Which specialized cells are responsible for transmitting messages throughout the body?

neurons

epithelial cells

blood cells

muscle cells

Answer: well by process of elimination we can get are answer.

1 muscle cells, what is there function locomotion of your skeletal system and in turn your body.

2 blood cells, can clot blood due to platelets within/making up blood. Plasma carries nutrients excluding oxygen to cells. Red blood cells carry that good old Oxygen necessary for ATP production via the electron transport chain. (Don't be confused by this ATP can be made in other process like the Krebs cycle, glycolysis, ETC) Finally white blood cells include lymphocytes, granulocytes, monocytes, and macrophages.

3 epithelial cells, epithelial cells line the outside of your body and certain things inside your body there main function is pathogen and or virus protection.

So the only possible answer is nerve cells or neurons.