Neurological function is the ability of neurons to send, receive, and process signals accurately, forming the basis of sensation, movement, thought, and the regulation of bodily systems. It depends on intact cell membranes, reliable ion gradients, and a steady supply of neurotransmitters and energy. In nutrition, several nutrients are directly tied to keeping this system running: thiamin, vitamin B6, and vitamin B12 support nerve metabolism, iron carries the oxygen neurons need, and iodine is essential for the brain development of the fetus and infant. Deficiency produces recognisable disorders, from the peripheral neuropathy of beriberi and B12 depletion to the irreversible cognitive damage of congenital iodine deficiency. Alcohol excess and certain toxins impair neurological function by damaging neurons and myelin directly.