You can send new ticket notices to all members of a department, from Admin Panel - Settings, scroll down to 'Alerts & Notices'
There is no option to send all ticket responses to all department members, since that would, under normal circumstances, create a lot of email and confusion. If that's what you need to do, I would suggest setting up an email forwarder on your mail server that forwards to multiple addresses and then having new message alerts sent to that forwarder, or simply use that forwarder as the department email.