11-22-11 Cutaneous Sense and Chemical Sense

11-22-11 Cutaneous Sense and Chemical Sense - PSY402...

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PSY402 Sensation and Perception November 22, 2011 Cutaneous Sense and Chemical Sense Somatosensory system: Proprioception : Ability to sense position of body and limbs Kinesthesis : Ability to sense movement of body and limbs Cutaneous senses: Perception of touch and pain from stimulation of the skin o Skin – heaviest organ in the body Epidermis : Outer layer of skin, dead skin cells Dermis : Below epidermis and contains mechanoreceptors Respond to pressure, stretching, and vibration Mechanoreceptors: o 2 types located close to surface of skin Merkel receptor fires continuously while stimulus is present Sensing fine details Meissner corpuscle fires only when stimulus is first applied and removed (pressure changes) Controlling hand-grip o 2 types located deeper in the skin Ruffini cylinder : Figures continuously to stimulation Stretching of skin Pacinian corpuscle : Fires only when stimulus first applied and when it’s removed Rapid vibrations and fine texture Pathways from skin to cortex: 2 major pathways through spinal cord o Medial lemniscal : Large fibers, proprioperceptive and touch o Spinothalmic : Small fibers, temperature and pain o Crossover to opposite side of body o 1 st synapse in thalamus Thalamus cortex Maps of body on the cortex Thalamus primary somatosensory area (S1) and secondary receiving area (S2) Body map ( homunculus ) in S1 and S2 o More cortical space allocated to parts of the body that are responsible for detail Hands, face, lips most cortical area o Perceiving details Measuring tactile activity Two-point threshold : Minimum separation needed between two points to perceive them as two units
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Grating acuity : Placing grooved stimulus on skin and asking participant to indicate orientation of grating (can change density of bars) Receptor mechanisms for tactile acuity o High density of Merkel receptors – similar to cones in fovea
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11-22-11 Cutaneous Sense and Chemical Sense - PSY402...

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