Pons

Pons
Brain bulbar region.svg
Pons in the brainstem
Gray679.png
Anteroinferior view of the medulla oblongata and pons
Details
Part ofBrain stem
Arterypontine arteries
Veintransverse and lateral pontine veins
Identifiers
MeSHD011149
NeuroNames547
NeuroLex IDbirnlex_733
TA98A14.1.03.010
TA25921
FMA67943
Anatomical terms of neuroanatomy

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

The pons is also called the pons Varolii ("bridge of Varolius"), after the Italian anatomist and surgeon Costanzo Varolio (1543–75).[1] This region of the brainstem includes neural pathways and tracts that conduct signals from the brain down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus.[2]

Structure

The pons is in the brainstem situated between the midbrain and the medulla oblongata, and in front of the cerebellum. A separating groove between the pons and the medulla is the inferior pontine sulcus.[3] The superior pontine sulcus separates the pons from the midbrain.[4] The pons can be broadly divided into two parts: the basilar part of the pons (ventral pons), and the pontine tegmentum (dorsal pons). Running down the midline of the ventral surface is the basilar sulcus, a groove for the basilar artery. Most of the pons is supplied by the pontine arteries, which arise from the basilar artery. A smaller portion of the pons is supplied by the anterior and posterior inferior cerebellar arteries.

The pons in humans measures about 2.5 centimetres (0.98 in) in length. Most of it appears as a broad anterior bulge above the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. They connect the cerebellum to the pons (middle cerebellar peduncle) and midbrain (superior cerebellar peduncle).[2]

Development

During embryonic development, the metencephalon develops from the rhombencephalon and gives rise to two structures: the pons and the cerebellum.[2] The alar plate produces sensory neuroblasts, which will give rise to the solitary nucleus and its special visceral afferent (SVA) column; the cochlear and vestibular nuclei, which form the special somatic afferent (SSA) fibers of the vestibulocochlear nerve, the spinal and principal trigeminal nerve nuclei, which form the general somatic afferent column (GSA) of the trigeminal nerve, and the pontine nuclei which relays to the cerebellum.

Basal plate neuroblasts give rise to the abducens nucleus, which forms the general somatic efferent fibers (GSE); the facial and motor trigeminal nuclei, which form the special visceral efferent (SVE) column, and the superior salivatory nucleus, which forms the general visceral efferent fibers (GVE) of the facial nerve.

Nuclei

Cross-section of lower pons, axons shown in blue, grey matter in light grey. Anterior is down and posterior is up

A number of cranial nerve nuclei are present in the pons:

  • mid-pons: the 'chief' or 'pontine' nucleus of the trigeminal nerve sensory nucleus (V)
  • mid-pons: the motor nucleus for the trigeminal nerve (V)
  • lower down in the pons: abducens nucleus (VI)
  • lower down in the pons: facial nerve nucleus (VII)
  • lower down in the pons: vestibulocochlear nuclei (vestibular nuclei and cochlear nuclei) (VIII)

Function

Functions of these four cranial nerves (V-VIII) include regulation of respiration, control of involuntary actions, sensory roles in hearing, equilibrium, and taste, and in facial sensations such as touch and pain, as well as motor roles in eye movement, facial expressions, chewing, swallowing, and the secretion of saliva and tears.[2]

The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.[2]

Within the pons is the pneumotaxic center consisting of the subparabrachial and the medial parabrachial nuclei. This center regulates the change from inhalation to exhalation.[2]

The pons is implicated in sleep paralysis, and may also play a role in generating dreams.[5]

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.[6] 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.[7]

Additional images

References

  1. ^ Henry Gray (1862). Anatomy, descriptive and surgical. Blanchard and Lea. pp. 514–. Retrieved 10 November 2010.
  2. ^ a b c d e f Saladin Kenneth S.(2007) Anatomy & physiology the unity of form and function. Dubuque, IA: McGraw-Hill
  3. ^ "BrainInfo". braininfo.rprc.washington.edu.
  4. ^ Carpenter, M (1985). Core text of neuroanatomy (3rd ed.). Williams & Wilkins. p. 42. ISBN 0683014552.
  5. ^ Koch, Christof. "Dream States: A Peek into Consciousness". Scientific American. Scientific American. Retrieved 17 September 2020.
  6. ^ Pritchard and Alloway Medical Neuroscience
  7. ^ Butler and Hodos Comparative vertebrate neuroanatomy: evolution and adaptation

External links

Media files used on this page

Gray719.png
Hind- and mid-brains; postero-lateral view.
Slide2cuc.JPG
Author/Creator: Anatomist90, Licence: CC BY-SA 3.0
Anatomical dissections
Brain stem sagittal section.svg
Author/Creator: Patrick J. Lynch, medical illustrator, Licence: CC BY 2.5
Sagittal cuts of the encephalic trunk. Number 7: the facial nerve nucleus, Number 6: abducens nucleus (Entzefalo enborraren mozketa sagitala. 7. Zenbakia: aurpegi nerbioaren nukleoa eta 6. Zenbakia abducens nukleoa)
Brain bulbar region.svg
Author/Creator: Image:Brain human sagittal section.svg by Patrick J. Lynch; Image:Brain bulbar region.PNG by DO11.10; present image by Fvasconcellos., Licence: CC BY 2.5

The corticobulbar (or corticonuclear) tract is a white matter pathway connecting the cerebral cortex to the brainstem (the term "bulbar" referring to the brainstem). The 'bulb' is an archaic term for the medulla oblongata. In clinical usage, it includes the pons as well.

See also [1] for reference.
Pons.gif
Author/Creator: Images are generated by Life Science Databases(LSDB)., Licence: CC BY-SA 2.1 jp
pons. Images are from Anatomography maintained by Life Science Databases(LSDB).
Lower pons horizontal KB.svg
Author/Creator:

Marshall Strother User:mcstrother

, Licence: CC BY 3.0

Diagram of a cross-section taken horizontally through the lower part of the pons of a human brainstem and stained with the Kluver-Barrera method. Due to the staining method, white matter (axons) appears blue and gray matter (cell bodies) appears light gray.

Notes:

  • Anterior is down, posterior is up.
  • The spinal tract of the trigeminal nerve can sometimes be seen surrounding the spinal nucleus of the trigeminal nerve, but it was impossible to distingusih from the inferior cerebellar peduncle on the original slide.
  • The spinal lemniscus (including the spinothalamic tract) and trapezoid body also could not be distinguished but probably lie anteromedially to the superior olivary nucleus, blending in with the central tegmental tract and medial lemniscus.
  • The pontine reticular formation (#9) and pontine nuclei (#22) are large, diffuse structures.
Colors, shapes, and locations are based loosely on slide "05-BBS-09. Pons, Nu VII, Sup. Olive Kluver-Berrara" from the Bacus collection at Washington University in St. Louis School of Medicine, supplemented with information from Gado, Thomas A. Woolsey ; Joseph Hanaway ; Mokhtar H. (2003) The brain atlas a visual guide to the human central nervous system (2nd ed.), Hoboken: Wiley, pp. 146−147 ISBN: 0-471-43058-7. and several of the public domain images from Gray's anatomy on the Wikipedia Commons. Locater image illustrating point of section is File:Brain_stem_sagittal_section.svg by Patrick Lynch. Special thanks to Dr. Joel Price for his assistance in verifying structures.
Gray701.png
Coronal section of the pons, at its upper part. Edit this at Structured Data on Commons
Gray679.png
Medulla oblongata and pons. Anterior surface.