Physiology of Pain Flashcards
Why is pain different from all other senses?
- Elicited by multiple stimuli
- “Pre-empts” all other signals
*** These differences result in multiple alterations in the physiological functioning of the pain pathways
Differentiate between Fast and Slow Pain.
Fast –> Sharp, Generally associated with an Injury
Slow –> Dull Pain, Generally associated with a while after an Injury
What are the two types of fibers that are associated with Bare Nerve Endings?
Why are these fibers ideal?
- Að Fibers - Small and myelinated (Sharp, Fast Pain)
- C Fibers - Unmyelinated and small in diameter (Dull, Slow Pain)
*** C fibers are going to be ideal because they have a VERY HIGH THRESHOLD!!!! (Not every touch is going to activate them, the stimulus is going to have to be great in order for them to fire!)
Describe the different types of mutations that are associated with pain receptors.
Loss-of-function Mutation –> Mutations in this channel lead to an absence of pain sensation
Gain-of-Function Mutation –> Produces paroxysmal pain syndrome
Nociceptors are going to respond to which types of ligands?
Nociceptors have Ligand-Gated Channels on the Peripheral end!
- Substance P (Activated Nociceptors)
- The Kinins (Recruited WBCs)
- ATP (Damaged Tissue)
- H+ (Damaged Tissue)
Which amino acids are released onto which structures when we are talking about Að and C Type Pain receptors?
Að Pain Fiber - Release EAA acting on non-NMDA receptors
C Pain Fiber - Release Substance P and EAA going to use Non-NMDA and NMDA channels!!!
Explain the Gate Theory.
Which pathway is this theory built upon?
Gate Theory –> Touching area where there is pain will block out the pain
- Built on the Spinoreticulothalamic Pathway
- Rubbing the area will activate an Aß Fiber (Two branches: 1. Travels in the Dorsal Root and 2. Stays in Spinal Cord)
- Aß fiber will release an EAA and activated an inhibitory interneuron in the spinal cord.
- Inhibitory neuron is going to release GLYCINE (Opens a Chloride Channel)
Opioid Pathways –> Descend down from the spinal cord and block out the pain
Which pathways are you going to use for pain?
- Spinothalamic Tract (~Fast Pain)
- Spinoreticulothalamic Tract (~Slow Pain)
Where do visceral afferents travel?
With the AUTONOMIC NERVES instead of the two pain pathways
Describe the distribution of pain fibers in the cortex.
WIDELY distributed in the Cortex
- S1 and S2 - Receive input from the nociceptors and play a role in LOCALIZING the pain
- Insular Cortex - Important in the INTERPRETATION of nociceptive inputs (If you damage, you will still be able to interpret pain but you wouldn’t be able to raise your blood pressure after a painful event)
- Amygdala - Becomes active in a painful sensation and is in charge of the EMOTIONAL response
*** Lesions in the cortex will NOT be able to ABOLISH PAIN!!!
Explain the modification of pain through the descending pathways in the brain.
What happens if this pathway stays active?
Opioid Pathways –> Descend down from the spinal cord and block out the pain
- Neurons in the Periaqueductal Gray (PAG) are activated by numerous inputs (opiate, EAA and the cannibinoids)
- Axons from PAG neurons travel to the midline Raphe Nuclei and release enkphalins, which activate raphe neurons
- Axons from Raphe neurons tralve to the spinal cord and release Serotonin, which activate inhibitory internuerons, causing them to release the Opiates
- Opitaes released by the interneurons activate mu receptors on the presynaptic terminal of a C-Fiber.
- This produces Pre-Synaptic Inhibition that reduces the release of substance P from hte nociceptor and reduces pain transmission
**** If this pathway stays active, you will learn pain and the spinal cord will give you a “chronic pain syndrome” even when the damage has been healed!
Why can the skin feel a fast-sharp pain AND a dull-achy pain?
Innervated by BOTH:
- Að - Fibers
- C - Fibers
Describe Deep Pain.
Usually occurs when you have a fracture to a bone!
- Leads to muscle spasms* and a *DULL-ACHY pain
- Ligaments and the Periosteum have many C fibers
Describe Intermittent Claudication.
Blood flow to the muscles in the legs is impeded during exercise
- Creates ischemia and local acidosis which will activate the pain fibers embedded in her Muscles
Muscle Pain –> Both Að (Group III) and C Fibers (Group IV) are present!
Describe Visceral Pain.
Which disease will present with LUQ pain?
- Poorly Localized
- Almost ALL C-Fibers
- Stretch receptors
- Often REFERRED PAIN –> Brain is going to guess where the pain is because the nociceptors from the “heart” are going to synapse with different areas in the body
**** Can have LUQ pain with Pneumonia!
