GATE CONTROL THEORY OF PAIN

What occurs at the cellular level when pain is experienced? The gate control theory of pain, by P. D. Wall and Ronald Melzack, offers a useful model of the physiological process of pain. Gate control is recognized as a major pain theory.

According to the gate control theory, pain is a balance between information traveling into the spinal cord through large nerve fibers and information traveling into the spinal cord through small nerve fibers. Without any stimulation, both the large and small nerve fibers are quiet, and the substantia gelatinosa (SG) blocks the signal to the transmission cell (T cell) connected to the brain. The “gate is closed,” and there is no pain. With pain stimulation, small nerve fibers are active. They activate the T-cell neurons but block the SG neuron, making it impossible for the SG to block the T-cell transmission to the brain. The result is that the “gate is open”; therefore, there is pain. In other words, pain is experienced whenever the substances that tend to propagate a pain impulse across each “gate” in a nerve pathway overpower the substances that tend to block such an impulse.

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The gate control theory of pain transmission

FIGURE. The gate control theory of pain transmission. The substantia gelatinosa (SG) accepts input both from large-diameter (nonpain) and small-diameter (pain) nerves. Based on the rate of input, the SG allows either the pain or nonpain stimulus to be passed on to the transmission cell (T cell) and up to the brain. Because nonpain impulses travel faster than pain impulses, stimulation of nonpain fibers can override the transmission of pain. In addition, the brain has an inhibiting influence both on the SG and the spinal cord that can work to limit the perception and reaction to pain. (From Starkey, C: Therapeutic Modalities for Athletic Trainers. FA Davis, Philadelphia, 1993, p 28, with permission.)

Studies of coping factors support a wider version of the gate control theory. These factors are to be considered before determining treatment for pain, and they raise a number of questions.

READ:   EFFECTIVE PAIN MANAGEMENT
  1. How well is the client experiencing life?
  2. Does the client have pain, and if so, does he or she think that it is under control?
  3. Does the client feel adequately informed about the painful condition?
  4. Is the client occupied? How does the individual fill his or her time?
  5. Is the client coping with other problems?
  6. Does the client feel dissatisfied with his or her past life, or does he or she have any substantial regrets?
  7. Are there any reasons why the client may not be coping?

Answers to these questions may help determine the best treatment protocol for pain.

WHAT IS PAIN? Definition of Pain In dictionaries, pain (ICD-9: 780.96) is defined as a sensation of hurting or of strong discomfort in some part of the body, caused by an injury, a disease, or a functional disorder and transmitted through the nervous system. A nurse, Margo McCaffery, who worked for years with clients in pain and conducted extensive research in the field of pain, defines pain as whatever the experiencing person says it is, existing when he or she says it does. This definition is perhaps the most useful because it acknowledges the client’s complaint, recognizes the subjective nature of pain, and implicitly suggests that diverse measures may be undertaken to relieve pain. The IASP and the American Pain Society (APS) define pain as an unpleasant sensory and emotional experience arising from actual or potential tissue damage or described in terms of such damage. Again, this definition further confirms the multiple components of pain in a person’s psychological and physiological exist...
PAIN AND ITS TREATMENT MODELS Pain affects everyone at one time or another. Many diseases and disorders of the human body are accompanied by pain. It is feared by many people, as much as or more than the disease itself. What is pain? What purpose, if any, does it serve? What happens in the body when a person feels pain? How is pain assessed? What are the different types of pain? Can pain be treated? If so, how? These are some of the questions addressed in this chapter. Pain is an expanding science, and an increasing number of specialty clinics are emerging. The International Association for the Study of Pain (IASP) identifies the following four models for pain treatment: Single service clinics are normally outpatient clinics providing specific pain treatment with the goal to reduce pain. These do not provide comprehensive assessment or management. Examples include a nerve block clinic and a biofeedback clinic. Pain clinics also are outpatient, but their focus is mainly on diagnosis and management of indivi...
Back pain Prevention The majority of patients responding to basic extension and flexion principles of treatment have been educated in the means of achieving pain relief and restoring function. They have carried out the self-treatment procedures and have to a large extent become independent of therapists. Following successful treatment it requires little emphasis to convince patients that if they were able to reduce and abolish pain already present, it should also be possible to prevent the onset of any significant future low back pain. Of all the factors predisposing to low back pain only postural stresses can be easily influenced and fully controlled. We must develop this potential ingredient of prophylaxis to the full. The patient must understand that the risks of incurring low back pain are particularly great when the lumbar spine is held in sustained flexed positions; and that when the lordosis is reduced or eliminated for prolonged periods, he must at regular intervals and before the onset of p...
Spine Health. PROCEDURE 16 — CORRECTION OF LATERAL SHIFT This procedure has two parts: first the deformity in scoliosis is corrected; then, if present, the deformity in kyphosis is reduced and full extension is restored. The patient, standing with the feet about thirty centimeters apart, is asked to clearly define the areas where pain is being felt at present. The therapist stands on the side to which the patient is deviating and places the patient’s near elbow at a right angle by his side. The elbow will be used to increase the lateral pressure against the patient’s rib cage. The therapist’s arms encircle the patient’s trunk, clasping the hands about the rim of the pelvis. Now the therapist presses his shoulder against the patient’s elbow, pushing the patient’s rib cage, thoracic and upper lumbar spine away while at the same time drawing the patient’s pelvis towards himself. In this manner the deformity in scoliosis is reduced and, if possible slightly overcorrected. Initially, there will be significant resistance to the procedure, wh...
Spine Health. PROCEDURE 7 — EXTENSION MOBILISATION The patient lies prone as for procedure 1. The therapist stands to one side of the patient, crosses the arms and places the heels of the hands on the transverse processes of the appropriate lumbar segment. A gentle pressure is applied symmetrically and immediately released, but the hands must not lose contact. This is repeated rhythmically to the same segment about ten times. Each pressure is a little stronger than the previous one, depending on the patient’s tolerance and the behaviour of the pain. The procedure should be applied to the adjacent segments, one at a time, until all the areas affected have been mobilised. Fig. Positioning of hands prior to extension mobilisation. Extension mobilisation. Effects: In this procedure the external force applied by the therapist enhances the effects on derangement and dysfunction as described for the previous extension procedures. In general, symmetrical pressures are used on patients with central and bilateral symptoms. Therapist-...