmitter is sending the message
how frequently it sends the message
whether it is working with/against other neurotransmitters that are talking to other parts of the same neuron at the same time
what is epigenetics
system that determines whether or not a gene is actually made into its RNA and protein or if it is ignored
how are genes turned on/off
by modifying the structure of chromatin in the cell nucleus
what determines the character of a cell
its chromatin
structure of chromatin
8 histones that DNA are wrapped around (nucleosome)
what does chromatin have to do with genes
its structure determines whether a gene is expressed or silenced
chemical modifications that can modify the structure of chromatin
methylation
acetylation
phosphorylation
what regulates acetylation and methylation of chromatin
neurotransmission
drugs
environment
