Pons

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The pons is a component of the brain stem of the brain. It is separated by the dorsally placed cerebellum by the fourth ventricle.

Surface landmarks and major structures

Ventrally, the corticopontine tract terminates in the pontine nuclei, which scatter in this portion of the pons. The axonal fibres of the pontine nuclei (ponto-cerebellar tract) cross the midline of the pons and travel beneath the surface of the contralateral pons to enter the cerebellum via the middle cerebellar peduncle. The horizontal striations seen on the ventral surface of the pons belong to the ponto-cerebellar tract. The corticobulbar and corticospinal tracts travel deep to the pontine nuclei and the ponto-cerebellar tract. Fibres of the corticobulbar tract decussate and terminate in the cranial nerve nuclei of the motor nucleus of the trigeminal nerve (CN V), abducent nerve (CN VI), and facial nerve (CN VII). The corticospinal tract passes through the pons and the medulla oblongata to the spinal cord.

Dorsally, the surface of the pons (and rostral medulla oblongata) is marked by three longitudinal grooves and two bilateral rows of elevations The median sulcus (the medial groove) is flanked by the bilateral sulcus limitans. Cranial nerve nuclei deep to the elevations between the median sulcus and the sulcus limitans are derived from the basal plate of the primitive neural tube. These medial rows of nuclei serve motor functions. Cranial nerve nuclei deep to the elevation lateral to sulcus limitans are derived from the alar plate, and serve sensory functions ("Principal" portion of Trigeminal nucleus, Vestibular nuclei, and Cochlear nuclei)