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Metro Science: How itching works, the real vampires, and sound smart with neuroscience

This week's science section takes you inside a real head-scratcher

Woman Scratching Her Arm on Isolated White Background

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Woman Scratching Her Arm on Isolated White Background

ANATOMY OF AN ITCH

The sensation of itch, more properly called pruritus, is phenomenally complicated.

But all itches have a few things in common: They occur in the skin and mucous membranes (such as inside the nose and mouth), not internal organs, and they cause the undeniable impulse to scratch.

SKIN

An itch starts with a pruritogen, or irritant, usually on the skin. It may come from inside the body, like a histamine chemical released during an allergic reaction, or outside the body, like a pesky mosquito.

Pruritogens send a signal to primary sensory neurons — nerve cells in the skin. These contain receptors, including nociceptors, which also sense pain.

SPINAL CORD

When those receptors receive the itch signal, they release chemicals called neurotransmitters that convey the message across the nervous system through the spinal cord.

BRAIN

Finally, the signal arrives at the brain. That's the organ that makes you consciously feel itchy and want to scratch.

One particular neurotransmitter, neuropeptide natriuretic polypeptide b, or Nppb, is released during itching, but not pain. The discovery of Nppb’s role helped bust the old idea that itching is simply low-level pain.

REFLEX

We developed scratching reflex as a response to itch because it’s advantageous – scratching can remove an insect or other source of irritation. But it also suppresses the sensation of itch.  Emerging research shows scratching stimulates the release of different neurotransmitters in the spinal cord that block the itch-producing ones. Functional MRI studies also show that the parts of our brain associated with rewards and pleasure are activated when we scratch: That's why it feels so good.

Science story: Twilight is real?

Who drinks blood and always avoids sunlight? Not just Edward Cullen. It’s also, maybe once upon a time, people with Erythropoietic protoporphyria (EPP). The authors of a new study in Proceedings of the National Academy of Sciences on EPP’s genetic origin suggested, somewhat fancifully, that in ancient times people with the disorder may have coped by drinking blood and staying indoors until dark. Sufferers blister (but don’t sparkle) in the sun and experience severe anemia.

Sound Smart: Mirror Neurons

DEFINITION: A mirror neuron is a brain cell that is activated both when an animal acts and when the animal observes the same action performed by a different animal.

USE IT IN A SENTENCE: Ooof. That video of Deborah getting her leg amputated hit me right in the mirror neurons.

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