Electrophysiology of the Nerve Cell

Question 1

what does the CNS use as its myelinated neuron?

what does the PNS use?

Answer 1

• oligodendrocyte:spit out meylin for more than 1 target neuron
• Schwann cell: myelinate portion of 1 axon, spaces are nodes of ranvier

Question 2

what are nongated ion channels important for. what kind of channel are they? are they always open?

Answer 2

important for establishment of resting potential
leak channel
always open

Question 3

what are ligand-gated ion channels activated by? where are they located

Answer 3

nt binding

located at sites of synaptic contact (primarily dendritic spins, dendrites and somata)

Question 4

what are voltage gated ion channels sensitive to? how are they at resting state? where are they predominantly on?

Answer 4

differences across membrane
typically closed in resting state
predominatly on axons and axon terminals

Question 5

what is conductance

Answer 5

ease with which ions flow across membrane

-how readily can membrane conduct the ions across itslef

Question 6

what is resistance

Answer 6

• inverse of conductance

- measured in ohms

Question 7

what is capacitance

Answer 7

membrane’s ability to store an electric charge

-kept apart= pot diff exists across

Question 8

Na/K ATPase pump 3 Na out and 2 K in…how do they leak

Answer 8

Na leak in

K leak out

Question 9

in most neurons, what is the trigger zone

Answer 9

axon hillock=> begin of axons

• lacks organelles
• high density Na/K channel => action in pot. originate after receiving adequate stimulus

Question 10

what does the generation and propagation of action potential contain

Answer 10

high density of voltage-gated Na and K channels

Question 11

when the membrane depolarizes, what channels open what does this cause?

Answer 11

Na channels open, results in further depolarization and more channels to open

Question 12

at threshold, incoming Na exceeds outgoing K and there is…

Answer 12

explosive opening of remaning Na channels

-all or none event

Question 13

what is depolarization in regards to na and k

what is repolarization

Answer 13

• influx of Na

- outflux of K, K flows out

Question 14

what is overshoot

Answer 14

membrane potentiial reverses, w/ the inside becoming positive

Question 15

what is afterhyperpolarization

Answer 15

K channels remain open

Question 16

what are the phases of action potential

Answer 16

resting level=> threshold => rising phase => overshoot => peak => repolarization => afterhyperpolarization

Question 17

at steady state, how are K and Na related

Answer 17

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

Question 18

in resting state, where is more negative

Answer 18

slightly more - inside

Question 19

larger diamter axons have _____ cytoplasmic resistance thereby permitting ……

Answer 19

less

a greater flow of ions and faster actin potentials

Question 20

in unmyelinated axons, what is electrotonic conductance

Answer 20

action potential in one axon segment depolarizes an adjacent section

Question 21

in propagation of an action potential in a myelinated axon, saltatory conduction occurs, what is this

Answer 21

the initiation of an action potential in one node of ranvier depolarizes the next node. jumping action potential from one node to the next

Question 22

wider diameter axons are faster bc why?

Answer 22

less resistance

Question 23

what does inactivation of sodium channels do to axons

Answer 23

makes axons temporarily refractory (resistant) to the generation of action potentials

Question 24

what are the phases of inactivation of sodium channels

Answer 24

1. absoulte refractory period: the membrane cannot generate an AP bc many of the Na channels are inactivated
2. 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

Question 25

what does the refractory period for a given cell determine

Answer 25

its maximum action potential firing rate and the direction of action potential propagation

Question 26

what lead to excitatory postsynaptic potentials (EPSPs)? | what lead to inhibitory postsynaptic potential (IPSPs)?

Answer 26

depolarization, causes + movement | hperpolarization, cuases - movement

Question 27

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?

Answer 27

closer to threshold | further away from threshold

Question 28

what is time constant

Answer 28

time required for the pot to decay to 37% of initial peak value -single contact of axon on single point on target cell

Question 29

what is temporal summation

Answer 29

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

Question 30

what is short constant

Answer 30

short amount of time for mem to head back to resting pot - action pot are independent events - action towards depolarization - NO SUMMATION (adding)

Question 31

what is long constant

Answer 31

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

Question 32

what is a space constant

Answer 32

distance at which voltage change has fallen to 37% of its peak value. -2 diff points of contact

Question 33

what is spatial summation

Answer 33

summation due to activation of several synapses located at different sites of contact; neurons w/ a long space constant are more likely to summate

Question 34

what is synaptotagmin | what does it bind to and wehre is that found?

