Nociceptive pathway

Stimulation of a nociceptor in the periphery of the body elicits action potentials in the first-order neuron, which transmits the signal to the second-order neuron in the dorsal horn of the spinal cord. From the spinal cord, the signal is transmitted to several regions of the brain. The most prominent ascending nociceptive pathway is the spinothalamic tract. Axons of the second-order sensory neurons project to the contralateral (opposite) side of the spinal cord and ascend in the white matter, terminating in the thalamus (see Figure 8.1). The thalamus contributes to the basic sensation or awareness of pain only it cannot determine the source of the painful stimulus. 

The dorsal horn is the first site of synaptic transfer in the nociceptive pathway 931... 

Causes of adverse effects over-dosage (A). The drug is administered in a higher dose than is required for the principal effect this directly or indirectly affects other body functions. For instances, morphine (p. 210), given in the appropriate dose, affords excellent pain relief by influencing nociceptive pathways in the CNS. In excessive doses, it inhibits the respiratory center and makes apnea imminent The dose dependence of both effects can be graphed in the form of dose-response curves (DRC). The distance between both DRCs indicates the difference between the therapeutic and toxic doses. This margin of safety indicates the risk of toxicity when standard doses are exceeded. 

Pezet S, Malcangio M, McMahon SB (2002) BDNF a neuromodulator in nociceptive pathways Brain Res Rev 40 240-249... 

Regional analgesia with neurolytic blocks (neurolysis) achieved by injection of alcohol or phenol involves the intentional destruction of a nerve or nerves to interrupt nociceptive pathways for weeks or months (Ferrer-Brechner 1989 Filshie 1988 Lipton 1989 Oran 2001). It is essential to inform the patient of the details, the benefits, and any side effects that might occur with the block technique. 

Pain caused by cancer of the pelvic viscera, and severe persistent tenesmus. All nociceptive pathways from the uterus and cervix pass through the lumbar sympathetic chain. In cases where persistent pain caused by cancer limited to the uterus is not amenable to the other forms of treatment, bilateral sympathectomy can be considered (Bonica 1990a,b). Block of the superior hypogastric plexus has been advocated as... 

Conduction blockade prior to incision can lessen the imprinting in the spinal cord of the nociceptive pathways thereby lessening the level of pain experienced over the next several days. The exact nature of this wind-up is being investigated. 

Figure 14.1 Summary of modulatory mechanisms in the nociceptive pathway. 5-HT, 5-hydroxytryptamine BK, bradykinin CGRP,...

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