PHARMACOLOGY - Pain Flashcards
What is pain?
Pain is the unpleasant sensory and emotional experience associated with actual or potential noxious stimuli
What is nociception?
Nociception is the detection and neural processing of actual or potential noxious stimuli
Which four emotional components influence pain perception?
Past experience
Individual pain threshold
Emotional state
Attention
What is physiological pain?
Normal, protective pain proportional to the intensity of the noxious stimus
What is pathological pain?
Degenerative and more persistent pain than the apparent noxious stimuli
Describe the pain pathway
Stimulation of nociceptors generates an action potential which is transmitted along afferent (sensory) neurones to the dorsal horn of the spinal cord, where the information is then transmitted to several regions of the brain to achieve the conscious perception of pain
Which four regions of the brain are involved in the conscious perception of pain?
Sensory cortex
Thalamus
Mesencephalon (midbrain)
Brainstem
What are the two classifications of nociceptive afferent (sensory) neurones?
C fibres
A-delta fibres
What is the structure and function of C fibres?
C fibres are small, un-myelinated fibres which transmit slow, dull and longer-lasting pain signals
What is the structure and function of A-delta fibres?
A-delta fibres are large, myelinated fibres which transmit fast, sharp and brief pain signals
What are the two main inhibitory influences on pain?
Descending inhibition
Gate-control
What is descending inhibition?
Descending inhibition is achieved due to the periaqueductal grey matter in the midbrain and the rostral ventromedial medulla (RVM) in the brainstem which have endogenous opiod pathways extending into the dorsal horn of the spinal cord, stimulating the release of endogenous opioids which reduce the transmission of pain signals
What is gate-control?
Gate-control is the activation of Aβ neurones in response to non-noxious stimuli which subsequently activate inhibitory interneurones in the dorsal horn of the spinal cord to inhibit the transmission of pain signals, reducing the intensity and perception of pain
What is peripheral sensitisation?
Peripheral sensitisation is the increased activation of nociceptors in response to inflammatory mediators, causing sensitisation of the afferent (sensory) neurones leading to the transmission of an amplified pain signal to the central nervous system (CNS)
What is central sensitisation?
Central sensitisation is the sensitisation of neurones in the dorsal horn of the spinal cord due to repetitive or prolonged nociceptive input, amplifying the transmission of pain signals
What is hyperalgesia?
Hyperalgesia is the increased sensitivity to noxious stimuli
What is the difference between primary and secondary hyperalgesia?
Primary hyperalgesia is increased sensitivity to noxious stimuli at the site of tissue damage whereas secondary hyperalgesia is increased sensitivity to noxious stimuli in the surrounding areas of tissue damage
What is allodynia?
Allodynia is the perception of a non-noxious stimulus as noxious
What is analgesia?
Analgesia is the absence or reduction in intensity of pain perception
What are the five main analgesic drug classifications?
Local anaesthetics
Non-steroidal anti-inflammatory drugs (NSAIDS)
Opioids
Ketamine
α2-adrenoreceptor agonists
What is preventative analgesia?
Administration of analgesic drugs before a noxious stimulus occurs
What is multimodal analgesia?
Administration of a combination of analgesic drugs which act on different regions of the pain pathway
What are opioids?
Endogenous or synthetic substance which produces a morphine like effect
What are opiates?
Synthetic substances which produce a morphine-like effect
What is opium?
Opium is the extract derived from the poppy (Papaver Somniferum)
What are the three families of endogenous opioids?
Enkephalins
Endorphins
Dyorphins
What are the three families of opioid receptors?
μ (mu)
κ (kappa)
δ (delta)
μ (mu) is the most important receptor
What type of receptor are μ (mu), κ (kappa) and δ (delta) receptors?
G-protein coupled receptors
What are the three potential mechanisms of action for endogenous opioids?
Inhibit adenylate cyclase thus reducing cAMP
Promote opening of potassium channels
Inhibit opening of voltage-gated calcium channels
How does promoting the opening of potassium channels allow opioids to decrease neuronal excitability?
Promoting the opening of potassium channels increases the efflux of potassium from the neurone which causes hyperpolarisation and decreases neuronal excitability
How does inhibiting the opening of voltage-gated calcium channels allow opioids to decrease neuronal excitability?
Inhibiting the opening of voltage-gated calcium channels prevents neurotransmitter release from the axon terminal as calcium would usually trigger this action
What are the two desired effects that opioids have on the central nervous system (CNS)?
Analgesia
Sedation
What are the five side affects that opioids can have on the central nervous system (CNS)?
Euphoria
Nausea/vomiting
Respiratory depression
Antitussive (suppresses cough reflex)
Miosis (pupil constriction)
How do opioids cause respiratory depression?
Opioids decrease the sensitivity of the respiratory centre in the brainstem to changes in partial pressure of CO2 (PCO2), so, when there is an increase in CO2 levels in the blood, the respiratory rate and tidal volume may not increase enough to compensate - resulting in respiratory depression
In which species will you see mydriasis rather than miosis as a side effect of opioids?
Cats