Pons

The pons is a key structure within the brainstem, measuring approximately 1 inch (2.5 cm) in length. It is positioned between the midbrain and the medulla oblongata, lying anterior to the cerebellum. It connects the right and left hemispheres of the cerebellum via transverse fibers that form the middle cerebellar peduncles. Additionally, it acts as a major relay center, facilitating communication between the cerebrum, cerebellum, and spinal cord while housing essential cranial nerve nuclei.

Anterior surface:

The anterior surface of the pons is notably convex, with transverse fibers extending laterally to form the prominent middle cerebellar peduncles, which connect the pons to the cerebellum. Along the midline of this surface lies the basilar groove, which houses the basilar artery.

Cranial nerves emerge from the anterior aspect of the pons and at its junction with the medulla. The trigeminal nerve (cranial nerve V) exits from the lateral aspect of the pons, featuring a smaller, medial motor root and a larger, lateral sensory root. At the pontomedullary junction, three additional cranial nerves emerge in a medial-to-lateral sequence: the abducens nerve (cranial nerve VI), the facial nerve (cranial nerve VII), and the vestibulocochlear nerve (cranial nerve VIII).

Posterior Surface:

The posterior surface of the pons, hidden lies beneath the cerebellum, forms the upper portion of the floor of the fourth ventricle—a cavity that contains and circulates cerebrospinal fluid. This surface exhibits several key features:

• Posterior median sulcus: A central groove that divides the surface into two symmetrical halves, continuing superiorly from the posterior median sulcus of the medulla oblongata.

• Medial eminence: A longitudinal elevation positioned on either side of the median sulcus.

• Facial colliculus: A rounded prominence located at the lower end of the medial eminence. It is formed by the internal looping of the facial nerve around the abducens nucleus near the floor of the fourth ventricle.

• Sulcus limitans: A lateral groove that separates the medial eminence from the vestibular area, the latter of which overlies the vestibular nuclei.

Internal Structure:

Internally, the pons is divided into two distinct regions, each with specific functional roles:

• Anterior Part (Basal Pons): The basal pons contains descending motor pathways, including the corticospinal and corticobulbar tracts, which are essential for voluntary motor control.

• Posterior Part (Tegmentum): Located between the basal pons and the fourth ventricle, the tegmentum is rich in sensory pathways, cranial nerve nuclei, and reticular formation. This region is crucial for numerous sensory and autonomic functions, as well as for the integration of motor and sensory signals.