Receptors and channels in pain

Published on April 2, 2014   45 min

Other Talks in the Series: Synapses, Neurotransmitters and Receptor Channels

So I'm Professor Tony Dickenson from University College London. And this presentation is based on receptors and channels in pain, how the integrated function of the nervous system, subjects to painful messages, deals with these external events.
Pain is an intriguing example of understanding and trying to gauge how external events, in this case from the body, impact upon function of the central nervous system. So peripheral events, peripheral sensory fibers, project into the spinal cord. The spinal cord then sends messages up to the higher centers. And in the case of pain, of course, it's an individual, personal experience that is built up. But what goes up, also comes down. And so the higher centers of the brain are able to alter mechanisms within the brain stem and change what we call descending controls, which, in turn, return to the spinal cord. And so the higher centers have the ability to modulate events at the first synapse within the spinal cord.
So if we look in a little bit more detail at these pathways, at the bottom left, incoming peripheral nerves, which are highly specialized, many of them respond to nonpainful stimuli, such as touch and temperature. But then we have a large number of pain-sensing fibers. And here there are a remarkable number of receptors and channels that respond to heat, to mechanical, and to chemical stimuli, all of which are painful. These are altered by damage to nerves themselves, or, indeed, damage to tissues, and they will input into the spinal cord. The spinal cord neurons integrate these messages, often, and unfortunately in the context of pain, amplify these messages and send them on to the higher centers of the brain. So at the top right, we have the cortex, the homunculus. These columns of neurons responding to particular parts of the body, and neurons within these columns are able to code the intensity of the stimulus. So our ability to locate pain and describe it are cortical mechanisms. But at the top left, there is the limbic brain and an equally important input from the spinal cord into these areas. The limbic brain's function is to control mood, to generate the sleep/wake cycle, to respond to external events. And so it's not surprising that ongoing painful inputs into these parts of the brain disrupt this function and lead not just to pain, but to fear, anxiety, and sleep problems that are common in patients. And then, from these limbic parts of the brain, we have the descending controls that return to the spinal cord. And so cognitive, proprioceptive, and mood changes occurring in the higher centers have the ability to modulate transmission at the spinal cord, and they can enhance it, or, in fact, they can inhibit it.