SDL: transmission I and II Flashcards
what type of cell produces myelin in the peripheral nervous system?
Schwann cells
What type of cell produces myelin in the CNS?
oligodendrocyte (a type of glial cell)
where a neuron receives inputs from many other neurons
convergence of inputs
types of synapses
axodendritic, axosomatic, dendrodendritic, axoaxonic
what is the function of the axon hillock?
the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon
where synaptic vesicles aggregate before release
presynaptic density
these function to terminate the activity of a neurotransmitter
degradative enzymes
where the receptors aggregate
postsynaptic density
which achieves better control over excitatory OR inhibitory synapses: chemical or electrical transmission?
chemical transmission
3 characteristics of electrical junctions
- uses gap junctions 2. bidirectional communication 3. faster than chemical synapses
3 characteristics of chemical transmission
- uses a chemical synapse 2. unidirectional communication 3. relatively slow
most neurons in the mammalian CNS use this type of transmission to communicate with one another.
chemical transmission
what are the 4 criteria of a neurotransmitter?
localization, release, mimicry, inactivation
describe “localization” to establish a substance as a neurotransmitter
it is present at the nerve terminal
describe “release” to establish a substance as a NT
it is released after an action potential reaches the nerve terminal
describe “mimicry’ to establish a substance as a NT
once its structure is identified, should be able to synthesize the compound, apply it to a post-syn cell, and observe the same response as from the native NT
describe “inactivation” to establish a substance as a NT
the neurotransmitter should be inactivated by a specific mechanism, e.g. by enzymatic rxn
examples of some NT that do not fit the criteria
nitric oxide , dynorphin (peptide)
what do the structures of dopamine, epi, and norepi all have in common?
a substituted 1, 2-dihydroxy benzene ring
dopamine, epi, and norepi are all derived from..
tyrosine, which must first be hydroxylated
enzymatic control of NT synthesis can be increased by..
increasing the synthesis of the enzyme molecules (relatively slow process)
activity of enzymes that produce NTs can be altered (increased/decreased) by..
phosphorylation (relatively fast)
what determines the overall speed of synthesis of NTs?
the rate-limiting step (usually the 1st enzyme in the pathway)
describe specificity of enzymatic control of NT synthesis
presence or absence of relevant synthetic enzymes e.g. need choline acetyltransferase (CAT) to make acetylcholine
what type of NTs undergo terminal synthesis?
small molecules like acetylcholine, norepinephrine
what type of NTs undergo somatic synthesis?
peptide neurotransmitters (like opioid peptides) are made in soma, then transported to the nerve terminal
what is the function of autoreceptors? where are they located?
on the presynaptic membrane, autoreceptors may bind NTs to modulate further release or uptake of the NT
action potential-dependent release of synaptic vesicle contents into the synaptic cleft happens in this order
depolarization, which leads to Ca2+ influx at the nerve terminal, which leads to exocytosis of the vesicles
3 characteristics of NT binding to postsynaptic receptor
- single NT may bind to mult types of receptors 2. binding is usually reversible 3. effect is conc. dependent i.e. low conc can activate specific receptors, high conc. can bind specific and non-specific receptors (can be undesirable)
enzyme that degrades acetylcholine
acetylcholine esterase (AChE)
ways that NT action can be terminated
- extracellular degradative enzymes 2. specific reuptake proteins 3. diffusion of NT away 4. internalization of ligand-receptor complex
transport of NT precursors into the nerve nerminal is usually active or passive process?
active
order of events in NT synthesis, release, action, inactivation
transport of precursors into the nerve terminal, precursors undergo enzymatic changes, NT is stored, action potential causes Ca2+ influx, vesicles are released, receptor binding, response to NT, then either reuptake, diffusion away, or autoreceptor binding occurs.
to terminate activity of NT, the released NTs must be..
taken up by presynaptic terminal, diffused away, or metabolized
enzyme required to form acetyl choline
choline acetyl transferase
2 major classes of post-synaptic receptors
ionotropic, metabotropic
which type of post-synaptic receptor is ligand-gated?
ionotropic e.g. ACh nicotinic receptor
which type of post-synaptic receptor is an ion channel?
ionotropic
which type of post-synaptic receptor is a GPCR?
metabotropic
this type of post synaptic receptor is linked to an ion channel with help of G protein
GPCR, e.g. ACh muscarinic receptor
muscarinic receptor refers to..
