| Pons | |
|---|---|
 Pons in the brainstem | |
 Anteroinferior view of themedulla oblongata and pons | |
| Details | |
| Part of | Brain stem |
| Artery | Pontine arteries |
| Vein | Transverse and lateral pontine veins |
| Identifiers | |
| MeSH | D011149 |
| NeuroNames | 547 |
| NeuroLex ID | birnlex_733 |
| TA98 | A14.1.03.010 |
| TA2 | 5921 |
| FMA | 67943 |
| Anatomical terms of neuroanatomy | |
Thepons (fromLatinpons,'bridge'code: lat promoted to code: la) is the part of thebrainstem that, inhumans and othermammals, lies inferior to themidbrain, superior to themedulla oblongata, and anterior to thecerebellum.
The pons is also called thepons Varoliicode: lat promoted to code: la ('bridge of Variolus'), after the Italian anatomist and surgeonCostanzo Varolio (1543–1575).[1] The pons containsneural pathways andnerve tracts that conduct signals from thebrain down to the cerebellum and medulla, as well as pathways that carry the sensory signals up into thethalamus.[2]
The pons in humans measures about 2.5 centimetres (0.98 in) in length.[2] It is the part of the brainstem situated between the midbrain and the medulla oblongata.[3][4] The horizontalmedullopontine sulcus demarcates the boundary between the pons and medulla oblongata on the ventral aspect of the brainstem, and the roots ofcranial nerves 6, 7, and 8 emerge from the brainstem along this groove.[5] The junction of pons, medulla oblongata, and cerebellum forms thecerebellopontine angle.[6] Thesuperior pontine sulcus separates the pons from the midbrain.[7] Posteriorly, the pons curves on either side into amiddle cerebellar peduncle.[4]
Across-section of the pons divides it into a ventral and a dorsal area. The ventral pons is known as thebasilar part, and the dorsal pons is known as thepontine tegmentum.[3]
The ventral aspect of the pons faces theclivus, with thepontine cistern intervening between the two structures. The ventral surface of the pons features a midlinebasilar sulcus along which thebasilar artery may or may not course. There is a bulge to either side of the basilar sulcus, created by thepontine nuclei that are interweaved amid the descending fibres within the substance of the pons. Thesuperior cerebellar artery winds around the upper margin of the pons.[4]
Most of the pons is supplied by thepontine arteries, which arise from the basilar artery. A smaller portion of the pons is supplied by theanterior andposterior inferior cerebellar arteries.
Duringembryonic development, themetencephalon develops from therhombencephalon and gives rise to two structures: the pons and the cerebellum.[2] Thealar plate produces sensoryneuroblasts, which will give rise to thesolitary nucleus and itsspecial visceral afferent (SVA) column; thecochlear andvestibular nuclei, which form thespecial somatic afferent (SSA) fibers of thevestibulocochlear nerve, the spinal and principaltrigeminal nerve nuclei, which form thegeneral somatic afferent column (GSA) of thetrigeminal nerve, and thepontine nuclei, which relay to thecerebellum.
Basal plate neuroblasts give rise to theabducens nucleus, which forms thegeneral somatic efferent fibers (GSE); the facial and motor trigeminal nuclei, which form thespecial visceral efferent (SVE) column; and thesuperior salivatory nucleus, which forms thegeneral visceral efferent fibers (GVE) of thefacial nerve.
A number ofcranial nerve nuclei are present in the pons:
Functions of these four cranial nerves (5–8) include regulation of respiration; control of involuntary actions; sensory roles in hearing, equilibrium, and taste; and in facial sensations such as touch andpain, as well as motor roles in eye movement, facial expressions, chewing, swallowing, and the secretion of saliva and tears.[2]
The pons containsnuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily withsleep, respiration, swallowing,bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.[2]
Within the pons is thepneumotaxic center consisting of thesubparabrachial and themedial parabrachial nuclei. This center regulates the transition from inhalation to exhalation.[2]
The pons is implicated insleep paralysis, and may also play a role in generatingdreams.[8]
The pons first evolved as an offshoot of the medullaryreticular formation.[9] Sincelampreys possess a pons, it has been argued that it must have evolved as a region distinct from themedulla by the time the firstagnathans appeared, 525 million years ago.[10]
