Pons Anatomy -Questions and Answers

 Pons Anatomy- Learning Objectives

After reading this post you will know the following about the pons anatomy:

  • External features of ventral and dorsal surface of pons.
  • Nerves attached to  ventral surface of pons.
  • Internal features of pons by studying the transverse sections of pons at the  level of:
    • lower part of pons (at the level of facial colliculi)
    • Upper part of pons
  • Blood supply of pons.
  • Anatomical basis of lesions of pons and pontocerebellar angle syndrome.

Pons Anatomy– External Features of Pons

Q. What is the location and extent of pons?

A. 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.

Brainstem parts

Q. Describe the external features of pons.

A. Pons has two surfaces ventral and dorsal

Pons Anatomy -External Features of Ventral Aspect of Pons

Pons anatomy -ventral aspect of ponsThe 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 collect laterally to form 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.

 

 

  Pons Anatomy -External Features of Dorsal Aspect of Pons

The dorsal  aspect of Pons shows the following features:Pons anatomy-dorsal surface of pons

  • 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.
  • Vestibular area: Superior and lateral verstibular nuclei lie deep to this area.

 Pons Anatomy-Internal structure of Pons

Q. Name the structural components forming  internal structure of pons.

A.  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

 

Pons Anatomy- Transverse Sections

Q. 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)

Pons anatomy -transverse section of lower pons at the level of facial colliculus

 

pons anatomy - transverse section of upper pons

Pons Anatomy – Arterial Supply

Q. Name the arteries that supply pons.

A. 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

 

Pons Anatomy – Lesions of Pons

Q . Name the structures affected and the sign and symptoms of following lesions of Pons.

A. Pontine Haemorrhage:  Haemorrhage into pons may occur from the basilar and  anterior inferior arteries. Is a catastrophic event, often fatal. The structures involved and the clinical signs ( PPPPinpoint Pupil, Pyrexia, Paralysis) are as follows:

Structure InvolvedResultant Signs and Symptoms
Reticular formationComma
Autonomic fibers from hypothalamusHyperpyrexia, Pinpoint pupil
Facial nerve nucleiBilateral paralysis of facial muscles
Corticospinal tractsQuadriplegia

 

B. Pontocerebellar angle syndrome

Pons anatomy - Pontocerebellar angle syndrome

Structure InvolvedResultant Signs and Symptoms
Vestibulocochlear nerveTinnitis , progressive defness, vertigo
Facial nerveIpsilateral paralysis of muscles of face.
Spinal nucleus and tract of trigeminal nerve ipsilateral loss of pain and temperature from face and loss of corneal reflex .
Cerebellar peduncleAtaxia

 

C. Millard-Gubler syndrome

Pons anatomy - Millard Gubler syndrome

Structure InvolvedResultant Signs and Symptoms
Corticospinal tractContraleral hemiplegia (UMN Paralysis)
Abducent nerveIpsilateral paralysis of lateral rectus muscle( results in medial squint)
Facial nerveIpsilateral paralysis of muscles of face.

 

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