Nozizeption und Schmerz: neurophysiologische Grundlagen

Zusammenfassung:

Nozizeption bezeichnet die Aufnahme, Weiterleitung und Verarbeitung schmerzauslösender Reize im peripheren und zentralen Nervensystem. Die periphere Aufnahme der Reize erfolgt an Endigungen nozizeptiver Nervenzellen der Dorsalwurzelganglien. Die meisten Nozizeptoren können durch mechanische, thermische und chemische Reize sowie durch Entzündungsmediatoren erregt werden. Die nozizeptiven Neurone projizieren über die Dorsalwurzel ins Rückenmark. Hier erfolgt die Umschaltung sowohl auf Motoneurone als auch auf aszendierende, in Richtung Gehirn projizierende Bahnen. Das aszendierende System verläuft über den Thalamus unter anderem zum limbischen System und zum Kortex. Die Verschaltung der nozizeptiven Neurone auf spinale Motoneurone ermöglicht das reflektorische Wegziehen einer Extremität bei Verletzung. Die wichtigsten Neurotransmitter des aszendierenden Systems sind Substanz P und Glutamat. Neben dem aszendierenden System verfügt der Körper über ein deszendierendes System, das der körpereigenen Schmerzunterdrückung dient. Die wichtigsten Transmitter des deszendierenden Systems sind die endogenen Opioide. Das deszendierende System kann auch durch andere körpereigene Substanzen wie Serotonin, Adrenalin und Noradrenalin aktiviert werden. Letztere spielen eine wichtige Rolle zur Schmerzunterdrückung in Stresssituationen.

Summary

Nociception means reception, conduction and processing of painful stimuli in the peripheral and central nervous system. Reception is done by nerve terminals originating from nociceptive neurones located in the dorsal root ganglia. Most nociceptors are excited by mechanical, thermal and chemical stimuli as well as by inflammatory mediators. Nociceptive neurones project via the dorsal root into the dorsal horn of the spinal cord. In the spinal cord, information is transferred to motoneurones and onto ascending circuits, projecting to higher centres. The ascending system projects via thalamus to the limbic system and the cortex. Projection to spinal motoneurones enables the animal to remove extremities from noxious stimuli. The most important neurotransmitters of the ascending system are substance P and glutamate. Besides the ascending system a descending system can also modulate painful stimuli. The descending system endogeneously suppresses the conduction of pain. The most important neurotransmitters of the descending system are endogenous opioides. The descending system can also become activated by serotonin, epinephrine and norepinephrine. The latter are especially important for suppression of pain in fight or flight reactions.

Schlüsselwörter

Nozizeptor - Sensibilisierung - deszendierendes System - endogene Opioide - Substanz P - Glutamat

Key words

Nociceptor - sensitivation - descending system - endogenous opioids - substance P - glutamate

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