Pain pathway

Signals are also transmitted to the reticular formation of the brainstem by way of the spinoreticular tract. The reticular formation plays an important role in the response to pain. First, it facilitates avoidance reflexes at all levels of the spinal cord and, second, it is responsible for the significant arousal effects of pain. Signals from the reticular formation cause an increase in the electrical activity of the cerebral cortex associated with increased alertness. Furthermore, it sends nerve impulses to the hypothalamus to influence its functions associated with sudden alertness, such as increased heart rate and 

Nerve signals from the thalamus and the reticular formation are transmitted to the limbic system as well as the hypothalamus. Together, these regions of the brain are responsible for behavioral and emotional responses to pain. The limbic system, in particular, may be involved with the mood-altering and attention-narrowing effect of pain. 

The cell bodies of third-order sensory neurons are located in the thalamus. These neurons transmit the pain signal to the somatosensory cortex. The function of this region of the brain is to localize and perceive the intensity of the painful stimulus. Further transmission of the signal to the association areas of the cerebral cortex is important for the perception and meaningfulness of the painful stimulus. 

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Without interruption, the neurochemicals ultimately lead to a firing of the unmyelinated or thinly myelinated afferent neurons. This sends messages along the pain pathway in the periphery and transfers the pain message to the central nervous... 

Describe the pain pathway and the role that each stimulated region of the brain plays in the response to pain... 

Figure 8.1 The pain pathway. The pain signal is transmitted to several regions of the brain, including the thalamus reticular formation hypothalamus limbic system and somatosensory cortex. Each region carries out a specific aspect of the response to pain.

The endogenous analgesic system is a built-in neuronal system that suppresses transmission of nervous impulses in the pain pathway. It functions by way of the following neurotransmitters produced in the CNS ... 

INTRODUCTION THE PAIN PATHWAY 927 PRIMARY SENSORY NEURONS 928... 

FIGURE 54-1. Algorithm for management of acute pain. (Data modified from Omnicare, Inc., Acute Pain Pathway.)... 

Caterina et al. The capsaicin receptor a heat-activated ion channel in the pain pathway. Nature 389, 1997. 

Binds to DNA and prevents separation of the helical strands Affects neuronal transmissions Binds to opiate receptors and blocks pain pathway Acts as central nervous system depressant Inhibits Na/K/ATPase, increases intracellular calcium, and increases ventricular contractibility Blocks the actions of histamine on Hi receptor Blocks ai-adrenergic receptor, resulting in decreased blood pressure Inhibits reuptake of 5-hydroxytryptamine (serotonin) into central nervous system neurons Inhibits cyclooxygenase, inhibition of inflammatory mediators Inhibits replication of viruses or tumor cells Inhibits HIV reverse transcriptase and DNA polymerase Antagonizes histamine effects... 

Vasoactive intestinal peptide 28 May be involved in pain pathways concentrated in neocor-... 

Mechanism of Action-. An opioid agonist that binds to opioid receptors at many sites in the CNS, particularly in the medulla. This action inhibits the ascending pain pathways. Therapeutic Effect Alters the perception of and emotional response to pain, suppresses cough reflex. 

The endogenous opioid system (Mansour et al., 1995) is the most important component of the pain inhibitory system of the body. Opioids act at different levels in the pain pathway and their action effects different aspects of pain processing (Lipp, 1991 Yaksh, 1997). This results in ... 

The common mechanism of voltage- and frequency-dependent block of sodium channels gives rise to a preferred block of hyperexcitable neurons within pain pathways and comparatively less interference with normal physiological sensory and motor function. In clinical studies, adverse effects are usually reported as mild or moderate however, there are also rare, but life-threatening incidents associated with the central nervous and cardiovascular systems. 

N-type Ca2+ channels for instance are located at presynaptic termini of neurons where they are directly involved in the regulation of neurotransmitter release. Staining of the dorsal laminae of the rat spinal cord revealed a complementary distribution of class A and class B Ca2+ channels in nerve terminals in the deeper versus the superficial laminae. Many of the nerve terminals immunoreactive for class B N-type Ca2+ channels also contain substance P, an important neuropeptide in pain pathways, suggesting the N-type Ca2+ channels are predominant at synapses that carry nociceptive information to the spinal cord (Westernbroek etal., 1998). 

Caterina, M.J., Schumacher, M.A., Tominaga, M., Rosen, T.A., Levine, J.D., Julius, D. The capsaicin receptor a heat-activated ion channel in the pain pathway, Nature 1997, 389, 816-824. 

An alternative strategy uses the combination of known drugs such as tramadol and acetaminophen, thereby targeting multiple components of the pain pathway (Silverfield et al., 2002). This combination of opioids with NSAIDs is a well-established strategy that is part of the WHO scale for treatment of chronic pain. 

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