NERVOUS SYSTEM PHYSIOLOGY OF PAIN - SEPT 2024 PDF

RNB 10603 Basic Anatomy & Physiology 1 TOPIC 5 NERVOUS SYSTEM PART 5: PHYSIOLOGY OF PAIN 1  LEARING OUTCOMES: At the end of the session, the students should be able to:  define pain;  explain physiology of pain;  describe referred pain;  explain br...

RNB 10603 Basic Anatomy & Physiology 1 TOPIC 5 NERVOUS SYSTEM PART 5: PHYSIOLOGY OF PAIN 1  LEARING OUTCOMES: At the end of the session, the students should be able to:  define pain;  explain physiology of pain;  describe referred pain;  explain briefly the gate control theory;  describe responses to pain. 2  INTRODUCTION  The ability to perceive and react to threats is an important protective homeostatic process  Pain perception is the sum of complex activities in the central nervous system that may shape the character and intensity of pain perceived and ascribe meaning of the pain  The extend of pain perceived depends on:  Interaction between body’s analgesia system and nervous system’s transmission  Mind interpretation of stimuli  Individual perception 3  DEFINITION OF PAIN  Pain is an unpleasant and highly personal experience (Kozier & Erb’s, 2008)  Pain is unpleasant sensory & emotional experience associated with actual or potential tissue damage (American Pain Society, 2003)  Pain is whatever the experiencing person says it is, existing whenever he says it does (Margo McCaferry)  The fifth vital sign, it cannot be measured objectively as other vital signs, e.g. HR, temperature, RR, BP 4  PHYSIOLOGY OF PAIN Nociceptor  Nociceptors are the sensory receptors for pain  They are free nerve endings that respond to painful stimuli, found in every tissue of the body except the brain  Dangeorus stimuli (noxious stimuli) will activate nociceptor, such as electrical, mechanical, thermal or chemical stimuli 5  PHYSIOLOGY OF PAIN Nociceptor  The nerve cell bodies are located in the dorsal root ganglia  Classified into 2 types of fiber  C fiber ▪ Conduct nerve impulse slowly ▪ Respond to thermal, mechanical and chemical stimuli  A-delta fiber ▪ Conduct nerve impulse faster 6  PHYSIOLOGY OF PAIN Nociception  When these nociceptors are activated, the signals must be transduced and transmitted to the spine and brain where signals are modified before they are “understood” and “felt”  The physiologic process related to pain perception are described as nociception 7  PHYSIOLOGY OF PAIN Nociception  Four physiologic process in nociception: i. Transduction ✓ release of substances that stimulate the nociceptors ii. Transmission ✓ movement of the pain sensation to the spinal cord iii. Modulation ✓ the brain send signals back down the spinal cord iv. Perception ✓ pain is recognised 8 9  PHYSIOLOGY OF PAIN Transduction  Begins when the free nerve endings (nociceptors) of C fibers and A-delta fibers respond to noxious stimuli  Noxious stimuli trigger the release of biochemical mediators that sensitize nociceptors 10  PHYSIOLOGY OF PAIN Transduction  Example of chemical mediators:  Subtance P  Prostaglandings  Bradykinin  Serotonin  Histamin 11  PHYSIOLOGY OF PAIN Transduction  In order for a pain impulse to be generated, an exchange of sodium and potassium ions (de-polarisation and re- polarisation) occurs at the cell membranes  This results in an action potential and generation of a pain impulse 12  PHYSIOLOGY OF PAIN File:Synapse Illustration2 tweaked.svg Transduction  Pain medications can work during this phase by blocking the production of prostaglandin or by decreasing the movement of ions across the cell membrane 13  PHYSIOLOGY OF PAIN Transmission  Includes 3 segments  First segment  the pain impulses travels from the peripheral nerve fibers to the spinal cord  Substance P serves as neurotransmitter, enhancing the movement of impulses across the synapse from the primary afferent neuron to the second-order neuron in the dorsal horn of spinal cord 14  PHYSIOLOGY OF PAIN Transmission Substance P serves as neurotransmitter, enhancing the movement of impulses across the synapse from the primary afferent neuron to the second-order neuron in the dorsal horn of spinal cord Pain control – e.g.. narcotic analgesics (opiods) block the release of neurotransmitter especially substance P 15  PHYSIOLOGY OF PAIN Transmission  Two types of nociceptor fibers:  Unmyelinated C fiber ▪ trasmit dull, aching pain  Thin A-delta fibers ▪ transmit sharp, localized pain  In the dorsal horn, the pain signal is modified by modulating factors (e.g.. excitatory amino acids or endorphins) 16  PHYSIOLOGY OF PAIN Transmission  Second segement Trasmission from the spinal cord to the brain stem and thalamus via spinothalamic tracts  Third segment transmission of signals between the thalamus to the somatic sensory cortex where pain perception occurs It also continues to the limbic system (emotional center) 17 18  PHYSIOLOGY OF PAIN Modulation  It is the process of amplifying the pain  Take place in the dorsal horn of the spinal cord  Often described as descending system  Occurs when neurons in the thalamus and brain stem send signals back down to the dorsal