Direct Contact
Direct contact is when molecules on the plasma membrane of one cell contact the receptor molecules on an adjacent cells. Direct contact is especially important because many interactions between cells in early childhood development occur by means of direct contact.
Animation-
http://media.pearsoncmg.com/bc/bc_0media_bio/blast/index.htm?signaling_direct
Animation-
http://media.pearsoncmg.com/bc/bc_0media_bio/blast/index.htm?signaling_direct