Medical Dictionary: N

narcolepsy: A sleep disorder marked by excessive sleepiness or sudden sleep attacks.

nasolabial folds: Lines or grooves leading from the nose to the outer corners of the mouth.

natural killer (NK) cells: Lymphocytes that are not B or T cells. NKs destroy cells that fail to display the right chemical “flags” signaling they are normal cells.

nebulizer: A device that takes a liquid form of medicine and converts it into a mist to be breathed in.

necrosis: Tissue death.

neoadjuvant therapy: Therapy with anticancer drugs or radiation given before surgery in order to shrink a tumor.

nerve block: One of several pain relief methods aimed at interrupting the function of nerves carrying pain. This technique involves injecting a local anesthetic or some other longer-acting agent into a nerve or nerves.

neuromuscular junction: A tiny space between the end of a nerve and the surface of a muscle.

neuron: A nerve cell, including its axon and dendrites.

neuropathy: A disease or condition affecting the peripheral nervous system; for example, diabetic neuropathy.

neuropathy: Impaired nerve function due to systemic damage of the peripheral nerves; may result from diabetes.

neuropathy: Nerve damage and resulting loss of sensation that can occur because of diabetes, alcohol abuse, vitamin B deficiency, and other disorders. Neuropathy may also develop with age.

neurotransmitter: A chemical, such as serotonin or norepinephrine, that permits nerve signals to bridge the gap, or synapse, between nerve cells.

neutropenia: An abnormally low number of white blood cells.

neutrophils: White cells, members of the phagocyte family of “gobbler” cells.

nitric oxide: A chemical released by the nerve endings in the penis when a man is sexually stimulated. This chemical prompts the release of other chemicals that dilate blood vessels in the penis, causing an erection.

nociceptors: Sensory nerve endings in which the sensation of pain originates.

nocturia: Regularly needing to urinate more than twice during the night.

nodule: A lump on the thyroid gland that sometimes contains active thyroid cells that produce thyroid hormone. Most nodules take up less iodine than normal thyroid tissue and make little, if any, thyroid hormone. Therefore 90% of thyroid nodules appear “cold” (demonstrate less than normal function) on thyroid tests that use radioactive materials.

non-ablative: Used to describe skin procedures that leave the surface of the skin intact.

non-REM sleep: The type of sleep that includes deep sleep, the period considered most important for preventing daytime fatigue.

nonsteroidal anti-inflammatory drug (NSAID): One of a class of drugs that reduce inflammation and pain.

norepinephrine: A neurotransmitter that constricts blood vessels and plays a role in the regulation of anxiety, mood, and responses to stress. Sometimes called noradrenaline.

NSAIDs: Nonsteroidal anti-inflammatory drugs, used to treat inflammation, fever, and pain. NSAIDs do not treat the inflammation of asthmatic airways. People with aspirin-sensitive asthma suffer flare-ups of symptoms after taking most NSAIDs. Aspirin, ibuprofen, and naproxen sodium are NSAIDs.

nucleus pulposus: The gel-like central portion of each intervertebral disk.

nutrients: Food-supplied substances that the body needs to survive.