Neurochemistry EPSP Excitatory Post Synaptic Potentials ...

LECTURE 5: Neurochemistry EPSP Excitatory Post Synaptic Potentials  Communication w. dendrites from other neurons can bring + ions into cell  + ions produce a small depolarization – an EPSP  Small EPSPs not enough to produce an AP, still excitatory SP  -80mV RMP usually, positive charge coming in, take it to -65mV  -50mV = threshold of excitability, thus no way -65mV can produce a AP – still a EPSP IPSP Inhibitory Post Synaptic Potentials  Communication w. dendrites from other neurons can bring in – iron into cell  - Ions produce a small hyperpolarization – an IPSP  IPSP will not produce AP (pushes potential down)  -80mV usually, negative charge coming in, taking it to -95mV

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An IPSP and EPSP can cancel each other A small depolarization (EPSP) will cancel the effect of a small hyperpolarsation (IPSP) More EPSPs, can exhibit an AP as it is more positive  Big ESPS will produce an action potential  Average together of IPSP (-95mV) + EPSP (-30mV) = average will be -45mV (which is bigger than -50mV)  Action Potential Consider the opposite, big IPSPs will inhibit Action potentials  Large IPSPs are due to negative ions entering the cell  Integration of charge at the axon hillock cant reach the excitation threshold  No AP

Neural integration  Many dendrites receive info from different transmitters at the same time – polarity of these dendrites may differ on the one neuron

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Some may have IPSP and some may have EPSP All ‘polarities’ produced by chemical transmission are integrated at AXON HILLOCK Neuron will only fire if hillock has an overall increase in + charge which exceeds the excitability threshold (-50mV) Depolarization of the neuron will occur – AP

Temporal or Spatial Summation Temporal: Positive charge is coming from the one neuron over time Spatial: neuronal integration is taking info that is coming from neurons of different sources (Amygdala and Hippocampus)

Why have action potentials?  Release of large amounts of neurotransmitters = sophisticated transfer of information between brain cells  Release of neurotransmitter – broad way of communicating different information between cells and therefore brain regions How does one cell ‘talk’ to another? Electrical communication: GAP JUNCTIONS (electric synapses  Rarely see them between neurons, seen between glial cells  Instead of using chemical messengers they transfer ions between plasma wall of neuritis via connexons  The junction is specialized so that it is only a small distance (3.5nm) between cells (usually around 20nm gap) – a a lot tighter together so io

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ns can jump a cross connexons