Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Medical Science II: Nervous System > 1.3 Signal Propagation, Transmission and Integration > Flashcards

1.3 Signal Propagation, Transmission and Integration Flashcards

Lecture 3

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

After injecting current into cells what happens to the associated membrane potential

A

the potential changed show transient, non-linear rising phases as well as a plateau

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

plotting the plateau membrane potential (Vm) against the injected current gives a …

A

linear relationship and obeys Ohm’s law

V = IRin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is Rin

A

neurons input resistance and depends on Rm normalised for SA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does Rm depend on

A

distribution of ion channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Equation for Rin

A

Rm/4(pi)(a^2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does injecting current in to a cell do

A

induces a voltage change in time which is caused by an outward current across the membrane (Im)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

equation for Im

A

Im = Ii + Ic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is Ii

A

current across Rin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what Ic

A

current discharging the membrane capacity Cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the equation to the rate of change of the membrane potential

A

𝚫𝑽𝒎(𝒕) = 𝑰𝒎𝑹𝒊𝒏 (𝟏 − (𝒆^(−(𝒕/ 𝝉)))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what gives the palteau value

A

ImRin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what affects the rate of change

A

exponent -𝒕/ 𝝉

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what does it mean if 𝑡 = 𝜏

A

63% of max voltage reached

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is 𝜏

A

𝜏 = 𝑅𝑖𝑛𝐶𝑚

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how to find the total current flow

A

sum of fast transient Ic discharging/charging Cm and slowly building up Ii through Rin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

why is there a leakage current

A

originally we assumed isotropic potential distribution but the membrane is not
a perfect insulator so there will be a leaky current whenever voltage change occurs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

how does local voltage changes propagate along different parts of the cell

A

it depends on the ration between the membrane resistance (rm) and the longitudinal resistance along the axon (ra)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is ra

A

result of the fact that ion-based current in the axon is less efficient as electrons flow in a copper cable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how can passive properties of an axon be modelled

A

by assuming distinct compartments connected by the axonal resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is the voltage change spreads along the axon

A

Δ𝑉(𝑥) = Δ𝑉o.𝑒^(− 𝑥/ 𝜆)

𝜆 = √(𝑟𝑚/𝑟𝑎)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what does lambda mean

A

indicates the distance from the initial voltage change at which the membrane potential drops to 37%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

efficiency of electronic conduction influences…

A

spatial summation in triggering synaptic potentials as well as the propagation of AP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is a factor in the propagation of AP

A

electronic conduction

  • once the membrane at any point on the axon reaches threshold depolarisation an AP is generated in that region
  • local depolarisation spreads passively causing successive adjacent regions to reach the threshold and generate an AP
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What happens when AP propagrates from right to left?

A

causes a difference in membrane potential in 2 adjacent regions of the axon and the difference creastes a local circuit causing the depolarisation to spread passively

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what happens when depolarisation spreads passively

A

current spreads from the more positive region to the less positive resting region ahead of the action potential so to the left as the AP travelling right to left as well asto the less positive area behind the action potential so towards the right

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what happens, with regards to the AP, due to an increase in membrane K+ conductance in the wake of an AP

A

the buildup of positive charge along the inner side of the membrane towards the right will be more balanced by the local efflux of K+ allowing the region to repolarise

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What happens a short time later after the first AP

A

the AP will trave; down the axon and process will repeat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what happens to axons with longer length constants (lambda)

A

they have local currents that spread a greater distance down the axon so AP propagates more rapidly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

is passive spread of depolarisation instantaneous

A

no, electronic conduction is rate limiting factor in propagation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what happens with AP in a section depolarises current to adjacent membrane

A

causes gradual depolarisation to threshold

- larger ra the smaller the current and the slower the propagation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what speeds up AP propagation

A

increasing lambda by increasing rm

- done by patches of myelin sheaths (addtional insulation) along axons (increasing rm so increases lambda)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

gain in propagation speed due to…

A

AP generation takes longer that passive electrotonic conduction of voltages along axon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

is signal propagation faster as internodes or nodes of Ranvier

A

faster at internodes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

increases speed about…

A

10x

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what are the 4 properties important for neuronal signalling with AP

A
  1. Threshold for initation
  2. All or nothing event
  3. self - regenerative
  4. refractory period
36
Q

whats threshold for initiation

A

as depolarising current increases, 𝑉𝑚 → −50 𝑚𝑉

37
Q

whats all or nothing event

A

AP stereotyped regardless of amount past threshold

38
Q

what self-regenerative

A

Can be conducted over great distances

39
Q

whats the refractory period

A

Limits frequency of signals

40
Q

whats responsible for the rising phase of the AP

A

Na+ influx
- depolarisation of the cell past threshold causes increase in Pna which overwhelms the dominant resting Pk which drives 𝑉𝑚 → 𝐸𝑁𝑎

