How to find command used to implement “Volume Up” shortcut in Ubuntu 18.04?

In Ubuntu 18.04, there are keyboard shortcuts for “Volume down” and “Volume up”, which, on a laptop computer, are usually bound to the media keys (e.g., XF86AudioRaiseVolume).

keyboard-shortcuts

When I press the shortcut, the volume increases and an OSD notification indicates the new volume level.

osd-notification

Question How can I find out what command is being run by GNOME to implement “Volume up” and “Volume down”, i.e., the command which increases the volume and shows the volume pop-up? I can write xdotool key XF86AudioLowerVolume in the terminal to simulate the behavior, but that still doesn’t tell me what commands are being run. Any help would be appreciated…