Me Talk Pretty – Nociceptive flexion reflex (NFR)

SU11_GTY_sb10064912a-001_a_hzKnown on the streets as the withdrawal reflex, NFR refers to our body’s involuntary, ninja-quick neuromuscular response to pain. It’s our super sexy physiology term of the week and quite possibly our spiciest one yet. I even like saying it out loud (sometimes in a French accent).

Isn’t it nice to know that our body has our best interests in mind despite our worst judgment? If you’ve ever not been paying attention for a moment and let your hand stray a little too close to a hot stove (like who hasn’t) then it’s highly likely that you’ve witnessed your NFR in action. You probably yanked your hand away at what felt like the same instant you experienced pain. We perceive pain and withdraw from it simultaneously and our body does this seamlessly. If you’re the least bit skeptical just think back to that scolding hot bowl of chili con queso you dropped. YOU didn’t drop it. Your hands let go of it.

What experience could be more direct than pain? In reality, pain may not be as direct a phenomenon as you might think. When it comes to our involuntary withdrawal from pain there are at least 3 stages that occur. Once any part of your body is injured nerves in the vicinity transform that moment into a lightning quick electro-chemical signal. That signal has to take a journey from the site of the injury to the spinal chord. A new signal is sent from the spinal column to the appropriate muscles to flex and manipulate that stray body part away from the pain stimulus. Perhaps one of the reasons this process is so blindingly fast is the fact that the nerve control center in this case is the spinal chord and not the brain.

Let me set the scene…

It’s a perfect July afternoon. The grills are out. The air is saturated in honeysuckle flowers and spicy, charcoal kissed meat. You’re barefoot in the grass, loving life in your favorite shorts and a barbeque stained t-shirt. Oh yeah, you know what I’m talking about. You have a half-eaten bratwurst in one hand. Your other arm is free, innocently reaching out to grab the Frisbee that your friend just tossed to you (you crazy kids). She tossed it high. You take a step back unaware that laying in wait in the grass is a jagged piece of gravel just begging to be stepped on by bare feet. You plant your foot on the rock…

1) Tiny, branching pain receptors suspended within the epidermal layer of your heel, like tree roots, transmit an electrical signal up a long network of neuron fibers that form an intricate junction at the spinal column not unlike a downtown D.C. intersection.

2) Once the message reaches the spinal column an alpha motor neuron sends a signal back down your leg.

3) The signal from the alpha motor neuron reaches a neuromuscular junction in the hamstrings of your leg, initiating their contraction. This flexes the knee, pulling your foot off of the ground to minimize damage to the soft tissue of your foot so you can frolic in the grass another day.

Stay curious, stay classy, and never stop learning my friends 🙂

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