The Gate Control Theory of Pain

The Gate Control Theory of Pain
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  • 0:02 What Is Pain?
  • 1:38 Pain Transmission
  • 2:36 Gate Control Theory
  • 6:37 Lesson Summary
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Lesson Transcript
Instructor: Sarah Lawson

Sarah has taught nursing courses and has a master's degree in nursing education.

The gate control theory of pain is a famous theory about how and why pain is perceived by humans. Learn more about this theory, and test your knowledge with a quiz.

What is Pain?

Everyone knows pain is a bad thing, right? Well, actually it is a good thing even though it is a bad or unpleasant feeling. In this lesson, we will discuss the gate control theory of pain, but before we do that, you need to have an understanding of what pain is.

Pain is an unpleasant feeling that can range from mild to excruciating and is caused by diseased or injured tissues in the body. Dull, achy, sharp, stabbing, shooting, burning, or a numb sensation are some of the words patients use to describe their pain. Since it is impossible for one person to experience another's pain, it can only be described by the person experiencing it. Patients are treated with the assumption that pain is present when they say it is and on the level that they say it is.

Although there are many sources and causes of it, pain can be divided into two main groups: nociceptive pain and neuropathic pain. Nociceptive pain is the result of tissue damage or injury. Pain from a broken bone, stubbing your toe, or burning your forehead with a curling iron are examples of this type of pain. Neuropathic pain occurs when there is damage or disease that affects the nervous system. Diabetes, limb amputation, and cancer are all conditions that can cause this type of pain.

Pain Transmission

Pain signals are transmitted to the spinal cord and the brain by primary afferent axons, which are nerve fibers that are connected to receptors in the skin, muscles, and organs. These axons vary in size and may be myelinated or unmyelinated. Myelin is insulation to nerve fibers that helps transmit pain stimulation quickly.

These primary afferent axons are classified into groups based on their size; these groups are known as A-alpha, A-beta, A-delta, and C-nerve fibers. All of the A nerve fibers are myelinated, while C fibers are unmyelinated. The thickness of a fiber determines how quickly it transmits information; the thicker the fiber, the faster it can transmit information.

The Gate Control Theory of Pain

The gate control theory of pain was written in 1965 by Patrick Wall, a neuroscientist and professor, and Ronald Melzack, a psychologist and professor. The gate control theory of pain is a scientific theory about the psychological perception of pain. According to the theory, pain is a function of the balance between the information traveling into the spinal cord through large and small nerve fibers.

Small nerve fibers carry nociceptive (pain) information. Large nerve fibers carry non-nociceptive (do not transmit pain) information. Small and large nerve fibers synapse on projection cells (P) to the brain and on inhibitory interneurons (I) within the dorsal horn of the spinal cord. The firing of the projection neuron signals pain to be perceived by the brain. The inhibitory interneuron decreases the chances that the projection neuron will fire.

Let's break down what the theory is saying step-by-step:

  • Small and large nerve fibers will remain inactivated without stimulation, and the inhibitory interneuron (I) will block the signal in the projection neuron (P) that connects to the brain. This means the gate is closed, and there is no pain.
  • Large nerve fibers are activated with non-painful stimulation. This activates the projection neuron (P) and the inhibitory interneuron (I), which blocks the signal in the projection neuron (P) to the brain. This means the gate is closed, and there is no pain.
  • Small nerve fibers are activated with painful stimulation. This activates the projection neurons (P) and blocks the inhibitory interneuron (I). Since the inhibitory interneuron (I) is blocked, it cannot block the signal from the projection neuron (P) to the brain. This means the gate is open, and there is pain.

Not all pain signals are free to reach the brain as soon as they are generated. Pain signals encounter neurological gates at the spinal cord level, and these gates determine whether the pain signal reaches the brain or not. This means that pain is perceived when the gate gives way to strong pain signals, and it is less intense or not perceived at all when the gate closes and makes signals unable to pass.

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