Positive symptoms of schizophrenia, specifically hallucinations and delusions, are thought to be caused by hyperactivity of which neurotransmitter?

Dopamine.

Explanation:

Schizophrenia is a mental illness characterized by psychotic episodes and the inability to relate thoughts, feelings and actions, accompanied by delusions, hallucinations (auditory, visual, olfactory and tactile), incoherent thoughts, memory disorders and, in occasions, confusion. Dopamine is a hormone synthesized by the brain that acts as a neurotransmitter and allows the connection between neurons. Studies suggest that some of these alterations in mental functions are caused by an excess in the activity of dopaminergic synapses, that is, there is a hyperactivity in those connections where dopamine is produced and expelled, which range from the ventral tegmental area to the nucleus accumbens and the amygdala, which are the main ones responsible for synthesizing and expelling dopamine from brain reward systems.

the right side of the picture going down is:

polymerase

protein

transport vesicle

modified protein

the left side of the picture going down is:

dna helix

single-stranded rna

endoplasmic reticulum

ribosome

golgi apparatus

protein released from vesicle

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cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!