The pons (from Latin ) is the part of the brainstem that, in humans and other mammals, lies inferior to the midbrain, superior to the medulla oblongata, and anterior to the cerebellum.

The pons is also called the ('bridge of Variolus'), after the Italian anatomist and surgeon Costanzo Varolio (1543–1575). The pons contains neural pathways and nerve tracts that conduct signals from the brain down to the cerebellum and medulla, as well as pathways that carry the sensory signals up into the thalamus.

Structure

The pons in humans measures about in length. The horizontal medullopontine sulcus demarcates the boundary between the pons and medulla oblongata on the ventral aspect of the brainstem, and the roots of cranial nerves 6, 7, and 8 emerge from the brainstem along this groove. The junction of pons, medulla oblongata, and cerebellum forms the cerebellopontine angle. The superior pontine sulcus separates the pons from the midbrain. Posteriorly, the pons curves on either side into a middle cerebellar peduncle.

The ventral aspect of the pons faces the clivus, with the pontine cistern intervening between the two structures. The ventral surface of the pons features a midline basilar sulcus along which the basilar artery may or may not course. There is a bulge to either side of the basilar sulcus, created by the pontine nuclei that are interweaved amid the descending fibres within the substance of the pons. The superior cerebellar artery winds around the upper margin of the pons.

Clinical significance

  • Central pontine myelinolysis is a demyelinating disease that causes difficulty with sense of balance, walking, sense of touch, swallowing and speaking. In a clinical setting, it is often associated with transplant or rapid correction of blood sodium. Undiagnosed, it can lead to death or locked-in syndrome.

Other animals

Evolution

The pons first evolved as an offshoot of the medullary reticular formation. Since lampreys possess a pons, it has been argued that it must have evolved as a region distinct from the medulla by the time the first agnathans appeared, 525 million years ago.

Additional images

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File:Pons.gif|Location and topography of pons (animation)

File:Gray701.png|Axial section of the pons, at its upper part

File:Gray719.png|Hind- and mid-brains; posterolateral view

File:Gray720.png|Median sagittal section of brain

File:Brain stem sagittal section.svg|Nuclei of the pons and brainstem

File:Slide2cuc.JPG|Cerebrum. Deep dissection. Inferior dissection.

</gallery>

References

  • Diagram at UCC