GENERAL ESTHESIOLOGY
Information from the outer environment is per-cieved by complicated systems named analyzers. The analyzer as a sensory system consists of the peripheral part (sensory receptors), intermediate part (neural pathways), and central part (the brain involved in sensory perception).
Sensory modalities are described as either special senses or general senses. The special senses are olfaction, vision, taste, hearing and vestibu-lar function. Afferent information is encoded by highly specialized sense organs (organa sensoria) and transmitted to the brain in cranial nerves I, II, VII, VIII, IX and X. The general senses include touch, pressure, vibration, pain, thermal sensation and proprioception (perception of posture and movement). Stimuli from the external and internal environment activate a diverse range of receptors in the skin, viscera, muscles, tendons and joints. Afferent impulses from the trunk and limbs are conveyed to the spinal cord in spinal nerves whilst those from the head are carried to the brain in cranial nerves.
Receptors of sense organs are subdivided into neurosensitive receptors and senso-epithelial receptors. Neurosensory cells are neurons which accept sensitive signals by the dendrites, provide them to nervous impulses and transfer in CNS by the axons. They are a part of the photoreceptor system and olfactory organ. Sensory epithelial cells are specialized cells which recognize sensitive signals; transmission of nervous impulses from them in the CNS is carried out due to their connections with dendrites of neurons. They are a part of the vestibu-locochlear apparatus and taste organ.
THE EYE AND RELATED STRUCTURES
The photoreceptor system (eye and related structures) consists of the eyeball (bulbus oculi) and accessory visual structures (structurae oculi ac-cessoriae). Accessory visual structures include the eyelids, eyebrow, conjunctiva, extra-ocular muscles, lacrimal apparatus, and structures of the orbit (periorbita, fascial sheath of the eyeball, ret-robulbar fat, orbital septum and fasciae). The eye is a sensory organ whose lens focuses rays of light originating in the external environment onto photosensitive cells of the retina. The intensity, location, and wavelengths of the transmitted light are partially processed by the retina, and the assembled information is sent via the optic nerve for further processing and interpretation by the visual cortex of the brain as three-dimensional color images.