why do nasty stuff triggers the brain to vomit?

Answer 1

We evolved from creatures that were foragers, grazers. When we moved from one venue to another, we found new plants to eat. Some of them would be unfamiliar. Our bodies evolved to improve our survival by developing the ability to eject food items that cause bad reactions in the lining of our stomachs. This is almost never a brain function. It is a reflex from a brain-stem function. (Saying "brain" function and saying "brain-stem" function are NOT the same.)

Diarrhea is the other side of this process. Any time we have something inside of us that causes the sensitive linings of our stomachs and intestines to react, we expend body water to flush that stuff out of us. One way or the other.

Which is why you will be very thirsty for a while after either method of ejecting stuff from your gastrointenstinal tract.

Answer 2

Vomit at brainstem level, is achieved by:

1.- Awareness of the eaten stuff (appearence, color, apparent consistency), and knowledge of origin.
If we do ignore the origin and the ingested stuff tastes well, no vomit will be produced (suppose you ingest, say, for instance, mushrooms that were cultivated in a filthy environment, or what you are eating are culturally not accepted, such as ox fried testicles, hard boiled sheep eyes, eaten in other cultures), our brain cortex, will trigger a response, (descending response), to the dorsal nucleus of the vagus in the back of the medula oblongata (brainstem), giving an intense vagal reaction, that generally ends up in vomit, even when we are eating "nasty stuff" for our standards..
This is what we call the "cortical" vomit, because its regulated by the areas of the brain cortex that are CONCIOUS of the kind of food or stuff we do ingest, even when we do know what we are eating after we starting to do so..(or even when somebody tells us a joke or a lie about the origin of what we are eating)

2.- The second class, is the peripheral vomit (ascending stimulus) that is caused by direct irritation of he stomach walls of the stomach or duodenum, just as it happens with rotten cheese, metallic residues of food (like cadmium), and solanine from green or budding potatos....just to mention a few.....
In this case, there is a mild toxin that triggers the vagal stimulus, from the irritation to the stomach or higher gut (duodenum), via the vagus nerve, to the brainstem, and this provokes vagal reaction, contraction of the smooth layer of muscle of the stomach.....and vomit---

As youu can see, we have TWO causes for vomiting stuff that can be harmful physically, or culturally unacceptable (for instance, raw fish, which is part of sushi, wont make a native japanese to feel any sense of nausea).......

Answer 3

A few friends of a Muslim mixed pork with meat and fed him without informing him . Half an hour after he finished eating ,they told him the truth. Muslim started vomiting and continued for half an hour.
Psychic vomiting is also is observed among pregnant women (Do they subconsciously dislike pregnancy? )

Answer 4

It's an autonomic defense mechanism to protect us when we're eating...

We have evolved with some "automatic reflexive" defenses against choking, or ingesting substances that would harm us...thus...

The "vomit trigger" within us...

Answer 5

me brain never vomit, my belly do dough