AMP Circuit (Buffer)
The output from the mic which comes in on MIC_IN_FA_P is going to have a relatively high impedance, i.e., it won't be able to drive very much current. The buffer amplifier is able to convert a low current on the input to a higher current on the output. 

C1735 AC-couples the MIC_IN_FA_P line to the DC bias, which is presumably in place so that the amp can be powered with only a single +DC rail. Similarly, C1742 AC-couples the output of the buffer to wherever it goes.