Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Sense Organs. Analyzers
General Concepts

Sense Organs are specialized structures capable of perceiving information about the surrounding world from the external environment via receptors. Receptors responsive to specific types of stimuli (light, sound, olfactory, thermal, etc.) evolved over the course of evolution. They became concentrated in specific organs: for example, visual receptors are located within the Eyeball, whereas tactile and thermal receptors reside in the Skin, and so forth. Over time, these organs developed accessory structures that enhanced the perception of environmental stimuli or protected the receptors from overly intense stimuli. For instance, the visual system developed extraocular Muscles to rotate the eyeball, eyelids and eyelashes, and the Lacrimal Apparatus, which together protect the eyes from mechanical, chemical, and excessive light stimulation.

There are six specialized sense organs in The Human Body:

1) The Organ of Vision — perceives light stimuli;

2) the Organ of Hearing — perceives sound stimuli;

3) the Organ of Equilibrium — perceives vestibular stimuli;

4) the Organ of Smell — perceives odors;

5) The ORGAN OF TASTE — perceives tastes;

6) somatosensory organs (skin and muscles) — perceive tactile stimulation (Touch), pain, Temperature, the sense of weight, pressure, vibration, and the spatial position of body parts.

All six types of sense organs supply the Brain's neural centers with diverse information from the external environment, which is reflected in consciousness as subjective images—sensations or perceptions. Thanks to this influx of information into the brain, humans can navigate their surroundings and adapt to changes within them. Sense organs function as the peripheral components of analyzers.

An analyzer is a complex of neural structures responsible for perceiving environmental stimuli, transforming the stimulus energy into nerve impulses, conducting these impulses to the corresponding neural centers in the Cerebral Cortex, and analyzing the received information. Based on this definition, an analyzer consists of:

1) the peripheral (receptor) component — the sense organ;

2) afferent pathways, which conduct nerve impulses to the neural centers;

3) subcortical and cortical neural centers, where the respective nerve impulses are perceived and analyzed.

The Theory of analyzers was developed by the eminent physiologist I. P. Pavlov. Corresponding to the sense organs, we distinguish the visual, auditory, vestibular, olfactory, gustatory, and somatosensory analyzers.