Anatomy & Physiology

Anatomy & Physiology Study Guide information transported by the spinocerebellar pathway ultimately arrives at the Purkinje cells of the cerebellar cortex. 16.4 Visceral Sensory Pathways Visceral sensory information is collected by interoceptors monitoring visceral tissues and organs. These interoceptors include nociceptors, thermoreceptors, tactile receptors, baroreceptors, and chemoreceptors, although none of them are as numerous as they are in somatic tissues. The axons of the first-order neurons usually travel with autonomic motor fibers innervating uniform visceral structures. Cranial nerves V, VII, IX, and X carry visceral sensory information from the mouth, palate, pharynx, larynx, trachea, esophagus, and related vessels and glands. This information is given to the solitary nucleus, a large nucleus in the medulla oblongata. The solitary nucleus is a major processing and sorting center for visceral sensory information; it has extensive connections with the various cardiovascular and respiratory centers, as well as with the reticular formation. 16.5 Olfaction There are five special senses: olfaction, gustation, vision, equilibrium, and hearing. The sense of smell, called olfaction, is provided by paired olfactory organs. The nasal cavity houses these organs on either side of the nasal septum. The olfactory organs consist 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 two percent) to the olfactory organs. Olfactory Receptors Olfactory receptors are highly modified neurons. The exposed tip of each receptor cell forms a prominent knob that projects beyond the epithelial surface. Up to 20 cilia extend into the surrounding mucus from the knob. Olfactory reception happens 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. The olfactory cells have no apparent structural differences, but distinctive sensitivities of receptor population are found on the epithelium. Effectively describing the sensory impressions represented by the over 50 different “primary smells” is almost impossible. It seems likely that the CNS interprets each smell by the overall pattern of receptor activity.

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