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NSCI 1051 (6)

Study terms for Somatosensory

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Neuroscience - CLA
NSCI 1051

Ch. 12 The Somatic Sensory System Somatic sensation • Enables body to feel, ache, chill • Sense position of joints, pressure, temperature • Sensitive to stimuli • Responsible for feeling of touch and pain • Somatic sensory system: different from other systems - Receptors: distributed throughout (different kinds of receptors) - Responds to different kinds of stimuli Types of skin: • Hairy vs. glabrous (hairless) Do not dwell too much on this material in yellow highlight, since it is peripheral function and the test will focus on central function. Know the mnemonic about the function of different cell type, otherwise but don’t compulse over the details. Epidermis: outer layer Dermis: inner layer Mechanoreceptors: • Meissner’s: light touch • Merkel’s: touch • Pacinian: deep pressure Thermoreceptors: • Ruffini’s: temperature Nocireceptors: • Free terminal: pain Meissner and pacini adapt fast Merkel and ruffini slowly adapt Division of spinal gray matter: • Dorsal horn: the dorsal region of the spinal cord containing neuronal cell bodies • Intermediate zone • Ventral horn: the ventral region of the spinal cord containing neuronal cell bodies Proprioception: sense of static and dynamic position of limbs and body Kinesthesia: the ability to feel movements of the limbs and body Stereognosis: ability to recognize objects based on touch alone Two-point discrimination: • Different levels of touch reception on different parts of the body, number of receptors in an area • Importance of fingertips over elbow • Much higher density of mechanoreceptors in the skin of the fingertips than any other part of the body • Fingertips are enriched in receptor types that have small receptive fields • More brain tissue devoted to sensory information of each square mm of fingertip than elsewhere Primary afferent axons (of the somatic sensory system): • Diameter of axons vary with type of sensory receptor (largest are the Aa slowest are the C axons) • Axons bringing information from the somatic sensory receptors to the spinal cord or brain stem • Enter the spinal cord through the dorsal roots; their cell bodies lie in the dorsal root ganglia • Axons innervating muscles are named with roman numerals (1-4), axons from skin sensory receptors are named with greek letters Dermatome: cervical, thoracic, lumbar, sacral: • The area of skin innervated by the right and left dorsal roots of a single spinal segment • 1-to-1 correspondence with segments First Order neurons: • Conveys information to the spinal cord (via the dorsal roots) or the brainstem Third-order sensory neurons: • Conducts impulses from the thalamus to the somatosensory cortex Second-order sensory neurons: • Conduct impulses from either the spinal cord or brainstem to the thalamus • The neurons that receive sensory input from primary afferents • Lie within the dorsal horn of the spinal cord • AB axons conveying information about touch to the skin enter the dorsal horn and synapse with second-order neurons – this connection can initiate or modify a variety of rapid and unconscious
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