7 Somatosensory System

7 Somatosensory System - OT 441 Foundations of Occupation...

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Unformatted text preview: OT 441: Foundations of Occupation - Neuroscience Somatosensory System Outline 1. Types of somatosensory information 2. Somatosensory receptors 3. Sensory pathways a. DCML tract b. Spinothalamic tract c. Spinoreticular tract d. Trigeminal thalamic tract e. Spinocerebellar tract 1. Clinical Testing 2. Clinical Correlations a. Neuropathy b. Complete SCI c. Incomplete SCI d. Brainstem, thalamic, cortical lesions e. Tactile Defensiveness Receptors Types of Somatosensory Information • Sensory information from the skin (called superficial, cutaneous or exteroceptive ▫ Pain, Temperature, Touch • Sensory info from the musculoskeletal system ▫ Pain ▫ Proprioception: provides information regarding stretch of muscles, tension on tendons, position of joints & deep vibration • Speed of information processing depends on: diameter of axons, degree of myelination, & number of synapses in the pathway Organization of Somatosensory Systems • 3 primary components of somatosensory pathways ▫ Receptors ▫ Sensory pathways ▫ Brain centers • Longitudinal and parallel systems • 3-neuron projection system Somatosensory Receptor Overview • Specialized component of the PNS • Located at the distal end of peripheral neurons • Function: transduction of stimulus into an electrical signal • Adaptation ▫ Slow adapting: receptor continues to fire during entire presentation of the stimulus  Tonic receptors ▫ Fast adapting: receptor adapts quickly to stimulus and stops responding  Phasic receptors Somatosensory Receptor Overview • Receptor density: number of receptors within a given area of body surface • Receptive field: area of skin innervated by a single afferent neuron ▫ Large: borders are difficult to define; often cover a large area ▫ Small: borders are sharply defined; cover small area • Distal regions tend to have greater density of receptors than proximal regions & smaller receptive fields Somatosensory Receptors • Touch: mechanoreceptors ▫ Respond to mechanical deformation of receptor • Proprioceptors (body part position & movement) ▫ Responds to length of muscle, tension of joints and tendons, etc. • Temperature: thermoreceptors ▫ Responds to heat or cooling • Chemicals: chemoreceptors ▫ Responds to substances released by cells • Pain: nocioceptors ▫ Sensitive to stimuli that damage or can damage • Information from all of these may reach awareness, but much of the information is used to make automatic adjustments Touch Receptors • Fine touch ▫ Meissner’s corpuscle: light touch & vibration, phasic ▫ Merkel’s disk: pressure; tonic ▫ Pacinian corpuscle: vibration; phasic ▫ Ruffini corpsucle/ending: skin stretch; tonic • Coarse touch ▫ Free nerve endings: crude touch, pressure, tickle, itch. Proprioceptors...
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This note was uploaded on 09/02/2010 for the course OT 441 taught by Professor Stein during the Summer '10 term at USC.

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7 Somatosensory System - OT 441 Foundations of Occupation...

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