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Sensory Pathway Outline

Sensory Pathway Outline - Chapter 15 Neural Integration I...

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Chapter 15: Neural Integration I: Sensory Pathways and the Somatic Nervous System I. An Overview of Sensory Pathways and the Somatic Nervous System, p. 496 Specialized cells called sensory receptors monitor specific conditions in the body or the external environment. II. Sensory Receptors and Their Classification, p. 496 General senses describes our sensitivity to: Temperature, pain, touch, pressure, vibration, and proprioception The special senses are: 1. olfaction (smell) 2. vision (sight) 3. gestation (taste) 4. equilibrium (balance) 5. hearing Sensory Receptors, p. 497 A sensory receptor detects an arriving stimulus and translates it into an action potential that can be conducted to the CNS. The Detection of Stimuli, p. 497 Free nerve endings are the branching tips of these dendrites that are not protected by accessory structures. The area monitored by a single receptor cell is its receptive field. The larger the receptive field, the poorer your ability to localize a stimulus. Transduction begins when a stimulus changes the transmembrane potential of the receptor cell. This is called a receptor potential. A receptor potential large enough to produce an action potential is called a generator potential. The Interpretation of Sensory Information, p. 497 Sensory information that arrives at the CNS is routed according to the location and nature of the stimulus. The following characteristics of the stimulus are conveyed by the frequency and pattern of action potentials: 1. Strength 2. Duration 3. Variation Tonic receptors are always active Phasic receptors are normally inactive, but become active for a short time whenever a change occurs in the conditions they are monitoring. They provide information about the intensity and rate of change of a stimulus. Adaptation, p. 498 Adaptation is a reduction in sensitivity in the presence of a constant stimulus. Your nervous system quickly adapts to stimuli that are painless and constant. The reticular activating system helps focus our attention and heightens or reduces our awareness of arriving sensations. This adjustment can occur under conscious or subconscious direction. The General Senses, p. 498 Receptors for the general senses are scattered throughout the body and have a relatively simple structure. They can be divided into: 1. exteroceptors provide information about the external environment 2. proprioceptors report the positions of skeletal muscles and joints 3. interoceptors monitor visceral organs and functions A more detailed classification system divides the general sensory receptors into four types by the nature of the stimulus that excites them: 1. nociceptors (pain) 2. thermoreceptors (temperature) 3. mechanoreceptors (physical distortion) 4. chemoreceptors (chemical concentration)
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Proprioception is a purely somatic sensation. There are no proprioceptors in the visceral organs of the thoracic and abdominopelvic cavities. You cannot tell where your spleen, appendix, or pancreas is at the moment.
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