Electrophysiology of the Nerve Cell Flashcards
what does the CNS use as its myelinated neuron?
what does the PNS use?
- oligodendrocyte:spit out meylin for more than 1 target neuron
- Schwann cell: myelinate portion of 1 axon, spaces are nodes of ranvier
what are nongated ion channels important for. what kind of channel are they? are they always open?
important for establishment of resting potential
leak channel
always open
what are ligand-gated ion channels activated by? where are they located
nt binding
located at sites of synaptic contact (primarily dendritic spins, dendrites and somata)
what are voltage gated ion channels sensitive to? how are they at resting state? where are they predominantly on?
differences across membrane
typically closed in resting state
predominatly on axons and axon terminals
what is conductance
ease with which ions flow across membrane
-how readily can membrane conduct the ions across itslef
what is resistance
- inverse of conductance
- measured in ohms
what is capacitance
membrane’s ability to store an electric charge
-kept apart= pot diff exists across
Na/K ATPase pump 3 Na out and 2 K in…how do they leak
Na leak in
K leak out
in most neurons, what is the trigger zone
axon hillock=> begin of axons
- lacks organelles
- high density Na/K channel => action in pot. originate after receiving adequate stimulus
what does the generation and propagation of action potential contain
high density of voltage-gated Na and K channels
when the membrane depolarizes, what channels open what does this cause?
Na channels open, results in further depolarization and more channels to open
at threshold, incoming Na exceeds outgoing K and there is…
explosive opening of remaning Na channels
-all or none event
what is depolarization in regards to na and k
what is repolarization
- influx of Na
- outflux of K, K flows out
what is overshoot
membrane potentiial reverses, w/ the inside becoming positive
what is afterhyperpolarization
K channels remain open
what are the phases of action potential
resting level=> threshold => rising phase => overshoot => peak => repolarization => afterhyperpolarization
at steady state, how are K and Na related
K = + inside cell
Na= + outside
-not the same amount, there is more + outside than inside
-inside is negative relative to amount of change on the outside
in resting state, where is more negative
slightly more - inside
larger diamter axons have _____ cytoplasmic resistance thereby permitting ……
less
a greater flow of ions and faster actin potentials
in unmyelinated axons, what is electrotonic conductance
action potential in one axon segment depolarizes an adjacent section
in propagation of an action potential in a myelinated axon, saltatory conduction occurs, what is this
the initiation of an action potential in one node of ranvier depolarizes the next node. jumping action potential from one node to the next
wider diameter axons are faster bc why?
less resistance
what does inactivation of sodium channels do to axons
makes axons temporarily refractory (resistant) to the generation of action potentials
what are the phases of inactivation of sodium channels
- absoulte refractory period: the membrane cannot generate an AP bc many of the Na channels are inactivated
- relative refractory period: some Na channels are responsive, but the stiumuls strenght must be greater than before bc the threshold is temporarily higher bc not all Na channels are available. amp is slow bc some K channels remain open. AP not propagated
what does the refractory period for a given cell determine
its maximum action potential firing rate and the direction of action potential propagation
what lead to excitatory postsynaptic potentials (EPSPs)?
what lead to inhibitory postsynaptic potential (IPSPs)?
depolarization, causes + movement
hperpolarization, cuases - movement
what potential change did the incoming signal from axon onto dendritic spine/process/cell body have on post synaptic cell membrane potential for EPSP? what about IPSP?
closer to threshold
further away from threshold
what is time constant
time required for the pot to decay to 37% of initial peak value
-single contact of axon on single point on target cell
what is temporal summation
postsynaptic pot are added w/ time; synapses w/ a long time constant are more likely to summate
-takes longer for mem pot to come back from baseline
what is short constant
short amount of time for mem to head back to resting pot
- action pot are independent events
- action towards depolarization
- NO SUMMATION (adding)
what is long constant
take longer for the induced pot change to come back to baseline
- more likely to summate
- pot change close enough to action pot triggered in axon hillock
- SUMMATION SIGNAL
what is a space constant
distance at which voltage change has fallen to 37% of its peak value.
