Neurology is a department that treats all congenital diseases related to the whole nervous system.
The nervous system is divided into to parts, the central nervous system and the peripheral nervous system.

Central nervous system is formed with what we normally think of such as the cerebrum, cerebellum, the brain stem, and the spinal cord, which is the fasciculus of the central nervous system located inside the spine.
As for the peripheral nervous system, it is the electric wire that reaches the distal end of the central nervous system. It contains 12 pairs of centric cerebral nerve including the olfactory nerve, optic nerve and the spinal nerves spread through the abdomen, arms, legs.

If we see it in a bigger picture, from the synapse which is the interspace between one nerve to another during the process of transmission cercal nerves, and to the distal muscles, as along as the nerves are spread, the disease could be related to Neurology treatments.

In other words, Neurology is a department that treats all congenital diseases that outbreaks at various nervous systems such as the brain, spinal cord, nerve root, synapse, and the muscle.