What is the definition or description of: receptor?

Receptor Def: An organ, cell or molecule that accepts an outside signal and causes an internal change. Eyes receive light, touch receptors send messages to the brain when stimulated by pressure and estrogen receptors bind Estradiol causing responses of normal breast, ovary and uterus cells to rising and falling levels of the female steroid hormones. Most of the time "receptor" refers to one of the molecular typ.

Info receiver: "receptor" can be viewed in a couple general contexts - physiologically, it is a specialized cell/group of nerve endings/tissue that changes stimuli to nerve impulses; biochemically speaking, a receptor is a subcellular molecular structure or site on either side of cell membrane that binds a particular neurotransmitter, hormone, antigen or drug.