What are the first three waveform components at the onset of Brainstem Auditory Evoked Responses (BAERs)?

The first three waveform components observed at the onset of Brainstem Auditory Evoked Responses (BAERs) are indeed cochlear microphonics, summating potential, and the action potential (AP) of cranial nerve VIII (CN VIII).

Cochlear microphonics are electrical potentials generated in the cochlea due to hair cell movement within the organ of Corti, reflecting the acoustic stimulus. They represent the first response and indicate the functioning of the outer hair cells. The summating potential follows and is generated from the interaction of the cochlear microphonics and the neural responses, providing information about the overall auditory system's status. Finally, the action potential of CN VIII confirms the presence of the auditory nerve's response to the stimulus, making this sequence critical for evoking auditory processing in the brainstem pathways.

Understanding this order is important for interpreting BAERs effectively, especially in clinical settings where monitoring the integrity of auditory pathways during surgeries is crucial.