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

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

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).

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.

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.

The system composed of neurons that coordinates physical, mental and physiological functions in response to external and internal stimuli of the body is called nervous system. The nervous system is divided into two main parts. Central nervous system and Peripheral nervous system

The transport of impulses across synapses is called synaptic transmission. It takes 7 milliseconds for an impulse to flow through a neuron. Its speed is faster than the speed of light. The process of impulse transport is-
1. As the nerve impulse reaches the synaptic knob of the presynaptic neuron, its permeability increases.
2. As a result, Ca++ ions from the surroundings enter the synaptic knob. Ca++ ion converts ATP-as enzyme into active enzyme.
3. The activated enzyme releases the neurotransmitter.
4. Neurotransmitters pass through the synaptic cleft to the receptors of the postsynaptic neuron in the diffusion process.
5. This increases the permeability of the synaptic knob of the postsynaptic neuron. As a result, Na+ ions enter the synaptic knob and K+ ions move out.
6. An action potential is generated by the exchange of Na+ and K+. A signal is generated as a result. Through this signal, the stimulus is carried to the postsynaptic neuron.

1. It acts as a transmission center or relay station for information.
2. It transmits impulses from one neuron to another.
3. Coordinates between different neurons.
4. Determines the course of nerve impulses.
5. Regulates arousal in extreme arousal.

Two parts of a neuron meet to form a synapse. The axon of a neuron that participates in the formation of a synapse is called a presynaptic neuron. Another neuron forming a synapse is called a postsynaptic neuron. There is a gap of about 20-30 nanometers between the synaptic knobs of two neurons. This gap is called a synaptic cleft. The synaptic knobs of both neurons contain neurotransmitters, neurofilaments and synaptic vesicles. These chemicals help in the transport of stimuli.

The word synapse is derived from the Greek word syn meaning union. A junction of two or more neurons is called a synapse. British neurologist Charles Sherrington (1897) first used the term synapse.