While you certainly never anticipate being put in the position of having to use deadly force against another in Memphis, it can indeed happen. The difference between you facing a potential murder charge and your actions qualifying as self-defense depend on the situation you are in. In general, the use of force is justified when you and/or others feel reasonably at risk of being killed or seriously injured by another if you feel to act. A few of the exceptions of this rule have been detailed in the past; this blog post will go in greater depth in defining others.
Your own actions leading up to and during the incident in which you use deadly force in defense will go a long way in determining the outcome you may face. Section 39-11-611(e) of Tennessee's Criminal Offenses Code clearly states that you cannot use deadly force in response to action that you consented to. The same is true if you were attempting to provoke the person against whom force is used into an altercation. The only exceptions to this would be if, after engaging in the altercation, you made an attempt to walk away from it, yet your opponent continued to act against you.
Similarly, you are not allowed to use force against a police officer attempting to stop, detain or arrest you. Again, there is a recognized exception in cases where the officer's actions against you are excessive and unjustified, and you feel as though your only option at stopping their actions from escalating is to use force against them.