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Chapter 2

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Laurie Manwell

 The Brain - The mind's computer  we take it for granted that the brain is responsible for mental functions  idea that the brain controls mental functioning is a modern idea o brief history of the physiological approach  early hypotheses about the seat of the mind  early philosopher Aristotle stated heart was seat of mind and soul  Greek physician Galen saw human health, thoughts and emotions being determined by four different spirits flowing from ventricles  accepted all the way until the early 1600s  Descartes accepted the idea of flowing spirits, but named the pineal gland as the seat of the soul  the brain as the seat of the mind  Thomas Willis concluded that the brain was responsible for mental functioning and that different parts of the brain were used for different functions  details of the mechanisms of the brain had to await development of new technology to allow researchers to see brain's microstructure and record electrical signals  signals traveling in neurons  two opposing ideas about the nervous system  reticular theory  stated that nervous system consisted of a large network of fused nerve cells  neuron theory  stated that nervous system consisted of distinct elements or cells  important development that led to acceptance of neuron theory is staining  never cells are coloured to stand out from other cells/tissue  developed by Camilo Golgi  by late 1800s, researches had shown that electricity is transmitted in groups of neurons  Johannes Mueller in 1842 proposed the doctrine of specific nerve energies  stated that perceptions depend on nerve energies reaching brain and specific quality we experience depends on which nerves are stimulated  activity in optic nerves results in seeing  activity in auditory nerves results in hearing  recording from neurons  Edgar Adrian was the first person to be able to record electrical signals from single sensory neurons  listening to activity from one single neuron provides valuable information about what is happening in the nervous system  important to listen to multiple neurons in a single system  ability to record individual signals ushered in modern brain research o Basic structure of the brain  brain is the most mysterious thing in the world  can achieve amazing feats and how it achieves them  most of the research is done on the cerebral cortex  cerebral cortex - 2mm thick layer that covers surface of brain and contains machinery for creating perception as well as other functions such as language, memory and thinking  modular organization - specific functions are served by specific areas of the cortex  basic principle of cortical function  senses are organized into primary receiving areas  first areas in cerebral cortex receive signals initiated by each sense's receptors  primary receiving area for vision is in the occipital lobe  hearing is in temporal lobe  area for skin senses is in parietal lobe  signals from all other senses are in the frontal lobe  Neurons: cells that create and transmit electrical signals o structure of neurons  cell body - contains mechanisms to keep cell alive  dendrites - branches from cell to receive electrical signals from other neurons  axon/nerve fiber - fluid filled to conduct electrical signals  receptors are important neurons for perception  each receptor type is specialized to respond to a different stimuli  look different, but all do the same thing, transmits electrical signals to neurons with axons o recording electrical signals in neurons  particularly concerned with recording the electrical signals from axons of neurons  important to distinguish between single neurons and nerves  nerves - consists of axons of many neurons  resting potential of nerve fibers is -70 mV (which means inside of neuron is 70 mV more negative compared to the outside)  signals passing through neurons cause the inside to become positive  action potential - signal that passes through neurons  lasts about 1 millisecond o chemical basis of action potentials  neurons are surrounded by liquid solution rich in ions  ions are created when molecules gain or lose electrons  changes in resting/action potential in neurons are caused by flow of sodium and potassium ions across the cell membrane  changes in sodium and potassium flow create action potentials and are caused by the changes in the neuron's permeability  permeability - ease with which molecules can pass through the membrane  selective permeability - when membranes are more permeable to specific types of molecules but not others  before action potential occurs, there is little permeability to sodium and potassium  when action potential reaches +40 mV, membrane only becomes permeable to potassium  therefore action potential is caused by permeability of the neuron to potassium and sodium ions o basic properties of action potentials  propagated response  once signal is triggered, it does not decrease in size, and constantly stays the same size  enables neurons to send signals over long distances  no matter how intense the stimulus is, the action potential remains the same size  increases in intensity can increase rate of firing, but will not increase size of action potential  upper limit on number of impulses per second that can be conducted from one nerve to another  due to refractory period  interval between time one never impulse and the next one can start  upper limit is about 500-800 impulses per second  action potentials are still active in neurons even in the absence of stimuli  known as spontaneous activity  establishes baseline level of firing for the neuron  presence of stimulation usually causes an increase in activity above this spontaneous level, but sometimes it can decrease be
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