Complete information on the structure of the human brain

Complete information on the structure of the human brain

Brain is the controlling centre of all the body activities. It is protected by cranium. It is covered by three membranes together known as meninges. The inner membrane is piamater the middle arachnoid and the outer mem­brane is duramater. Outer part of the brain has grey matter and its inner part has white matter.

Inside the brain there are 2 spaces- subdural space which is the space between duramater and arachnoid and subarachnoid space which is the space between arachnoid and piamater. These are con­tinuous with the spinal canal of the spinal cord and are filled with cerebro­spinal fluid. The human brain weighs about 1,400 gms in volume. Divisions of Human Brain:

Human brain has three primary divisions (with subdivisions): Forebrain, Midbrain, Hindbrain

Forebrain:

It is the largest part of the brain constituting about 2/3 of the human brain. The forebrain is distinguished into cerebrum, olfactory lobes and diencephalon.

1. Cerebrum:

The cerebrum is the largest and most prominent part of the brain. It is divided into the right and left cerebral hemispheres. Each hemi­sphere is divided by sulci into distinct areas known as frontal, parietal, temporal and occipital lobes. Ventrally, the two cerebral hemispheres are connected by a transverse band of white medullated fibres the corpus cal- losum. Its outer wall is the cerebral cortex which is thrown into folds form­ing elevations called gyri with depressions between them termed as sulci.

2. Olfactory lobes:

These form the anterior most part of the forebrain and are more distinct on the ventral side.

3. Diencephalon:

It is a small structure covered dorsally by cerebral hemi­spheres. Its dorsal surface is raised into a pineal stalk bearing a small rounded pineal body. From the floor of diencephalon arises a funnel-shaped pituitary body. The dorasl wall of diencephalon is thin and vascular and represents the anterior choroid plexus. The cavity of diencephalon consti­tutes the third ventricle. It communicates through the Foramen of Monro with the cavity of cerebral hemispheres.

Midbrain:

The midbrain consists of optic lobes and cura cerebri.

1. Optic lobes:

The optic lobes are four solid lobes lying behind the dien- cephalon. They collectively constitute the corpora quadrigemina. The an­terior two lobes are slightly larger than the posterior lobes. The anterior and posterior lobes are connected by means of posterior commissure. They are devoid of optic ventricles, but between them passes a narrow cavity, the iter, which connects the third and fourth ventricles together.

2. Cura cerebri:

These are two longitudinal bands of nervous matter situ­ated on the ventral side of the optic lobes which connect the medulla ob­longata with the cerebral hemisphere.

Hindbrain:

The cerebellum and medulla oblongata constitute the hind- brain.

1. Cerebellum:

The cerebellum is large and projects anteriorly upto the cerebrum. Its surface is produced into numerous folds. The cerebellum consists of a central lobe, the vermis, two lateral lobes and two floccular lobes attached to the lateral lobes. The vermis is divided by transverse furrows into anterior, middle and posterior portions. Its grey matter pre­sents a branched tree like structure which is known as arbor vitae.

2. Medulla oblongata:

It is the posterior most part of the brain and is located underneath the cerebellum. Its floor is beset with a transverse broad band of fibres of white matter which is known as pons varolii. The anterior triangular part of medulla possesses thick floor and lateral walls but its roof is exceptionally thin and is formed of highly vascular piamater. It represents the posterior choroid plexus. It is perforated by a small aper­ture which is known as foramen of Magendie. Its cavity is known as metacoel.