Topic 13
The Somatic Sensory System
Lange
Biology 463 - Neurobiology
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
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
Touch
• Mechanoreceptors • Pacinian corpuscles• Ruffini's endings• Meissner's corpuscles• Merkel's disks• Krause end bulbs
Touch
Mechanoreceptors – Small and large receptive fields
Touch
Mechanoreceptors – Two-point
discrimination• Receptive field
density• Receptive field
size
Touch
Primary Afferent Axons– AC– C fibers mediate pain and temperature– Amediates touch sensations
Pain Perception
Primary Afferents and Spinal mechanisms– First pain and second pain– Referred pain: Angina
Touch
The Spinal cord– Spinal segments (30)- spinal nerves within 4 divisions of spinal
cord
Touch
The Spinal cord– Dermatomes- 1-to-1 correspondence with segments– Shingles
Touch
Dorsal Column–Medial Lemniscal Pathway
– Touch and proprioception
Touch
Homuncular Mapping
Touch
Homuncular Mapping of a variety of mammals shows differences in distribution of sensory structures that relate to habitat and environmental success.
Temperature
Thermoreceptors– Hot and cold receptors
END.