system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do hallucinogens make you hallucinate if they are just binding to the same dopamine and serotonin receptors as other drugs. Why and how do shrooms and lsd and stuff physically alter your vision and make you see stuff you dont see?
gpt
Neurotransmitters are critical in the process of creating neural "pathways", the transmission of electrical signals from synapse to synapse to synapse.  Part of that process is for the neurotransmitters to "bind" (attach) to certain types of receptors on the synapses.  LSD and other hallucinogens disrupt how this process is supposed to work, as they can bind to the receptors but don't work like the natural neurotransmitters are supposed to.  
   
In this way, they actually create spurious pathways in the brain that would not otherwise occur.  In addition, in some parts of the brain they appear to inhibit the operation of the normal pathways, reducing the function of those areas. Part of that action seems to inhibit some of the sensory filtering that normally occurs in the thalamus (IIRC), so other areas of the brain are bombarded with information they usually doesn't have to deal with.  This may cause the formation/use of more pathways than normal, or at least, different pathways.