QS Study

The floor of Fourth Ventricle

The fourth ventricle is a median cavity in the hindbrain. It is one of the four connected fluid-filled cavities within the human brain. It contains cerebrospinal fluid (CSF). It is located within the pons or in the upper part of the medulla oblongata. It is divisible into a right and left half by the median sulcus and a superior and inferior triangle by the striae medullares.

Shape: Rhomboidal in shape, so also caned rhomboid fossa. It lies within the brainstem, at the junction between the pons and medulla oblongata.

Formation: Formed by –

  1. The posterior surface of the pons. Its rhomboid in shape (diamond shaped) and as a result of its shape, the floor of the 4th ventricle is usually referred to as rhomboid fossa.
  2. The posterior surface of the upper part of the medulla. The upper triangular part is jumping on every side by the superior cerebellar peduncle, while the lower triangular part jumps on every side by gracile and cuneate tubercles and the inferior cerebellar peduncle.

Structure:

  • The floor is lined by ependyma,
  • A layer of grey matter containing cranial nerve nuclei lies deep to the floor.

Features –

(1) Median sulcus – divides the floor into right and left halves.

(2) Median eminence – elevation on either side of the midline.

Facial colliculus: An elevation over the upper part of eminences opposite the superior fovea; abducent nucleus and fibres of facial nerve present here.

Hypoglossal triangle: Occupies the lower part of eminence; hypoglossal nucleus lies here.

Floor of 4th Ventricle 1

Fig- Floor of the fourth ventricle

(3) Sulcus limitans – Limits median eminence laterally. It presents from above downwards.

  1. Locus coeruleus with substantial ferruginea.
  2. Superior fovea, a depression just lateral to facial colliculus.
  3. Inferior fovea, a depression above the vagal triangle.

(4) Vestibular area – Lies lateral to the fovea, forms auditory tubercle.

(5) Striae medullares – Represents fibres from the accurate nucleus to the opposite cerebellum.

(6) Vagal triangle – Lies below the inferior fovea between the hypoglossal triangle and vestibular area.

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