The Pons
Structures and Connections
The anterior pons is dominated by the basal pons, which looks (deceivingly) like a bridge (pont, en francais) between the two cerebellar hemispheres. The middle cerebellar and superior cerebellar peduncles attach the pons to the cerebellum.
The trigeminal nerve (CN V) enters the middle of the pons.
The abducent nerve (CN VI) leaves the anterior pons medially at its connection with the medulla.
The facial nerve (CN VII) enters and leaves the pons in two parts lateral to the abducens nerve.
The vestibular nerve (CN VIII) enters the pons in two parts as well, lateral to the facial nerve.
Basal Pons
Middle Cerebellar Peduncle
primarily connection between pontine nuclei and cerebellum
Superior Cerebellar Peduncle
anterior spinocerebellar pe
Tracts and Nuclei
- corticopontine fibres and pontine nuclei
- pontine nuclei
- abducens (VI) nucleus
- facial (VII) nucleus
- vestibular (VIII) nuclei
- medial lemniscus
- trapezoid body
corticopontine fibres and pontine nuclei
Originate in many areas of the cortex, communicating intention to make skilled movements; these fibres terminate on ipsilateral pontine nuclei before crossing the midline and entering the middle cerebellar peduncle.
abducens nucleus
facial nucleus
- principal sensory nucleus - fine touch of tongue etc
- motor nucleus - distributed to muscles of mastication - temporalis, masseter, tensor tympani, others
- mesencephalic nucleus -proprioreception; cell bodies in CNS after passing through the trigeminal ganglion (weird)
- signals to cerebellum, principal nucleus, and reticular formation
- neurons pass through the facial ganglion, where sensory pseudounipolar cell bodies lie
- also smaller muscle groups - stapedius, posterior digastric
- genu of facial nerve, along 4th ventricle, forms facial colliculus
- exits at the boundary between the pons and medulla
superior and lateral vestibular nuclei
Signals arrive from the vestibular system in the four vestibular nuclei in the pons.
send signals through medial longitudinal fasciculus:
- distributed to neck muscles
- and CN III, IV, VI in control of head and eye movements in reflex fashion
trapezoid body
- structure of crossed fibres from trochlear nucleus
- auditory
- same relative position as medial lemniscus
medial lemniscus
The medial lemniscus, carrying sensory information from the body, takes on a transverse orientation en route through the midbrain to the ventral posterolateral nucleus in the thalamus.
anterior spinocerebellar tract
The anterior spinocerebellar tract leaves the midbrain through the superior cerebellar peduncle