PAIN

PAIN

1. Congenital Analgesia - do not have pain response

2. chronic pain / overactive pain response

   • can lead to depression, anxiety, insomnia, impaired movements,
     • chronic pain syndrome - pain is the focus of life

3. ‘an unpleasant sensory & emotional experience associated with actual or potential tissue damage, or described in terms of such damage’

   • psychological / cultural

4. Involves peripheral & central nerve pathways

   • impact signal by nerves, impact pain

5. parasympathetic responses: decreased blood pressure and pulse, nausea and vomiting, weakness, pallor, lose of consciousness

6. sympathetic responses: pallor, increased blood pressure, increased pulse and respiration, skeletal muscle tension, sweating

7. somatic vs visceral

   • somatic = NSAIDS
     • anti-inflammatory
     • inhibit prostaglandins
   • visceral = opioids (ADRs)

8. pain tolerance v pain threshold

9. nociceptors

   • specialised nerve endings that respond to painful stimuli
     • detect pain, initiate pain signal

10. A Delta Fibres: a type of nerve that transmits painful information that is often interpreted by the brain as burning or stinging pain - requires immediate response - myelinated to conduct a fast signal

    • A-δ fibers (Myelinated) conduct fast pain (a sensation experienced immediately after an injury that indicates location of injury)

11. C - Fibres: a type of nerve that transmits painful information that is often interpreted by the brain as throbbing or aching

    • C-fibers (Unmyelinated) conduct slow pain (follows sharp pain and can be characterized as a dull, throbbing ache with poor localization)

12. Endorphins & Dynorphins

    • morphine-like substances. • Located in the brain, spinal cord & GIT • Produce analgesia when attached with opiate receptors in the brain • Activate µ receptors (endogenous opiates)

13. withdrawal reflex - only spinal cord involved: If stimulus is strong, higher brain centres are not involved in response, since it needs to be fast. Such responses are automatic and mediated by A-δ fibers

14. chemical mediators of pain - serotonin, substance P, bradykinin, leukotrienes, thromboxjnes, prostaglandins, histamine

    • Bradykinin- most potent pain producing chemical - excitatory
    • Prostaglandins- increase sensitivity to pain experience - excitatory
    • Substance P- transmits pain impulses to brain centers and causes vasodilatation and oedema - excitatory
    • Serotonin- causes pain by altering Na+-caused nerve depolarisation - excitatory
    • Histamine, leukotrienes and nerve growth factor are released

15. Local Anesthetics- • Lidocaine • Bupivacaine; They block nerve depolarisation - sodium channel block

16. analgesic ladder.

    • 1:non opioid analgesics, NSAID or paracetamol, 2:weak opioid (e.g. codeine) 3.Strong opioid (morphine)
    • classes:
      • paracetamol
      • opioids
      • NSAIDs

17. ADJUVANTS

    • A number of other drug classes whose usual primary role is other than the relief of pain are also used. These drugs, usually called adjuvants, or 'co-analgesics', are used to supplement analgesics to improve pain control or to control symptoms.
      • Clonidine, an alpha2-adrenergic agonist, is a centrally acting antihypertensive drug. • NMDA-receptor antagonists (eg ketamine). • Tricyclic antidepressants (TCAs) are nonselective uptake inhibitors of noradrenaline and serotonin. • Antiepileptic drugs decrease the excitability of neurons at spinal and brain levels. Antiarrhythmic drugs (flecainide). • Corticosteroids (hydrocortisone, cortisone) have both anti- inflammatory (glucocorticoid) and salt-retaining (mineralocorticoid) properties. • Bisphosphonates act as inhibitors of osteoclastic bone resorption (for bone pain) • Benzodiazepines act by potentiating the action of GABA at the GABAA receptor. • Muscle relaxants are used in the treatment of acute low back pain. • Anticholinergic drugs have muscle relaxant properties but anticholinergic adverse effects are prominent. • Calcium channel blocker (nifedipine) has been used as a co-analgesic to relieve smooth muscle spasm.

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