Pons

What is the location and extent of pons?

Pons

• is the middle part of the brainstem .
• is continuous below with the medulla oblongata and above with midbrain.
• is located in the  posterior cranial fossa  and  is related to clivus anteriorly and cerebellum posteriorly.
• is separated from the cerebellum by the presence of cavity of fourth ventricle.

Describe the external features of pons.

Pons has two surfaces – ventral and dorsal

External Features of Ventral Aspect of Pons

The ventral aspect of pons shows the following features:

• Ventral surface is convex and has a shallow groove in the midline called basilar groove which lodges basilar artery.
• Transversely running fibers ( pontocerebellar) can be seen on this surface. These fibers connect cerebrum to cerebellum via middle cerebellar peduncle.
• The two roots of trigeminal nerve ( sensory- thicker and motor -thinner) emerge at the junction of ventral surface of pons and middle cerebellar peduncle.

  External Features of Dorsal Aspect of Pons

The dorsal  aspect of Pons shows the following features:

• Median sulcus: in the median plane.
• Medial eminence : shows  rounded elevation in the lower part , called facial colliculus.  Facial colliculus overlies the nucleus of  abducent nerve. It is so named because the  fibers of  the facial nerve wind around the  dorsal aspect of abducent nerve, thereby producing this elevation.
• Sulcus limitans:  is lateral to the medial eminence and separates medial eminence from vestibular area.

Name the structural components forming internal structure of pons.

Pons is divided into two parts:

• Ventral /basilar part: structural components remain same in  the upper and lower part of pons.
• Dorsal/tegmental part: structural components differ in the upper and lower part of pons,

Structural components of internal structure of Basilar part  of Pons :

White Matter has following descending fibers

• Longitudinal fibers 
  • Corticospinal
  • Corticonuclear
  • Corticopontine
• Transverse fibers
  • Pontocerebellar

Grey matter has following nuclei

• Pontine nuclei

Structural components of internal structure of Tegmental part  of Pons:

White Matter has following tracts

Ascending tracts

• Medial lemniscus  (Posterior column tract –  carries conscious proprioception))
• Spinal lemniscus   (Lateral spinothalamic tract- carries pain and temperature sensation from the body except head region)
• Lateral lemniscus (Auditory pathway) ( in upper pons only)
• Trigeminal lemniscus (  Carries  pain, temperature sensation from head region)
• Ventral spinocerebellar peduncle ( in lower pons only)

Grey matter has following cranial nerve nuclei

• Spinal nucleus of trigeminal
• Chief sensory nucleus of trigeminal
• Motor nucleus of trigeminal
• Abducent nucleus
• Facial nucleus
• Vestibular and cochlear nuclei

Draw transverse sections of pons to show the internal features at the following levels:

• Lower pons ( at the level of facial colliculus)
• Upper pons ( at the level of trigeminal nerve)

Name the arteries that supply pons.

Pons is supplied by branches of basilar artery.

• Ventral part of pons
  • Median area – by paramedian branches.
  • Lateral area -by short circumferential branches.
• Dorsal part of pons – by
  • Long circumferential branches.
  • Anterior inferior cerebellar
  • Superior cerebellar

Applied Aspects