Causes and mechanisms of efferent control disorders
Pathology of efferent innervation occurs due to failures along the pathway from the neuron to the target cell. Several basic mechanisms for the development of such disorders are distinguished. First, it is a disruption of a specific type of nervous activity affecting movement control, sensitivity, tissue trophism, or higher nervous activity (HNA). Second, dysfunction is caused by post-traumatic (partial or complete) interruption of impulse transmission. Failures of axonal transport of substances also play an important role.
The problem may also lie on the side of the target tissues themselves, when their perception of nerve signals is disrupted. This occurs against the background of hypoxia, transmembrane ionic imbalance, or changes in the number and affinity of receptors for neurotransmitters.
In clinical practice, the main causes are divided into two large groups:
- Acquired: ischemia, encephalitis, intracranial tumor growth, various intoxications.
- Genetically determined: often characterized by polygenic dependence (interaction of genes and environmental factors). A striking example is multiple sclerosis: concordance in monozygotic twins reaches 50%, and in close relatives the risk of falling ill is eight times higher than in the general population.
Denervation syndrome and locomotion disorders
With partial or complete cessation of neural control, denervation syndrome develops. At this point, postsynaptic neurons, as well as deinnervated target organs, undergo a series of transformations. Deep metabolic shifts occur within them, neurotransmitter metabolism is restructured, and cell structure and function are grossly impaired.
If efferent disorders affect the motor sphere, neurogenic locomotor disorders occur. They are characterized by changes in the basic parameters of motor activity: the total number of movements performed, their pace, and spatial coordination are impaired.
Pathological phase states
A special manifestation of higher nervous activity dysfunction and autonomic reactions is represented by parabiotic phase states. Normally, the nervous system responds adequately to external influences: the stronger the stimulus, the more pronounced the conditioned or unconditioned reflex response. With the development of pathological phase states, this correspondence is lost: the reaction no longer matches either the stimulus parameters or the biological needs of the organism. This is accompanied by the appearance of pathological reflexes and a drop in adaptation.
These states are based on three fundamental mechanisms:
- Functional "disintegration" — the loss of normal interneuronal connections developed during ontogenesis.
- Pathological integration — neurons form new connections not characteristic of a healthy individual, building a stable "pathological system".
- Decreased plasticity — a global loss of adaptability of nervous tissue structures.
Classification of phase reactions
Pathological reactions are classified depending on how the nervous tissue responds to stimuli of varying strength:
- Equalizing phase: the response is identical regardless of whether a weak or strong stimulus (visual, painful, verbal) is applied.
- Phase of medium stimuli: the maximum response is registered exclusively for stimuli of medium intensity.
- Paradoxical phase: strong stimuli cause an extremely weak response (or none at all), whereas weak signals provoke a preserved or enhanced reaction.
Terminal phases of reactivity are distinguished separately:
- Narcotic state: gradual fading of responses (reactions to weak stimuli disappear first, then to strong ones).
- Inhibitory state: absolute areactivity to any stimulus.
- Ultraparadoxical state: qualitative inversion of reactions. A negative response occurs to positive stimuli, and a positive one to negative stimuli (for example, a burst of anger in a patient in response to news of a favorable prognosis).
The development of phase states obeys the laws of "temporal mosaic" (phases sequentially replace each other as the disease progresses) and "spatial mosaic" (different phase states can be observed simultaneously in different areas of the nervous system).
Briefly: answers to topical questions
What stages of parabiosis did N.E. Vvedensky distinguish?
N.E. Vvedensky distinguished three successive stages of parabiosis, reflecting changes in tissue response to stimuli of varying strength.
- Equalizing stage — weak and strong stimuli cause a response of equal strength.
- Paradoxical stage — weak stimuli cause strong responses, while strong stimuli lead to weak responses or their absence.
- Inhibitory stage — the tissue ceases to respond to any stimuli, and complete unexcitability develops.
In some experimental models, a phase of hyperexcitability may also be recorded prior to the equalizing phase, when the muscle responds with a contraction to subthreshold stimuli.
What specific changes in the receptor apparatus occur during skeletal muscle denervation?
Skeletal muscle denervation leads to hypersensitization to the missing neurotransmitter: the sensitivity of denervated structures increases. Specific changes in the receptor apparatus include:
- activation of acetylcholine receptor synthesis;
- insertion of acetylcholine receptors across the entire surface of the muscle fiber, rather than only in the postsynaptic membrane.
These changes are described as a manifestation of Cannon's law of denervation.
To remember the paradoxical phase state, imagine inverted scales: a "heavy" (strong) stimulus gives a minimal response, while a "light" (weak) one gives a maximum response.
Class and exam questions
What is denervation syndrome?
It is a complex of metabolic, neurotransmitter, and structural-functional changes in tissues that occurs due to a decrease or complete loss of neural control over them.
How does the ultraparadoxical state differ from the paradoxical one?
In the paradoxical phase, the evaluation of stimulus strength is impaired (a weak one causes a strong reaction, a strong one — a weak reaction). In the ultraparadoxical phase, the quality of the response is inverted: a pleasant stimulus causes a negative reaction, and vice versa.
What is the essence of the formation of a "pathological system"?
Due to the mechanism of pathological integration, new functional connections that are not characteristic of a healthy organism are formed in the nervous system, consolidating the course of the disease.
What else to study on this topic
- Mechanisms of axonal transport impairment
- The effect of hypoxia on neurotransmitter receptor affinity
- Metabolic shifts in target cells during denervation
- Polygenic mechanisms of nervous system pathology inheritance
Master the entire topic in the "Pathophysiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Efferent Nervous System Disorders" and 4,913 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 135 video lessons on the subject
Other topics in "Chapter 28. Standard forms of pathology of the nervous system"
Free video lessons: pathophysiologyShort lessons with lecture notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.