1. Autocrine signaling: Cells release signaling molecules that bind to receptors on their own cell surface, leading to a response within the same cell.
2. Juxtacrine signaling: Cells directly communicate with each other by physical contact, without the need for diffusible signaling molecules.
3. Synaptic signaling: Neurons release neurotransmitters at synapses, which bind to receptors on the postsynaptic cell to transmit signals.
4. Endocrine signaling: Cells release hormones into the bloodstream, which travel to target cells in distant parts of the body to elicit a response.
5. Neuroendocrine signaling: Neurons release hormones into the bloodstream, acting as both neurons and endocrine cells.
6. Neurotransmitter signaling: Neurons release neurotransmitters at synapses to transmit signals to target cells.