Answer 34

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

Question 35

how do tetanus and botulinum toxins exert their effects?

Answer 35

by disrupting the function of SNARES, preventing synaptic transmission

Question 36

in tetanus toxin pathogenesis, once the toxin enters the CNS, it diffuses to the terminals of inhibitory glycinergic and _____ neurons

Answer 36

GABA

Question 37

what class of nt are glutamate and aspartate (excitatory), GABA and glycine (inhibitory)

Answer 37

amino acids

Question 38

what is acetylcholine derived from | what is the rate limiting step

Answer 38

choline availability of choline -choline is taken back up by high-affinity sodium-dependent mech; ach itself is not taken up

Question 39

what are the cholinergic receptors

Answer 39

nicotinic -2 alpha, 1 beta, 1 gamma, 1 delta | muscarinic - 5 subtypes

Question 40

in nicotinic, which subunit binds to Ach to induce a conformational change? what does nicotonic do?

Answer 40

alpha | increases Na and K conductance. K goes in, Na goes out

Question 41

what does muscarinic act through what do receptors M1 and M3 binding do? what does this result in? what does M2 binding do?

Answer 41

- G protein - decrease K conductance which results in depolarization. (m3 = role in acc) - increases K conductance which results in hyperpolarization

Question 42

what is the rate limiting enzyme for the catecholamine L-Tyrosine?

Answer 42

tyrosine hydroxylase

Question 43

where is MAO, the catecholamin nt in | what is mao inhibitory

Answer 43

mit in pre and post synaptic terminals | mao inhibitory is an antidepressent, inhibits the reuptake of serotonin

Question 44

where is COMT, the catecholamine nt located in

Answer 44

postsynaptic cytoplasm of muscle and glands, and CNS glia and extracellular space

Question 45

the catecholamine receptor, dopamine has 5 subtypes: D1-like (D1 and D5) is coupled with what? D2-like (D2-4) is copuled w/ what

Answer 45

stimulatory G proteins | inhibitory G proteisn (on pre and post synaptic membranes)

Question 46

how many adrenergic receptors are thre

Answer 46

lots.

Question 47

how many receptor subtypes does serotonin have what is it dependent on what kind of mech does it have

Answer 47

14. | - sodium dependent, active uptake mech

Question 48

what are selective serotonin reuptake inhibitor (SSRI)

Answer 48

class of anti-depressants used to treat depression, anxiety disorders, and some personality disorders

Question 49

waht do astrocytes do for glutamate and aspartate what does it convert glutamate to?

Answer 49

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

Question 50

some glutamate receptors are ....while others are......which are they the most of?

Answer 50

ionotropic (most are cationic) while others are metabotrpic

Question 51

activation of ionotropic receptors increases gNa and gCa, what type of receptor is this

Answer 51

NMDA

Question 52

activation of metabotropic receptors inhibits Ca channels and thus leads to what

Answer 52

presynaptic inhibition

Question 53

what do GABA and glycine hyperpolarize? how do they produce IPSPs? removed from cleft into what?

Answer 53

postsynaptic membrane - produce IPSPs by increasing Cl flux - presynaptic neuron and glia

Question 54

what is an increase in Cl conductance facilitated by

Answer 54

benzodiazepines, which are anti-anxiety drugs

Question 55

``` 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? ```

Answer 55

- 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

Question 56

what do opoids do? | what does substance P do?

Answer 56

- control pain, enkephalins, endorphins, morphine | - pain transmission

Question 57

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

Answer 57

L-argine by nitric oxide synthase (NOS) - release is calcium dependent - not packaged into vesciles bc lipid soluble - nitrergic neurons

Question 58

what is the ligand for endocannabinoids (membran soluble membranes)? what is it released by? lipid soluble?

Answer 58

ligand for THC - released by the postsynaptic cell and act on presynaptic cell - yes

Question 59

what is the stimulus like for short term memory | what is the stiumuls like for long term memory

Answer 59

- a single stimulus strenthes the synapse | - repeated stimulation causes kinases to move into the nucleus, leading to gene expression and growth of new synapses

Question 60

what is the functional basis of short and long term memory

Answer 60

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