Neural control of ventilation (breathing) is a special case that behaves like other autonomic functions, but where the main control elements are not autonomic neurons. Areas of the reticular formation in the lower brainstem receive viscerosensory information about the oxygen and carbon dioxide status of the body, and generate commands to control breathing. Axons descend from this area to synapse on lower motor neurons in upper spinal cord levels, whose axons travel in nerves to the skeletal muscle of the diaphragm, as well as other skeletal muscles of the torso that may participate in ventilation. This system operates unconsciously most of the time, but it can also be controlled voluntarily. Lesions of the lower brainstem or the upper spinal cord may cause the loss of neural control of ventilation. Autonomic neurons are involved in other aspects of lung function, such as dilation or constriction of the airways.