Astrocytes provide support and nutrition to neurons within the brain and spinal cord. Myelin sheath insulates the axons of some neurons which allows them to conduct impulses faster. Nerve fibers are single nerve axons that are surrounded by a sheath of connective tissue. Nerves themselves are cordlike structures that transmit nerve impulses.

C fibers are associated with chronic pain perception because they transmit "slow pain". This is due to the fibers being unmyelinated. In addition, these fibers send projections to the limbic system and the thalamus which causes the brain to develop chronic pain associations.

Both A delta and C fibers are associated with the perception of pain. This can be broken down more specifically to A delta fibers that are slightly mylinated and carry "Fast" sharp pain that is immediately felt. While C fibers carry "slow" pain due to being unmyelinated and is associated with chronic pain.

The dermatome responsible for sensation at the level of the nipple is T4.

C2 is responsible for sensation at the posterior half of the skull "cap" and C4 at the level of a low collar shirt. T10 is responsible for sensation at the level of the navel (to remember this think bellybutton...belly buTEN). L4 includes the kneecaps.