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PSY100.Lecture (3).docx

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University of Toronto St. George
Dan Dolderman

PSY100: The Brain Neurons: Consciousness as an Emergent Property -consciousness: something that you can’t find in the parts, they are needed, but consciousness does not exist in any of them, it emerges from all of the parts together -one ant is no ant -a million ants is a viable community of organisms that exhibits coordinated, “self- directed” behaviour -one neuron is no neuron -100 billion neurons creates the whole complexity of a person -nothing is external, the consciousness is an interdependent thing -afferent neurons: go from body to brain, give sensory information -efferent neurons: go from brain to body -interneuron: process all the information between afferent and efferent neurons Interneurons -interneurons vastly outnumber motor and sensory neurons (several million of each compared to ~100 billion interneurons) -interneurons facilitate within-CNS transmission of information Structure of a Neuron -dendrites: receive information (receptor cites) from other neurons and transmit towards the cell body, neurotransmitters either add negative charge (make the neuron less likely to fire) or add positive charge (more likely to fire) -synapse: space between dendrites and axon terminals, contain neurotransmitters -cell body: keeps the neuron alive and determines whether it will fire -axon: extending fiber that conducts impulses away from the cell body -myelin sheath: fatty insulation that may surround the neuron’s axon -myelin: prevents signals in adjacent cells from interfering with each other, reducing resistance, thereby speeding up the conduction of neural impulses  multiple sclerosis is caused by a loss of myelin  myelination is fundamentally important for many developmental abilities (ex. language, reading, motor skills) -terminal buttons (axon terminals): receive the action potential from the axon and transmit information on to other neurons through release of neurotransmitters Information Information Information Transmission Integration Collection Neurons are Communication Devices -whether neurons “talk” or not depends entirely on electrical charges, which in turn depend on chemical interactions -neurons communicate through the rapid exchange of chemical neurotransmitters, which in turn influence the electrical potential of the next neuron, which determines whether or not it will fire its own information forward Electrical  Chemical -at the terminal buttons, the electric charge causes little sacs (vesicles) to release chemicals called neurotransmitters -these are released into the synaptic cleft, the space between the terminal button’s membrane, and the dendrites of other neurons Neurotransmitters Bind to Receptors Across the Synapse -neurotransmitters are synthesized from chemical building blocks called precursors -neurotransmitters are stored in vesicles -action potentials cause vesicles to fuse to the presynaptic membrane and release their contents into the synapse -released neurotransmitters bind to the postsynaptic receptors -neurotransmission is terminated by reuptake (brought back into the presynaptic membrane, most powerful method of termination, many drugs affect reuptake), enzyme deactivation, or autoreception Key Neurotransmitters -glutamate: excitatory neurotransmitter – cognitive, seizures, motivation -GABA: inhibitory, seizures, anxiety; ex. anti-anxiety meds (benzodiazepines (valium, Xanax) help GABA bind more effectively to post-synaptic receptors) -acetylcholine (ACh): PNS vs. CNS – muscle/motor vs. higher cognition (learning, memory), plasticity, Alzheimer’s, etc. -epinephrine/nor-e: fundamental arousal/alertness functions -serotonin: mood, emotion, motivation, impulse control, etc. -dopamine: reward (increase motor functions, planning and many higher-level interactions with cognitive functions) -huge variety of other peptides, implicated in basically everything -consider the staggeringly enormous number of small effects that particular neurotransmitters have over your daily life -for example, what guides what we do? everyday, we make countless choices, why? hedonism -what is pleasure to my neurons? Dopamine -dopamine activity in the nucleus accumbens is a practically universal pleasure mechanism and the common bond among drugs of enjoyment, experimentation and abuse The Dopamine System -Nestler and Malenka (2004): Drugs of abuse commandeer the brain’s natural reward circuitry. Stimulation of this pathway reinforces behavior, ensuring that what you just did you will do again. -therefore, learning is strongly affected by reward, and the rewarding effects of, for example, cocaine are mediated through the same mechanisms which have evolved for highly functional, adaptive reasons, like learning and motivation -VTA: initiating point of the pleasure response, feeds signals forward, releases dopamine into N.A., amygdala, PFC, etc., activation of motor and attentional systems The Mind is what the Brain Does -the fact that our experience of the world relies intimately on the brain is shown in the bizarre perceptual experiences of patients with certain kinds of neurological damage or dysfunction The Split Brain -the two hemispheres of the brain are actually two mini-brains connected by a bundle of fibers, the corpus callosum -from the late 1900s until the 1960s, debate raged as to whether cutting the corpus callosum would help people with epilepsy (it was not uncommon) Being of Two Minds -left hemisphere: logic, linear thinking, language -right hemisphere: emotion, spatial processing, music -“The great pleasure and feeling in my right brain is more than my left brain can find the words to tell you.” – Roger Sperry Split-Brain Experiments -when asked to point to the item that was seen, the left hand (RH) pointed to the item seen by the right hemisphere The Frontal Lobes -1930’s and 40’s: frontal lobes subserved “abstract attitude, foresight, and intell
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