For years, investigators have searched for the message that the receiving cell sends backwards.

They said they had evidence that the cell sent the money to cells in Pakistan that were loyal to Al Qaeda.

There are multiple ways that a cell can send signals to other cells.

Every cell knows what to do with this message (increase heart rate, constrict blood vessels, dilate air passages) and does not sent a confirmation.

This cell then sends a message back to the near end.

That cell uses an electrical charge to separate the oxygen from the carrier and sends it back to pick up more oxygen.

Each cell sends messages to other cells only when this stimulus, such as a certain kind of edge, is perceived.

Different cells send signals, flag down messages, kill other cells or eat the remains of conquered pathogens.

The solar cell collects the light, turns it into energy and sends it through a diode to the battery.

These molecules activate sensory cells to send pain signals to the brain.