Lecture 4 - Integration At The Level Of Neuron

Question 1

What is the importance of threshold?

Answer 1

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

Question 2

What is the stereotypical impulse properties a reminiscent of?

Answer 2

Transistor-transistor-logic (TTL) pulse

Question 3

What does action potential frequency encode?

Answer 3

Intensity

Question 4

How can intensity of a sensation be encoded by?

Answer 4

Variable action potential frequency

Question 5

What did Baker et al do?

Answer 5

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

Question 6

How can threshold change?

Answer 6

Second messenger pathway (G-protein)

Question 7

What can protein kinase control?

Answer 7

The functional effect of one sub type sodium channel

Question 8

What are the two ways of measuring threshold?

Answer 8

Current threshold

Voltage threshold

Question 9

What is current threshold?

Answer 9

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

Question 10

What is voltage-threshold?

Answer 10

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

Question 11

What is threshold-tracking in frog nerve?

Answer 11

Continuous measure of how excitable an axon is

Test the threshold repeatedly

Question 12

What did Raymond design?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

Ranged from 3-30 m/sec

Consisted of myelinated axons

Question 15

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

Answer 15

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

Question 16

How do you get another action potential in the nerve?

Answer 16

Longer stimulus

More charge

Question 17

What happens when there is more charge present?

Answer 17

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

Question 18

What is H1 sub excitability caused by?

Answer 18

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

Question 19

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

Answer 19

There is DAP in the axons

Question 20

What contributes to refractory period?

Answer 20

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

Question 21

What are the two ways that sodium channel gates?

Answer 21

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

Question 22

What can persistent current be blocked by?

Answer 22

TTX

Question 23

What can channels that gate persistently activate?

Answer 23

Negative potential transient current

Question 24

What can persistent currents be involved in?

Answer 24

Controlling thresholds

Question 25

What is latent addition?

Answer 25

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

Question 26

What is threshold tracking?

Answer 26

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

Question 27

Latent addition

Answer 27

Brief hyperpolarising current Axons less excitable Excitability returns to normal

Question 28

Motor axons

Answer 28

Exponential return to normal excitability | Passive properties of the axon

Question 29

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

Answer 29

Excitable

Question 30

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

Answer 30

100pA

Question 31

Where is ATP placed?

Answer 31

Outside of the neuron

Question 32

What can ATP activate?

Answer 32

G-protein kinase receptors

Question 33

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

Answer 33

If small ion of a sensory neuron is exposed to ATP

Question 34

What happens when GTP Gamma S is placed inside neuron?

Answer 34

There is no large change in threshold

Question 35

What is spatial summation?

Answer 35

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

Question 36

What can synapses give rise to?

Answer 36

Excitatory and inhibitory events in the postsynaptic cells

Question 37

What is temporal summation?

Answer 37

One presynaptic neuron releases neurotransmitter many times over a period

Question 38

Spatial summation

Answer 38

With respect to space

Question 39

Temporal summation

Answer 39

With respect to time

Question 40

Where does impulse initiation in neuron occur?

Answer 40

Initial segment at the sensory ending

Question 41

What confers high excitability?

Answer 41

High density of Na+ channels

Question 42

Somatic synapses would be expected to be stronger than what?

Answer 42

Those on distal dendrites

Question 43

How can Membranes be explained in terms of?

Answer 43

Series of electronic elements that contain resolution and capacitors

Question 44

What is Cable Theory?

Answer 44

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

Question 45

Cable structures

Answer 45

Applicable to axons and dendrites in neurons

Question 46

A broader spine

Answer 46

More current flow

Question 47

Less resistance to current flow than an axon

Answer 47

Faster conduction velocity

Question 48

Where does la afferent carry information from?

Answer 48

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

Question 49

What makes a synaptic contact on motor neuron?

Answer 49

3 la afferent | Multiple connections for each axon

Question 50

How does neurons integrate synaptic inputs over?

Answer 50

Dendritic fields (space) and over time

Question 51

What does cable theory explain?

Answer 51

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

Question 52

What are dendritic spines thought to modify?

Answer 52

How important a synapse is by limiting current flow

Question 53

What are K+ current activated in response to?

Answer 53

Membrane depolarisation - delayed rectification

Question 54

What does K+ current incorporate?

Answer 54

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

Question 55

What did this cable theory explain?

Answer 55

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

Question 56

What does dendritic spine modify?

Answer 56

How important a synapse is by limiting current flow

Question 57

What does delayed rectifier channel restrict?

Answer 57

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

Question 58

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

Answer 58

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

Question 59

What can you do with K channel

Answer 59

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

Question 60

What is the role of K channel?

Answer 60

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

Question 61

What does potassium channel incorporate?

Answer 61

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

Question 62

What can potassium channel contribute to?

Answer 62

Depolarisation of AP | Control repetitive firing

Question 63

When does potassium current inactivate?

Answer 63

Over a longer time base

Question 64

Voltage gated potassium channel

Answer 64

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

Question 65

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

Answer 65

A current

Question 66

What can A current enable?

Answer 66

Pacemaker potential | Slow repetitive firing