Human Anatomy
Pons
Pons anatomy for MBBS: surface features, basal pons and tegmentum, cranial nerve nuclei and the cortico-pontine-cerebellar relay, mapped to NMC codes AN59.1 to AN59.3.
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Pons
Pons anatomy for MBBS: surface features, basal pons and tegmentum, cranial nerve nuclei and the cortico-pontine-cerebellar relay, mapped to NMC codes AN59.1 to AN59.3.
This chapter covers the surface features and internal transverse anatomy of the pons at its upper and lower levels. It emphasises the cranial nerve nuclei it contains and its role as the great relay between the cerebral cortex and cerebellum.
High-yield: Pons
- The pons lies between the midbrain above and the medulla below, forming the middle part of the brainstem.
- Its bulging anterior surface is made of transverse pontine fibres that continue laterally as the middle cerebellar peduncles.
- The basilar groove on the ventral surface lodges the basilar artery.
- The trigeminal nerve emerges from the ventral surface at the junction of the pons and the middle cerebellar peduncle.
- The abducent, facial and vestibulocochlear nerves emerge in sequence from medial to lateral at the pontomedullary junction.
- The pons is divided into a ventral basal part and a dorsal tegmentum.
- The basal pons contains the pontine nuclei, which relay cortical input to the opposite cerebellar hemisphere via the middle cerebellar peduncle.
- The facial nerve fibres loop around the abducent nucleus to form the facial colliculus in the floor of the fourth ventricle.
- The motor nucleus of the trigeminal nerve supplies the muscles of mastication and lies in the upper pons.
- The main sensory nucleus of the trigeminal nerve, in the pons, handles fine touch from the face.
- The medial lemniscus, spinothalamic tract and lateral lemniscus run through the pontine tegmentum.
- A lesion of the abducent nucleus impairs both eyes looking to the same side, because the nucleus also drives the opposite medial rectus through the medial longitudinal fasciculus.
- The superior olivary nucleus and trapezoid body in the lower pons process auditory information.
- The pontine tegmentum contains the reticular formation with respiratory pneumotaxic and apneustic influences.
- The upper part of the fourth ventricle lies behind the pons, roofed by the superior medullary velum.
Cranial nerves related to the pons
- **Trigeminal (fifth):** Emerges from the ventral pons at the middle cerebellar peduncle. Motor and main sensory nuclei lie in the pons.
- **Abducent (sixth):** Emerges at the pontomedullary junction, medially. Its nucleus underlies the facial colliculus.
- **Facial (seventh):** Emerges at the pontomedullary junction. Its fibres loop around the abducent nucleus.
- **Vestibulocochlear (eighth):** Emerges laterally at the pontomedullary junction at the cerebellopontine angle.
NMC competencies in this chapter
- **AN59.1:** External features of the pons
- **AN59.2:** Transverse section of the pons at the upper and lower levels
- **AN59.3:** Cranial nerve nuclei of the pons and their functional groups
Frequently Asked Questions
Which cranial nerve nuclei lie in the pons?
The motor, main sensory and spinal nuclei of the trigeminal nerve, the abducent nucleus, the facial motor nucleus, and the vestibular and cochlear nuclei are all related to the pons.
What forms the facial colliculus?
The fibres of the facial nerve loop over the abducent nucleus in the floor of the fourth ventricle, raising a small elevation called the facial colliculus.
Why does the pons connect the cortex to the cerebellum?
Cortical fibres synapse in the pontine nuclei of the basal pons, which then send transverse fibres across the midline into the opposite cerebellar hemisphere through the middle cerebellar peduncle.
What happens with a lesion at the cerebellopontine angle?
Structures near the angle, chiefly the vestibulocochlear and facial nerves, are affected, giving hearing loss, imbalance and facial weakness, as seen with a vestibular schwannoma.
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