Fornix Of The Brain: Anatomy And Functions

Fornix

1. Fornix Definition: It is a bundle of white matter lying beneath the corpus callosum.
2. Parts of fornix
   • Alveus,
   • Fimbria,
   • Crus,
   • Body, and
   • Column.

Read And Learn More: Anatomy Important Question And Answers

1. Fornix Contents: It contains
   • Association fibres arising from dentate gyrus.
   • Commissural fibres which connect two hippocampi.
   • Projection fibres which project to tegmentum of midbrain. It consists of
     • Mammillotegmental tract.
     • Mammilloreticular tract.
     • Papez circuit: It is a neuronal circuit in the limbic system. It consists of
       1. Hippocampus.
       2. Fornix.
       3. Mammillary body (mammillothalamic tract).
       4. Anterior thalamic nuclei.
       5. Cingulate gyrus: Through cingulum again to hippocampus.
          
2. Fornix Functions
   • It is involved in experiencing the emotions.
   • It also decides the response to the emotions.

Septum Brain Function

Describe 3rd ventricle under following heads

• 3rd ventricle Gross anatomy,
• 3rd ventricle Boundaries,
• 3rd ventricle Recesses, and
• 3rd ventricle Applied anatomy.

Fornix Brain Function

1. 3rd ventricle Gross anatomy
   • 3rd ventricle Introduction: It is a narrow, midline cavity. It is present between two diencephalons of cerebral hemisphere.
   • 3rd ventricle Extent: It extends from lamina terminalis to upper end of cerebral aqueduct.
   • 3rd ventricle Communications
     • Cranially, it communicates with both the lateral ventricles through interventricular foramen.
     • Caudally, it communicates with 4th ventricle through cerebral aqueduct.
2. 3rd ventricle Boundaries
   • Roof is formed by
     • Ependyma: It is a thin membrane lined by cuboidal or columnar epithelium. It lines the ventricle and stretches across the thalamus.
     • Tela choroidea: It is a fold of pia mater projecting into ventricle.
     • Body of fornix: It is a prominent bundle of fibres present on the medial aspect of cerebral hemisphere. It arises from hippocampus. It is suspended from corpus callosum by septum
     • pellucidum.
   • Floor is formed by following structures from anterior to posterior OT IMP Optic chiasma: Crossing of the optic nerves.
     • Tuber cinereum (tuber-tubercle, cinereus-ash colour): It is ash-coloured elevation formed by grey matter present between mammillary body and optic chiasma.
     • Infundibulum: It is a funnel
     • shaped structure of the stalk of pituitary gland.
     • Mammillary body: It is an important part of limbic system.
     • Posterior perforated substance: It is a triangular interval between mammillary bodies and the midbrain which is pierced by numerous blood vessels.
     • Tegmentum of midbrain: It is a part of cerebral peduncle of midbrain.
   • Anterior wall: From above downwards
     • Anterior column of fornix: The body of fornix anteriorly divides into anterior column of fornix. It contains important connections of limbic system. It correlates olfactory and visceral activities.
     • Anterior commissure: It is a round bundle of white matter formed by
       1. Archipallial (archicortex): It belongs to rhinencephalon. It connects olfactory bulb and piriform area of both the sides (pear shape paleocortex present on the anterior part of parahippocampal gyrus).
       2. Neopallial: It is a larger commissure which connects two temporal lobes.
       3. Lamina terminalis: Thin plate derived from telencephalon (cranial end of neural tube) extending from rostrum of corpus callosum to dorsum of optic chiasma. It is encroached by anterior commissure in the upper part.
   • Posterior wall 
     • Pineal body It is a small conical organ present between and above two superior colliculi.
     • Posterior commissure: It connects two superior colliculi and also contains
       1. Corticotectal fibres, and
       2. Pretectal fibres.
     • Cerebral aqueduct.
   • Lateral wall
     • Anteriorly: Anterior column of fornix.
     • In upper part:
       1. Anterior two-thirds of thalamus and
       2. Interthalamic connexus.
     • Lower part:
       1. Lower part of thalamus.
       2. Hypothalamic sulcus: Separates thalamus and hypothalamus and represents sulcus limitans of diencephalon.
          
3. 3rd ventricle Recesses: These are prolongations of the 3rd ventricular cavity. These are described as
   • Anteriorly:
     • Anterior recess: It is present between anterior column of fornix and anterior commissure.
     • Optic recess: It is present at the junction of anterior boundary and floor immediately above optic chiasma.
   • In the floor: Infundibular recess: It is present in the stalk of infundibulum.
   • Posteriorly:
     • Pineal recess: In stalk of pineal body
     • Suprapineal recess: It is present above the pineal body
4. 3rd ventricle Applied anatomy
   • Ventriculography: It is a visualization of ventricles for determining the obstruction or dilatation of the 3rd ventricle.
   • Obstruction of 3rd ventricle leads to raised intracranial pressure in adults and hydrocephalus in infants.