Nursing Preparation Study Guide

Nursing Preparation Study Guide

7.2.3 General Sensory Receptors The general senses have receptors scattered throughout the body, and they are relatively simple in structure. They can be divided into exteroceptors, proprioceptors, and interoceptors. Exteroceptors provide information about the external environment; proprioceptors report the positions of skeletal muscles and joints; and interoceptors monitor visceral organs and functions. A more detailed classification system further divides the general sensory receptors into four types, each classified by the nature of the stimulus that excites them: nociceptors (pain), mechanoreceptors (physical distortion), thermoreceptors (temperature), and chemoreceptors (chemical concentration). Each class of receptors has distinct functional and structural characteristics. 7.2.4 Special Senses There are five special senses: olfaction, gustation, vision, equilibrium, and hearing: 1. Olfaction: The sense of smell, or olfaction, is granted by paired olfactory organs. These organs are located in the nasal cavity on either side of the nasal septum, which are comprised of two layers: the olfactory epithelium and the lamina propria. The olfactory epithelium contains the olfactory receptor cells, supporting cells, and regenerative basal cells (stem cells). This layer contains olfactory glands, or Bowman glands, whose secretions absorb water and form a thick, pigmented mucus. A normal, relaxed inhalation carries a small sample of inhaled air (about 2%) to the olfactory organs. Olfactory Receptors: Olfactory receptors are neurons that are highly modified. The unprotected tip of each receptor cell forms a knob that projects beyond the epithelial surface. This knob offers a foundation for up to 20 cilia that extend into the surrounding mucus. Olfactory reception occurs on the surfaces of the olfactory cilia as dissolved chemicals interact with receptors, called odorant-binding proteins, on the membrane surface. Olfactory Discrimination: The olfactory system can make subtle distinctions among 2000-4000 chemical stimuli. No apparent structural differences exist among the olfactory cells, but the epithelium contains receptor populations with distinct sensitivities. At least 50 “primary smells” are known, and it is near impossible to effectively describe these sensory impressions. It is likely that the CNS interprets each smell on the basis of the overall pattern of receptor activity. 2. Gustation: Gustation, or taste, provides information about the foods and liquids we consume. Taste receptors, or gustatory receptors, are distributed over the superior surface of the tongue and adjacent portions of the larynx and pharynx. Taste buds are sensory structures that are formed by receptors and specialized epithelial cells. An adult human has approximately 3000 taste buds. The superior surface of the tongue houses epithelial projections called lingual papillae. The human tongue bears four types of lingual papillae: filiform, papillae, fungiform

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