1. Same signal -> different response in different targets

ex. epinephrine in heart cell causes increased heart rate, epinephrine in liver cell causes breakdown of liver glycogen

2. Fast Responses

signal pathways that act on proteins and structures that are already established and take seconds or less (ex. nerve cells, muscle cells, respiratory system)

3. Slow Responses

signal pathways that have to create new proteins and take hours or longer (ex. cell growth and development, digestion)

4. Endocrine signaling

long distance signaling used throughout the body, often hormones through blood stream

5. Paracrine signaling

signal molecule stays local and only affects targets in that area (ex. swelling, immune responses, tumor formation and growth, some fetal development)

6. Neuronal signaling

fast, specific pathways carried out by neurotransmitters

7. Contact-dependent signaling

cell signaling to a cell in contact, very localized, signal molecule is often membrane-bound (ex. fetal development)

8. Intracellular Receptors

small hydrophobic molecules can only get to these (ex. Nitrogen Oxygen (NO) does this because it is so small)

9. Cell-surface Receptors

more common, takes larger signal molecules that can't fit through a membrane

10. Signaling by protein phosphorylation

adding or removing a phosphate to turn on or off a signaling pathway inside the cell (ex. tyrosine kinases)