Neuroanatomy of the Pons

Overview

• The lecture focuses on the internal structures of the pons and their functions.
• Two cross sections are analyzed:
  • Left: At the level of the trigeminal motor nucleus.
  • Right: At the level of the facial nerve and abducens nerve.

Cross Section at the Trigeminal Nerve Level

Anatomic Orientation

• Ventral vs. Dorsal: Anterior (ventral) and posterior (dorsal) aspects.
• Trapezoid Body: Divides the pons into:
  • Basilar Part: Anterior to trapezoid body.
  • Tegmentum: Posterior to trapezoid body.

Basilar Part Structures

• Pontine Nuclei: Orange dots
  • Receive descending motor fibers from the cerebral cortex.
  • Send ponto cerebellar fibers to the contralateral cerebellum via middle cerebellar peduncles.

Tegmental Part Structures

• Trapezoid Body: Crossing of cochlear fibers.
• Ascending Tracts:
  • Medial Lemniscus: Sensory info (proprioception, touch, vibration).
  • Trigeminal Lemniscus: Sensory info from the face.
  • Spinal Lemniscus: Pain, temperature, pressure from neck down.
  • Lateral Lemniscus: Auditory pathway.
• Descending Tracts:
  • Rubrospinal Tract: Flexor muscles.
  • Tectospinal Tract: Head and neck movement.

Key Nuclei

• Trigeminal Motor Nucleus (Red): Supplies muscles of mastication.
• Principal/Chief Sensory Nucleus (Green): Sensory info from the face.
• Fourth Ventricle: Fluid-filled, containing CSF.
• Superior Medullary Velum: Dorsal part.

Cross Section at the Facial and Abducens Nerve Level

Anatomic Orientation

• Facial Colliculus: Formed by fibers of facial nerve wrapping around the abducens nerve.

Basilar Part Structures

• Pontine Nuclei and Pontocerebellar Fibers: As described above.

Tegmental Part Structures

• Similar to trigeminal level but includes:
  • Spinal Nucleus of Trigeminal: Extends to medulla.
  • Superior Olivary Complex: Auditory processing.
  • Cochlear Nuclei: Receives auditory info.

Important Nerves and Tracts

• Facial Nerve (VII): Muscles of facial expression, taste from anterior 2/3 tongue.
• Abducens Nerve (VI): Lateral rectus muscle, abduction of the eye.
• Vestibular Nuclear Complex: Balance and posture via vestibulospinal tract.

Functional Overview

Corticoponto-Cerebellar Pathway

• Motor fibers from cortex synapse on pontine nuclei, cross via ponto cerebellar fibers to contralateral cerebellum.

Ascending Pathways

• Medial Lemniscus: Proprioception and touch.
• Trigeminal Lemniscus: Facial sensations.
• Spinal Lemniscus: Pain and temperature.
• Ventral Spinocerebellar Tract: Proprioception to cerebellum.

Vestibular and Auditory Pathways

• Vestibular Nuclear Complex: Extensor muscle stimulation.
• Cochlear Pathway: From cochlear nuclei via trapezoid body to lateral lemniscus.

Descending Pathways

• Tectospinal Tract: Eye and neck movements.
• Rubrospinal Tract: Upper limb flexors.

Ventricular System

• Fourth Ventricle: CSF movement, connects via cerebral aqueduct.

Summary

• The pons contains crucial pathways for motor and sensory processing, balance, and auditory functions.
• Understanding the cross sections helps relate the anatomical structures to their functional roles.