Reticular Formation


    Part of the brain that is involved in actions such as awaking and the sleep cycle. It also filters incoming to discriminate irrelevant background stimuli. It is one of the oldest portions of the brain.
It is also involved in the functions of:

1. Arousal
2. Attention
3. Cardiac reflexes
4. Motor Functions
5. Regulates awareness
6. Relays nerves signals to the Cerebral Cortex

It is centered roughly in the pons. The reticular formation is the core of the brain stem, running through the  mid brain, pons and medulla.
At most levels of the brain stem the reticular formation can be divided into three longitudinal zones that
are arranged in a medial to lateral sequence.

1. Raphe nuclei
2. Medial zone
3. Lateral zone.

More information: http://www.neurocomputing.org/Reticular.aspx