Anatomy & Physiology

Anatomy & Physiology Study Guide

Chapter 16: Senses Human senses can be divided into two categories: general and special. The “general senses” provide information about the body and its environment. The “special senses” refer to smell, taste, sight, equilibrium (balance), and hearing. Sensory information from all parts of the body is routed to the somatosensory cortex. Sensory receptors are specialized cells that monitor specific conditions in the external environment or within the body. A receptor is stimulated by a change in conditions and passes sensory information to the CNS in the form of action potentials along the axon of a sensory neuron. Axons are discrete parts of sensory pathways that deliver somatic and visceral sensory information to the CNS—the nerves, nuclei, and tracts that deliver somatic and visceral sensory information to their final destinations inside the CNS. The afferent division of the nervous system is comprised of receptors, sensory neurons, and sensory pathways. Somatic and visceral sensory information often travel along the same pathway. Processing centers in the brain receive somatic sensory information. It is delivered to either the primary sensory cortex of the cerebral hemispheres or appropriate areas of the cerebellar hemispheres. Visceral sensory information is distributed primarily to reflex centers in the diencephalon and brain stem. 16.1 Sens ry Receptors Sensory receptors join our internal and external environments with the nervous system. Sensory receptors are specialized cells or cell processes that provide the central nervous system with information about conditions inside or outside the body. The term general sense is used to describe the sensitivity to temperature, pain, touch, pressure, vibration, and proprioception. The body is heavily populated with general sensory receptors, and they are relatively simple in structure. Some of the information they send to the CNS reaches the primary sensory cortex and conscious awareness. Sensation describes the arriving information. The conscious awareness of a sensation is called perception . The special senses are olfaction (smell), vision (sight), gustation (taste), equilibrium (balance), and hearing. Their receptors are structurally more complex than those of the general senses and thus provide the specialized sensations. Special sensory receptors are found in sense organs, such as the eye or ear, where the receptors are protected by surrounding tissues. These receptors provide information that is distributed to certain regions of the cerebral cortex (the auditory cortex, the visual cortex, and so forth) and centers throughout the brain stem. Sensory receptors represent the interface between the nervous system and the internal and external environments. Action potentials are generated when a sensory receptor detects an arriving stimulus and translates it. The action potential is then conducted to the CNS. This process of translating the stimulus is called transduction . If transduction does not occur, then as far as the brain is concerned, the stimulus does not exist.

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