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neur2006 > deck 1 > Flashcards

deck 1 Flashcards

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1
Q

patch clamp methods

A

whole cell
inside out
outside out
cell attached

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2
Q

dis/advantages of cell attached

A

measurement of ion channels in a specific region.
can change the voltage or add ligand. cell remains whole more physiological conditions inside the cell. each cell= 1 point on a dose response curve

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3
Q

dis/advantages of inside-out

A

inside= extracellular medium experimenter in control of the intracellular side of the membrane (bath). e.g cell activated by internal ligand. often forms a vesicle have to stop from forming vesicle through low ca2+ solution

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4
Q

dis/advantages of outside out

A

pippete= intracellular medium
can test the effect of external ligand.
often used for conc jumps

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5
Q

dis/advantages of whole cell

A

cell membrane ruptured electrode sees all channels contribution to membrane potential etc. cell contents washed out.

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6
Q

what is charge measured in?

A

Charge (Q) measured in Coulombs (C)
1 mole of monovalent ion= Faraday’s constant
Faradays constant=avogadro’s number x charge on ion (charge of +/- 1 = 1.6x10-19C)

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7
Q

what is current measured in?

A

Currrent (I) is measured in Amps
1 Ampere =flow of 1 C of charge in 1 second
I=dQ/dT

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8
Q

Ohms law

A

V=IR

I=V/R

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9
Q

Conductance

A

Conductance is the reciprocal of resistance

G=1/R so I=VG

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10
Q

summing up resistance

A

Series: add up resistance
Parallel: add up reciprocal of resistance

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11
Q

Capacitance

A

capacitance (C) in Farad (F)

1F= capacitance of an element that can store 1C of charge given 1V pd

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12
Q

How do you increase capacitance?

A
  • Increase plate area (larger diameter axon)
  • decrease interplate distance
  • better conducting material between the two plates
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13
Q

summing up capacitance

A

in series: reciprocal adds up

in parallel: adds up

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14
Q

properties of ion channels

A

voltage dependence
activation
inactivation
timing of activation in respect to each other.

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15
Q

technical approaches to study ion channel

A

patch clamp
molecular cloning
crystallisation

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16
Q

main features of VGIC

A 
water filled pore
passive movement of ion down conc gradient
selectivity filter
gating properties to MP
inactivation->refractory period
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17
Q

cause of selectivity filter

A

weak interaction between ion and charged AA

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18
Q

gating current

A

very small current
1/1000 of a normal current
recorded after all ionic currents are removed
confirmational change moves the charged portion of the channel- causes current ( ithink)

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19
Q

Cloning of Nav channel

A

isolate mRNA including ones encoding Na+ channel and make cDNA library

aa sequence of small region of Nav channel purified
oligonucleotide probe with sequence corresponding to aa sequence.
hybridise to cDNA library containing Na+ channel cDNA
isolate and sequence Na+ channel cDNA. deduce protein sequence
aa sequence of entire Na+ channel

tested in oocytes

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20
Q

hydorphobicity/philicity

A

ability of an aa to interact with water.

each aa has a specific value

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21
Q

how do you get DNA into eukaryotes

A

electroporation
ballistic method
DNA containing vesicle
calcium phosphatase

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22
Q

what changes the magnitude of an AP

A

conc gradient
motility of ions ( depends on size and interactions with water
temperature

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23
Q

what forms the resting membrane potential

A

selective permeability
unequal distribution
ion exchange pumps
(maintained by Na+/k+ ATPase)

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24
Q

Eion

A

membrane potential at which the concentration gradient is equal to the electrical gradient

