STEP 1: Determine the device id (the device name should be something with touchpad or glidepoint)
STEP 2: Disable it (e.g. here the device id is 13)
xinput set-prop 13 "Device Enabled" 0
you can also dis/enable some other devices.
You may run the command during session startup
Original link: https://help.ubuntu.com/community/SynapticsTouchpad