National Geographic - USA (2020-01)

Peripheral

sensory neurons

Nociceptors

Nerve

bundle

Axons

Axonal m

embrane

Axon

Pore Sodium ions Small molecules

INACTIVE OPEN CLOSED INACTIVE OPEN

HOW THE BRAIN FIGHTS PAIN

Pain has a purpose: self-preservation. It signals to the brain that the body is in danger and

needs to react. Pharmaceuticals can suppress those signals and ease pain, but new research

offers the hope that the body’s own systems—made up of an ascending pathway and a

descending one—can be amplified to reduce pain organically and with minimal side effects.

A MESSAGE TO THE BRAIN

Acute pain calls attention to actual or poten-

tial tissue damage. Signals to the brain travel

an ascending pathway to motivate the body

to respond quickly.

THE PROMISE

OF PAIN GATES

Multiple “pain gates,”

including the sodium

channel Nav1.7, regulate the

passage of sodium ions into

axons, which can cause pain.

Obstructing the gates with

molecules via drugs or gene

therapy may help doctors

tailor pain treatment to

individual patients.

Sensing pain

Neurons called nociceptors

respond to external stimuli,

such as sharp objects, fire,

or chemical reactions.

Transmitting pain

Electrical signals are routed

from the nociceptors to axons,

nerve fibers that relay the

signal to the spinal cord.

“A beta” fibers

With thick sheaths, these transmit

touch, pressure, and vibrations.

“A delta” fibers

With thin sheaths, these are first

to sense quick, acute pain signals.

“C” fibers

Without sheaths, these sense slow

pain: heat, burns, and dull aches.

Anatomy of a nerve

Nerves include bundles of axons. These fibers,

reaching from nerve cells called neurons,

conduct electrical activity. Different sensations

travel on separate axonal fibers.

As a neuron fires, electricity- sensitive pores along its surface

cycle through three states: inactive, open, and closed.

An attached particle

blocks the pore in

the inactive state. In the open state

sodium ions can enter

the unblocked pore. Some molecules

(naturally occurring or

synthetic) can block

the top of the pore.

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