History: What does each track in a mixer have?

What does each track in a mixer have?

• An input, a gain, and a meter.
  Amazing!
• An input, routing, and gain.
  Routing is common, but not always...
• A gain module, a meter, and panning.
  Panning is common, but not always...
• An input, gain, and filtering.
  Filtering is common, but not always...