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Chapter 2

sensation - chapter 2 .doc

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Wilfrid Laurier University
Phillip Servos

Chapter 2 Introduction to the Physiology of Perception Pages 23-41 The brain: the mind’s computer Early hypotheses about the seat of the brain - aristotle - heart was seat of the mind and soul - galen - saw human health, thoughts and emotions as being determined by four different spirits flowing fro the ventricles - 1630s - philosopher decartes specified the pineal gland - thought to be located over the ventricles, as the seat of the soul The brain as the seat of the mind - 1664 - thomas willis - brain was responsible for mental functioning - different functions were located in different regions of the brain - disorders of the brain were disorders of chemistry Signals traveling in neurons - 1800s - two opposing ideas about the nervous system - 1. reticular theory - nervous system consisted of large network of fused nerve cells - 2. neuron theory - nervous system consisted of distinct elements or cells - staining - chemical technique that caused nerve cells to become coloured so they stood out from surrounding tissue - led to acceptance of neuron theory - only a few cells were strained - so it was useful - johannes mueller 1842 - doctrine of specific nerve energies - stated our perceptions depend on nerve energies reaching the brain and the specific quality we experience depends on which nerves are stimulated Recording from neurons - 1920s - edgar adrian could record electrical signals from single sensory neurons - awarded nobel prize in 1932 - recording from single neurons gives valuable info about what is happening in nervous system - just like listening to individual voices - ability to record electrical signals from individual neurons ushered in the modern era of brain research and in 1950s and 60s development of more sophisticated electronics and availability of computers and electron microscope made more detailed analysis of how neurons function possible Basic structure of the brain - william james - brain is “most mysterious thing in the world” - connection between brain and perception - cerebral cortex - also used for other functions, i.e. language, memory, thinking - basic principle of cortical function is modular organization - specific functions are served by specific areas of the cortex - e.g. of modular organization - how senses are organized into primary receiving areas - primary receiving area for vision - occupies most of occipital lobe - hearing - temporal lobe - senses - parietal lobe - frontal lobe - receives signals from all senses, plays important role in perception that involves coordination of info received through two+ senses Neurons: cells that create and transmit electrical signals - one purpose of neurons involved in perception - respond to stimuli from environment and transduce these stimuli into electrical signals - also to communicate with other neurons, so these signals can travel long distances Structure of neurons - cell body - contains mechanisms that keep cell alive - dendrites - branch out from cell body to receive electrical signals from other neurons - axon or nerve fiber - filled with fluid that conducts electrical signals - receptors - specialized to respond to environmental stimuli, e.g. pressure for touch - receptors may look different, but all have something in common - part of each receptor reacts to environmental stimuli and triggers the generation of electrical signals, which eventually are transmitted to neurons with axons Recording electrical signals in neurons - important to distinguish between single neurons and nerves - nerve - e.g. optic nerve - carries signals out the back of the eye - consists of axons and many neurons - recording from an optic nerve fiber involves recording not from the optic nerve as a whole, but from one of the small fibers within the optic nerve - when nerve fiber is at rest, oscilloscope records a difference in potential of -70 millivolts - called resting potential - charge inside the fiber reverses course and starts becoming negative again until it returns to the resting level - action potential - lasts about 1 millisecond Chemical basis of action potentials - neurons are surrounded by a solution rich in ions - molecules that carry an action charge - ions are created when molecules gain or lose electrons - happens when compounds are dissolved in water - permeability - property of the cell membrane that refers to the ease with which a molecule can pass through the membrane - selective permeability - occurs when a membrane is highly permeable to one specific
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