Week 5 ELM 11: Synaptic Integration

Flashcards for Synaptic Integration lecture review.

Synaptic Integration

The process by which multiple synaptic potentials combine within one postsynaptic neuron.

Convergence (neural networks)

When multiple presynaptic neurons synapse onto a single postsynaptic neuron (e.g., motor neuron, a single motor neuron receives input from multiple sources).

Divergence (neural networks)

When one presynaptic neuron synapses onto multiple postsynaptic neurons (e.g., pain receptor, a single pain receptor can send signals to multiple areas of the brain

Excitatory Postsynaptic Potential (EPSP)

A small depolarization caused by excitatory input, usually due to Na+ influx.

Summation

The process by which postsynaptic potentials add up to reach the threshold for an action potential.

Spatial Summation

PSPs from multiple synapses combine to reach threshold. Proximity to the axon hillock/initial segment is a factor. Coming from stimuli arriving at different locations on the neuron.

Temporal Summation

Multiple PSPs from a single synapse combine to reach threshold. The frequency of inputs firing is a factor. Multiple stimuli arriving at same location on a neuron.

FM Code

Neurons use a frequency modulation code where both the frequency and pattern of action potentials convey information.

Resting potential, threshold, and action potential peak values

-70mV, -55mV, +40mV

Depolarization

The membrane potential becomes more positive

Repolarization

The membrane potential returns to its resting state

Factors influencing action potential firing

1. Net sign of combined input: neurons integrate both EPSPs and IPSPs to determine their response

2. Strength of synaptic input: different inputs can have varying strengths

3. Location of synapse: synapses closer to hillock/initial segment have greater influence

4. Firing frequency of the presynaptic neuron: higher firing rates can lead to greater postsynaptic effects

Cable theory formula

V = V_0 e^{-x/\lambda}

V= voltage at distance x

V0 = original voltage at the source

x = distance from the source

Why do synapses closer to the hillock/initial segment have more influence

They attenuate more

Hillock

The location where action potentials are initiated. A weak signal far from it may not trigger an AP, strong signal near it is more likely to trigger an AP. High density of voltage-sensitive sodium channels (VSSC)

FM encoding details

The rate of firing is determined by the relative refractory period (RRP).

Reward pathway

Components: Ventral tegmental area (VTA), nucleus accumbens, ventral pallidum

Dopamine release

Tonic (1-8 Hz): baseline level of DA release

Phasic (15-20 Hz): burst of DA release

Expected reward = tonic activity

Better than expected reward = phasic activity

Worse than expected reward = pause in activity

Reasons for encoding

To prevent firing at low stimulation levels (reduce noise)

To allow patterns of activity to convey information