Nociceptive circuits anatomy
Ever wondered how your body senses harm and generates pain? What is "pain" anyway? While we all have an intuitive understanding of what it means to feel pain, the process of detecting harmful events is both complex and fascinating.
This is part 1 of a lecture on Spinal Cord Circuits and Pain Gating that I give at the University of Zurich. Here you will find an overview of the anatomy of neuronal circuits that allow us to detect and process potentially harmful stimuli, centered around the spinal cord.
In a few simple slides, the different components of nociceptive circuits from the periphery to the brain are summarized with up-to-date information that includes the latest findings in this field.
While most people use the word pain an nociception almost interchangeably (including people in the field), they really mean different things:
Nociception is the ability of the body to sense potential harm, while pain is conscious and encompasses a sensory, emotional and cognitive aspect. There can be nociception without pain, during sleep or coma for example, or pain without nociception. Have you ever heard about phantom limb pain?
Nociceptive information collected from the periphery by primary sensory neurons is first integrated in the spinal cord, which not only sends processed signal to the brain but also receives plenty of inputs from it. In fact, as we will see later in the lecture, there are many factors that influence nociception at the spinal cord and make us either more sensitive to painful stimuli, or give us the ability to shut down nociception altogether.
First, some important definitions and a word of caution when using the word "pain"
The first neurons to sense noxious events are specialized neurons called nociceptors.
There are two main types of fibers that convey noxious information, with differnt properties. That is why bumping a toe on a door will hurt immediately, but anohter throbbing only comes a second or two later, because the transmission speed for these fibers is onlt 1 to 2 meters per second.