Chapter Eight PSY290.docx

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Stuart Kamenetsky

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Chapter Eight: General Principles of Sensory Processing, Touch and Pain Sensory Processing Sensory Receptor Organs Detect Energy or Substances -all animals have specialized body parts that are particularly sensitive to some forms of energy -sensory receptor organs: an organ (such as the eye or ear) specialized to receive particular stimuli (light reaching eye, sound waves reaching ear) -receptor cells within the organs detect particular kinds of stimuli and convert them into language of the nervous system: electrical signals -eventually info from sensory receptors organs enters the brain as a series of action potentials travelling along millions of axons and our brains make sense of it all -adequate stimulus: type of stimulus for which a given sensory organ is particularly adapted -mechanical- touch, pain, hearing, vestibular, joint, muscles -visual- seeing -thermal- cold, warmth -chemical- smell, taste, common chemical, vomeronasal -electrical- electroreception What Type of Stimulus was That? specific nerve energies: the doctrine that the receptors and neural channels for the diff senses are independent and operate in their own special ways and can produce only one particular sensation each (Muller) (ex: no matter how the eye is stimulated, light, mechanical pressure, its resulting sensation is visual) -today we know the messages for diff senses-- such as seeing, hearing etc, all use the same type of "energy": action potentials -labeled lines: the concept that each nerve input to the brain reports only a particular type of info (diff nerve tracts) (ex pressing finger on eyelid) Sensory Processing Begins in Receptor Cells -specialized to detect particular energies or chemicals -upon exposure to stimulus, receptor cell converts that energy into a change in the electrical potential across its membrane (sensory transduction) -receptor cells are transducers that convert energy around us into neural activity that leads to sensory perception -some receptor cells have axons to transmit info. Others stimulate associated nerve endings either mechanically or chemically. (the eye and ear) The initial stage of sensory processing is a change in electrical potential in receptor cells -structure of a receptor determines the forms of energy to which it will respond -receptor potentials: local change in the resting potential of a receptor cell that mediates between the impact of stimuli and the initiation of nerve impulses -mechanical stimuli delivered to the corpucle produce a graded eletrical potential with an amplitude that is directly proportional to the strength of the stimulus. When big enough, an action potential is generated (reaches threshold) 1. Mechanical stimulation deforms the corpuscle 2. Deformation of the corpuscle stretches the tip of the axon 3. Stretching the axon opens mechanically gated ion channels in the membrane allowing sodium ions to enter 4. When the receptor potential reaches threshold amplitude, the axon produces one or more action potentials. Sensory Info Processing is Selective and Analytical coding: sensory events are represented by action potentials -through some form of coding, the pattern of electrical activity in the sensor
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