Lecture 4 - Integration At The Level Of Neuron Flashcards Preview

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Flashcards in Lecture 4 - Integration At The Level Of Neuron Deck (66):
1

What is the importance of threshold?

Action potential (nerve impulses) are all-or-none events
Action potentials are regenerative and are propagated over long distances
Action potentials are the currency of information transmission throughout the nervous system

2

What is the stereotypical impulse properties a reminiscent of?

Transistor-transistor-logic (TTL) pulse

3

What does action potential frequency encode?

Intensity

4

How can intensity of a sensation be encoded by?

Variable action potential frequency

5

What did Baker et al do?

Sensory neuron in a dish
Inject current pulses that depolarises the membrane
As the depolarising current stand increases, incrementally increasing depolarising sub-threshold response

6

How can threshold change?

Second messenger pathway (G-protein)

7

What can protein kinase control?

The functional effect of one sub type sodium channel

8

What are the two ways of measuring threshold?

Current threshold
Voltage threshold

9

What is current threshold?

How much current needs to be applied to activate a neuron/axon and induce an action potential

10

What is voltage-threshold?

By how much does the membrane potential of a neuron have to change from rest to elicit an action potential

11

What is threshold-tracking in frog nerve?

Continuous measure of how excitable an axon is
Test the threshold repeatedly

12

What did Raymond design?

An electric box to alter the duration of the current he was applying to a single frog axon

13

What was measured as a single function of the impulse activity in the fibre?

The firing thresholds of a single myelinated fibres of frog sciatic nerves

14

What does conduction velocities range from and what does consist of ?

Ranged from 3-30 m/sec
Consisted of myelinated axons

15

What was the temperature, current strength and conduction velocity of a overnight tracking of threshold of a fibre?

Temperature: 18.5
Current strength: 0.4Ma
Conduction velocity: 14.7 m/sec

16

How do you get another action potential in the nerve?

Longer stimulus
More charge

17

What happens when there is more charge present?

More current is required to initiate action potential because sodium channels inactivate

18

What is H1 sub excitability caused by?

Activation of kinetically slow K+ channel in the node of Ranvier

19

In humans, what does a period of super excitability mean?

There is DAP in the axons

20

What contributes to refractory period?

Fast K+ channels
Makes axons less excitable when open
Hyperpolarising membrane

21

What are the two ways that sodium channel gates?

In a mode which gives rise to:
Transient current
Persistent current

22

What can persistent current be blocked by?

TTX

23

What can channels that gate persistently activate?

Negative potential transient current

24

What can persistent currents be involved in?

Controlling thresholds

25

What is latent addition?

Applying brief hyperpolarising pulse to sensory/motor axons to see the effects this has on excitability

26

What is threshold tracking?

Test nerve excitability which depends on the membrane properties of axons at site of stimulation

27

Latent addition

Brief hyperpolarising current
Axons less excitable
Excitability returns to normal

28

Motor axons

Exponential return to normal excitability
Passive properties of the axon

29

Sensory axons in people are more ... than motor axons

Excitable

30

What is required to depolarise the neuron before GTP Gamma S goes in?

100pA

31

Where is ATP placed?

Outside of the neuron

32

What can ATP activate?

G-protein kinase receptors

33

How do you get a functional upregulation of Nav1.9?

If small ion of a sensory neuron is exposed to ATP

34

What happens when GTP Gamma S is placed inside neuron?

There is no large change in threshold

35

What is spatial summation?

Simultaneous inputs at different points upon dendritic tree
Eliciting an action potential in a neuron with input from multiple presynaptic cells

36

What can synapses give rise to?

Excitatory and inhibitory events in the postsynaptic cells

37

What is temporal summation?

One presynaptic neuron releases neurotransmitter many times over a period

38

Spatial summation

With respect to space

39

Temporal summation

With respect to time

40

Where does impulse initiation in neuron occur?

Initial segment at the sensory ending

41

What confers high excitability?

High density of Na+ channels

42

Somatic synapses would be expected to be stronger than what?

Those on distal dendrites

43

How can Membranes be explained in terms of?

Series of electronic elements that contain resolution and capacitors

44

What is Cable Theory?

Understand how electrical signals are affected by the properties of the cable

45

Cable structures

Applicable to axons and dendrites in neurons

46

A broader spine

More current flow

47

Less resistance to current flow than an axon

Faster conduction velocity

48

Where does la afferent carry information from?

Periphery (sensory nerve) into spinal cord making a synapse into the motor neuron

49

What makes a synaptic contact on motor neuron?

3 la afferent
Multiple connections for each axon

50

How does neurons integrate synaptic inputs over?

Dendritic fields (space) and over time

51

What does cable theory explain?

Epps initiates further away from the initial segment will have slow rise-times and amplitudes at the soma

52

What are dendritic spines thought to modify?

How important a synapse is by limiting current flow

53

What are K+ current activated in response to?

Membrane depolarisation - delayed rectification

54

What does K+ current incorporate?

Permenantly charged amino acids that can respond to changes in membrane potential by translocating and altering the polypeptide conformation

55

What did this cable theory explain?

EPSP imitated farther away from initial segment, will have slower rise time and amplitude at the soma

56

What does dendritic spine modify?

How important a synapse is by limiting current flow

57

What does delayed rectifier channel restrict?

Duration of the nerve impulse and participate in regulation of repetitive firing of neuron

58

Why was the K channel of axon given the name “delayed rectifier”

It changes the membrane conductance with a delay after a voltage step

59

What can you do with K channel

Regulate pace make potential
Generate burst of action potential
Make long plateus in action potential
Regulate the overall excitability of cell

60

What is the role of K channel?

Set the resting potential
Keep fast action potential short
Terminate period of intense activity
Lower effectiveness of excitatory inputs on a cell

61

What does potassium channel incorporate?

Permanently charged amino acid that can respond to changes in membrane potential by translocating and altering the polypeptide conformation

62

What can potassium channel contribute to?

Depolarisation of AP
Control repetitive firing

63

When does potassium current inactivate?

Over a longer time base

64

Voltage gated potassium channel

Activate in response to depolarisation
Undergo inactivation process
Participate in action potential repolarisation in neurons
Contribute to refractoriness and accommodation

65

What is the current generated called where inactivation kinetics are rapid?

A current

66

What can A current enable?

Pacemaker potential
Slow repetitive firing