module 11- synaptic intergration

2 types of simple neural networks

convergence & divergence

what is a convergence neural network

different neurons attach to the same target neuron that sends a signal down the axon

what is a divergence neural network

a single neuron makes contact with many other neurons (eg: pain receptors)

4 things a neurons decision to fire an action potential depends on

1. net sign of combined input (EPSP-IPSP)

2. strength of synaptic input

3. location of synapse

4. firing frequency of presynaptic neuron

what is summation + 2 types

the way postsynaptic potentials add together

• temporal & spatial

current (PSP) in dendrites & axons

attenuates in dendrites (leaks out) & doesn’t in axons

relationship between PSP distance needed to travel, attenuation & influence on the neuron

further PSP distance needed to travel = more attenuation = weaker influence over the neuron

what is spatial summation

• multiple inputs to the neuron

• synapses fire simultaneously

• the closer neurons are to axon hillock the more they’ll contribute to summated potential

what is temporal summation

• multiple stimuli via the same neuron

• action potential fires in presynaptic neuron & PSP is generated

• more action potential in presynaptic neuron is fired in quick succession

• the PSP hasn’t fully decayed so its partly added with new PSP to get over threshold

relationship between amount of neurotransmitter released and concentration of Ca

proportional

• in temporal summation more NT’s are released

what happens when more neurotransmitters are released in temporal summation

NT’s accumulate in the synapse which stimulates a bigger PSP

what is shunting inhibition

• excitatory & inhibitory synapses are both active

• EPSP is cancelled out

• when EPSP travels down the dendrite it increases membrane potential to more positive values

• chloride ions move through inhibitory receptors in the inhibitory synapse & into the dendrite

why is location important for shunting inhibiton

a single inhibitory synapse close to the cell body can cancel out all excitatory PSPs/inputs from that dendrite

how do most neurons encode information (AM/FM)

• uses FM frequency modulation → increased stimulus size = increased action potential firing rate

• encoding information about a stimulus in the frequency & pattern of action potentials fired

• have to convert AM signals to FM signals

strength of using FM frequency modulation

FM signals allow neurons to send info via frequency & pattern of action: different frequencies of action potentials have different effects on postsynaptic cell (temporal summation)

how are FM signals encoded

• converted from AM signals

• firing another action potential during the relative refractory period needs a bigger stimulus for threshold to be reached

• translated into a faster firing rate

reward pathway & FM frequency modulation

• when something better than expected happens there’s a faster firing rate that happens in bursts (phasic)

• increased amount of dopamine released → reward feeling

• when something worse than expected happens there’s a pause in activity of the VTA neurons → no dopamine released