Physiology of pain

PAIN MANAGEMENT IN NURSING

PHYSIOLOGY OF PAIN

PREPARED BY;SEIF SAID KHALFAN(BSc.N STUDENT)

UNDER SUPERVISION OF;RN, BSc.N, MENTAL HEALTH SPECIALIST; SULTAN MUKKY

Introduction

Physiology of pain explains how pain is transmitted and perceived. The mechanism of pain physiology is still incompletely understood. Whether the pain is perceived and to what degree depend on the interaction between the body’s analgesia system and the nervous system’s transmission and interpretation of stimuli

Key words

1. Nociceptors

The receptors that transmit pain sensation.

2. Neurotransmitters

are the chemicals which allow the transmission of signals from one neuron to the next across synapses.

3. Substance P

a substance that functions as a neurotransmitter and as a neuromodulator. To be specific, substance P is an undecapeptide - a peptide composed of a chain of 11 amino acid residues.

Serotonin•Serotonin is a chemical created by the human body that works as a neurotransmitter. It is regarded by some researchers as a chemical that is responsible for maintaining mood balance, and that a deficit of serotonin leads to depression.

1. Prostaglandin

The prostaglandins are a group of lipids made at sites of tissue damage or infection that are involved in dealing with injury and illness. They control processes such as inflammation, blood flow, the formation of blood clots and the induction of labour. Mechanism of action of the drug aspirin.

5. Bradykinin

Peptide formed from the degradation of protein enzymes. It is a powerful vasodilator that also cause contraction of smooth muscle.

6. Histamine

An enzyme that cause local vasodilatation and increase permeability of the blood vessel walls.

Physiology of Pain

NOCICEPTION

The peripheral nervous system includes primary sensory neurons specialized to detect tissue damage and to evoke the sensation of touch, heat, cold, pain and pressure.

The receptors that transmit pain sensation are called Nociceptors.

The pain receptors or nociceptors can be excited by mechanical, thermal, or chemical stimuli.

The physiologic processes related to pain perception are described as nociception. There are four processes involved in nociception: transduction, transmission, perception and modulation.

i. Transduction: • During the transduction phase, noxious

stimuli (tissue injury) triger the release of biochemical mediators i.e. prostaglandins, bradykinin, serotonin, histamine and Substance P that sensitize receptors.

• The painful stimulation also cause movement of movement of ions across cell membranes, which excites nociceptors.

• Pain medications can work during this phase by blocking the production of prostaglandin (e.g. ibrufen) or by decreasing the movement of ions across the cell membranes (e.g. local anaesthetic).

ii. Transmission: The second phase of nociception, transmission of pain, includes three segments.

• The first segment the pain impulse travel from the peripheral nerve fibres to the spinal cord. Substance P serves as neurotransmitter. Two types of nociceptors cause this transmission to dorsal horn of the spinal cord: C fibres transmit dull pain and A-delta fibres which transmit sharp, localized pain.

• The second segment is transmission from the spinal cord to the brain stem and thalamus.

• The third segment involves transmission of signals between the thalamus to the somatic sensory cortex where pain perception occurs.

• Pain control can take place during this second process of transmission. For example block of release of neurotransmitters, particularly substance P, which stops the pain at the spinal level.

iii. Perception

It is the third process of nociception. It is when a person becomes conscious of the pain. It is believed that pain perception occurs in the cortical structures, which allows for different cognitive behavioural strategies to be applied to reduce the sensory and affective component of pain

• For example, non-pharmacological interventions such as distraction, guided imagery, and music can help direct the client’s attention away from pain.

iv. Modulation

This is the fourth system, often describes as the “descending system,”. This fourth system occurs when neurons in the brainstem send signals back down to the dorsal horn of the spinal cord. These descending fibres release substances such as endogenous opioids, serotonin and norepinephrine which can inhibit the ascending of noxious impulses in the dorsal horn

GATE CONTROL THEORY•Peripheral nerve fibres carrying pain to the spinal cord can have their input modified at the spinal cord level before transmission to the brain.•Synapses in the dorsal horn act as gates that close to keep impulses from reaching the brain or open to permit impulses to ascend to the brain

• Small-diameter nerve fibres carry pain stimuli through a gate, but large-diameter nerve fibres going through the same gate can inhibit the transmission of the pain impulses, that is, close the gate.

• The gate mechanism is thought to be situated in in the substantia gelatinosa cells in the dorsal horn of the spinal cord.

• Because s limited amount of sensory information can reach the brain at any given time.

• The brain also appears to influence whether the gate is open or closed. For example previous experience with pain are known to affect the way an individual response to pain.

RESPONSES TO PAIN

Body’s response to pain is a complex process rather than a specific action. It has both physiologic and psychological aspects. Initially the sympathetic nervous system responds, resulting in the fight-or-flight response. As pain continues, the body adopts as the parasympathetic nervous system takes over,

reversing many of the initial physiologic responses.

References

1. Medical News Today: www.medicalnewstoday.com/articles/232248.php

2. Kozier B, Erbs G, Berman A & Snyder S (2004). Fundamentals of Nursing: Concepts, Process and Practice (7th edition). Pearson Education, Inc., Upper Saddle River, New Jersey 07458.