-2 diff points of contact
what is spatial summation
summation due to activation of several synapses located at different sites of contact; neurons w/ a long space constant are more likely to summate
what is synaptotagmin
what does it bind to and wehre is that found?
calcium sensor is an integral vesicular membrane protein called synaptotagmin, which undergoes a conformational change
-SNARES, found on the vesicle and terminal that causes vesicles to dock and bind to the presynaptic terminal membrane
how do tetanus and botulinum toxins exert their effects?
by disrupting the function of SNARES, preventing synaptic transmission
in tetanus toxin pathogenesis, once the toxin enters the CNS, it diffuses to the terminals of inhibitory glycinergic and _____ neurons
GABA
what class of nt are glutamate and aspartate (excitatory), GABA and glycine (inhibitory)
amino acids
what is acetylcholine derived from
what is the rate limiting step
choline
availability of choline
-choline is taken back up by high-affinity sodium-dependent mech; ach itself is not taken up
what are the cholinergic receptors
nicotinic -2 alpha, 1 beta, 1 gamma, 1 delta
muscarinic - 5 subtypes
in nicotinic, which subunit binds to Ach to induce a conformational change?
what does nicotonic do?
alpha
increases Na and K conductance. K goes in, Na goes out
what does muscarinic act through
what do receptors M1 and M3 binding do? what does this result in?
what does M2 binding do?
- G protein
- decrease K conductance which results in depolarization. (m3 = role in acc)
- increases K conductance which results in hyperpolarization
what is the rate limiting enzyme for the catecholamine L-Tyrosine?
tyrosine hydroxylase
where is MAO, the catecholamin nt in
what is mao inhibitory
mit in pre and post synaptic terminals
mao inhibitory is an antidepressent, inhibits the reuptake of serotonin
where is COMT, the catecholamine nt located in
postsynaptic cytoplasm of muscle and glands, and CNS glia and extracellular space
the catecholamine receptor, dopamine has 5 subtypes:
D1-like (D1 and D5) is coupled with what?
D2-like (D2-4) is copuled w/ what
stimulatory G proteins
inhibitory G proteisn (on pre and post synaptic membranes)
how many adrenergic receptors are thre
lots.
how many receptor subtypes does serotonin have
what is it dependent on
what kind of mech does it have
14.
- sodium dependent, active uptake mech
what are selective serotonin reuptake inhibitor (SSRI)
class of anti-depressants used to treat depression, anxiety disorders, and some personality disorders
waht do astrocytes do for glutamate and aspartate
what does it convert glutamate to?
have high affinity, active transport mech that removes these from the synapse (in addition to neruonal removal)
-converts glutamate to glutamine, which enters neuron and is recycled back to glutamate by action of glutaminase
some glutamate receptors are ….while others are……which are they the most of?
ionotropic (most are cationic) while others are metabotrpic
activation of ionotropic receptors increases gNa and gCa, what type of receptor is this
NMDA
activation of metabotropic receptors inhibits Ca channels and thus leads to what
presynaptic inhibition
what do GABA and glycine hyperpolarize?
how do they produce IPSPs?
removed from cleft into what?
postsynaptic membrane
- produce IPSPs by increasing Cl flux
- presynaptic neuron and glia
what is an increase in Cl conductance facilitated by
benzodiazepines, which are anti-anxiety drugs
what are neuropeptides removed from the synaptic cleft by? what does this ensure? what are they degraded by? is there a recycling mech? may modify what?
- diffusion
- longer action
- proteases in the extracellular space
- no, need to be replenished by a steady supply of -new vesicles from the soma
- response of co-leased nt; modulator function
what do opoids do?
what does substance P do?
- control pain, enkephalins, endorphins, morphine
- pain transmission
what is nitric oxide (membrane soluble) synthesized from
- what kind of release is it?
- why is it not packaged into vesicles
- what kind of neurons
L-argine by nitric oxide synthase (NOS)
- release is calcium dependent
- not packaged into vesciles bc lipid soluble
- nitrergic neurons
what is the ligand for endocannabinoids (membran soluble membranes)?
what is it released by?
lipid soluble?
ligand for THC
- released by the postsynaptic cell and act on presynaptic cell
- yes
what is the stimulus like for short term memory
what is the stiumuls like for long term memory
- a single stimulus strenthes the synapse
- repeated stimulation causes kinases to move into the nucleus, leading to gene expression and growth of new synapses
what is the functional basis of short and long term memory
cAMP responsive element binding protein 1 (CREB1) binds the cAMP response element, a DNA nucleotide sequence present in many cellular promoters.
-the binding of CREB stimulates transcription
