Question

Briefly describe the structure of the Brain.

Answer 1

brain structure:

In humans, the brain remains protected within the skull or cranium. The brain is covered with three covers, which are called meninges. These are the meninges:

1. Tendon: made of white fibrous tissue.
2. Reticle: This is the middle layer.
3. Meningioma: This is the innermost covering which remains in contact with the brain.

There is a network of blood vessels in this layer.

Diagram showing the sagittal section of the human brain

There is a liquid filled between these membranes, which is called cerebrospinal fluid. This fluid is helpful in nutrition, respiration and excretion. It also protects the soft brain from external shocks. The brain can be divided into three parts-

1. Forebrain
2. Midbrain
3. Hindbrain

1. forebrain or prosencephalon
There are three parts of the forebrain.

1. Olfactory part
2. Cerebrum and
3. Diencephalon

i. Olfactory part: In humans, the olfactory part is vestigial and the main part of the forebrain is the cerebrum.

ii. Brain or Cerebrum:

• About 2/3 of the brain is the cerebrum. The cerebrum is divided into two lobes called cerebral hemispheres. Both cerebral hemispheres are connected by a band of nerve fibre called the corpus callosum.
• The nerve cells in the cerebrum are located in such a way that other cells are located outside. This part is called the cerebral cortex. Inside it, axons are located on the navicular nerve. This part is the medulla oblongata. The outer part is grey in colour. This is called grey matter. It has a white colour. It is called white matter.
• Due to the large number of nerve fibres on the dorsal surface of the cerebrum, it is solid, thick, and valanced. This surface is called neopallium. In Neopallium, the raised stones are called grand or gairai and the buried part of the beach is called khancha or sultanate.
• Three deep depressions divide each cerebral hemisphere into four main lobes. Examples: frontal lobe, parietal lobe, temporal lobe, and iodinepithelal lobe. The cerebral cortex is called the lateral cerebellum or paracele.

iii. Posterior forebrain or diencephalon:

• This is the posterior part of the forebrain. Its dorsal part is thin and the ventral part is thick, which is called the hypothalamus.
• On the ventral surface of the hypothalamus, there is the pituitary gland attached to the infundibulum. The pineal body and anterior blood plexus are found on the dorsal surface of the diencephalon.
• The cavity of the diencephalon is the third ventricle or diecoel, which is connected to the lateral cavities by the foramen of Monro.

2. Midbrain or mesencephalon:

• This part is not well developed in mammals. Its dorsal part is in the form of four visual lobes, which are called corpora quadrigemina.
• There are bands of nervous tissue in the lateral and ventral parts of the midbrain, which are called crura cerebrae. These work to connect the hindbrain with the forebrain.
• Here, the optic nerves cross each other and form the optic chiasm. The narrow cavity of the midbrain is called the auricle, which connects the third ventricle to the fourth ventricle.

3. Hindbrain or rhombencephalon:

This is the posterior part of the brain. It is also called brain stem. There are two parts of the hind brain:

1. Cerebellum,
2. Brain tail or medulla oblongata

i. Cerebellum:  

• It is adjacent to the posterior part of the cerebrum. The cerebellum is made up of two lateral hemispheres. The cerebellum contains external grey matter and internal white matter.
• At various places, grey matter enters the white matter and forms a structure like the branches of a tree. It is called Praanvriksha or Arbour Viti.
• The cavity is absent in the cerebellum. There is a band of white matter in the ventral part of the cerebellum, which is called pons veroli.

ii. Brain tail or medulla oblongata: 

• This is the most posterior part of the brain, which further comes out of the cranial cavity in the form of the spinal cord.
• The posterior blood plexus is situated on the dorsal wall of the medulla. The cavity of the medulla is called the fourth ventricle or metacoel.