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Chapter 14

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Western University
Psychology 2015A/B
Patrick Brown

Chapter 14 – Cutaneous System  Waterman, 17, got flu, turned into loss of ability to feel skin sensations o Caused breakdown of somatosensory system which includes:  Cutaneous (touch and pain)  Proprioception (position of body and limbs)  Kinesthesis (movement of body and limbs) Cutaneous System  THE SKIN o Heaviest organ o Visible surface is actually layer of tough dead skin cells called epidermis o Below the epidermis is the dermis o In these layers we find the mechanoreceptors  MECHANORECEPTORS o Respond to mechanical stim such as pressure, stretch, vibration o (4) Types Fires/ Responds continuously Fires/ Responds only when applied and removed Near the MERKEL RECEPTOR MEISSNER CORPUSCLE Surface Deeper in the RUFFINI CYLINDER PACINIAN CORPUSCLE skin  PATHWAYS FROM SKIN TO CORTEX o Nerve fibers from travel in bundles called peripheral nerves that enter spinal cord through dorsal root o Then go up along 2 major pathways  Medial lemniscal pathway – has large fibers that carry signals related to sensing the positions of the limbs and perceiving touch  Spinothalamic pathway – smaller fibers transmit signals related to temperature and pain  MAPS OF THE BODY ON THE CORTEX o Important characteristic of the somatosensory cortex is that it is organized into maps that correspond to locations on the body o Penfield – surgery on patients, epilepsy symptoms o Resulting body map called Homunculus  PLASTICITY OF CORTICAL BODY MAPS o Cortical rep can become bigger if used often o Early experiments were carried out in the somatosensory system Perceiving Details  Braille – can read 100 words/ minute  Normal – 250-300/minute  Consider how researchers have measured our capacity to detect details of stimuli presented to the skin o RECEPTOR MECHANISMS FOR TACTILE ACUITY  Merkel is sensitive to details, lots in finger tips  Better acuity is associated with less spacing between Merkel receptors o CORTICAL MECHANISMS FOR TACTILE ACUITY  Parallel b/w the representation of the body in the brain and the acuity at diff locations on the body  The receptive field for a neuron in the visual system is the area on the retina that when stimulated influences the firing rate of the neuron  Receptive field for neuron in the cutaneous system is the area on the skin that when stimulated influences the firing rate of the neuron Perceiving Vibration  Primary receptor is (PC) Pacinian Corspuscle  These fibers respond poorly to slow or constant pushing Perceiving Texture  1925 – KATZ – our perception of texture depends on both spatial cues and temporal cues – Duplex Theory of Texture Perception o Spatial cues – caused by relatively large surface elements (bumps and grooves, braille) o Temporal Cues – occur when skin moves across a textured surface like sandpaper Perceiving Objects  Active touch – touch in which a person
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