Interaction with the Environment and Physiological Isolation
The habitat represents a strictly organized space-time continuum. On Earth, it is defined by gravity, atmosphere, temperatures, and the electromagnetic field. External phenomena are divided into episodic (e.g., earthquakes) and periodically recurring ones (day-night cycle, seasons). It is precisely these regular rhythmic influences that play a key role in shaping biological properties across generations.
Despite their close connection with the environment, living organisms are isolated from inanimate nature. This boundary is maintained by phospholipid membranes. Their structure is universal: the membranes of a human nerve cell and a sea urchin egg cell are organized almost identically. The emergence of such structures allowed living forms to separate from the primordial aquatic environment, complicate their internal organization, and begin actively influencing the surrounding world.
Stimuli and Types of Irritability
Any environmental factors acting on cell membranes are called stimuli. They can be physical (temperature, mechanical), chemical (hormones, acids), physicochemical (changes in pH, osmolarity), biological (viruses), and informational (speech, emotions).
The ability to respond to these factors by altering the structure of membranes and protoplasm is called irritability. There are two main types:
- Nonspecific (trigger) irritability. Independent of the stimulus type. The stimulus acts as a trigger that initiates internal membrane processes, bringing molecules to a threshold state.
- Specific (selective) irritability. Manifests in response to biologically active substances (ligands). Protein receptors on the cell membrane interact with stimuli according to the lock-and-key principle, triggering a cascade of intracellular reactions. This selectivity is also regulated by the size of ion channels.
Memory and Anticipatory Reflection of Reality
The fixation of molecular changes resulting from the action of stimuli is ensured by the universal genetic apparatus—this is the basis of biological memory. It is formed most vividly during repetitive exposures or single yet powerful emotional stimuli.
Based on memory, Academician P.K. Anokhin formulated the concept of anticipatory reflection of reality. This is the fundamental ability of an organism to foresee the course of external events and respond to them faster than they actually occur.
The process is formed in three stages:
- Stage A (Primary Reaction): External events follow one after another, provoking isolated internal reactions. There is no connection between the reactions yet.
- Stage B (Chemical Continuum): Upon repeated recurrence of external events, molecular changes in the organism become linked into a single sequential chain.
- Stage C (Realization): Now, the action of only the initial trigger stimulus is sufficient. In response, the organism instantly launches the entire chain of internal chemical reactions, preparing for subsequent influences even before they occur in reality.
Briefly: answers to topical questions
Which tissues of the body are classified as excitable tissues?
Excitable tissues of the body include three types of tissue: nervous, muscular, and glandular (secretory).
- Nervous tissue possesses the highest excitability; its specific function is the generation of a nerve impulse (the initiation and conduction of excitation).
- Muscular tissue possesses lower excitability; a specific sign of its excitation is contraction (a decrease in muscle fiber length or a change in tension).
- Glandular tissue has the lowest excitability; its specific response is secretion (the release of a secretion).
What are the main principles of the physiological regulation of body functions?
The main principles of physiological regulation are the maintenance of homeostasis by functional systems, the use of feedback (the reflex arc), and the integration of different modes of signal transmission. The regulation of functions is carried out in three ways:
- Nervous regulation is implemented rapidly and acts for a short duration via the nervous system.
- Humoral regulation proceeds relatively slowly through substances (hormones, cytokines, mediators) circulating in body fluids.
- Neurohumoral regulation is the main form of regulation, combining rapid nervous and prolonged humoral influences on organs and neural centers.
What is the principle of negative feedback in physiology?
The principle of negative feedback in biochemical autoregulation is that when the end product of a reaction chain accumulates to a certain level, it inhibits the further progression of the process. The end product N acts as an allosteric inhibitor of the key enzyme. The accumulating product can bind to the enzyme, alter its conformation, and transition it into an inactive state; the inhibition of chain reactions begins with the rate-limiting step, and product production ceases until its concentration decreases.
To memorize the five groups of stimuli, use the Russian acronym FIHFIB: Fizicheskie (Physical), Informatsionnye (Informational), Himicheskie (Chemical), Fiziko-khimicheskie (Physicochemical), Biologicheskie (Biological).
Class and exam questions
What is the difference between trigger and selective irritability?
Trigger irritability does not depend on the quality of the stimulus—it merely initiates a reaction like a trigger mechanism. Selective irritability operates in a strictly specific "lock-and-key" manner via protein receptors.
What is the chemical continuum in Anokhin's theory?
This is an inseparable chain of molecular changes formed within the organism that arises upon repeated recurrence of external stimuli and allows for anticipatory responses to them.
How is irritability related to excitability?
Irritability is the primary, basic property of living matter to respond to stimuli. During evolution, in specialized tissues (nervous and muscular), it transformed into excitability.
What else to study on this topic
- Mechanisms of Molecular Receptors and Ligand-Receptor Interaction
- Principles of Selectivity of Protein Ion Channels
- The Role of the Genetic Apparatus in Forming Memory Traces
- Transition of Irritability into Excitability: An Evolutionary Aspect
- Impact of Episodic and Periodic Phenomena on Biorhythms
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