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Topic 13
The Somatic Sensory System
Lange
Biology 463 - Neurobiology
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Introduction
Somatic Sensation– Enables body to feel, ache, chill– Responsible for touch and pain– Somatic sensory system: Different from other systems
• Receptors: Broadly distributed• Responds to many kinds of stimuli
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Touch
• Types and layers of skin– Hairy and glabrous (hairless - e.g., palms)– Epidermis (outer) and dermis (inner)
• Functions of skin– Protective – Prevents evaporation of body fluids– Provides direct contact with world
• Mechanoreceptors– Most somatosensory receptors are mechanoreceptors
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Touch
• Mechanoreceptors • Pacinian corpuscles• Ruffini's endings• Meissner's corpuscles• Merkel's disks• Krause end bulbs
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Touch
Mechanoreceptors – Small and large receptive fields
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Touch
Mechanoreceptors – Two-point
discrimination• Receptive field
density• Receptive field
size
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Touch
Primary Afferent Axons– AC– C fibers mediate pain and temperature– Amediates touch sensations
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Pain Perception
Primary Afferents and Spinal mechanisms– First pain and second pain– Referred pain: Angina
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Touch
The Spinal cord– Spinal segments (30)- spinal nerves within 4 divisions of spinal
cord
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Touch
The Spinal cord– Dermatomes- 1-to-1 correspondence with segments– Shingles
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Touch
Dorsal Column–Medial Lemniscal Pathway
– Touch and proprioception
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Touch
Homuncular Mapping
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Touch
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Homuncular Mapping of a variety of mammals shows differences in distribution of sensory structures that relate to habitat and environmental success.
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Temperature
Thermoreceptors– Hot and cold receptors
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END.