The sympathetic nervous system, like the rest of the nervous system, works through a network of linked neurons. Postganglionic neurons mostly release noradrenaline in response to this stimuli (norepinephrine). Prolonged stimulation might cause the adrenal medulla to produce adrenaline. The release of these hormones into the blood causes specific changes to occur in most organ systems of the body. For example, the heart beats faster, the lungs breathe more deeply, and the liver releases glucose into the blood stream for use by other tissues. Sympathetic nerves arise from two primary sources: the cranial nerves and the spinal cord. The cranial nerves are numbered according to which part of the head they control. The twelve major cranial nerves all contain sympathetic fibers that go to different organs including the tongue, lips, ears, nose, eyes, brain, and neck muscles. The fibers from each nerve communicate with the central nervous system (CNS) via one of three pathways: anterior, posterior, or lateral. Anterior ganglia connect directly with the CNS via the anterior horn cells of the spinal cord. Posterior ganglia receive input only from neighboring ganglia using synapses in the dorsal root entry zones of the spinal cord. Lateral ganglia receive input only from adjacent ganglia using synapses in the ventrolateral funiculi of the spinal cord. Spinal sympathetic nerves originate in the brain and spine.