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Anatomy Chapter 6.docx

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University of Toronto Scarborough
Biological Sciences
Connie Soros

Chapter 6 PNS: Afferent Division • Basics - information carried toward CNS 1. from viscera 2. from surface areas a. somatic sensation - includes somesthetic sensation (skin) and proprioception (muscles, joints, inner ear) b. special senses - vision, hearing, taste, smell - perception: our conscious interpretation of the world created by the brain from a pattern of nerve impulses from sensory receptors • Receptor Physiology - peripheral ends of afferent neurons have receptors that detect stimuli (changes in internal or external environment) 1. convert stimulus to an AP (transduction) 2. each kind of receptor is specialized to respond to one kind of stimulus (the adequate stimulus) a. receptor may respond to other stimuli as well, but it will lead to the sensation usually detected by that receptor 3. receptor may be a special cell associated with the peripheral ending of a neuron - types of receptors (based on what they respond to) 1. photoreceptors - light 2. mechanoreceptors - mechanical stimuli 3. thermoreceptors - temperature 4. osmoreceptors - concentration of body fluids 5. chemoreceptors - chemicals 6. nociceptors (pain receptors) - tissue damage or distortion (intense stimulation of any receptor perceived as pain) - graded receptor potentials 1. stimulus alters membrane permeability of receptor + a. opens ion channels - main effect is Na flowing in (depolarization), if summation of depolarizations reaches threshold, AP generated (called a generator potential) b. if receptor is a separate cell, it releases a chemical messenger that opens + chemically-gated Na channels in the nearby neuron, which generates an AP when threshold reached (called a receptor potential) c. stronger stimuli  greater frequency of APs (frequency code) d. stronger stimuli often result in stimulation of a larger area  more receptors activated (population code) - adaptation 1. continued stimulation does not result in APs 2. tonic receptors do not adapt or adapt slowly a. important when continuous information is useful (posture and balance sensed by proprioceptors, nociceptors) 3. phasic receptors adapt quickly a. useful when more information not necessary (touch) b. will exhibit an off response - respond again when stimulus removed
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