Lecture 4 - Integration At The Level Of Neuron Flashcards
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
What is the stereotypical impulse properties a reminiscent of?
Transistor-transistor-logic (TTL) pulse
What does action potential frequency encode?
Intensity
How can intensity of a sensation be encoded by?
Variable action potential frequency
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
How can threshold change?
Second messenger pathway (G-protein)
What can protein kinase control?
The functional effect of one sub type sodium channel
What are the two ways of measuring threshold?
Current threshold
Voltage threshold
What is current threshold?
How much current needs to be applied to activate a neuron/axon and induce an action potential
What is voltage-threshold?
By how much does the membrane potential of a neuron have to change from rest to elicit an action potential
What is threshold-tracking in frog nerve?
Continuous measure of how excitable an axon is
Test the threshold repeatedly
What did Raymond design?
An electric box to alter the duration of the current he was applying to a single frog axon
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
What does conduction velocities range from and what does consist of ?
Ranged from 3-30 m/sec
Consisted of myelinated axons
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
How do you get another action potential in the nerve?
Longer stimulus
More charge
What happens when there is more charge present?
More current is required to initiate action potential because sodium channels inactivate
What is H1 sub excitability caused by?
Activation of kinetically slow K+ channel in the node of Ranvier
In humans, what does a period of super excitability mean?
There is DAP in the axons
What contributes to refractory period?
Fast K+ channels
Makes axons less excitable when open
Hyperpolarising membrane
What are the two ways that sodium channel gates?
In a mode which gives rise to:
Transient current
Persistent current
What can persistent current be blocked by?
TTX
What can channels that gate persistently activate?
Negative potential transient current
What can persistent currents be involved in?
Controlling thresholds
What is latent addition?
Applying brief hyperpolarising pulse to sensory/motor axons to see the effects this has on excitability
What is threshold tracking?
Test nerve excitability which depends on the membrane properties of axons at site of stimulation
Latent addition
Brief hyperpolarising current
Axons less excitable
Excitability returns to normal
Motor axons
Exponential return to normal excitability
Passive properties of the axon
Sensory axons in people are more … than motor axons
Excitable
What is required to depolarise the neuron before GTP Gamma S goes in?
100pA
Where is ATP placed?
Outside of the neuron
What can ATP activate?
G-protein kinase receptors
How do you get a functional upregulation of Nav1.9?
If small ion of a sensory neuron is exposed to ATP
What happens when GTP Gamma S is placed inside neuron?
There is no large change in threshold
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
What can synapses give rise to?
Excitatory and inhibitory events in the postsynaptic cells
What is temporal summation?
One presynaptic neuron releases neurotransmitter many times over a period
Spatial summation
With respect to space
Temporal summation
With respect to time
Where does impulse initiation in neuron occur?
Initial segment at the sensory ending
What confers high excitability?
High density of Na+ channels
Somatic synapses would be expected to be stronger than what?
Those on distal dendrites
How can Membranes be explained in terms of?
Series of electronic elements that contain resolution and capacitors
What is Cable Theory?
Understand how electrical signals are affected by the properties of the cable
Cable structures
Applicable to axons and dendrites in neurons
A broader spine
More current flow
Less resistance to current flow than an axon
Faster conduction velocity
Where does la afferent carry information from?
Periphery (sensory nerve) into spinal cord making a synapse into the motor neuron
What makes a synaptic contact on motor neuron?
3 la afferent
Multiple connections for each axon
How does neurons integrate synaptic inputs over?
Dendritic fields (space) and over time
What does cable theory explain?
Epps initiates further away from the initial segment will have slow rise-times and amplitudes at the soma
What are dendritic spines thought to modify?
How important a synapse is by limiting current flow
What are K+ current activated in response to?
Membrane depolarisation - delayed rectification
What does K+ current incorporate?
Permenantly charged amino acids that can respond to changes in membrane potential by translocating and altering the polypeptide conformation
What did this cable theory explain?
EPSP imitated farther away from initial segment, will have slower rise time and amplitude at the soma
What does dendritic spine modify?
How important a synapse is by limiting current flow
What does delayed rectifier channel restrict?
Duration of the nerve impulse and participate in regulation of repetitive firing of neuron
Why was the K channel of axon given the name “delayed rectifier”
It changes the membrane conductance with a delay after a voltage step
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
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
What does potassium channel incorporate?
Permanently charged amino acid that can respond to changes in membrane potential by translocating and altering the polypeptide conformation
What can potassium channel contribute to?
Depolarisation of AP
Control repetitive firing
When does potassium current inactivate?
Over a longer time base
Voltage gated potassium channel
Activate in response to depolarisation
Undergo inactivation process
Participate in action potential repolarisation in neurons
Contribute to refractoriness and accommodation
What is the current generated called where inactivation kinetics are rapid?
A current
What can A current enable?
Pacemaker potential
Slow repetitive firing
