Excitable cells: SYnaptic integration II

Question 1

Difference in PSP summation at soma when Inhibitory synapse is:

1) On a different dendrite to an excitatory synapse
2) On the same dendrite between the excitatory synapse and soma

Answer 1

1) Linear summation of currents in soma (EPSP and IPSP)

2) Membrane potential is altered by IPSP -> net outflow of ions counteracts current induced at excitatory synapse
- opening of ion channels also lowers membrane resistance
- Results in (more inhibitory) non-linear summation EPSP and IPSP

Question 2

What are coincidence detectors and temporal regulators and what physiological roles to they play?

Answer 2

Temporal regulators -> neurons with long time constant, PSPs result in summation in larger time periods
- e.g. Oculomotor integrator: integrates eye movement signals over time to code eye positions

Coincidence detectors -> neurons with short time constant, only near simultaneous PSPs result in summation
- e.g. sound localisation (comparing time differences between ears) , visual processing

Question 3

Explain ‘silent’ post synaptic inhibition (and shunting inhibition)

Answer 3

When synaptic reversal potential = resting membrane potential

• > neurotransmitter binds to receptors
• > opening of post synaptic ion channels
• > change in membrane resistance, but no current flow and no change in membrane potential

If a shunting inhibitory synapse is activated, the input resistance is reduced locally and, following Ohm’s law, the amplitude of subsequent excitatory postsynaptic potential (EPSP) is reduced