FISIOLOGIA DA DOR Prof. Pedro Dal Lago

Localização Intensidade Duração Receptores polimodais Sistema de Nociceptivo Reação de aversão Localização Intensidade Duração Receptores polimodais Fig. 1 Scheme of the nociceptive system with nociceptive free nerve endings in the peripheral tissue, afferent nerve fibres and their synapses in the dorsal horn of the spinal cord. From there the medial and lateral spinothalamic tracts ascend to the medial andlateral thalamus, and interneurons project into motor and sympathetic reflex pathways

Vias ascendentes

Inflamação neurogênica Fig. 7-5B Release of substance P (SP) and calcitonin gene-related peptide (CGRP) from a nociceptor after an axon reflex causes changes in the local environment. One action is vasodilation, resulting in reddening of the skin and warming. Another is increased capillary permeability, resulting in plasma extravasation. RBC, Red blood cell.

Tipos de dor Fig. 2 Sketch of a nociceptive afferent with its synapse in the dorsal horn of the spinal cord. Noxious stimulation of the nociceptor at its sensory ending causes nociceptive pain. Pathological stimulation of the axon, the dorsal root ganglion or of neurons in the central nervous system causes neuropathic pain

Sensibilização Periférica Fig. 3 Flowchart of the generation of pain in different pain states.Central sensitisation can result both from peripheral sensitisation (redução do limiar de disparo e recrutamento de fibras C que estão em silência por ação da reação inflamatória – mediadores (prstaglandina, bradicinina, histamina, ATP, AcH), hipertermia, vermelhidão, vasodilatação etc..) and from pathological discharges in the afferent nerve fibre

Sensibilização Periférica Fig. 7-5A A sensitization of the terminals of a nociceptor. A noxious stimulus that causes damage to cells results in the local release of proteolytic enzymes that react with circulating proteins to produce bradykinin. Bradykinin then binds to a receptor on the membrane of the nociceptive afferent fiber and sensitizes it (after activation of a second messenger system). The nociceptor is now more responsive to further stimulation. Other agents that would have similar effects include prostaglandins, serotonin, histamine, leukotrienes, and K+ ions, although these have different actions at the membrane level (e.g., serotonin would act on a receptor that opens an ion channel).

Sensibilização Periférica Fig. 7-4 A, Curves show magnitude ratings of pain in a human in response to heat pulses applied to the hairy skin before and after a mild burn. Arrows indicate the beginning and end of the stimuli. B, The responses of a C-polymodal nociceptor innervating the hairy skin in a monkey in response to the same heat pulses before and after the mild burn. (From LaMotte RH, Thalhammer JG, Robinson CJ: J Neurophysiol 50:1, 1983.)

Sensibilização Periférica Prof. Pedro Dall’Ago

Sensibilização Central Prof. Pedro Dall’Ago Sensibilização Central Fig. 5 Development of central sensitisation in a spinal cord neuron. In normal tissue (top) this spinal cord neuron is activated (see action potentials at the right) only by pressure on its normal receptive field (shaded area) but not by pressure on adjacent or remote tissue (no action potentials elicited). During inflammation in the receptive field (bottom), stimulation of the inflamed area within the receptive field elicits a stronger response. A stronger response is also elicited by stimulation of the adjacent area, and the total receptive field expands. This creates a zone of secondary hyperalgesia, i.e. an area which is hyperalgesic although the tissue is normal

Mecanismo de transdução do estímulo doloroso Fig. 4 Sketch of the enlarged ending of a nociceptor in the tissue and its axon and cell body. Bottom the proposed ion channel that is activated by mechanical stimuli, and the TRPV1 receptor complex that is activated by capsaicin, protons and by noxious heat. Top receptors for inflammatory mediators. The circles in the cone symbolise vesicles filled with neuropeptides (substance P, CGRP) that can be released from the ending

Campo inibitório lateral Fig. 6-11 Excitatory and inhibitory receptive fields of a central somatosensory neuron located in the SI (primary) somatosensory cerebral cortex. The excitatory receptive field is on the forearm and is surrounded by an inhibitory receptive field. The graph shows the response to an excitatory stimulus and the inhibition of that response by a stimulus applied in the inhibitory field.

Vias de analgesia endógena Fig. 7-11A Some of the neurons thought to play a role in the endogenous analgesia system. Neurons in the midbrain periaqueductal gray activate the raphe-spinal tract, which in turn inhibits nociceptive spinal neurons, such as those of the spinothalamic tract. Interneurons containing opioid substances are involved in the system at each level. (Redrawn from Henry JL: In Porter R, O'Connor M, editors: Ciba Foundation Symposium 91, London, 1982, Pitman.)

Teoria da comporta (GATE) para controle da dor

Vias de analgesia endógena

FISIOLOGIA DA DOR Prof. Pedro Dal Lago