Plan
► Concept of sensory organ, sensory analyzer and sensory system.
► General characteristics of peripheral sensory systems: concept of receptor, classification of receptors, mechanisms of their stimulation.
► Characteristics of central part of sensory systems.
Concept of Sensory Organ, Analyzer and Sensory System
For an adequate interaction with the external environment, an organism must receive information about the outside world and about conditions of all its physiological systems. This task is performed by specialized reflective mechanisms called sensory systems. Evolution of the idea of sensory systems in Russia is associated with acad. I.P. Pavlov, who proposed a concept of an ?analyzer? in 1909. Be reminded that the term ?analysis? means breaking an integral whole into parts with the aim of better understanding the essence of this whole. I.P. Pavlov defined an analyzer as ?a complex of sensory nervous structures that perceive and analyze external and internal stimuli?. According to I.P. Pavlov, an analyzer consists of three parts: peripheral, conducting and central.
The peripheral part is represented by sensory receptors. The conducting part is represented by afferent nerves, and the central part - by populations of neurons in the brainstem and the cortex of the brain. The cortical part of an analyzer is represented by its nucleus (aggregation of neurons in a particular part of the cerebral cortex) and by elements scattered throughout a relatively large area of the cerebral cortex. When the nucleus of an analyzer is damaged, the lost functions may be partly taken over by these scattered elements.
For example, the visual analyzer is represented by the following structures: 1) receptors of the eye retina (the peripheral part); 2) optic nerves (the conducting part); 3) a region in the occipital lobe of the cortex and nervous centers