Quick Answer. The function of motor neurons is to release the neurotransmitter acetylcholine, which are released at a junction known as the neuromuscular junction, that bind to postsynaptic receptors, causing the muscle fiber to respond and result into a muscle movement.
The frontal lobe is what really sets us apart from animals, which controls one important aspect of humans: Self awareness. The thinking in terms of I am.. Animals don't do that. (although they DO have sex for pleasure.
The reason for. the variation we see is that organisms, like humans, have different forms of genes, which we term. alleles. These alleles code for different proteins, and therefore result in the expression of different. traits or phenotypes.