parasympathetic effects
nicotinic receptor refers to..
autonomic stimulation
onset of effects mediated by ionotropic vs. metabotropic receptor
ionotropic is fast, metabotropic is slow
duration of effects mediated by ionotropic vs. metabotropic receptor
ionotropic is short, metabotropic is long
which is an ion channel itself, ionotropic or metabotropic?
ionotropic
which has a direct effect on the channel, ionotropic or metabotropic?
ionotropic
which acts as a second messenger, ionotropic or metabotropic?
metabotropic
which possesses the ability to amplify, ionotropic or metabotropic?
metabotropic
excitation or inhibition is determined by the _____ and not the _____
receptor, not the NT being released
an excitatory NT causes ____ of the membrane potential
depolarization, towards the firing threshold.
an inhibitory NT causes ____ of the membrane potential
hyperpolarization, away from the firing threashold
too much excitation results in..
epilepsy
too much inhibition results in..
coma, anesthesia
regulatory mechanisms that maintain proper balance between inhibition and excitation of neurons
presynaptic receptors, second messengers, feedback inhibition, presynaptic inhibition (axoaxonic synapses)
examples of amine NTs
ACh, dopamine, norepi, epi, serotonin, histamine
examples of amino acid NTs
glutamate, GABA, glycine
examples of neuropeptide NTs
opiod peptides
examples of gas NTs
nitric oxide
similarities between classical and peptide NTs
both bind to specific receptors, both are released from vesicles in a Ca2+ dependent manner.
how are peptide NTs synthesized?
synthesis is directed by mRNA
peptide precursors usually exist as ..
inactive precursor proteins first
where are peptide NTs made
in the cell body and transported to the axonal terminal (instead of made in the terminal)
how do peptide NTs become active?
during transport, they’re cut into smaller pieces because of peptidase activity, become active after this process
the acetylcholine receptors
nicotinic, muscarinic
the dopamine receptors
D2, D1 both inhibitory
the norepi and epi receptors
alpha, beta
receptors for serotonin
many receptors
receptors for histamine
H1, H2
glutamate receptors + are they ionotropic, metabotropic?
NMDA (ionotropic), and the other one is metabotropic
GABA receptors + are they ionotropic or metabotropic?
GABAa (ionotropic); GABAb (metabotropic)
which GABA receptor has a quick onset of action?
GABAa (ionotropic)
opioid peptides
beta-endorphin, enkephalin, dynorphin
pituitary peptides
oxytocin, vasopressin
where is dynorphin synthesized?
in the cell body and transported to the axon terminal; usually exists as an inactive precursor.
catecholamines are derived from..
tyrosine
rate limiting enzyme of catecholamine synthesis?
tyrosine hydroxylase (puts the second hydroxyl group on the benzene ring of tyrosine, making it a “catechol”
cold medicines mimic activation of..
sympathetic nervous system; call them sympathomimetics
precursor of serotonin
tryptophan
Zoloft and anti-anxiety meds are..
selective serotonin reuptake inhibitors (SSRIs), they allow serotonin to remain active longer
precursor of histamine
histidine
precursor of acetylcholine
choline
rate-limiting step of ACh synthesis
uptake of choline
biosynthetic enzyme of acetylcholine
choline acetyl transferase (CAT)
ACh nicotinic receptor; where are these found?
ionotropic; found in a neuromuscular junction
ACh muscarinic receptor
metabotropic
where is acetylcholine esterase located?
extracellularly in the synaptic cleft
is acetylcholine an excitatory or inhibitory transmitter?
it depends what receptor it binds to (N is excitatory, M is excitatory or inhibitory)
are nicotinic receptors located on the neuron or the muscle cell?
muscle cell
what does myasthenia gravis have to do with ACh nicotinic receptors?
autoimmune disease that produces antibodies against the post-synaptic ACh receptor, causing reduced responsiveness of the muscle to the activity of the motor neurons
what does Lambert-Eaton syndrome cause?
produces antibodies against the Ca2+ channels in the presynaptic terminals that interfere with NT relase
glutamate is considered this type of NT because all of its receptors lead to depolarization
excitatory
precursor of glutamate
glutamine
after glutamate function is completed..
