Consist of the Central Nervous System and the Peripheral Nervous System Central Nervous System: cerebrum, cerebellum and spine Peripheral Nervous System: Comprises of neurons   A nerve cell which is able to receive, transmit and react to messages Each neurone is consists of a neuron cell body and nerve fibers Nerve fibers are further divided into dendrites and axon. Dendrites are used to receive message and axons are used for transmitting message. There is a layer of myelin sheath covering the axon, its function is similar to the plastic layer of the wires, which is preventing short-circuit and to ensure the message are transmitted smoothly. Neurones are not connected. Neurotransmitters are used to transmit the nerve impulse between neurons. The transmission of nerve impulse is mainly occur at synapse   Disturbance of cognitive function: Lethargy, coma, epilepsy Damage to brain function: Mental deficiency, loss of memory, abnormal behavior Neurological disease: Dizziness, Tinnitus, Difficult in swallowing, slurred speech Disturbance of the motor function: Numbness of limbs, paralysis, muscle atrophy, muscle cramps, involuntary movements Others: insomnia, depression, anxiety, neurasthenia