Anatomy of the Central Nervous System - Fourth Ventricle and Rhomboid Fossa

Introduction

• Focus on the anatomy of the fourth ventricle and the structures and cranial nuclei of the rhomboid fossa.
• Central Nervous System (CNS) consists of the encephalon and the spinal cord.
  • Encephalon subdivisions: brainstem, cerebellum, diencephalon, telencephalon.
• Fourth ventricle location: between the Pons, medulla, and cerebellum.

Ventricular System Overview

• Fourth Ventricle:
  • Inferior continuation: central canal within the spinal cord.
  • Superior continuation: aqueduct of the midbrain.
• Other Ventricles:
  • Third Ventricle: communicates with lateral ventricles through the interventricular foramen.
  • Lateral Ventricles: located laterally in the brain.
  • Cerebrospinal fluid (CSF): fills the ventricles and subarachnoid space, providing nutrients and removing waste.

Anatomy of the Fourth Ventricle

• Structure:
  • Roof: formed by superior and inferior medullary vela.
    • Superior Medullary Velum: between superior cerebellar peduncles, thin white matter.
    • Inferior Medullary Velum: between inferior cerebellar peduncles.
    • Fastigium: apex of the fourth ventricle.
  • Tela Choroidea: membrane associated with the inferior medullary velum.
  • Choroid Plexus: produces cerebrospinal fluid, present in all ventricles.

Communications of the Fourth Ventricle

• Communicates with:
  • Third Ventricle: via aqueduct of the midbrain.
  • Spinal Cord: via the central canal.
  • Subarachnoid Space: through lateral apertures (Foramina of Luschka) and median aperture (Foramen of Magendie).

Rhomboid Fossa

• Regions:
  • Upper region: Pons.
  • Lower region: Medulla oblongata.
  • Bordered by superior and inferior cerebellar peduncles.
• Anatomical Structures:
  • Median Sulcus: divides the fossa into symmetrical halves.
  • Medial Eminence: elevation where motor nuclei are situated.
  • Facial Colliculus: elevation above medullary striae.
  • Hypoglossal Trigone & Vagal Trigone: nuclei locations for cranial nerves 12 and vagal part of nucleus ambiguus.
  • Vestibular Area: contains vestibular nuclei for balance.
  • Locus Cellulareus: produces norepinephrine, linked to sleep-wake cycle.

Cranial Nerves in the Rhomboid Fossa

• Cranial Nerves 5 to 12:
  • Trigeminal Nerve (CN V): sensory and motor roots; nuclei include mesencephalic, principal, and spinal nucleus.
  • Abducent Nerve (CN VI): motor function for eyeball abduction, innervates lateral rectus muscle.
  • Facial Nerve (CN VII): motor root for facial muscles; intermediate nerve carries sensory and parasympathetic fibers.
  • Vestibulocochlear Nerve (CN VIII): balance and hearing; vestibular and cochlear nuclei.
  • Glossopharyngeal Nerve (CN IX): motor, sensory, and parasympathetic fibers, including taste.
  • Vagus Nerve (CN X): innervates thoracic and abdominal organs, associated with parasympathetic function.
  • Accessory Nerve (CN XI): motor function, innervates sternocleidomastoid and trapezius.
  • Hypoglossal Nerve (CN XII): motor function for tongue muscles.

Conclusion

• Overview of nuclei in the rhomboid fossa and their corresponding cranial nerves.
• Suggested practice: identify cranial nerves and their functions based on structures of the rhomboid fossa.