Main characteristics and mechanisms
According to I.P. Pavlov's teaching, unconditioned reflexes are genetically determined and present in the organism from birth. Their realization is carried out on the basis of innate reflex arcs that are anatomically fixed.
The main condition for the occurrence of such a reaction is the action of an adequate stimulus on strictly defined receptors. Under normal conditions, these reflexes occur constantly and unfailingly. A classic example of a basic unconditioned reflex is salivation, which is triggered by the direct contact of food with the receptors of the oral cavity. At the same time, I.P. Pavlov equated the most complex forms of such innate reactions with instincts.
Classification of complex unconditioned reflexes
Complex innate reflexes are not just a single response, but a whole complex of specific behavioral and autonomic reactions. It is customary to distinguish the following main groups:
- Feeding
- Defensive
- Sexual
- Parental
- Exploratory
Exploratory behavior
Among all types of innate reactions, exploratory behavior occupies a special place. As a rule, it manifests in response to any unexpected changes in the environment.
I.P. Pavlov characterized this reaction to novel stimuli as the "what is it?" reflex. This activity has a pronounced adaptive character, allowing the organism to quickly assess environmental changes. In addition, the orienting reflex serves as the fundamental basis for the formation of many complex forms of learning.
Components of complex reflexes
Any complex unconditioned reflex is realized through a combination of motor (behavioral) and autonomic manifestations.
1. Complex feeding reflex Triggered by the action of food on the receptors of the gastrointestinal tract or on distance receptors (e.g., olfactory). Includes:
- Motor activity (searching for and capturing food);
- Secretory activity (secretion of digestive juices);
- Autonomic changes (accompanying changes in respiration and cardiac activity).
2. Complex defensive reflex Arises in response to threatening stimuli and is accompanied by:
- Motor reaction (avoidance, fight);
- Global change in autonomic functions, including restructuring of heart rate (HR), respiration, sweating, and changes in the secretory activity of digestive glands.
Types of defensive reactions
The behavioral component of the defensive reflex can be realized according to two fundamentally different scenarios:
- Passive defensive reaction. The animal performs a passive action in response to a conditioned signal. For example, it may simply move to a safe compartment of the experimental chamber, thereby preventing painful stimulation without engaging in active opposition.
- Active defensive reaction. In this case, the animal performs active instrumental actions. An example is pressing a lever or manipulating objects, the purpose of which is to completely stop or physically avoid the damaging effect.
Briefly: answers to topical questions
Where are the nerve centers of the main unconditioned reflexes localized?
The centers of various unconditioned reflexes are localized in the structures of the spinal cord and brain.
- Salivatory center — located in the medulla oblongata.
- Sympathetic centers — the first neurons are located in the lateral horns of the thoracic and upper lumbar segments of the spinal cord.
- Parasympathetic centers — localized in the sacral segments of the spinal cord.
- Respiratory centers — the inspiratory and expiratory components are located in the medulla oblongata, the apneustic center in the pons, and the pneumotaxic center in the midbrain.
What are the main differences between unconditioned and conditioned reflexes?
The main differences lie in their origin, variability, and formation conditions.
| Sign | Unconditioned reflexes | Conditioned reflexes |
|---|---|---|
| Origin | Innate, genetically determined | Acquired during individual life |
| Degree of variability | Relatively constant | Qualitatively special, extremely variable form |
| Conditions of occurrence | Action of adequate stimuli on corresponding receptors | Associated with the learning process, coincidence of indifferent and unconditioned stimuli |
| Nature of the reaction | Reaction to actual impact | Anticipatory reaction reflecting the properties of a future event |
What mechanisms of inhibition of unconditioned reflexes exist?
The sources directly describe the following mechanisms and types of inhibition of reflex activity:
- Sechenov inhibition — a classic example of descending central inhibitory influence: placing a salt crystal on the area of the optic thalami (thalamic structures of the RF) in a frog causes suppression of the passive defensive reaction—withdrawing the paw in response to acid.
According to electrophysiological nature, the following are distinguished:
- Hyperpolarizing inhibition — occurs on postsynaptic membranes under the action of inhibitory neurotransmitters and reduces tissue excitability.
- Persistent depolarizing inhibition — occurs at a high frequency of excitation; the accumulation of excitatory neurotransmitter prevents the potential of the postsynaptic membrane from returning to the resting state.
- Stabilizing inhibition — associated with the action of a number of biologically active substances: sodium permeability of membranes is blocked without changing the resting potential, which makes the generation of excitation impossible.
Class and exam questions
What did I.P. Pavlov call the «what-is-it?» reflex?
This is what I.P. Pavlov called the orienting-investigatory reaction of the organism to any novel or unexpected stimuli. It has adaptive significance and underlies learning.
What is the difference between active and passive defensive reactions?
In a passive reaction, the animal moves away from the threat (e.g., moves to a safe place), preventing pain. In an active reaction, it performs instrumental actions (e.g., presses a lever) to forcibly terminate the damaging effect.
What components are included in a complex feeding reflex?
The complex feeding reflex consists of motor activity, secretory activity of glands, and autonomic changes (restructuring of respiration and cardiac activity).
What else to study on this topic
- Mechanisms of functioning of innate reflex arcs
- The role of distant receptors in the initiation of feeding reflexes
- Autonomic support of complex behavioral reactions
- Instrumental actions in the structure of active defense
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