Afferent division - Pain

what are specialized pain receptors called? what are the three types?

nociceptors (noxious = pain)

• mechanical (pinch/cut/crush)

• chemical (ex: capieisin in chili peppers)

• thermal (burn, really cold metal)

what are the two pathways of pain? name and state which fibers are involved, as well as what it feels like

Fast pain: A delta fibers, which are fast because they are myelinated. Sharp pain (like sting)

Slow pain: C fibers, which are smaller (smaller diameter) and unmylinated. Dull pain (like lingering dull soreness)

what are the function of prostaglandins? where do they come from? how does medicine take advantage of their function?

• prostaglandins are released from injured tissues themselves or immune cells

• lower the firing threshold, making it easier to reach and fire an AP (increasing sensitivity)

• Tylenol and other like drugs block the production of prostaglandins, reducing the sensitivity of pain receptors to pain

what is the role of substance P?

it is the neuropeptide released by the afferent pain fiber which (via excitatory synapse) will stimulate the 2nd order interneuron (in dorsal horn of spinal cord) to activate higher brain areas

what is the first pathway of pain? purpose?

thalamus to somatosensory cortex

for perception - where is it coming from?

what is the second pathway of pain? purpose?

• to reticular formation in brain stem, which wakes up higher areas of the brain (increase in awareness)

• then to hypothalamus and limbic system (for emotional response to pain)

why might we be crying even after the pain sensation has subsided?

because the second pathway - involved in behavioral and emotional response, takes awhile to calm down

what is the role of glutamate in pain? (2)

1. activates AMPA receptors - transmits pain signals to the brain

2. activates NMDA receptors - makes second order interneuron more excitable, increasing the sensitivity of the affected area, to try keep you from re-injuring it

list three endogenous analgesics, how do they work (explain and give term for this)?

• endorphins, enkephalins, dynorphins

• as pain signals ascend, signals also descend from periaqueductal grey matter that reach inhibitory pain interneuron that sits in dorsal horn. This will secrete endogenous opiates which block opiate receptors on the afferent pain receptor and stop the release of substance P

• this is a form of PREsynaptic inhibition

how do exogenous opiates work? how does their effect differ from endogenous opiates? why do they give feeling of pleasure?

• on the same mechanism as endogenous opiates… but they last much longer

• feeling of pleasure due to high concentration of opiate receptors in the reward centers