system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What causes anger?

Neurologically ?
gpt
Let me try to tie some of these responses together.

The connection between the brain and the body is a constant circle. The brain sends signals to our body and the body sends information to the brain. The amygdala is the area of the brain that is responsible for determining the emotional value of those incoming stimuli. Although inhibition is possible via the neocortex, emotional stimuli can illicit strong responses like the "fight or flight" response. 
Fight or flight is an operation of the sympathetic nervous system, which normally maintains homestasis within the body, however during the F or F response the SNS slows blood flow to many areas of our body that would not be useful in a F or F situation. One of these areas is the frontal lobes, which are responsible for inhibition, critical, and logical thinking, with these shut down our body is ready to defend or run. 
Anger theoretically can arise when a person is confronted with a stimuli that has illicited an emotional response in the past, and with the frontal lobes not functioning at full capacity the person may lash out in verbally or physically, which is percieved as anger.
Think of a time when someone made you so angry you did something irrational, childish, or violent. Thats your brain trying to defend itself from something that was damaging in the past.

TL;DR
The amygdala, the part of the brain that determines the value of emotional stimuli, can initiate the fight or flight response via the sympathetic nervous system This in turn shuts down many of the higher brain functions, which can result in a verbal or physical outburst.