Theory of motor-visceral reflexes
The motor analyzer plays a key role in human vital activity, connecting the musculoskeletal system with higher autonomic centers via the pyramidal and extrapyramidal tracts and the reticular formation.
The main law of this theory states that proprioceptive afferentation from the motor analyzer systematically and markedly influences the work of internal organs, adapting the autonomic sphere to the needs of skeletal muscles. If these neural connections are disrupted, pathological changes occur in both motor and autonomic activity.
The main instrument of the therapeutic effect of physical exercise is training. Due to the high plasticity of the central nervous system, systematic loads allow the formation of new functional systems that ensure precision, coordination, and significant economization of motor responses.
Main types of physical exercise effects
Physical exertion has a complex effect on the body through four main mechanisms:
- Tonic (stimulating) — activates the general activity of the central nervous system and peripheral organs;
- Trophic — improves metabolic processes and tissue nutrition;
- Compensatory — utilizes reserve capabilities to replace impaired functions;
- Normalizing — restores optimal regulatory and coordinating influences of the nervous system.
Anatomical and physiological features in early age
By the time of birth, the subcortical centers of the extrapyramidal system are already formed, but the cerebellum and neostriatum are insufficiently developed. Because of this, newborns' movements are chaotic, aimless, and athetosis-like, and flexion physiologically predominates in muscle tone.
At birth, the spinal cord is morphologically more mature than the brain, which ensures innate spinal automatisms. The lower end of the spinal cord in a newborn is projected at the level of LIII, whereas in an adult it rises to the upper margin of LII. The final correspondence between spinal levels and vertebral levels is established by 5–6 years of age.
Patterns of nerve fiber myelination
The process of axon myelination occurs heterochronously and follows strict rules:
- Centrifugal direction — myelination proceeds from the neuron soma to the periphery.
- Evolutionary principle — phylogenetically and ontogenetically older structures mature earlier.
- Functional principle — motor fibers are myelinated first, along with structures ensuring vital functions (respiration, suckling, swallowing).
Cranial nerves actively become myelinated in the first months of life (except for n. vagus), and pyramidal tracts complete this process by 4 years of age, which clinically manifests as an increase in the precision of voluntary movements.
Myelination follows the rule "from center to periphery and from movement to sensation": first the ancient structures, motor fibers, and vital functions (respiration and suckling), and then complex voluntary movements.
Class and exam questions
What is the core essence of the theory of motor-visceral reflexes?
The essence of the theory is that proprioceptive afferentation from working muscles via the CNS adapts the activity of internal organs to the current demands of the musculoskeletal system.
Why are a newborn's movements chaotic and aimless?
This is due to the insufficient maturity of the cerebellum and neostriatum by birth, although the subcortical centers of the extrapyramidal system are already formed.
What are the main rules of nerve fiber myelination?
Myelination proceeds centrifugally (from the soma to the periphery), primarily affecting evolutionarily ancient structures and motor fibers that ensure critical vital functions.
How does the topography of the spinal cord change during growth?
In a newborn, the lower end of the spinal cord is located at the level of the third lumbar vertebra (LIII), while in an adult it is at the level of the upper margin of the second lumbar vertebra (LII).
What else to study on this topic
- Structure and functions of the brain and spinal cord
- Classification of neurons and glial cells
- Extrapyramidal system and hyperkinesia
- Basal nuclei and striopallidal system
- Role of the thalamus and motor cortex in movement
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