Fourth ventricle Question And Answers

Fourth ventricle Question And Answers

Describe the Floor’s Fourth ventricle Under the Following Heads

1 Fourth ventricle Glous autotomy.
2. Fourth ventricle Development,
3. Fourth ventricle Applied anatomy, and
4. Fourth ventricle Communications

1. Floor Fourth Ventricle Gross anatomy

• Introduction: The fourth ventricle is a cavity of the rhombencephalon. It is situated between the pons, medulla in front and cerebellum behind.

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• Morphology
  • Shape: Rhomboid
  • Angles: It has four angles.
    1. One rostral,
    2. One caudal, and
    3. Two laterals.
• Formation: It is formed by the posterior surface of
  • The lower part of the pons.
  • The upper part of the medulla.
• Contents: Nuclei of VIth, VIIth, VIIIth, IXth, Xth and XIth cranial nerves.
• Features
  • Median sulcus: It divides the entire floor into two equal parts.
  • Median eminence: It is a longitudinal elevation on either side of the median sulcus.
  • Sulcus limitans: It limits the median eminence laterally.
  • It divides each 1⁄2 into medial and lateral areas.
    The medial area contains motor nuclei and sensory nuclei “m” for “m” and the lateral area contains Sensory nuclei.
  • Superior fovea: It is the depression present at the intermediate widest part present on the sulcus limitans.
  • Inferior fovea: It is the depression present on the caudal part of the sulcus limitans.
• Division: The floor is described into
  • Upper lar area
    1. It is formed by the posterior surface of the lower part of the pons.
    2. In the upper part of the superior fovea, it presents a bluish-grey discoloured area called locus ceruleus (Locus-point, ceruleus-dark colour).
    3. Colour is due to melanin formed by substantia ferruginea (blue). It belongs to reticular formation.
    4. It is rich in noradrenaline.

• • Lower lar area
    1. It is formed by the posterior surface of the upper part of the medulla oblongata.
    2. It consists of a raised lar area present on the median eminence called a hypoglossal triangle.
    3. It shows the following nuclei deep into the
       1. Hypoglossal nuclei situated medially, and
       2. Intercalatus nuclei (peri hypoglossal nuclear complex) are situated laterally.
    4. Vagal: It is the area between the hypoglossal overlies dorsal nucleus of the vagus and the vestibular area. It overlies the dorsal nucleus of the vagus.
    5. Funiculus separans: It is a narrow ependymal thickening and separates vagal and area postrema.
    6. Area postrema (post-beyond, trema-opening):
       1. It is a small tongue-shaped area, present inferolaterally.
       2. It is composed of highly vascular neuroglial and neuronal tissue.
       3. It is devoid of the blood-brain barrier.
       4. It is closely related to vomiting and respiratory centres.
    7. Calamus scriptorius (Calamus-reed, scriptorius-relating to script): It is the lowest part of the floor which resembles the pointed nib of a writing pen called calamus scriptorius.
    8. Obex (Obex-bolt): It is the meeting point of the lower area.
  • Junction of upper and lower parts:
    1. Facial colliculus: Present on the median eminence at the level of the superior fovea. It is caused by
       1. Axons of the facial nerve (VIIth cranial nerve), and
       2. The nucleus of the abducent nerve (VIth cranial nerve).
    2. Vestibular area: Rounded elevation present lateral to sulcus limitans overlies vestibular nuclei.
    3. Striae medullaris (auditory striae)

2. Floor Flourth Ventricle Development

• Upper lar. Isthmus rhombencephalon.
• Intermediate part: Metancephalon.
• Lower lar: Myelencephalon.

3. Floor Fourth Ventricle Applied anatomy

• Lesion of the floor of the IVth ventricle may result in loss of control of swallowing, respiration, movements of tongue.
• The tumour on the floor may produce symptoms and signs of cerebellar deficiency. It may press vital nuclear centre and produce cardiac irregularities, tachycardia and irregular respiration
• Hydrocephalus: The blockage of the foramina leads to the accumulation of cerebrospinal fluid proximal to the foramen in the brain.

4. Floor Flourth Ventricle Communications