The posterior column has a prominent role in the pain system , it is the first central relay in the nociceptive pathway. The first order afferent neuron carries sensory information to the second order neuron in the dorsal horn. The axon of the second order neuron, if it is a projection neuron and not an interneuron, then goes to the third order neuron in the thalamus . The thalamus is known as the "gateway to the cortex". The third order neuron then goes to the cerebral cortex . The afferent neurons are either A fibers or C fibers. A fibers are myelinated allowing for faster signal conduction. Among these there are A beta fibers which are faster and carry information about non-painful touch and A delta fibers which are slower and thinner than the A beta fibers. The C fibers are not myelinated and therefore slower.  C fibers that carry nociceptive signals can be divided into two types: fibers that contain neuropeptides , like substance P , and fibers that do not contain neuropeptides.  The two types terminate in very different areas. Non-peptidergic C fibers are linked to the skin, where they innervate the epidermis while peptidergic C fibers innervate other tissues and deeper parts of the skin.