sensory pathways and pain

• mechanoreceptors:

  meissner corpuscles have a tactile function

  Merkel discs for pressure sensation

  Pacinian corpuscles for vibration

  muscle cells for limb position
• Nociceptors:

  A-delta mechanical (encapsulated) for pin prick

  C- polymodal (free nerve endings) to sense tissue damage

  thermoreceptors:

  free nerve endings sense warmth and cold
• somatosensory nerve fibres:

  A-alpha is for proprioception

  A-beta is for pressure and vibration

  A-delta is for fast pain and cold

  C fibres are unmyelinated and for slow pain and warmth
• nociception is a physiological response to noxious stimuli

  Pain is commonly a response to nociception

  pain is possible without nociception
• what are the 4 stages of pain physiology?

  transduction

  transmission

  perception

  modulation
• transduction: noxious stimuli causes cell damage and releasing sensitising chemicals (prostaglandins, bradykinins, serotonin, substance P and histamine). These substances activate nociceptors and generate action potential. These nociceptors are activated by stimuli like mechanical pressure, temperature extremes, or chemical irritants. When stimulated, nociceptors generate electrical impulses that convey information about the stimulus. Nociceptors are polymodal meaning they can respond to different types of stimulation
• transmission: Once nociceptors are activated and generate electrical signals that are transmitted along nerve fibres (A-delta and C fibres). A-delta fibres are larger and transmit sharp, fast pain signals, while C fibres are smaller and transmit dull, slower pain signals. The signals travel through the peripheral nerves toward the spinal cord and then ascend to the brainstem, thalamus and the cortex for processing.
• Perception: brain processes incoming pain signals. The pain signals are relayed and processed at different levels of the central nervous system, including the spinal cord, brainstem, thalamus, and various regions of the brain (such as the somatosensory cortex and limbic system). The perception of pain involves interpreting the intensity, location, quality, and emotional aspects of the pain sensation.
• Modulation: The central nervous system has mechanisms to amplify or diminish the perception of pain. Various neurotransmitters, such as endorphins and enkephalins, act to inhibit pain transmission by blocking pain signals in the spinal cord or modifying their perception in the brain. Additionally, descending pathways from the brain can either enhance or suppress the transmission of pain signals. Endogenous opioids can inhibit nociceptive impulses.
• •Pain: conscious experience

  •Nociception: physiological process
• excitatory:

  NTMers- glutamate

  neuropeptides- Substance P

  inhibitory:

  NTMers- GABA , norepinephrine , 5HT

  neuropeptides- enkaphalins
• key points in modulation:

  gate theory

  cortical influence

  descending inhibitory pathway