The intercostal muscles are controlled by the intercostal nerves. The medulla tells the intercostals when to contract by sending messages through these nerves. The intercostal nerves are not as well protected as the phrenic nerves. The intercostal nerves run along the thoracic spine (which is in the upper to middle back) and connect to the intercostal muscles. This means that if a person injured their thoracic spine, they might not be able to use their intercostal muscles. They would then lose 30% to 40% of their ability to breathe. However, since the nerves that control the diaphragm are much farther up in the spine and better protected, the person would still be able to use their diaphragm to breathe. They would still have 60% to 70% of their ability to breathe.