Causes and Mechanisms of Hyperactivation
Pathological amplification of neural influences occurs when the normal balance between stimuli in the central nervous system is disrupted. The main factor is an excessive increase in the level of neuronal excitation, as well as a pathological increase in the duration of this excitatory process.
According to their origin, hyperactivation is divided into two categories:
- Primary genesis — initial pathological excitation of the neural structures themselves.
- Secondary genesis — occurs indirectly, including via disinhibition (when the restraining influence of other centers is lost).
As a result of these processes, persistent foci of excitation are formed in the brain tissue. Their stable and continuous functioning becomes the foundation for the development of a number of neuropathological syndromes that exhaust the body's reserves.
Clinical Syndromes in Hyperactivation
The presence of persistent excitation foci manifests with a striking clinical picture. Depending on the localization of hyperactive neurons, three main groups of pathological syndromes are distinguished:
- Pain syndromes. Occur when sensory pathways and centers are damaged. Classic examples include thalamic pain syndrome and phantom limb pain following amputation.
- Seizure syndromes. Characteristic of pathology in motor cortical centers and subcortical structures. The most well-known example is epilepsy.
- Autonomic disorders. Manifest as systemic failures in internal organ function. These include arterial hypertension, cardiac arrhythmias, and polyphagia (pathologically increased appetite).
The Role of Inhibition in Analyzer Damage
In organic damage to neural structures (e.g., development of paralysis), the severity of the clinical deficit is determined not only by the tissue destruction itself. Two factors play a huge role:
- The direct size of the organic lesion focus.
- Protective inhibition — temporary depression of activity in nearby undamaged neurons.
The clinical significance of protective inhibition is that it is reversible. As this inhibitory influence is lifted, the patient's motor function can partially recover. This occurs even if the initial structural damage to the brain tissue remains unchanged.
Hyperactivation of Inhibitory Systems and Reduced Excitation
Pathological changes can affect not only excitatory but also inhibitory neurons, and can be characterized by a global decrease in activity.
Decrease in the Intensity of the Excitatory Process in the CNS Often caused by external chemical exposure (e.g., the effect of narcotic drugs). The pathogenesis of this state boils down to a global reduction in driving influences on effector structures of various organs and tissues.
Hyperactivation of CNS Nuclei Exerting Inhibitory Influence Even the activation of neural centers can lead to the suppression of functions if these centers are inhibitory.
- Example: excessive activation of neurons in the reticular formation of the medulla oblongata.
- Mechanism: powerful descending inhibitory influences emanate from these nuclei to the spinal cord structures. Under the influence of these stimuli, suppression of polysynaptic reflexes occurs.
- Clinical picture: the patient develops severe movement disorders (up to marked muscle paresis) and a noticeable decrease in tissue sensitivity.