Mechanisms of the nervous system's influence on cell metabolism
To understand the essence of the pathology, it is necessary to examine how exactly the nervous system controls metabolism in healthy tissues. There are five basic pathways of action on target cells:
- Impulse activity patterns. A specific temporal pattern of neural discharges serves as a kind of code that transmits information necessary to regulate metabolic cascades.
- Changes in axonal transport. Trophogens—special proteins and peptides—are constantly delivered to peripheral tissues along neural processes (axons).
- Modulation of membrane permeability. Nerve endings are capable of altering the ion homeostasis of the target cell, which directly affects the activity of intracellular enzymes.
- Trophic secretion of neurotransmitters. The so-called "small" (background) number of neurotransmitter quanta is constantly released into the synaptic cleft. This process occurs spontaneously, outside of excitatory signal transmission, and is critically important for maintaining the life of the postsynaptic structure.
- Shift in electrical potential. The effect on the static potential of both the presynaptic and postsynaptic membranes alters substance transport and the overall excitability of the cell.
How the trophic function is implemented
Neurotrophic control is provided through three main mechanisms, the disruption of which triggers dystrophy:
- Modulation of impulse activity. Both the frequency of action potential generation and the time intervals between them (forming patterns) are extremely important for target cells.
- Synthesis and delivery of neurotrophic factors. Growth factors play a key role here. The life cycle of these substances is strictly defined: they are synthesized in the neuron soma, transported along the axon, secreted into the synapse, and finally bind to receptors on the postsynaptic membrane.
- Support of the innervated structure. Constant functional interaction is necessary to maintain the optimal level of vital activity of the postsynaptic cell.
Denervation syndrome and deafferentation
A typical etiological basis of the neurodystrophic process is denervation syndrome. It is based on the cessation of axonal transport, which has been studied in detail in skeletal muscle denervation models. As a result, typical metabolic disorders develop in postsynaptic structures.
However, pathology can occur not only when efferent (motor) pathways are damaged, but also when afferent structures are damaged (for example, during transection or mechanical trauma to a sensory nerve). This condition is called tissue deafferentation. The loss of sensory impulse flow entails trophic shifts that are comparable in severity to the consequences of classical motor denervation.
The neurodystrophic component is present in almost all forms of human disease—from mechanical trauma to functional disorders.
Clinical and structural manifestations
Trophic disorders lead to severe consequences for the body. The main manifestations of the neurodystrophic process include:
- Alteration of the normal activity of innervated organs.
- Development of gross structural defects, primarily hypotrophy.
- Formation of integumentary tissue defects, such as neurotrophic ulcers.
- Malignant transformation (the process of malignant conversion of tissues deprived of normal neural control).
Against the background of somatic disorders, one must not forget about the functional disorders of the nervous system itself, such as neuroses (disorders of higher nervous activity). They occur in 20–30% of the population and are of colossal socio-economic significance, exacerbating the general condition of patients.
Briefly: answers to topical questions
What specific biochemical and metabolic disorders develop in the cell during denervation syndrome?
During denervation syndrome, dysenzymasia and "embryonalization" of metabolism develop in the cell. Metabolism acquires features of the early stages of ontogenesis: oxidative processes decrease, anaerobic glycolysis dominates, and the pentose cycle is activated. Lysosomal membrane labilization with enzyme release and impaired selective permeability of the plasmalemma also occur.
What specific types of neurotrophic factors (trophogens) are transported along axons to peripheral tissues?
Various groups of trophogens are transported along axons to peripheral tissues.
- Main trophogens include nucleotides, certain amino acids, prostaglandins, catecholamines, serotonin, acetylcholine, complex lipids, gangliosides, substance P, and CGRP.
- Oligopeptides include liberins, statins, enkephalins, endorphins, bradykinin, neurotensin, cholecystokinin, ACTH fragments, and oxytocin.
- Growth factors include nerve growth factor (NGF), epidermal growth factor (EGF), insulin-like growth factor (IGF), and tumor necrosis factor (TNF).
To memorize the 3 stages of growth factor action: Synthesis (in the neuron) → Transport (along the axon) → Secretion (into the synapse). Abbreviated as STS.
Class and exam questions
What is the essence of denervation syndrome?
This is a complex of typical disorders in the postsynaptic cell arising due to impaired axonal transport of trophogens and neurotransmitters after nerve damage.
Is tissue dystrophy possible while motor innervation is preserved but sensory innervation is lost?
Yes, damage to afferent (sensory) pathways causes deafferentation, which leads to trophic disorders comparable to the consequences of motor nerve destruction.
How does neurotransmitter release at rest affect trophic function?
Spontaneous release of small amounts of neurotransmitter (without transmission of an excitation signal) is necessary to maintain the baseline viability and structural integrity of the postsynaptic cell.
What else to study on this topic
- Molecular mechanisms of axonal transport of trophogens
- The role of growth factors in neurotrophic control
- Pathogenesis of neurotrophic ulcer formation
- The connection between higher nervous activity disorders (neuroses) and somatic pathology
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