Lecture

• There are 2 elements to pain: peripheral nerve irritation and recognition of pain in CNS
• Nociceptors are free nerve endings
• Nociception has 4 phases: Transduction, Transmission, Perception and Modulation
• In transduction, painful stimuli is converted to neuronal action potential at sensory receptor
• In transmission, movement of action potential along neurons from peripheral receptors to spinal cord and brain occurs
• In perception, the brain receives the signals and interprets them as painful
• In modulation, there's alteration of synaptic transmission of pain signals. Genetics play a role in this and it's a big reason why diff ppl feel pain differently
• Healing can be delayed with unmanaged pain so analgesics are useful for that purpose as well
• Characteristics of pain: can be either acute or chronic and peripheral sensitization can lead PTs to perceive normal stimuli as painful
• Neuropathic pain is chronic and it can also be intermittent. It's caused by abnormal signals and trapped nerves
• There's 2 types of pain management: opioid analgesics and nonopioid analgesics
• There are 4 types of opioids: endogenous, natural, synthetic and semi-synthetic
• Endogenous opioids are natural peptides produced within the body such as Endorphins
• Natural opioids are obtained from poppies and examples are codeine and morphine
• Oxycodone and diacetylmorphine(Heroin) are examples of semi-synthetic opioids
• Fentanyl and methadone are examples of synthetic opioids
• Opioids are centrally acting analgesics and have no effect of the peripheral nerves(Pain sensation is still present but the CNS doesn't care)
• Endogenous peptides fxn with a survival function; pain relief to flee from danger.
• Endogenous peptides are endorphins, enkephalin and dynorphin\
• Endogenous peptides are 4x more potent than morphine
• Non-opioids only work at the site of injury
• There are 3 types of opioid receptors: Mu, Kappa and Delta
• Each opioid receptor responds to a different endogenous opioid and they inhibit the release of neurotransmitters(Prostaglandins, bradykinins, histamine and other shit that causes pain)
• Substance P is a neurotransmitter that excites nociceptors and is active during tissue damage/injury which causes pain
• Fentanyl is predominantly used for cancer treatments but is now being used in emergency medicine
• The opioid analgesics we use work on the Mu and Kappa receptors
• Different Opioid receptors being activated effects what pharmacological effects will be present
• Pharmacological effects of Opioids: analgesia, sedation, euphoria/dysphoria, constipation, urinary retention, miosis and respiratory depression
• Opioids cause spasms within the GI tract that inhibits peristalsis. This causes decreased gastric motility and causes constipation. This is a very common effect.
• Opioids cause spasms of bile duct which causes pressure and pain
• Opioids cause spasms of the ureter and causes urine to be retained. It also stimulates release of ADH which causes less urine formation
• Opioids cause bronchial smooth muscle spasms in the lungs and also release histamine which causes bronchoconstriction. It can induce an asthma attack
• Opioids have no effect on cardiovascular function at therapeutic doses and its effective for treating pain induced by anxiety in an MI
• Only exogenous opioids cause the adverse effects of nausea and vomitting
• Low doses of opioids cause nausea and vomitting while high doses inhibits it
• Most opioids produce miosis while a few (meperidine) induces mydriasis.
• Nausea and vomitting via Opioids occurs through the direct activation of the Chemoreceptor trigger zone(CTZ) and direct stimulation of vomit center in medulla oblongata by the CTZ
• Respiratory depression is caused by activation of Mu receptors in the pons and medulla
• Antitussives includes opioids that suppress the cough reflex. It's not a cure but it decreases intensity and frequency of cough.
• Antitussives are codeine, hydrocodone and dextromethorphan(Available OTC)