Neuronal signalling

Question 1

Electrical properties of membranes can be measured using

Answer 1

• a black-lipid bilayer
• membrane acts as a capacitor

Question 2

Capacitance

Answer 2

C = Q/V

Question 3

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

Answer 3

reconstituted into black-lipid bilayers

Question 4

Channels act as conducters

Answer 4

allowing ion flow across the membrane

Question 5

conductance (g)

Answer 5

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

Question 6

Give the circuit analogue view of a channel

Answer 6

• pump
• membrane capacitance
• channel conductance

Question 7

The average current-voltage relationship of open channels follows

Answer 7

Ohm’s Law

Question 8

The convention for ion currents is that

Answer 8

positive charge flowing out of the cytoplasm is a positive current

Question 9

Conductance is measured graphically as

Answer 9

the gradient (m)

Question 10

A concentration gradient of an ion establishes

Answer 10

a diffusion potential

Question 11

Give the The Nernst Equilibrium potential for K+:

Answer 11

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

Question 12

The equilibrium potential shifts

Answer 12

the average current-voltage relationship along the axis

Question 13

Give the equilibrium potential for chloride

Answer 13

-70mV

Question 14

Give the equilibrium potential for potassium

Answer 14

-90mV

Question 15

Give the equilibrium potential for sodium

Answer 15

+60mV

Question 16

Give the equilibrium potential for calcium

Answer 16

+130mV

Question 17

The activity of single ion channels can be measured using

Answer 17

patch-clamp techniques

Question 18

Describe the effect of patch clamp configuration

Answer 18

• 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

Question 19

Time-averaged current depends on

Answer 19

frequency and duration of channel opening events

Question 20

Membrane potential affects

Answer 20

the open probability of the channel: voltage-gating

Question 21

Describe the KcsA channel from Streptomyces lividans

Answer 21

• 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

Question 22

Ion selectivity is determined by

Answer 22

• ionic radius
• hydration energy

Question 23

Ionic radius is measured in

Answer 23

angstrom

Question 24

Hydration energy is measured in

Answer 24

kcalmol-1

Question 25

Describe Li+ and Na+ trying to pass through a K+ channel

Answer 25

- 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

Question 26

Describe the selectivity filter in KcsA

Answer 26

created by juxtaposition of the four P-loop chains

Question 27

Describe the S4 membrane spanning domain

Answer 27

- 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

Question 28

Kirs

Answer 28

rectifying K+-channels

Question 29

MSDs

Answer 29

membrane spanning domains

Question 30

Voltage gating is associated with

Answer 30

movement of charges within the protein

Question 31

Channels may show

Answer 31

time-dependent kinetics

Question 32

Describe delayed-rectifier channels

Answer 32

- delay before full conductance due to recruitment of channels from an inactive form - time-dependent inactivation - e.g. K+

Question 33

Describe a voltage-gated Na+ channel

Answer 33

- activates rapidly - followed by rapid decrease in conductance due to channel inactivation

Question 34

Describe time-dependent inactivation

Answer 34

via pore occlusion

Question 35

Describe chemical coupling via synapses

Answer 35

- pre-synaptic axon - synaptic cleft - post-synaptic dendritic spine

Question 36

Describe the initiation of an action potential via nAChR

Answer 36

- 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

Question 37

nAChR

Answer 37

nicotinic acetylcholine receptor

Question 38

Describe a channel conductance graph

Answer 38

- foot - rising phase - falling phase - refractory period

Question 39

List the types of synapse

Answer 39

- neuromuscular junctions - synapses with another neurone - neuroglandular synapses

Question 40

Describe neuromuscular junctions

Answer 40

- neurone - collateral branch - telodendria - synaptic terminals - neuromuscular junctions - skeletal muscle fibres

Question 41

Describe synapses with another neurone

Answer 41

- dendrites - collateral branch - synapses with another neurone - axolemma - neurone 2

Question 42

Describe neuroglandular synapses

Answer 42

gland cells

Question 43

The motor end-plate is

Answer 43

a modified synapse

Question 44

Describe the sarcomere

Answer 44

- 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

Question 45

SR

Answer 45

sarcoplasmic reticulum

Question 46

How can sarcomeres be visualised?

Answer 46

X-ray crystallography

Question 47

Describe EPSPs

Answer 47

- increase the likelihood of a post-synaptic action potential occurring - typically mediated by glutamate receptors - allow influx of Na+ or Ca2+

Question 48

EPSPs

Answer 48

Excitatory Post-Synaptic Potentials

Question 49

Describe Inhibitory PSPs

Answer 49

- decrease the likelihood of a post-synaptic action potential - typically mediated by GABA receptors - allow influx of Cl-

Question 50

Describe optogenetics

Answer 50

- bringing neurons under experimental control in intact organisms - modulate targeted neurone activity using light

Question 51

List some light-activated channels and pumps

Answer 51

- blue-light dependent depolarisation using ChR2 - yellow-light hyperpolarisation using Halorhodopsin chloride pumping

Question 52

ChR2

Answer 52

- Channel Rhodopsin 2 - K+ out - Na+ + Ca2+ in - controls neuronal activity - visualised in nematode mobility

Question 53

Six steps to optogenetics

Answer 53

- 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

Question 54

opsin

Answer 54

light-sensitive ion channel

Question 55

oprtode

Answer 55

fibre-optic cable plus electrode

Question 56

Describe optogenetics and aggression

Answer 56

pptogenetic stimulation of neurons in VMHvl

Question 57

VMHvl

Answer 57

ventromedial hypothalamus, ventrolateral subdivision

Question 58

What happens if you touch and optogenetic nematode's body muscles?

Answer 58

forward locomotion

Question 59

What happens if you touch and optogenetic nematode's neck muscles?

Answer 59

head movements