Short answers, pulled from the story.
The first nervous system appeared in wormlike organisms between 550 and 600 million years ago. This evolutionary leap transformed simple life into creatures capable of sensing and reacting to their environment. Before this time, animals like sponges and placozoans existed without any nervous tissue.
The two main types of cells in the nervous system are neurons and glial cells. Neurons communicate with other cells via synapses and possess an axon that extends to distant parts of the body. Glial cells provide structural and metabolic support and form myelin to insulate neurons.
The vertebrate nervous system is divided into the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and spinal cord, while the peripheral nervous system comprises nerves that connect the central nervous system to every other part of the body.
Mirror neurons fire both when an animal acts and when it observes the same action performed by another. These neurons have been found in the human premotor cortex, supplementary motor area, primary somatosensory cortex, and inferior parietal cortex. They are thought to provide the physiological mechanism for perception and action coupling.
The central nervous system is protected by major physical and chemical barriers including the meningeal membranes and the blood-brain barrier. The brain is protected by the skull and the spinal cord is encased in the vertebrae. These structures shield the brain and spinal cord from most chemicals and physical trauma.