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25
potential difference
work needed to move 1 unit of +ve charge
26
give the cellular equivalent of a battery
concentration gradient across an ion
27
give the cellular equivalent of resistor/conductor
ion channel
28
give the cellular equivalent of capacitor
ability of a membrane to store charge
29
why does Vm decrease further from site of injection
more ion channels available- more leak
30
effect of lambda (membrane length constant) on signalling
High Rm, high lamda, PSP can travel further along axon before being lost low Rm low lambda, lots of ion leakage increase diameter of axon, increase lambda, potential spreads faster- less to impede current flow
31
lambda
effectively is the electrical conductivity of a neuron
32
what is an action potential
transient reversal of the membrane potential that sweeps along the membrane of a neuron
33
voltage clamp
xxxx
34
how can you separate ion currents
- modifying conc gradient of ion - substituting critical ion with impermeable ion of same charge so electrochemical gradient is not changed - selective ion blocker
35
difference between Na+ and K+ conductance
Na+ channels open faster and inactivate faster | K+ channels open more slowly and stay open longer
36
threshold potential
is the membrane voltage at which, enough Na+ channels are open to allow the overall flow of ions to be inwards
37
Refractory period generated by?
inactivation of Na+ channels and increased K+ conductance
38
AP propagation velocity depends on
axon diameter | passive membrane properties
39
effect of Ra and Cm on velocity
rate of passive spread inversely proportional to RaCm because: -large Ra, smaller current so will take longer to depolarise the adjacent membrane -lage Cm, takes longer to charge the membrane therefore longer to depolarise.
40
how to speed up an AP
increase diameter of axon- reduces Ra as Ra=rax (pi x d^2/4) C increases but linearly with radius. Ra massively reduced Cm only slightly increased->RaCm decreased-speeds up AP Myelination C is inversely proportional to thicknes of membrane as capacitance increseases if conductors are closer together. saltatory conduction boosts the AP amplitude preventing it from dying out
41
active transport
movement of substances against their concentration gradient.
42
power sources for active transport
ATP hydrolysis | ion gradients
43
function of AT
``` establish electrochemical gradients pH regulation solute accumulation termination of synaptic transmission 2nd messenger regulation ```
44
an example of adhesion junctions
Cadherins mechanical joining of cells open lattice- allows fluid to penetrate deeper cell layers
45
Impermeable junctions
tight junction in vertebrates prevents molecules and transporters on one side of cell from moving to the other allows specific functionality of different sides
46
example of tight junctions
sealing of extracellular space in gut epithelium active transporter on one side absorbs glucose passive transporter on other side transport it to extracellular space so that glucose can not be lost back into the lumen of the gut
47
what are gap junctions made up of?
connexins- assemble into channels (either heteromeric or homomeric) form half a channel- connexon
48
what do gap junctions do?
``` make cytoplasm continuous between cells can move cells up to 1000 molecular weight: -RNA -peptides -nucleotides -vitamins -sugars ```
49
where were they discovered
NMJ of cuttlefish 1958 Furshpon + potter hyperpolarising current both from nerve terminal to muscle and muscle to nerve terminal can demonstrate their existence using voltage clamp- as they form the potential of 2 cells come closer together (loewenstein) increasing size of dyes (pon et al 2007) radioactive thymidine in healthy cell attatched to 1 mutant cell ko for thymadine kinase. radioactive thymidine found in both
50
where are they utilised?
heart to spread transmission between myocytes.- facilitates cotractile wave. causes delay between atria and ventricles smooth muscle in gut + uterus
51
function of glia
regulate excitability- regulates K+ and glu | signals to neurons
52
how many specialised processes do astrocytes have?
1- endfoot wraps around blood vessels brings glucose into brain removes excess k+ BBB
53
what happens if glia do not remove excess K+
AP comes in K+ leaves cell in a train of APs the extracellular K+ can rise by 10-20mM this rise in K+ can cause change in membrane voltage- depolarisation- cell more excitable more likely to fire AP. This can lead to epileptic discharge waves of spreading depression
54
how does a wave of depression spread
K+ released from firing cell. makes neighbouring cells more excitable, makes them fire. wave of excitation causes Nav inactivation- depression in the brain moves a few mm at a time migraine
55
How do glia deal with high K+
take up K+ through channel- K+ taken up until there is no driving force take up K+ through Na+/K+ exchanger
56
how much can a 10mM change in extracellular K+ change RMP
around 60mV
57
what is glial RMP
almost exactly Ek+ - not permeable to Na+
58
how does pump work
pump usually at 50% level. pump rate increases with K+ increase ( sigmoidal curve) K+ pumped into glia with water- glia swell
59
Spatial buffering
if K+ rises on one side of the glial cell it will take it up and release some in other areas to maintain its own MP and to not raise K+ too much through out the cell. K+ rise has to be all around the cell in order to depolarise the cell. depolarised cell will cause K+ release. may be relesed 100s of micrometers from where the rise is as glia are electrically connected by gap junctions form large networks large amounts of K+ dumped by endfoot near the blood vessel and taken out of the brain Proven by Newman 1984 K+ added externally at different area and extracellular measurements taken all round cell. largest change at endfoot- 90% of ion channels in end foot
60
what NT do glia cells help remove
Glutamate taken up into glia and broken down into glutamine via glutamate synthase either enters kreb cycle or taken up into presynaptic neuron by glutamine transporter if not taken up quickly by glia can be neurotoxic
61
how does glutamate cause neurotoxicity
AMPA receptors activated, Ca2+ enters cell and activates Ca2+ dependent enzymes (phospholipases [breaks down membrane] and ribonucleases [breaks down genetic material]) AMPA- Na+ moves in depolarises cell, Cl- drawn in followed by water- cell swells and bursts NMDA do not desensitise
62
what is needed for uptake of glut?
3 Na+ for 1 glutamate | causes depolarisation
63
how is blood flow increased to sites based on activity
Glia activated astrocytes receive GABA B or mGlu stimulation-> Ca2+ rise-> PLA2 converts arachidonic acid into prostaglandin. released onto smooth muscle- causes relaxation through hyperpolarisation- increases blood flow
64
what is calcium used as a second messenger to do
``` NT release membrane excitability synaptic plasticity change in gene expression growth and differentiation neuronal death ```

neur2006 (1 decks)

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