Der Schmerz
-
Cerebral potentials evoked by cutaneous heat stimuli from an infrared laser (LEP) enable overall controls of thin fibre function and anterolateral tract projection, which is of special meaning in the diagnosis of normal and disturbed pain pathways. Owing to the long-wave radiation, the laser energy is completely absorbed within the most superficial skin layers only a few 100 mum in depth and activates only the most superficial afferents, i.e. the thermo- and nociceptive A, delta and C fibres. According to the particular fibre spectrum activated, a single laser stimulus elicits a typical double pain sensation: the first pain appears with a mean reaction time of approximately 400 ms and is described as a sharp and stinging, well-localizable pinprick sensation; this pain is induced by A delta fibre activity with a mean conduction velocity of 14 m/s. ⋯ Both sensations and both evoked potentials can emerge to very different degrees in healthy subjects and in patients with neurological diseases. The diagnostic practicability of LEP is individuals illustrated with reference to patients with syringomyelia suffering from a dissociated sensory loss in cutaneous sensibility. In contrast to conventional electrical nerve stimuli, the laser stimuli allow monitoring of disturbances in the protopathic system projected to the anterolateral columns.
-
In contrast to pain from the skin, muscle pain is often referred to regions remote from the lesion. For instance, trigger points in neck muscles can elicit pain in the head. The convergence-projection theory of Ruch is still the central concept for the explanation of pain referral. ⋯ Therefore, the present paper presents another mechanism, which consists in acute changes in dorsal horn synaptic connections following nociceptive input from muscle. Results from animal experiments indicate that dorsal horn neurons possess ineffective synaptic connections with the body periphery, which become effective under the influence of a painful stimulus and lead to a mislocalization of pain. The neuropeptide substance P is probably involved in the changes in functional organization that occur in the dorsal horn during muscle pain and its referral.
-
In the present article aspects of reflex sympathetic dystrophy (RSD) and sympathetically maintained pain (SMP) are discussed from the point of view of a basic scientist. The main focus is on the sympathetic nervous system. ⋯ Finally, clinical observations are discussed that seem to bear little or no relation to the models that are available. The general synopsis puts the problem into a wider context.
-
The gate-control theory of pain, as originally proposed by Melzack and Wall [8], is nothing but a hypothesis concerning the spinal processing of non-noxious and noxious afferent information. Its basic tenant is that the P cells (projecting neurons) convey noxious information to supraspinal pain systems only after a critical threshold of excitation has been passed, and that access to the P cells is controlled by the SG cells (cells of the substantia gelatinosa Rolandi) or, in other words, the SG cells act as the gate. Since the primary afferent fibres have monosynaptic connections with the P cells the gate can only operate-and this is the critical point of the whole hypothesis-via presynaptic inhibition exerted by axoaxonic contacts on these afferents (Fig. 1). ⋯ As a consequence, Melzack and Wall [9] have now modified their hypothesis considerably. Its present formulation is not much more than a very general statement to the effect that all kinds of afferent input, including noxious input, is under the modulating influence of various mechanisms operating both at the spinal level and from supraspinal (descending) structures. No implications for therapy can be derived directly from such an undefined, in many ways trivial, assumption.