pain pathways

• terms associated with pain

  1. Noxious - poisonous or harmful
  2. Hyperalgesia - heightened pain intensity as a response to noxious stimulus
  3. Analgesia - absence of pain or inability to feel pain
  4. Dysaesthesia - abnormal sensation felt when touched caused by damage to peripheral nerves
  5. Paraesthesia - abnormal sensation with no apparent physical cause (e.g. a tingling, pricking, chilling, buring, or numb sensation)
  6. Allodynia - innocuous (harmless) stimuli cause pain
• physiology of pain

  1. An irritation or injury e.g., cut or burn is detected in the peripheral nervous system by special nerves called the nociceptors.
  2. A nerve impulse is then generated, sending a pain impulse towards the central nervous system.
  3. The message is received by the brain where the extent and significance of the irritation or injury is interpreted, and pain is sensed
• nociceptors

  • Free nerve endings present in every tissues in the body except for the brain.
  • Activated by noxious stimuli such as:
  • thermal - severe heat or cold
  • mechanical - trauma, disease, injury, ischaemia, hypoxia, ulceration, infection, peripheral nerve damage, inflammation
  • chemical - histamine, kinins, prostaglandins, which are released due to tissue damage and inflammation
• What initiates the ascending pain pathway?

  Nociceptor stimulation
• What types of fibers transmit pain impulses in the ascending pain pathway?

  1. delta and C fibers
• Where do pain impulses travel towards in the brain?

  The thalamus and somatosensory cortex
• What aspects of pain are analyzed in the somatosensory cortex?


  Location, severity, seriousness, and meaning of pain
• What are the three types of neurons in the ascending pain pathway?


  • First-order neurons
  • Second-order neurons
  • Third-order neurons
• What is the function of first-order neurons in the ascending pain pathway?


  They travel from the nociceptors to the spine
• Where do second-order neurons travel in the ascending pain pathway?


  Upwards through the spinal cord towards the thalamus
• What is the role of third-order neurons in the ascending pain pathway?


  They run from the thalamus to the somatosensory area of the cerebral cortex
• What maintains the line of communication in the ascending pain pathway?


  Neurotransmitters such as Substance P and Serotonin
• What neurotransmitters are involved in the ascending pain pathway?


  • Substance P
  • Serotonin
• What is the primary function of descending pain pathways?


  To inhibit the sensation of pain
• How do descending pain pathways inhibit pain sensation?


  By releasing neuropeptides that bind to opiate receptors
• What is the role of neuropeptides in pain inhibition?


  They have analgesic properties and block Substance P action
• What are the natural opiates released during stress and pain?

  Endorphins, encephalins, and dynorphins
• What effects do endogenous opiates have on the body?


  They promote feelings of euphoria and wellbeing
• What are the four major categories of opiate receptors?


  Mu, kappa, sigma, and delta
• What are the characteristics of the analgesic effect of neuropeptides?


  • Referred to as endogenous or natural opiates
  • Includes endorphins, encephalins, and dynorphins
  • Increased release during stress and pain
  • Promotes feelings of euphoria and wellbeing
• spinal cord transmission pathways

  • Ascending tracts
  • Spinothalamic
  • Spinoreticular
  • Dorsal column – medial lemniscal system
  • Trigeminal system
  • Sensation from Head and oral cavity carried by trigeminal, facial, glossopharyngeal and vagus nerves
• other parts of the pain pathway - perception and integration

  • Spinal cord – the first part of the pathway
  • Brainstem - Periaqueductal grey matter, Reticular formation
  • Thalamus – final link in transmission to cortex through 6 groups of nerves (called nuclei) which have a wide range of connections
  • Limbic system - modulate emotions, aversive behaviours and motivational aspects of pain)
  • Basal ganglia (role in movement control and are connected with the memory and emotional aspects of movement and eye movement
  • Cerebral cortex (discriminative, affective, autonomic and motor components)
• classification

  • We use different classifications of pain such as duration, type and severity
  • Duration
  • Transient
  • Acute
  • Chronic
  • Type
  • Nociceptive
  • Inflammatory
  • Neuropathic
  • Severity – mild, moderate, severe (often report it on a numeric system)
• What is nociceptive pain?


  Detection of a noxious stimulus by nociceptors (C fibre)
• What types of stimuli can cause nociceptive pain?


  Mechanical, inflammatory, and ischemic stimuli
• What does inflammatory pain describe?


  Pain signaling and transmission behavior during an inflammatory process
• What is neuropathic pain?


  A specific type of pain resulting from damage to neurons' signaling and transmission
• What is peripheral sensitization?


  It is caused by multiple chemical mediators from nerve tissue damage and inflammatory response
• What is central sensitization?


  Change in the sensitivity of spinal cord synapses in the dorsal horn and nervous system
• How does central sensitization affect the nervous system?


  It makes the whole system hyperexcitable and more sensitive to inputs
• What are the three types of pain discussed?

  • Nociceptive pain
  • Inflammatory pain
  • Neuropathic pain
• different sources of nociception

  • Cutaneous - skin can be termed superficial somatic
  • Deep somatic - from body structures, deeper than skin and muscle such as bone, tendon and joint
  • Viceral - from internal organs
  • Referred pain - pain perceived in an area other than the site of the pain stimulus
• What are the causes of peripheral and central sensitization?

  • Peripheral sensitization: Chemical mediators from nerve damage and inflammation
  • Central sensitization: Changes in spinal cord synapse sensitivity and hyperexcitability of the nervous system
• What is transient pain?


  Transient pain is short duration pain, such as from a stubbed toe or cut finger.
• Why do people typically not seek medical attention for transient pain?


  Because it has no significant consequence.
• What characterizes acute pain?


  Acute pain is associated with severe sudden onset and can be intolerable.
• What autonomic responses may occur due to acute pain?


  Responses include diaphoresis, tachycardia, hypertension, tachypnoea, grimace, and guarding.
• How does the brain respond to acute pain to achieve homeostasis?


  The brain initiates autonomic responses through the hypothalamus, thalamus, and reticular formation.
• What is chronic pain also known as?


  Chronic pain is also known as persistent pain.
• dimensions of pain

  • Sensory type, area of pain, intensity of pain, behaviour of pain
  • Cognitive thoughts about pain
  • Affective feelings about the pain, emotional impact