abnormal Raphe nucleus morphology abnormal median column reticular nuclei any structural anomaly of the subgroup of the reticular nuclei of the brain stem that are located in and along the median plane of the medulla oblongata, pons, and mesencephalon that include neurons that synthesize serotonin and extend ascending fibers to parts of the limbic system and descending fibers to other brain stem nuclei, the medulla oblongata, and the pons MP:0004861 MPheno.ontology abnormal Raphe nuclei abnormal brainstem morphology