Where and how do anaesthetics act? Mechanisms of action in the central nervous system

General anaesthesia is a balance of hypnosis, amnesia, analgesia, and immobility, including the inhibition of noxious autonomic reflexes. Local anaesthesia implements the latter two elements in a conscious patient. This review article discusses several important aspects of anaesthesia, beginning with basic concepts such as the minimum alveolar concentration and afterwards developing into a discussion about the mechanisms of action of anaesthetics on a cellular level, introducing electrophysiological investigations in the brain to study hypnosis and amnesia, in the dorsal horn of the spinal cord to study analgesia and the inhibition of noxious reflexes, and in the ventral horn of the spinal cord to study immobility, separately. In accordance with the results of electrophysiological patch clamp studies, researchers have confirmed that the modulation of neurotransmission input from dorsal afferent neurons into the dorsal horn of the spinal cord and effects on the spinal reflex arc from the dorsal horn to ventral horn motor neurons are important anaesthetic action mechanisms. Accordingly, intraoperative body movement of patients is not a sign of insufficient muscle relaxation, but rather insufficient analgesia. In conclusion, sufficient analgesia is a correct strategy (rather than muscle relaxant administration) for performing intraoperative patient immobility and for providing patients with good and safe intraoperative anaesthesia management by protecting them from noxious reflexes and stress including autonomic reactions such as hypertension and tachycardia.