Pons Anatomy

Question 1

Identify the pons and the fourth ventricle in this MRI sagittal section.

Answer 1

Question 2

What structures form the floor (diamond shape) of the fourth ventricle?

Answer 2

The superior medulla along with the lower posterior parts of the cerebellar peduncles form the floor of the fourth ventricle. The superior and inferior cerebella peduncles form a diamond shape by forming the lateral borders of the fourth ventricle.

Question 3

Identify these basic structures of the pons.
*4 is bonus

Answer 3

1. Middle cerebellar peduncle (very prominent anteriorly).
2. Superior cerebellar peduncle.
3. Inferior cerebellar peduncle.
   *4. Facial colliculus. (The facial nerve leaves the facial nucleus and wraps arounds the abducens nucleus before traversing anterior within the pons. This pathway forms an elevation within the base of the fourth ventricle = the facial colliculus).

Question 4

What is the name of the white matter that runs from the anterior region of the pons laterally towards the middle cerebral peduncles?

Answer 4

Transverse Pontine Fibres.

Question 5

Describe what the pyramidal fasicles / fibres are and where they are located within the pons.

Answer 5

The pyramidal fasicles are located within the anterior region of the pons. The are a continuation of the pyramidal tract that runs through the midbrain, however upon entering the pons they from fasciles. These fasicles / tracts run in between the Transverse Pontine fibres of the anterior pons.

Question 6

What are these two structures observable at both the trigeminal nucleus level and the facial colliculus (inferior level)?

Answer 6

The two main sensory tracts of the brainstem are observable in the pons posteriorly. The 1. Spinal lemniscus (pain / temperature) and the
2. DCML (proprioception and vibration).

Question 7

List the three motor
nuclei located posteriorly in the pons.
One of these nuclei also has a sensory component located here, what is it called?

Answer 7

1. Abducens motor nuclei,
2. Facial motor nuclei,
3. Trigeminal motor nuclei, and
4. the Trigeminal chief sensory nuclei.
   (These nuclei are listed proximal and posterior to lateral and anterior).

Question 8

How is the facial colliculus formed and where is it observed within the Pons?

Answer 8

The facial colliculus is observed as two rounded elevations located medially within the floor of the 4th ventricle.
It is formed by the facial nerve as it wraps around the abducens nucleus.

Question 9

At what level is this axial MRI image of the pons taken?
Think about the features shown ie the 4th ventricle size and shape.

Answer 9

Trigeminal motor nucleus level (middle)

Question 10

Identify the structures of the pons in this axial MRI image.

Answer 10

1. 4th ventricle
2. Middle cerebellar peduncle.
3. Pyramidal tracts / fasicles.
4. Trigeminal motor nucleus.
5. Sensory tracts (DCML anterior and more midline); spinal lemnisius mor lateral and posterior).
6. Floor of the 4th ventricle.