The part of the nervous system that lies along the axis of the body and is secured between the skull and the spinal cord is called the central nervous system. It consists of three parts. Meninges, brain and spinal cord.
1. Meninges: The covering of the central nervous system is called meninges. The meninges are made up of three membranes or screens. These are-
(i) Dura Matter : The outer layer of meninges is called dura matter. The dura mater is bilayered in the brain and unilayered in the spinal cord. It contains veins and sinuses.
(ii) Arachnoid Matter : The second layer of meninges is called arachnoid matter. It is transparent and thin. Between the dura mater and the arachnoid mater lies the subdural space. It is filled with fluid
(iii) Pia mater: The innermost layer of meninges is called pia mater. It is thin, transparent and vascular. Between the arachnoid mater and the pia mater lies the subarachnoid space. It is filled with a fluid called Cerebro Spinal Fluid (CSF).
Functions of the meninges
(i) It protects the central nervous system from injury.
(ii) Protects against microbial attack.
(iii) It secretes cerebrospinal fluid.
(iv) It supplies nutrients to the central nervous system.
2. Brain: The swollen, large and complex part of the central nervous system located at the tip of the spinal cord is called the brain. It is located in the crown and controls the functions of all the organs of the body. The brain is divided into three parts. Namely – fore brain, mid brain and hind brain.
3. Spinal Cord
The part of the central nervous system below the medulla oblongata is called the spinal cord. It originates from the medulla oblongata and extends through the foramen magnum to the lumbar vertebrae. Its lower narrow part is called conus medullaris. Its inner layer is made up of gray matter and outer layer is made up of white matter. Gray matter looks like the English letter H or a butterfly. The cavity of the ventricles is called the terminal ventricle. It is filled with cerebrospinal fluid. 31 pairs of afferent nerves arise from the axon. Each root has two parts. dorsal root and digital root. Human hymen is about 45 cm long, 1.25 cm wide and weighs about 40 grams.
Work of Susushmakand
(i) It exchanges information and instructions.
(ii) Controls movement and walking.
(iii) Regulates reflex action.
(iv) 5th-8th carotid nerves arising from the pons perform various functions of the body.