Three functional divisions
The classical concept of the analyzer structure implies a clear division of the signal pathway into three successive levels. Each of them performs a strictly defined task.
- Peripheral division. This is the initial link that directly contacts the stimulus. It includes receptors, an auxiliary (additional) apparatus ensuring optimal perception, and the primary afferent neuron that receives the generated signal.
- Conductor division. Acts as a transport highway. It includes sensory nerves and specific afferent pathways passing through the spinal cord structures and the brainstem. Through these pathways, excitation is directed to higher centers.
- Central division. The highest authority of the analyzer. It is represented by specific areas of the sensory cerebral cortex. It is these cortical zones that specialize in receiving and final processing of excitation of a specific modality (e.g., visual, auditory, or tactile).
Role of the peripheral division
The peripheral division serves as the gateway for all sensory information. Its most important and primary component is the receptors.
Physiologically, receptors are specialized nerve endings. Their main fundamental function lies in the process of transduction — they convert the energy of an external physical or chemical stimulus into the energy of an electrical potential. Only in this form is the nervous system able to perceive, transmit, and decode information about the surrounding world.
Principles of analyzer functioning
Analyzers do not work simply as passive receivers, but as active tracking systems. They are constantly tuned to search for and anticipate significant information from the external or internal environment.
In the process of analyzer operation, researchers distinguish two completely opposite functional tendencies:
- Data maximization. The system constantly strives to extract the absolute maximum of information about the surrounding space and the state of the organism itself.
- Data limitation. Simultaneously, a mechanism operates to protect the central nervous system (CNS) from overload by redundant and irrelevant information.
The balance of these tendencies plays a critical role in the behavioral act. The obtained and filtered information is actively used by the nervous system both at the stage of preparation for any action and for continuous control during the direct execution of this action.
Briefly: answers to topical questions
Where are the cell bodies of the primary afferent neurons of analyzers located?
The cell bodies of primary afferent (sensory) neurons are located in sensory ganglia:
- Spinal ganglia / dorsal root ganglia — cell bodies of the first neurons of the somatosensory system; cell bodies of the first neurons of all modalities of sensitivity lie in the spinal ganglia.
- Spiral ganglion — cell bodies of sensory neurons of the auditory pathway in the inner ear.
- Trigeminal ganglion (semilunar, Gasserian) — an analogue of the spinal ganglion; contains pseudounipolar ganglion cells and provides sensory innervation of the face.
Into what two parts did I.P. Pavlov divide the cortical end of the analyzer?
The cortical division of any analyzer consists of two parts:
- Core — occupies a specific area of the cortex;
- Scattered part — nerve cells located outside the core.
What specific conduction pathways form the conductor division of the proprioceptive analyzer?
The conductor division of the proprioceptive analyzer is formed by:
- Fasciculus gracilis and cuneatus — gracile and cuneate fasciculi; conscious proprioceptive pathways in the posterior funiculi.
- Posterior spinocerebellar tract (tractus spinocerebellaris posterior, Flechsig) — conducts impulses from muscle and tendon receptors to the cerebellum.
- Anterior spinocerebellar tract (tractus spinocerebellaris anterior, Gowers) — proprioceptive pathway of the lateral funiculi.
PCC: Peripheral, Conductor, Central — the three divisions of the analyzer in the order of signal transmission.
Class and exam questions
What parts does the analyzer consist of according to I.P. Pavlov?
The analyzer includes three functional parts: peripheral, conductive, and central.
What is the main component of the peripheral division?
The main component is receptors — specialized nerve endings, as well as the auxiliary apparatus and the primary afferent neuron.
What is the main function of the receptor?
The receptor is responsible for converting the energy of an external stimulus into the energy of an electrical potential.
What two opposite tendencies are characteristic of analyzer function?
This is the drive to extract maximum information from the environment while simultaneously protecting the CNS from overload by redundant information.
What else to study on this topic
- Structure and functions of the auxiliary apparatus of receptors
- Specific afferent pathways of the spinal cord
- Brainstem pathways
- Localization of sensory cortex areas for various modalities
- Mechanisms of analyzer operation as tracking systems in behavior
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