glutamate is taken up by axon terminals and recycled
ionotropic glutamate receptor
NMDA, non-NMDA
effect of metabotropic receptor of glutamate
IP3, diacylglycerol are released after the receptor is activated
what is the NMDA glutamate receptor important for?
learning and memory
the NMDA ionotropic glutamate receptor requires co-activation of the..
glycine binding site
ligand-binding of NMDA ionotropic glutamate receptor causes opening of.
non-specific cation conducting channel i.e. calcium influx can lead to generation of NO (2nd messenger effect although the ionotropic receptors are not true second messengers)
excessive glutamate release during stroke and CNS trauma can lead to neuronal death; this is a type of _____
excitotoxicity
precursor of GABA
glutamate
type of NT that GABA is considered to be; why?
inhibitory because all receptors lead to hyperpolarization
the GABAa ionotropic receptor causes
Cl- influx, thus hyperpolarization
the GABAb metabotropic receptor causes
K+ efflux, thus hyperpolarization
glycine is considered this type of NT because activation of its receptors leads to..
inhibitory NT; activation of its receptor leads to hyperpolarization
what mechanism does glycine receptor activation lead to hyperpolarization?
influx of Cl-
T/F: glutamate is an inhibitory transmitter
false; its excitatory (depolarization)
T/F: GABA is an inhibitory NT
true
T/F: ACh is an excitatory NT
it depends: nicotinic receptor is excitatory; muscarinic can be excitatory or inhibitory
T/F: glycine is an excitatory NT
false; glycine is an inhibitory NT
T/F: activation of ionotropic receptor always causes excitation
false; ionotropic receptors can be excitatory (nicotinic) or inhibitory (GABAa)
T/F: activation of metabotropic receptor always causes excitation
false; metabotropic can be excitatory (glutamate) or inhibitory (GABAb)
areas of conc of ACh
neuromuscular, autonomic, parasympathetic
areas of conc of norepi
sympathetic
*areas of conc of glycine
spinal cord (major inhibitory NT in the spinal cord is glycine)
responsible for runner’s high
beta-endorphin (opiod peptide)
mammalian neutopeptides
growth hormone releasing hormone, coricotropin, oxytocin, insulin, cholecystokinin, beta-endorphin, epidermal growth factor
which NT acts as a retrograde messenger (going from postsynaptic to presynaptic cell?)
nitric oxide
in the periphery, NO causes what type of muscle to relax, resulting in dilation
smooth muscle
drug that contains NO
viagra
an agonist does what to surface receptors
activates
an antagonist does what to surface receptors
blocks them
blocks binding of acetylcholine to its nicotinic receptor in the neuromuscular jucntion
alpha-bungarotoxin (snake venom)
drug that increases the FREQUENCY of GABAa Cl- channel opening
benzodiazepine (valium)
valium causes a neuron to become..
hyperpolarized
drug that causes blockade of release of ACh from the nerve terminal
botulinum toxin
under what conditions do we see botulinum toxin in food?
some improperly canned/preserved foods; also some c. botulinum spores can be found in honey and cause infantile botulism
compound that irreversibly inactivates acetylcholinesterase, i.e. blocking degradative enzyme
organophosphates (insecticides)
muscarinic receptor blocker
atropine
GABAb receptor antagonist
baclofen (for epilepsy)
increase duration of GABAa Cl- channel opneing
barbiturate/phenobarbital
blocks monoamine reuptake at synapse to prolong action of NTs
cocaine
blocks binding of ACh to its N receptor on skeletal muscle
curare
agonist at postsynaptic serotonin receptors
LSD
mimics binding of opioid peptodes to produce analgesia
morphine
inhibit AChE activity prololonging ACh activity
neostigmine
a NMDA glutamate receptor blocker
phencyclidine (PCP, angel dust)
glycine receptor blocker (in rat poison)
strychnine
block monoamine reuptake
tricyclic antidepressants
selective serotonin reuptake
zoloft
what are the unique properties of NMDA glutamate receptor?
ionotropic opening of channels, can permit Ca2+ influx if membrane is depolarized (can act as a 2nd messenger, which is unusual for normal ionotropic receptors)
does the thymus play a role in myasthenia gravis?
yes, it remains large and abnormal in adults with the disease, and scientists think that it may send incorrect messages to the immune system to develop antibodies against the ACh post synaptic receptor
