Cells in the human body that are the building blocks of the nervous system (the system that records and transmits information chemically and electrically within a person). Nerve cells, or neurons, are made up of a nerve cell body and various extensions from the cell body that receive and transmit impulses from and to other nerves and muscles. Nerve tissue in the breast makes breasts sensitive to touch, allowing the baby's sucking to stimulate the let-down or milk-ejection reflex and milk production.