when input Vin reach to -2.5, output voltage is lowest, at the time the current 200uA flow through the MOS and the resistor 10kOhm
when input Vin reach to +2.5, output voltage is highest, the MOS cuts off, the current 200uA flow into the resistor 10kOhm
when input Vin step from -2.5 to +2.5, SR+ equal to the current which flow through the MOS formerly divided by the capacitor 50pF(the current can be less than 200uA)
when input Vin step from +2.5 to -2.5, the MOS reach to ON state from Cut-off state, and can draw very large current, so SR- is very large
for the MOS work in saturation region, the output resistor is 1/gm approximately
good luck