Levels of Physiological Response Formation
The response to a painful stimulus is formed in stages, engaging various levels of the nervous system:
- Peripheral level. It all starts with the stimulation of primary afferent fibers. At this stage, the axon reflex is triggered, which occurs without the participation of CNS neuron cell bodies. Its main effect is local vasodilation. This increases local blood flow and oxygen supply, leading to enhanced oxidative processes (tissue respiration).
- Spinal level. The dorsal horns of the spinal cord act as the first relay station. Primary signal processing and the formation of the ascending excitation flow occur here. Concurrently, segmental reactions are triggered—rapid activation of skeletal musculature (reflex withdrawal of a limb) for immediate elimination of the noxious factor.
- Brainstem and reticular formation (RF). The midbrain RF ensures the generalization of excitation. Ascending pathways activate the cortex and sensory systems (vision, hearing) to assess the situation. Descending pathways (according to H. Magoun) exert a facilitatory influence on spinal reflexes, increasing the readiness of the motor system.
- Thalamus. This is the main relay station receiving impulses from lemniscal and extralemniscal pathways. The thalamus forms sensations associated with epicritic and protopathic pain, determining the nature, severity, and exact localization of the damage.
- Hypothalamus. The involvement of this structure is accompanied by complex autonomic and hormonal shifts. Together with the limbic system, the hypothalamus forms a pronounced negative emotional state.
Components of the Systemic Pain Response
According to L.V. Kalyuzhny's classification, several relatively independent components are distinguished in the body's systemic response:
- Perceptual component: the pain sensation itself, arising from the excitation of mechano- and chemo-nociceptors.
- Reflex protective motor response: executed at the spinal cord level.
- Pain activation: mediated by the excitation of the reticular formation.
- Negative emotion: the result of hypothalamic-limbic-reticular complex activity.
- Motivation to eliminate sensations: activation of the frontal and parietal cortical areas to form goal-directed behavior (treating wounds, avoiding threats).
- Activation of memory mechanisms: retrieving past experience on how to escape from a damaging factor.
Important rule of specificity: in this integration, only one component is specific—the perceptual one. All other links (emotions, autonomic responses, movements) are non-specific, as they can manifest in response to any other stressors.
Pain from the Perspective of Functional Systems Theory
Within this concept, pain is viewed as a negative biological need that mobilizes the body. The process includes the following stages:
- Incoming signals (Etiology): External or internal damaging impact.
- Reception and transmission: Stimulation of nociceptors and transmission of nociceptive afferentation to the CNS.
- Central processing: The emergence of a localized pain sensation in the somatic analyzer under the mandatory control of the antinociceptive system.
- Effector reactions: Three key adaptation mechanisms are triggered: behavioral elimination of the factor, functional restriction (sparing the affected organ), and compensatory mobilization of defensive forces.
- Final useful result: Complete restoration of normal function in damaged organs and tissues.