short notes on pons

1. DEPT OF RACHANA SHARIR
DR SAMADHAN M PATIL
M.D. RACHANA SHARIR

2. TOPIC
• Pons

3. INTRODUCTION
• Pons, (Latin word means bridge) also called metencephalon
• V (trigeminal), VI (abducent), VII (facial), VIII (vestibulocochlear) nerves are
attached here
• 2.5 cm long
• Extends from cranial end of medulla oblongata to the cerebral peduncles of
midbrain

4. RELATIONS
• Anteriorly: Clivus, basilar artery
• Laterally: Middle cerebellar peduncle
• Posteriorly: 4th Ventricle

5. EXTERNAL FEATURES
• The pons has:
• Two surfaces: Ventral and Dorsal
• Two borders: Superior and Inferior

6. SURFACES
1. Ventral or Anterior surface:
• Convex in both directions
• Transversely striated
• In the median plane a vertical basilar sulcus which lodges the basilar artery
• Laterally continuous with the middle cerebellar peduncle
• Trigeminal nerve attached at the junction of the pons with the peduncle
• At the lower border abducent, facial and vestibulocochlear nerves are attached
2. Dorsal or Posterior surface:
• Hidden by cerebellum
• Forms floor of the 4th Ventricle

7. BORDERS
1. Superior border:
• Crus cerebri are attached
• III and IV nerves are also seen
2. Inferior border:
• Lies at the junction of pons and medulla oblongata

8. INTERNAL STRUCTURE OF PONS
• In transverse sections is seen to be divisible into ventral and dorsal parts
1. Ventral or Basilar part:
• Uniform structure throughout its length
• Continuous inferiorly with the pyramids of the medulla and each side
with the cerebellum through the middle cerebellar peduncle
2. Dorsal Or Tegmental part:
• Direct upward continuation of the medulla (excluding the pyramid)
• Structure differs in the upper and lower part

9. INTERNAL STRUCTURE OF VENTRAL PART
• Grey matter:
• Represented by nuclei pontis form an important part of the cortico-ponto-
cerebellar pathway
• Some of these nuclei displaced during development and form the arcuate
nucleus and pontobulbar body
• All fibres of these nuclei go to the opposite half of the cerebellum
• White matter: consists of longitudinal and transverse fibres
• Longitudinal fibres: Corticospinal and Corticonuclear (Pyramidal) tract
• Transverse fibres: Pontocerebellar fibres

11. INTERNAL STRUCTURE OF DORSAL PART
• Upper part of Pons
• Grey matter: Motor and superior sensory nucleus of the trigeminal nerve
• White matter: Transverse band of fibres – Trapezoid body, medial
lemniscus, trigeminal lemniscus, spinal lemniscus and lateral lemniscus
(from medial to lateral), Superior cerebellar peduncle and medial
longitudinal bundle

13. • Lower part of Pons
• Grey matter: VI (abducent), VII (facial) nerve nucleus, vestibular and
cochlear nuclei, spinal tract of trigeminal nucleus, superior olivary nucleus
• White matter: Trapezoid body/ corpus trapezoideum, medial lemniscus,
lateral spinothalamic tract, trigeminal lemniscus, inferior cerebellar
peduncle, medial longitudinal bundle and facial colliculus

14. BLOOD SUPPLY
• The pontine arteries (from either side of basilar artery)

15. CLINICAL ANATOMY
• Pontine heamorrhage
• Cerebellopontine angle
• Millard-Gubler’s syndrome
• Tumours of pons