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Trinity Term 1 > Neuronal signalling > Flashcards

Neuronal signalling Flashcards

1
Q

Electrical properties of membranes can be measured using

A
  • a black-lipid bilayer
  • membrane acts as a capacitor
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2
Q

Capacitance

A

C = Q/V

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3
Q

How to measure the conductance of purified ion channels or vesicle preparations?

A

reconstituted into black-lipid bilayers

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4
Q

Channels act as conducters

A

allowing ion flow across the membrane

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5
Q

conductance (g)

A
  • reciprocal of resistance
  • 1/R
  • unit = Siemens, S
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6
Q

Give the circuit analogue view of a channel

A
  • pump
  • membrane capacitance
  • channel conductance
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7
Q

The average current-voltage relationship of open channels follows

A

Ohm’s Law

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8
Q

The convention for ion currents is that

A

positive charge flowing out of the cytoplasm is a positive current

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9
Q

Conductance is measured graphically as

A

the gradient (m)

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10
Q

A concentration gradient of an ion establishes

A

a diffusion potential

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11
Q

Give the The Nernst Equilibrium potential for K+:

A

2.3 (𝑅𝑇/𝑧𝐹) 𝑙𝑜𝑔^10 ([𝐾^+ ]𝑜𝑢𝑡/[𝐾^+ ]𝑖𝑛)

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12
Q

The equilibrium potential shifts

A

the average current-voltage relationship along the axis

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13
Q

Give the equilibrium potential for chloride

A

-70mV

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14
Q

Give the equilibrium potential for potassium

A

-90mV

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15
Q

Give the equilibrium potential for sodium

A

+60mV

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16
Q

Give the equilibrium potential for calcium

A

+130mV

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17
Q

The activity of single ion channels can be measured using

A

patch-clamp techniques

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18
Q

Describe the effect of patch clamp configuration

A
  • different patch-clamp configurations give access to either side of the membrane
  • pulling without suction = inside-out patch
  • pulling with gentle suction = outside-out patch
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19
Q

Time-averaged current depends on

A

frequency and duration of channel opening events

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20
Q

Membrane potential affects

A

the open probability of the channel: voltage-gating

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21
Q

Describe the KcsA channel from Streptomyces lividans

A
  • four subunits, each with 2 membrane helices (outer and inner) and a pore loop
  • surround a central pore cavity
  • turret
  • K+ ion and crystal water
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22
Q

Ion selectivity is determined by

A
  • ionic radius
  • hydration energy
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23
Q

Ionic radius is measured in

A

angstrom

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24
Q

Hydration energy is measured in

25
Describe Li+ and Na+ trying to pass through a K+ channel
- small enough - only if sufficient energy is recouped from interactions with pore residues to overcome the hydration energy required to strip off the associated water molecules
26
Describe the selectivity filter in KcsA
created by juxtaposition of the four P-loop chains
27
Describe the S4 membrane spanning domain
- inward Kirs have four subunits - each subunit has six MSDs - Na+ and Ca2+ channels have four domains, each with six-membrane spanning alpha-helices, including four copies of the S4 voltage sensor - positively charged arginine or lysine amino acids every third residue - helix moves in response to the membrane potential; affects the conformation of the channel protein opening (or closing) the pore
28
Kirs
rectifying K+-channels
29
MSDs
membrane spanning domains
30
Voltage gating is associated with
movement of charges within the protein
31
Channels may show
time-dependent kinetics
32
Describe delayed-rectifier channels
- delay before full conductance due to recruitment of channels from an inactive form - time-dependent inactivation - e.g. K+
33
Describe a voltage-gated Na+ channel
- activates rapidly - followed by rapid decrease in conductance due to channel inactivation
34
Describe time-dependent inactivation
via pore occlusion
35
Describe chemical coupling via synapses
- pre-synaptic axon - synaptic cleft - post-synaptic dendritic spine
36
Describe the initiation of an action potential via nAChR
- acetylcholine released from the pre-synaptic membrane activates the receptor - a low conductance K+ ‘leak’ channel sets the resting membrane potential close to Ek - although the ACh receptor will conduct both Na+ and K+, only Na+ moves initially as Na+ is far from equilibrium - influx of Na+ causes membrane depolarisation
37
nAChR
nicotinic acetylcholine receptor
38
Describe a channel conductance graph
- foot - rising phase - falling phase - refractory period
39
List the types of synapse
- neuromuscular junctions - synapses with another neurone - neuroglandular synapses
40
Describe neuromuscular junctions
- neurone - collateral branch - telodendria - synaptic terminals - neuromuscular junctions - skeletal muscle fibres
41
Describe synapses with another neurone
- dendrites - collateral branch - synapses with another neurone - axolemma - neurone 2
42
Describe neuroglandular synapses
gland cells
43
The motor end-plate is
a modified synapse
44
Describe the sarcomere
- fibrils - outer vesicles of SR - PM - longitudinal tubules of SR - transverse tubule - Z line - I band - thin filament - H zone - M line (bare zone) - overlap region - A band - triad
45
SR
sarcoplasmic reticulum
46
How can sarcomeres be visualised?
X-ray crystallography
47
Describe EPSPs
- increase the likelihood of a post-synaptic action potential occurring - typically mediated by glutamate receptors - allow influx of Na+ or Ca2+
48
EPSPs
Excitatory Post-Synaptic Potentials
49
Describe Inhibitory PSPs
- decrease the likelihood of a post-synaptic action potential - typically mediated by GABA receptors - allow influx of Cl-
50
Describe optogenetics
- bringing neurons under experimental control in intact organisms - modulate targeted neurone activity using light
51
List some light-activated channels and pumps
- blue-light dependent depolarisation using ChR2 - yellow-light hyperpolarisation using Halorhodopsin chloride pumping
52
ChR2
- Channel Rhodopsin 2 - K+ out - Na+ + Ca2+ in - controls neuronal activity - visualised in nematode mobility
53
Six steps to optogenetics
- piece together genetic construct of promotor (to drive expression) and gene encoding opsin - insert construct into virus - inject virus into animal brains (opsin expressed in targeted neurones) - insert optrode - laser light of specific wavelength opens membrane ion channel in neurones (sodium influx) - record electrophysiological and behavioural results
54
opsin
light-sensitive ion channel
55
oprtode
fibre-optic cable plus electrode
56
Describe optogenetics and aggression
pptogenetic stimulation of neurons in VMHvl
57
VMHvl
ventromedial hypothalamus, ventrolateral subdivision
58
What happens if you touch and optogenetic nematode's body muscles?
forward locomotion
59
What happens if you touch and optogenetic nematode's neck muscles?
head movements

Trinity Term 1 (38 decks)

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