41
Q

the falling phase is due to…

A

↑ 𝑃𝐾

42
Q

whys it difficult to measure Na and K conductance as function of Vm

A

due to the strong interdependence between membrane potential and Na+/K+-VGCs due to the +ve feedback nature of AP generation

43
Q

why does the voltage-clamp technique make measuring the conductance

A

it interrupts this interdependence by adding/withdrawing current from the axon equal to the current flowing through VGCs
This prevents 𝑉𝑚 from changing
The amount of current needed to prevent this change is a direct measure of current flowing across the membrane

44
Q

how to analyse the current waveform in more detail

A

by applying the pharmacological drugs

45
Q

how to reveal the contribution of potassium current

A

An ion channel blocker of the Sodium channels, tetrodotoxin (TTX)

46
Q

how to show the sodium current

A

Tetraethylammoniom (TEA), which blocks the Potassium channels

47
Q

what determines the size of Na and K currents

A

2 factors:
- magnitude of the conductance which reflects the number of channels open for each species
- the electrochemical driving force
𝐼n𝑎 = 𝑔n𝑎 × (𝑉𝑚 − 𝐸n𝑎) 𝑎𝑛𝑑 𝐼k = 𝑔𝑘 × (𝑉𝑚 − 𝐸𝑘)

48
Q

what are the voltage gated ion channels three states

A
  • closed activatable
  • open
  • closed inactivatable
49
Q

what do ion channels achieve

A

variable conductances

50
Q

What happens with ion channels if at resting Vm?

1st part

A

The channels are closed

  • membrane capacity is discharged and threshold potential is reached
  • “activation gate” opens
  • Na+ flux initiated
51
Q

What happens when activation gate open?

2nd part

A

causes further depolarisation due to Na flux

more VGC are opened

52
Q

how is the channel inactivated

A

after a short period it gets inactivated by means of a slow “inactivation gate”
(ball and chain hypothesis so channel gets blocked)

53
Q

what happens if the membrane potential drops below the threshold

A

“the inactivation gate” is replaced with the “activation gate” in the closed position

54
Q

what happens when there is a depolarisation of the membrane beyond the threshold (-50mV)

A

↑ 𝑔𝑁𝑎 as 𝑁𝑎+-VGCs open rapidly

Inward 𝑁𝑎+ current

55
Q

what causes further depolarisation (AP stuff)

A

membrane capacitance discharged causes it

  • Positive feedback causes more 𝑁𝑎+-VGCs to open
  • Increase in inward 𝑁𝑎+ current
  • Regenerative process drives 𝑉𝑚 → 𝐸𝑁𝑎
  • This is the rising phase of the AP
56
Q

what happens when Na channels gradually inactivate and K channels open

A

K channels opens with a delay (delayed rectifier)
↓ 𝑔𝑁𝑎 and ↑ 𝑔𝑘
- Outward 𝐾+ current tends to repolarise the membrane

57
Q

what happens when hyperpolarisation occurs

A

𝑉𝑚 depolarises past resting potential

  • 𝐾+-VGCs take time to close so 𝑔𝐾 > 𝑔𝑘,𝑟𝑒𝑠𝑡𝑖𝑛𝑔 for a few ms
  • 𝑉𝑚 is closer to 𝐸𝑘
58
Q

whats the absolute refractory period

A

Impossible to fire another AP as all 𝑁𝑎+-VGCs inactivated

59
Q

what causes the relative refractory period to be entered

A

As some 𝐾+ channels close and 𝑁𝑎+ channels recover from inactivation the relative refractory period is entered
Stimuli greater than threshold triggers AP

60
Q

What is the patch clamp experiment

A

A specialised glass micropipette with a tight seal between it and the membrane allows the recording of current through a single channel
o Allows understanding of properties of ionchannel molecules
o Demonstrate that VGC have two conductance states: open and closed

61
Q

What does the patch clamp show as a result of depolarisation

A

a channel opens in allor-none fashion
o Brief current pulses of variable duration but constant amplitude
o Rapidly terminated by inactivation
 Averaging over many channels gives the same result as voltage-clamp experiments

