Anatomy & Physiology I and II

Anatomy & Physiology Study Guide • The posterior column pathway carries fine touch, pressure, and proprioceptive sensations. The axons ascend within the fasciculus gracilis and fasciculus cuneatus and relay information to the thalamus via the medial lemniscus. Before the axons enter the medial lemniscus, they cross over to the opposite side of the brain stem. This crossing over is called decussation. • The spinothalamic pathway transports inadequately localized perceptions of temperature, touch, pressure, and pain. The axons intersect in the spinal cord and rise within the anterior and lateral spinothalamic tracts to the ventral nuclei of the thalamus. Abnormalities along the spinothalamic pathway can lead to referred pain, which are inaccurate localizations of the source of pain. • The spinocerebellar pathway, including the posterior and anterior spinocerebellar tracts, carries sensations to the cerebellum concerning the position of muscles, tendons, and joints. • Visceral sensory pathways carry information collected by interoceptors. Sensory information from cranial nerves V, VII, IX, and X is delivered to the solitary nucleus in the medulla oblongata. Dorsal roots of the spinal nerves T1–L2 transport visceral sensory data from organs between the diaphragm and the pelvic cavity. Dorsal roots of spinal nerves S2–S4 carry sensory information from more inferior structures. Olfaction, the sense of smell, involves olfactory receptors responding to chemical stimuli: • The olfactory organs contain the olfactory epithelium with olfactory receptors, supporting cells, and basal (stem) cells. The surfaces of the olfactory organs are coated with the secretions of the olfactory glands. • The olfactory receptors are highly modified neurons. • Olfactory reception involves detecting dissolved chemicals as they interact with odorant- binding proteins. • In olfaction, the arriving information reaches the information centers without first synapsing in the thalamus. • The olfactory system can distinguish thousands of chemical stimuli. The CNS interprets smells by the pattern of receptor activity. • The olfactory receptor population displays a substantial turnover. The quantity of olfactory receptors decreases with age. Gustation, the sense of taste, involves taste receptors responding to chemical stimuli: • Taste (gustatory) receptors are clumped in taste buds. • Taste buds are associated with epithelial projections (lingual papillae) on the dorsal surface of the tongue. • Each taste bud contains basal cells, which appear to be stem cells, and gustatory cells, which extend taste hairs through a narrow taste pore. • The number of taste buds declines with age. • The primary taste sensations are sweet, salt, sour, and bitter. Receptors also exist for umami and water. • Taste sensitivity exhibits significant individual differences, some of which are inherited. ©2018 Achieve Test Prep Page 201 of 367