magnocellular neuron

Magnocellular neurons are the large hypothalamic cells that supply the posterior pituitary with its two hormones. Picture them as long-distance couriers: their cell bodies sit in the hypothalamus, but their axons reach all the way down into the back of the pituitary, where they release hormone directly into the blood. The name simply means big-bodied cell.

These neurons cluster in two hypothalamic nuclei, the supraoptic and paraventricular nuclei. One population makes oxytocin and another makes vasopressin; each peptide is synthesized in the cell body, packaged into granules, and transported down the axon to the posterior pituitary. There it waits until an electrical impulse triggers calcium-dependent release into the circulation, the textbook case of neurosecretion.

Magnocellular neurons are contrasted with the smaller parvocellular neurons, which secrete releasing hormones into the portal system to control the anterior pituitary. The two cell types embody the two ways the hypothalamus speaks to the pituitary: directly to the posterior lobe, and indirectly, through portal blood, to the anterior lobe.