62
Q

whats a synapse

A

site at which one neuron communicates with another

63
Q

what are the 2 forms of synaptic transmission

A

electrical or chemical

64
Q

what does cellular activity do to the strength of a synapse

A

enhance or reduce

65
Q

what are electrical synapses used for

A

used to send rapid, stereotyped depolarising signals

66
Q

what are chemical synapses uses for

A

capable of more varying signalling
o Can produce more complex behaviours
o Mediate excitatory or inhibitory actions in postsynaptic cells
o Produces electrical changes of varying durations
o Amplify neuronal signals

67
Q

First part of electrical synapses

A

ion channels in presynaptic cell generates a current that depolarises the postsynaptic cell
presynaptic terminal has to be big enough to contain many channels to generate a large enough current
postsynaptic cell must be smaller so Rin is larger and Δ𝑉 greater

68
Q

Second part of electrical synapses

depolarising and hyperpolarising currents

A

Depolarising and hyperpolarising currents can be transmitted
o Similar to passive propagation of sub-threshold electrical signals along axon (aka electrotonic transmission)
o Some synapses have VGCs that permit unidirectional transmission (rectifying synapses)

69
Q

Third part of electrical synapses (gap junction)

A

transmission happens through region called the gap junction which is about 20 nm and is bridged by gap junction channel proteins

70
Q

what are gap junction channel proteins

A
  • arranged in arrays
  • conduct the ion current
  • conformational changes in these channels can modulate conductance
71
Q

How do chemical synapses work

A

nothing with structural continuity of pre and post synapse
chemical transmission depends on diffusion of neurotransmitter
- NS binds to receptors in post-synaptic membrane

72
Q

size of synaptic cleft

A

winder than normal intercellular space (20-40 nm)

73
Q

First part of chemical synapses (pre)

A

Transmitter is released from the presynaptic terminals
o These contain hundreds of synaptic vesicles with thousands of NS molecules each
o Clustered specialised regions called active zones

74
Q

what happens during the presynaptic AP (chem synapse)

A

𝐶𝑎2+-VGCs open causing calcium influx
o This causes fusion of the vesicles with membrane in exocytosis and release of NS into synaptic cleft
o Diffusion across cleft and binding with postsynaptic receptors cause opening of ion channels and altering of membrane potential and conductances
 This process takes time so a delay is introduced (>0.3 ms)

75
Q

where can amplification occur (chem syn)

A

it can occur as each synaptic vescile contains thousands of NS molecules

76
Q

2 ways neurotransmitters control the opening of ion channels in the post-syn cell

A

directly (ionotropic) or indirectly (metabotropic).

These two classes of transmitter actions are mediated by receptor proteins derived from different gene families.

77
Q

what is direct gating

A

5 subunits each which has 4 membrane spanning alpha helix regions

78
Q

What is indirect gating

A

receptors composed of single subunit with 7 membrane-spanning alpha helical regions that bind the ligand to membrane
receptors activate GTP - binding protein (G protein)
this activates a second messenger cascade that modulates the channel activity
G protein stimulates adenlyl cyclase converting ATP to cAMP
cAMP activates cAMP-dependent protein kinase (PKA) which phosphorylates the channels (P) changing the function

79
Q

what do central neurons receive

A

receive both excitatory and inhibitory inputs and respond to a range of neurotransmitters through both ionotropic and metabotropic receptors
o These diverse inputs must be integrated

80
Q

Type 1 of morphological types

A

Type 1: Glutamatergic
o Excitatory
o Contact at dendrites

81
Q

Type 2 of morphological types

A

Type 2: GABAergic
o Inhibitory
o Contact at soma

82
Q

what is the process of neural integration

A

Neurons integrate the various signals they receive into a single output
 Synaptic potential produced by a single presynaptic potential are not large enough to depolarise a postsynaptic cell to AP threshold
o The net effect of the inputs will depend on several factors: the location, size, and shape of the synapse, the proximity and relative strength of other synergistic or antagonistic synapses, and the resting potential of the cell.

83
Q

What is the trigger zone

A

the axon hillock at the somatic base of the axon has a lower threshold for AP generation due to a higher density of 𝑁𝑎+-VGCs

84
Q

whats does neuronal intyergration involve

A

summing the synaptic potentials that spread to the trigger zone and is critically affected by 2 passive membrane properties of the neuron

85
Q

whats the membrane time constant

A

𝜏: determines the time course of the synaptic potential and so controls temporal summation
 The greater 𝜏 the greater the likelihood two consecutive signals will summate to bring 𝑉𝑚 to threshold

86
Q

what is the length constant of the cell

A

𝜆: determines degree of local depolarisation by passive spreading and so affect spatial summation
 Longer 𝜆, more minimal decrement of signal

Medical Science II: Nervous System (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions