Synaptic Integration Flashcards
What is synaptic integration?
The process by which neurons combine multiple inputs to determine their output response.
It involves the integration of excitatory and inhibitory signals.
Define divergence in neural networks.
The phenomenon where a single neuron sends outputs to multiple neurons.
Example: pain receptor.
Define convergence in neural networks.
The phenomenon where multiple neurons send inputs to a single neuron.
Example: motor neuron.
What factors influence the decision to fire an action potential?
- Net sign of combined input
- Strength of synaptic input
- Location of synapse
- Firing frequency of the presynaptic neuron.
What is spatial summation?
The additive effect of postsynaptic potentials (PSPs) from multiple synapses.
It depends on how close the inputs are to the hillock/initial segment.
What is temporal summation?
The additive effect of multiple PSPs from a single synapse over time.
It depends on how often the inputs are firing.
What is the length constant (λ) in cable theory?
The distance over which the voltage drops to 37% of its original value.
How do PSPs travel to the hillock/initial segment?
They travel passively and attenuate as they move further away.
Synapses close to the hillock/initial segment have more influence over event as as the action potential decays less
What is the significance of synapses close to the hillock/initial segment?
They have more influence on the neuron’s decision to fire an action potential.
What is the absolute refractory period?
The period during which a neuron cannot produce another action potential.
Duration = 1-2 ms
What is the relative refractory period?
The period when a neuron is less excitable and requires a larger stimulus to fire.
Duration 4-5 ms
This is due to inactivation of Na current and activation of K current.
What is FM encoding in neurons?
The use of both frequency and pattern of action potentials to convey information.
Frequency of action potentials is the same but temporal summation
What are the two types of firing patterns in the reward pathway?
- Tonic (1-8 Hz)
- Phasic (15-20 Hz).
Hz refers to number of APs per second
Expected = tonic
Better than expected = phasic
Worse than expected = pause in activity of VTA neurons so no dopamine release in nucleus accumbens
What happens during high dopamine release in the reward pathway?
It is associated with the sensation of reward.
May explain why routes of drug administration that achieve fast/high concentrations are more rewarding
Fill in the blank: A single inhibitory synapse located close to the soma can ______ all other inputs to that dendrite.
switch off
True or False: Neurons primarily encode information through changes in the amplitude of action potentials.
False
Why is encoding important for neurons?
- To prevent firing at low stimulation levels
- To allow patterns of activity to convey information.
What are convergence neurons?
Several different neurons impinging on the same target neuron
E.g. motor neurons
Describe spatial summation of PSPs
- neurons have multiple inputs with synapses firing/generating PSPs at the same time
- the closer the neurons are to the axon hillock, the more they’ll contribute to the summated potential
Describe temporal summation of PSPs
- to be effective, PSPs must be additive
- if new APs arrive before previous PSP decays, then it will be compounded (added to the first one)
- each AP adds on to each other until threshold is reached
Action potentials in the chemical synapse
- Action potential triggers opening of Ca2+ channels
- Summation causes accumulation of Ca2+ in the synapse
- so more neurotransmitter is released and a bigger postsynaptic potential is stimulated
What is ‘shunting inhibition’?
A single inhibitory synapse located close to the soma (cell body) can switch off all other inputs to that dendrite
- As EPSP travels down the dendrite, membrane potential becomes more positive
- so Cl- moves through the inhibitory synapse and into the dendrite = cancels out the ESPS
How does FM encoding occur?
Stimulus triggers firing of multiple APs
Rate is determined by relative refractory period (threshold is higher)
Describe the reward pathway
- Ventral tegmental area contains cell bodies of dopaminergic neurons
- Either tonic or phasic firing pattern to nucleus accumbens
- Nucleus accumbens contains axons of dopaminergic neurons = dopamine is released here
- Produces response in ventral palladium —> direct response = high dopamine (feel good) or indirect response
