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  1. The case of a woman who seems unable to experience fear despite being able to express all the other array of emotions and performing well on mental tests puzzled scientists. They eventually knew a disease in childhood destroyed the amygdala on his brain, and could link this organ with the ability to experience fear
  3. The case shows how the brain controls behavioural function, but the brain is a highly complex organ, so much we haven´t been able to simulate it by computer. It makes sense for psychologysts to focus on the biological aspect of behavior to try and achieve better understanding of what the brain does
  5. =====================
  7. Communication in the nervous system
  9. - Behavior depends on rapid information processing
  11. The nervous system is a complex communication network which constantly transmits, receives and integrates signals, handling information just as the circulatory system handles blood
  13. Nervous system = tissue composed of cells
  15. Cells = two categories, neurons and glia
  17. Neurons = individual cells in the nervous system that receive, integrate and transmit information
  18.     Basic links that permit communcation within the nervous system
  19.     Most of them only communicate with other neurons
  21. Parts of a neuron=
  22.       Soma or body - Has the nucleus and the chemical machinery common to most cells
  23.       Dendritic Trees = branch like structures that are specialized to receive information
  24.       Axon = long thin fiber that transmits signals away from the soma to other neurons or to muscles or glands. Can be quite long and branch off to communcate with a number of other cells
  25.       Myelin sheath = Insulating material encasing the axons and acting to speed up transmission of signals
  26.              Multiple sclerosis disease is an example of myelin sheaths deteriorating
  27.       Neurotransmitter, small knobs that secrete chemicals, located at the end of the axon. the chemicals serve as messengers to activate nearby neurons
  28.       Synapses= Junctions where information travels  is transmitted from one neuron to another
  30. Information Flow
  31.         Dendrites -> Soma -> Axon -> SYnapse -> Communication OK
  33. Glia= cells that provide various types of support for neurons. Smaller but outnumber neurons 10 to 1
  34. Glial cells account to the majority of brains volume
  36. Functions = nourishment to neurons, help removing waste products and provide insulation around axons.
  37. Myelin sheaths are derived from some special types of glial cells
  39. Glia helps development of the nervous system in the human embryo
  41. Recent research shows glial cells also play a part in information processing
  42.        Memory formation (deterioration linked with Alzheimers), experience of chronic pain, impaired communcation between neurons and glials linked with psychological disorders
  44. =======================================
  46. The Neural Impulse, using energy to send information
  48. Research by Alan Hodgkin and Andrew Huxley on 1952  showed what happens when the neuron is stimulated
  50. A complex electrochemical reaction involving ions
  51.   ions = electrically charged atoms and molecules
  53. The neuron at rest behaves like a tiny battery with these charged particles, without stimulation it retains a negative charge due to flow rates of the particles
  55. Resting potential = stable, negative charge when the cell is inactive
  57. When the neuron is stimulated channels are opened in the cell membrane and positive ions can rush in, creating action potential
  59. Action Potential = Very brief shift in a neurons electrical charge that travels along an axon
  61. After the action potential, the cell membrane closes up again and requires a bit of time before being ready to repeat the process, this is called refractory period
  63. Absolute Refractory period = minimum length of time after an action potential  during which another action potential can begin - 1 or 2 milliseconds
  65. Relative refractory period = The neuron can fire, but requires more intense stimulation than usual
  67. Neural impulse is an all of none proposition, either the neuron fires or it doesn't. Weaker stimuli doesn't produce smaller action potentials
  69. To understand strength of stimulus, neurons vary the rate at which they fire action potentials
  71. The stronger the stimulus, the faster the firing
  73. Thicker axons transmit information faster
  75. Neural impulses can travel up to 100 meters per second (+200 miles per hour)
  77. ==============================
  79. The Synapse
  81. The neurons don't touch each other to transmit information, they are separated by the synaptic cleft
  83.     Synaptic cleft = Microscopic gap between the terminal button of one neuron and the cell membrane of another
  85. Signals jump the gap to allow communication
  87. Presynaptic neuron = neuron that sends the signal
  88. Postsynaptic neuron = receives it
  90. Arrival of action potential triggers the release of neurotransmitters
  92. Neurotransmitter, chemical that transmits information from one neuron to another
  94. SYnaptic vesicles = small sacks within the terminal buttons that store the neurotransmitters
  96. Process flow
  98.  Action Potential -> Vesicle fuses with membrane  of presynaptic cell -> Synaptic vesicles open -> Neurotransmitter released to the synaptic cleft -> Neurotransmitters jump the synapse and reach the membrane of the receiver
