Headaches: 50% of the blood supply to the brain travels through the vertebra via the vertebral arteries.  When this is compromised by subluxation of the vertebra, headaches can result.  The head is also enervated by the upper cervical nerves.  Migraine Headaches:  The muscle coat or covering which controls the diameter of the blood vessels to the brain goes into spasm with this condition.  This defines the prodromal sensation of when the migraine sufferer knows the migraine is coming. The muscle coat fatigues and the blood vessel gets flaccid as a result, causing a throbbing of the vessel with each heartbeat, creating severe, debilitating symptoms which often include nausea and light sensitivity.  This condition often responds dramatically to Chiropractic care.