horn of the spinal cord 19  PHYSIOLOGY OF PAIN Modulation  The body has built in chemical mechanism to manage pain – endogenous opiods  Descending fibers release substances such as endogenous opioids, serotonin, & norepinephrine, which can inhibit the ascending noxious (painful) impulses in the dorsal horn  In contrast, excitatory amino acids (e.g. glutamate, N-methy-D-aspartate / NMDA）can facilitate these pain signals 20 Modulation 21  PHYSIOLOGY OF PAIN Perception  The final process, when pain is felt  The basic pain sensation occurs in thalamus and continuous to the limbic system (emotional centre) and cerebral cortex where pain is perceived and interpreted  The psychological context, the meaning of the pain based on past experiences and future hopes help to shape the behavioral response 22 23  Recap … Nociception  Transduction: begins when tissue damage causes the release of substances that stimulate the nociceptors  Transmission: movement of the pain sensation to the spinal cord  Modulation: occurs when neurons in the brain send signals back down the spinal cord  Perception: when the pain impulses reach the brain and the pain is recognised 24 Clinical Application … Pain control 25 Clinical Application Epidural Analgesia 26  Clinical Application Patient control analgesia (PCA) 27  REFERRED PAIN  In many instances of visceral pain, the pain is felt in or just deep to the skin that overlies the stimulated organ, or in a surface area from the stimulated organ  This phenomenon is called referred pain  Referred pain is the pain perceived at a location other than the site of the painful stimulus 28  REFERRED PAIN  Visceral pain (pain arising from organs or hollow viscera) often presents this way, being perceived in an area remote from the organ causing the pain  It is believed that sensory nerve from the injured organ stimulate the spinal cord nerve nearby and it transmit the impulses to sensory area in cerebral cortex, where pain is perceived originate from the area supplying by somatic nerve concerns 29 REFERRED PAIN 30  REFERRED PAIN Example of referred pain Tissue of origin of pain Site of referred pain Heart Left shoulder Liver and biliary tract Fight shoulder Kidney and ureter Loin and groin Uterus Low back Male genitalia Low abdomen Prolapsed intervertebral disc Leg 31 32  GATE CONTROL THEORY  Melzack and Wall’s described their gate control theory in 1965  This theory suggested that sensory input from peripheral fibres is transmitted to the dorsal horn of the spinal cord, where it is modulated and then transmitted to the brain for perception  “Gates” occur at afferent synapses in the spinal cord and brain that are responsible for pain signal transmission  When gates are open, uninhibited signals from the periphery ascend via the spinothalamic tract to the brain, where the pain is perceived  The pain can be moderated or reduced if the gates are closed 33 34 35  GATE CONTROL THEORY  Peripherally, large-diameter A-delta nerve fibers, which typically send message of touch, or warm or cold temperature, have an inhibitory effect, may activate descending mechanisms that can lessen the intensity of pain perceived or inhibit transmission of those pain impulses – that is, close the (ion) gates  Higher centers in the brain, especially those associated with affect (the predominant emotion in a person’s mental state) and motivation, are capable of modify and influence the opening or closing of the gates 36  GATE CONTROL THEORY  Clinically, nurses can use this model to stop nociceptor firing (treat the underlying cause), for example:  apply topical therapies, such as, cold compress, hot water bag, massage  address the patient’s mood and emotion, such as, reduce fear, anxiety and anger  This concept forms the basis of transcutaneous electrical nerve stimulation (TENS), which is therapeutic intervention that can reduce pain through sensory stimulation of the affected area 37  GATE CONTROL THEORY Transcutaneous electrical nerve stimulation (TENS) 38 39  RESPONSES TO PAIN  The body’s response to pain is a complex process rather than a specific action  It has both physiologic and psychosocial aspects  Initially the sympathetic nervous responds, resulting the fight-or-flight response, with a noticeable increase in pulse and blood pressure  The person may hold his and her breath, or have short, shallow breathing  There may also be some reflexive movements as the person withdraws from the painful stimuli What is your responses to pain?? 41  RESPONSES TO PAIN  Over a matter of minutes, or hours, the pulse and blood pressure return to baseline despite the persistence of pain  Contrary to adaptation noted in vital signs, the pain fibers themselves adapt very little and become sensitized in a way that intensifies, prolong and/or spreads the pain  Unrelieved pain has been noted to have potentially harmful effect on the person’s wellbeing  Pain interferes with sleep, affects appetite, and lowers the quality of life  A natural response to pain is to stop activity, tense muscles, and withdraw from the pain-provoking activities 42 43 44