Medulla oblongata: region of the hindbrain that joins the spinal cord to the cerebellum; one of the most important sites of autonomic nerve control

Medulla: area inside the cortex.

Meninges: protective membranes that surround the brain and spinal cord

Mineralocorticoids: hormones of the adrenal cortex important for regulation of salt-water balance

Motor neurons: neurons that carry impulses from the central nervous system to effectors; also known as efferent neurons

Myelin sheath: insulated covering over the axon of a nerve cell

Negative feedback: process by which a mechanism is activated to restore conditions to their original state.

Nephrons: functional units of the kidneys.

Neurilemma: delicate membrane that surrounds the axon of some nerve cells

Neurons: nerve cells that conduct nerve impulses

Neurotransmitters: chemicals released from vesicles into synapses

Nodes of Ranvier: regularly occurring gaps between sections of myelin sheath along the axon

Norepinephrine: also known as noradrenaline, it initiates the fight-or-flight response by increasing heart rate and blood sugar

Olfactory lobes: areas of the brain that process information about smell

Osmoreceptors: specialized nerve cells in the hypothalamus that detect changes in the osmotic pressure of the blood and surrounding extracellular fluids (ECF)

Ovulation: release of the egg from the follicle held within the ovary