Pain Flashcards
• Differentiate and define peripheral nociceptive fiber types.
o A delta and C fibers are the two peripheral fiber types. A delta is slower than A alpha and A beta but faster than C. Myelinated, sharp pain, fades quickly. C fibers are slow, unmyelinated, second aching and lasting pain.
• Differentiate and define nociceptive specific neurons and wide dynamic range neurons.
o Nociceptive specific—respond only to nociceptive signals. Reside in superficial layers of dorsal horn. Wide dynamic range graded responses, many stimuli. Deep layers of dorsal horn. Pressure, stretch etc.
• Describe the distribution of sensory input in the dorsal and ventral horns.
o A alpha fibers go to ventral horn because they sense motor information. A beta fibers go deep into dorsal horn. A delta fibers go to tip of dorsal horn. C fibers go to LII directly below A delta. Ventral=motor dorsal=sensory
Define pain
perception of bodily sensations reflecting the presence of tissue damaging stimulation combined with a feeling of unpleasantness or other negative emotion
Describe the steps of pain processing
Transduction—noxious stimuli converted to electrical signals in nerve endings. Transmission—neural events relayed from periphery to cortex. Modulation—nervous system can selectively inhibit/facilitate transmission of pain. Perception—subjective interpretation by cortex (sensory-intensity, location; affective-psychological)
• Peripheral mechanisms of pain transmission. A delta and C fibers
Central mechanisms of pain transmission
Nociceptive specific neurons and wide dynamic range neurons.
Describe the difference between acute and chronic pain:
acute warns of impending or actual injury. Aids in survival. Chronic pain—injury has healed or arises idiopathically. Has no survival value.
Wind up (temporal summation) vs. central sensitization.
Windup is when nociceptive stimuli placed close together over time lead to an increase in pain sensation without stimulus increase. This is because of the removal of the voltage gated magnesium block in NMDA ion channels. This allows nociceptive signals to integrate. Central sensitization is plasticity in the spinal cord that alters input/output relationship of pain processing by lowering threshold of nociception. Symptomatically: allodynia (pain from nonpainful stimuli) and hyperalgesia (enhanced pain to nociception). Phosphorylates post-synaptic receptors to make them more excitable long term.
Gate control theory
When a nociceptive signal is sent through a second order pain transmission neuron, activation of an a beta low threshold mechanoreceptor with a non-nociceptive stimulus activates interneurons that inhibit the pain signal (maybe GABA or ENK) i.e. non-painful input closes the gates to painful input.
Ascending and descending control.
Primary ascending pain fibers (A delta and C) reach the dorsal horn and innervate nociceptors in Rexed Laminae. These give rise to ascending spinothalamic tracts. Activation of opiate receptors at interneuronal levels produces hyperpolarization of neurons which inhibits pain transmission. Pain stimuli activate descending fibers in the dorsolateral fasciculus. Descending: PAG, brainstem, spinal cord. Enkephalin containing cells mediate.