  100. Receptor sites: Special molecules in the postsynaptic cell membrane  tuned to recognize specific kinds of neurotransmitters and respond to them
  103. Reactions in the cell cause a postsynaptic potential when the neurotransmitter combines with the receiver
  104.       Postsynaptic potential = Voltage change at a receptor site on a postsynoptic cell membrane. This potential doesn't follow the all of none approach, the voltage change dependes on the strength of the signal and carries with him an increase or decrease on the capacity of that neuron to perform neural impulses, also linked to the voltage change
  106. Types of Message = Excitatory and  Inhibitory
  107.       Excitatory = positive voltage shift that increases the likelihood of the neuron firing action potentials
  108.       Inhibitory: Negative, decreases the likelihood
  110. Direction of the voltage shift depends on which receptor sites are activated in the neuron
  112. The effects of the synapse only last a fraction of a second, after this, neurotransmitters drift away or are inactivated by enzymes to metabolize them into an inactive form
  114. Reuptake - A process in which neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane (enables recycling of materials)
  116. A neuron receives thousands of signals, and it must integrate the signals arriving at a synapse before deciding if firing a neural impulse is the best case
  118. The decision works adding up the excitation  or inhibition that arrives from other neurons and comparing the resulting voltage against the threshold. If it surpasses the threshold an action potential will fire
  120. "Millions of neurons must fire in unison to produce the most trifling thought"
  122. Firing a single neuron won't do anything, most neurons are heavily interlinked in complex ways.
  124. Our perceptions, thoughts and actions depend on patterns of neural activity found in these complex neural networks, which involve firing together or sequentially interconnected neurons
  126. As we use neurons, some new synaptic connections are made and some wither away, it seems to be more important the elimination of old synapse than the creation of the new to create neural networks. The nervous system normally forms more synapses than needed and then gradually eliminates the inactive
  128. SYnaptic pruning, process of  removing the old synapses
  130. =====================================================
  132. Neurotransmitters and behavior
  134. Neurotransmitters are fundamental on behavior, palying a key role in everything from muscle movements to moods and mental health
  136. 9 classic transmitters, 40 chemicals that can function as neurotransmitters, and a variety of recently recognized novel ones.
  138. Specific neurotransmitters work with specific kinds of synapses, the binding process of a neurotransmitter to a membrane works like a lock and a key. This specialization helps making the nervous system more precise by reducing cross talk
  140. Acetylcholine Ach =
  141.           Transmitter between motor neurons and voluntary muscles, all our voluntary movement relies on Ach
  142.           Contributes to attention, arousal and memory
  143.           Lack of supply associated with memory losses like Alzheimers
  145. Activity of neurotransmitters can be influenced by other chemicals in the brain, an example is tobacco which fools the system into thinking is Ach and activating neurons.
  147. Agonist = chemical that mimics the action of a neurotransmitter
  149. Some chemicals block the pathway needed for neurotransmitters to bind to the mcell membrane
  151. Antagonist = Chemical that opposes the action of a neurotransmitter
  153. Monoamines
  154.     Dopamine
  155.     Norepinephrine
  156.     Serotonin
  158. Regulate many aspects of daily behaviour
  160. Dopamine - Controls voluntary movements, degeneration causes Parkinsonism
  161. Serotonin - Sleep and Wakefulness, eating behavior, aggresive behavior
  163. Abnormal levels of monoamine in the brain have been linked with psychological disorders
  165. Depressive disorders= low activation norepinephrine and serotonin
  166. Eating Disorders = abnormal activation levels of Serotonin
  167. OCD = abnormal activation levels of Serotonin
  168. Schizophrenia = abnormally high  activation levels Dopamine
  170. Drugs like amphetamines and cocaine seem to work by highly stimulating dopamine and norepinephrine synapses. Dopamine pathways are believed to be what leads to the craving and addiction of drugs
  173. Gaba and Glutamante
  175. Gaba = gamma-aminobutyric acid
  176. - produces only inhibitory post synaptic potentials
  177. - present in 40% of all synapses
  178. - regulation of anxiety, abnormal levels linked to anxiety disorders
  180. Glutamate
  181. - only excitatory effects
  182. - Linked with learning and memory
  183. - Abnormal levels linked to schizophrenic disorders
  185. Endorphins
  186. - Resemble opiates in structure and effects
  187. -Contribute to modulation of pain
  188. - Contribute to eating behavior and body response to stress
  190. Discovery of endorphine ha led to new theoriesand findings on the neurochemical bases of pain and pleasure
  192. Researchers believe endorphins are capable of producing pleasure
  194. Much still remains to be discovered regarding the nervous system, even if discovery of neurotransmitters helped to gain a lot new insights into it.
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