Human Anatomy and Physiology - N. I. Fedyukovich 2003

Nervous System
Conditioned and Unconditioned Reflexes

Reflexes are regular Responses of the body to Changes in the internal or external environment, mediated by the Central Nervous system in response to receptor stimulation.

Based on their biological significance, reflexes are classified into alimentary (the acts of swallowing, chewing, salivation, etc.), sexual (reproduction), and locomotor (body movement). Depending on receptor Location, reflexes can be exteroceptive (perceiving stimuli from the external environment), visceroceptive (stimuli coming from Internal Organs), or proprioceptive (stimuli coming from skeletal Muscles, joints, and tendons).

Based on The Nature of the response, reflexes are distinguished as secretory, trophic, and motor. Reflexes are divided into simple and complex. Pupillary constriction in response to bright light or a tendon tap are simple reflexes, whereas the Regulation of Respiratory, cardiovascular, and digestive systems are complex. Depending on which part of the CNS is involved in reflex activity, cortical (Cerebral Cortex Neurons), mesencephalic (Midbrain neurons), bulbar (Medulla Oblongata neurons), and spinal (Spinal Cord neurons) reflexes are distinguished.

Conditioned reflexes are individual adaptive responses of the body that develop gradually under the repeated influence of stimuli. They are absent in newborns and can only be developed and executed with the participation of the cerebral cortex. Human conditioned reflexes are temporary; they can disappear if the conditioned stimulus is not reinforced by an unconditioned one.

The formation of conditioned reflexes requires specific conditions: 1) the presence of two stimuli—an indifferent one, which can become conditioned, and an unconditioned one, which triggers some bodily activity, such as salivation, etc.; 2) the indifferent stimulus (light, sound, etc.) must precede the unconditioned one; 3) the unconditioned stimulus must be stronger than the conditioned one; 4) the absence of distracting or other stimuli; 5) an active state of the cerebral cortex, and the absence of pathological processes or other persistent stimuli.

Unconditioned reflexes are innate, hereditary, consistently transmitted responses common to all animals and humans. The primary unconditioned reflexes include sucking, alimentary, protective, and sexual reflexes.

Unconditioned reflexes have pre-existing, anatomically formed reflex arcs (Fig. 143).

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Fig. 143. Diagram of a reflex arc:

1 — nerve endings of a sensory neuron in the Skin; 2 — peripheral process of a sensory neuron; 3 — axon of a motor Cell; 4 — nerve ending in a Muscle; 5 — motor cell of the anterior horn; 6 — interneuron; 7 — central process of a sensory neuron; 8 — spinal ganglion

In the execution of unconditioned reflexes, the leading role belongs to the subcortical nuclei, Brainstem, and spinal cord. Unconditioned reflexes are relatively constant, minimally changing, and inert reflex responses; consequently, it is impossible to adapt to new environmental conditions solely through unconditioned reflexes.