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+This document contains a detailed description of which variables are accessed by the OpenMP threads in NEST-2.6.0 simulation.
+
+Scheduler::update()
+-------------------
+
+The main simulation runs through the function ```nest::Scheduler::update()```. The simulation progresses in discrete time windows. A certain number of timesteps sum up to the minimum synaptic delay, ```min_delay_```, also called a timeslice. During this interval of length ```min_delay_```, individual threads can work separately. Thus all spike events are delivered (by each thread) at the beginning of each timeslice, and spike events are gathered (from all threads) at the end of each timeslice.
+
+Roughly, the call hierarchy inside ```Scheduler::update()``` looks like the following:
+    - for each thread in parallel do until simulation is over
+        - Only at the beginning of a timeslice, call ```Scheduler::deliver_events_()```
+        - for each node (neuron/device) assigned to this thread do
+            - call ```Node::update()```
+        - Synchronize threads
+        - Using a single thread, do the following
+            - After each ```min_delay_``` interval, call ```Scheduler::gather_events_()```
+            - ```Scheduler::advance_time_()```