Nervous System (Part-II)

The origin of human nervous system is ectodermal. The whole nervous system is divided into three parts.

Central Nervous System: It comprises the brain and the spinal cord.

1. Brain

Brain accommodate in the skull while spinal cord is enclosed by the vertebral column. To support brain and protect it from external pressures, it is surrounded by a covering of triple membrane of connective tissue called the meninges. The three layers of meninges are duramater, arachnoid and piamater. The innermost layer, piamater is thin, delicate and highly vascular. It is firmly adhere to the brain. The middle layer is arachnoid membrane, which is thin and highly folded structure in front of cranial venous sinus. The villi like folding helps to reabsorb the cerebrospinal fluid (CSF). The outermost layer is very thick, strong and non-elastic called duramatter, is made up of collagen fibre. The space between duramater and arachnoid is known as sub-dural space which is filled by serous fluid. The space between arachnoid and piamater is known as sub-arachnoid space and is filled by CSF.
CSF is lymph like clear and alkaline fluid whose function is to provide support as well as to protect the brain. It also helps in exchange of metabolic substances between the brain and blood capillaries. CSF mainly present in ventricle of brain, sub-arachnoid space and spinal cord.
The human brain is divided into three parts-

1. Fore brain or Prosencephalon: It includes cerebrum, diencephalon and olfactory lobes.
2. Mid brain or Mesencephalon: It consists of corpora quadrigemina and crura cerebri.