a. Discuss the nociceptive mechanisms, including the postsynaptic receptors of the spinal neurons, transmitters, pathways and nuclei that are activated when the injury occurs. Also include in your answer the explanation for the sharp pain and the long lasting pain that you experience with this injury.
Nociceptors are specialized peripheral sensory neurons that are activated by noxious stimuli. These nociceptors are the free nerve endings of primary sensory neurons. Upon tissue injury, in this case the stomping on the big toe, the noxious stimuli causes tissue damage. The damaged tissues in the big toe releases a host of substances including prostaglandins, bradykinins, substance P, ATP, acetylcholine, …show more content…
The released Glutamate binds to and activates receptors in the postsynaptic nerve terminal (the dorsal horn neuron). Specifically activation of α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-type and N-methyl-D-aspartate (NMDA)-type glutamate receptors lead to depolarization and the generation of action potentials which transmits the pain impulses through ascending pathways (e.g. spinothalamic tract ) to the brain. Neuropeptides like substance P are also released into the synapse and have been shown to prolong the depolarization wave elicited by Glutamate (Kandel et al, 2013). The transmission of the signal results in elevated release of norepinephrine from the locus coeruleus neurons which project to the thalamus. This in turn relays the nociceptive signal to the somatosensory cortex, hypothalamus and hippocampus[4, 5].
Parts of the brain shown to be involved in decoding the pain stimulus to cause perception include the thalamus, sensory cortex, reticular formation and hypothalamus. The somatosensory cortex identifies the location and intensity of the pain. The brain also modulates the pain response through the use of inhibitory neurotransmitters like GABA and glycine.
Figure 1 summarizes the processes described above. (Please find Fig 1 attached as a