The heater lamp is an incandescent halogen lamp actually running at 200 centigrades and heating the roller by radiations and also one most likely to fail without giving explicit message, the indication when the lamp is failed is when the fuser doesn’t get hot you can use the multi meter to test it integrity. Set the multimeter at 100 k ohm scale don’t touch the lamp.
2 .upper roller or heater roller
The upper fuser roller is an hollow aluminum tube the inner surface of the roller is coated to absorb light and heat. The outer couting is a fluorocarbon polymer such as Teflon or atleast a halogenated hydrocarbon.
3.Lower fuser roller
Its just a silicon rubber roller on a metal shaft its held in thight contact with the upper roller by springs
The thermistor is simply a resistor its usually held against the hot roller just before the point where it will touch the paper a pair of low current wires come from thermistor.
A pair of high current leads for its heater these run through a thermal cutout which prevent the fuser overheating cutting off the main power.