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Ch 2 - The Human Brain.docx

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PSYC 208
Paul Wehr

Form & Function of the Human Brain 9/24/2012 9:03:00 AM Human Brain  Weight: 1300 – 1400 grams (adult); 350-400 grams (newborn)  Number of total neurons: 100 billion o Send/receive signals, process information (most important part of brain)  Umber of cortical neurons: 20 billion o When studying human type brain/human-like psychology behavior o Outside in cerebrum  Number of synapses in cortex: 150000000000000 o Synapse: interface between two neurons to communicate with each other  Percentage of genes expressed in the brain: 55% o Suggests that brain is primary target of natural selection in human evolution Neural Communication  Two types of neurons o Gray matter: neurons without myelin sheath (processing information) o White matter: neurons with myelin sheath (connect different regions)  Myelin sheath insulates and it accelerates the speed by which info travels  Primarily used to transport information (super highways) o Two neurons don’t touch each other (synaptic cleft) o Information travels only in one direction o Soma: body of the cell (genes are housed there) o Info comes in from dendrites  Presynaptic Neuron – transmitter  Postsynaptic Neuron – receiver  Action Potential: electrical charge indicating a neuron has “fired” o When it sends its message  Two types of messages that can be received o Excitatory  Transmitting telling receiving neuron to fire o Inhibitory  Transmitting telling receiving don’t fire  Plasticity: formation and disintegration of synapses throughout the lifespan o Synaptic pruning: remove synapses that aren’t used anymore Neurotransmitters  Acetylcholine (Ach): synapses with muscle tissue; involved in learning, memory, and emotion o Alzheimer’s: degeneration of Ach neurons  Inappropriate emotional responses, bad memory  Dopamine: involved in voluntary motor activity (move around) o Parkinson’s: degeneration of the substantia nigra  Substantia nigra: factory that produces all dopamine o Schizophrenia: excessive activity in frontal cortex  Epinephrine: mobilizes energy resources  Norepinephrine: regulates sensory arousal and attention o Deficiency can lead to attention deficit/hyperactivity disorder (ADHD), impulsivity, lower pain threshold  Serotonin: sleep, wakefulness, temperature regulation, appetite; aggression, social status and risk taking o Deficiency associated with depression o Excess activity associated with antisocial personality o Deficiency or excess associated with obsessive-compulsitve disorder Amino Acids and Neuropeptides  Amino Acid Neurotransmitters: o Glutamate: primary general excitatory neurotransmitter involved in learning processes and consciousness (brings up activity everywhere in the brain)  Excessive activity associated with psychotic symptoms  Hallucination: hearing voices that obviously aren’t there  Delusion: believe something unreasonable to be true o GABA: primary general inhibitory neurotransmitter  Deficiency associated with epileptic seizure, catatonic syndromes  Seizure: whole brains firing until it runs out of fuel and you pass out to wake up later with no memory  GABA normally puts it out  Neuropeptides: synthesized in the hypothalamus and pituitary gland; modulate neurotransmitter activity o Beta-endorphin: pain relief and relaxed euphoria in response to tissue damage or fearful stimuli  Hand “throbbing” is an illusion, it’s not actually throbbing o Oxytocin: reduces aggression and promotes parental and partner bonding (released during breastfeeding and orgasm); more abundant in females  Kind of opposite from testosterone  The “love drug”  orgasm makes you feel love o Vasopressin: promotes male sexuality and aggression o Neurotrophins: neurogenesis – creation of new neurons, and migration Hierarchy of the Nervous System  Pain from toe travels from somatic nervous system through spinal chord to brain to feel pain  Sympathetic nervous system increases activity, release hormones  Parasympathetic nervous system shuts everything down, stops releasing hormones Organization and Functions of the Brain  Brain  Rhombencephalon (hindbrain) / Mesencephalon (midbrain) / Prosencephalon (forebrain) o Hindbrain: basic physiological functions  E.g. takes care of things like breathing o Midbrain: neurotransmitter production  E.g. dopamine  Forebrain  Diencephalon (thalamus & hypothalamus) / Telecephalon (limbic system & cerebrum) o Thalamus & hypothalamus: sensory information & endocrine system (4 Fs)  Smell is the only sensory info that doesn’t go through the thalamus first  Hypothalamus controls endocrine system  Fighting, fleeing, feeding, mating o Limbic system & cerebrum (emotion & cognitive functioning)  Oldest structures of the brain, shares these three parts with many other species Brainstem  Hindbrain o Cerebellum: fine tunes motor movement; learning repeated motor movement  E.g. ballet, dance, piano…  Classical conditioning  Vocalizing language (precision movements between lips, jaws, tongue) o Pons: sleeping, waking, dreaming o Medulla: involuntary body functions (breathing, heartrate…) o Localization of function: different regions of the brain are specialized to do different, but overlapping tasks  Midbrain o Basal ganglia: action selection (motor) o Substantia Nigra: dopamine production o Integrates sensory information o Reticular Activating System (RAS): monitors background information and arouses higher order processes for events that warrant closer attention  Oh, somebody’s throwing a snowball at me  Oh, he’s really good looking  Wait, what are the kids up to Forebrain  Thalamus o Reroutes sensory information  Hypothalamus o Basic survival & reproduction o Pituitary (master) gland  Limbic System o Amygdala: emotion  Facial expressions, when you experience emotions, evaluation stimulus to decide what’s the proper emotion o Hippocampus: long-term memory  Long-term memory stored in cerebrum, but gateway is hippocampus o Mammilary body: smell & memory  Tags smell to memory o Septal nuclei: pleasure center The Four Lobes of the Cerebrum  Occipital lobe o Visual cortex (info from eyes – color, shading, shapes)  Parietal lobe o Somatosensory cortex (bodily physical senses)  Temporal lobe o Auditory cortex o Wernicke’s Area  Taking sounds and comprehending language (speech, reading)  Frontal lobe o Motor cortex & Broca’s Area  Broca’s Area (production of language) o Prefrontal lobe: personality o Social judgment, planning, rational decision making Lateralization  Right & left hemisphere specialized for different tasks; connected by the corpus callosum  Left-hemisphere specialization: o Control right-side of body o Linear speech: production, grammar, comprehension o First-person perspective  Right hemisphere specialization: o Control left-side of body o Holistic speech: intonation, metaphor, emotional prosody (musical aspect of speech, not monotone) o Spatial tasks o Third-person perspective  Women are less lateralized than men o Female brains are more symmetrical, right and left hemispheres will share tasks Evolution of the Human Brain 9/24/2012 9:03:00 AM Announcements:  Midterm: October 5h  Chapter 1- 3 (no heavy neuroscience content)  All of Ch. 1, except for Genetics  Ch. 2, neurotransmitters – don’t really need to answer questions (class notes only)  Ch. 1, genetics (1.4) will not be tested  Ch. 2, anything to do with brain evolution will be tested o Neuroscience (lateralization, pseudo-architecture of cortex, how it works) Triune Brain  Reptilian: changed little throughout mammalian evolution o Basic vital functioning (temperature, blood, pressure, respiration, sleep); instinctual behavior (classical conditioning)  Palaeomammalian: changed much throughout primate evolution o Limbic system (primary target of natural selection) o Regulation of emotion & motivation of complex behavior (e.g. parental care, exploration)  Neomammalian: significant changes during hominid evolution o Cognition (behavioral flexibility, perception, consciousness, decision making, memory…)  Older parts of the brain operate independently of newer parts of the brain (e.g. breathing vs. perception) Encephalization  Brain size increases with body size but at a slower rate o Rat (400 g):2g (0.5%) o Elephant (5,455,000g):4783g (0.1%) o Human (68,000g):1400g (2%)  Progression Index (PI): brain weight of the species/average brain weight of similarly sized species o Primate brains are 2-3 times larger than expected for a mammal of comparable size o Human brains are about 8 times larger than expected o Humans are most encephalized species  Frontal cortex: where all the uniquely human activities occur  Skull thickness o Human skull isn’t that thick compared to a chimp’s Brain Volume Over Time  Capacity to use tools  explosion of evolution of brain size o Rapid increase in brain size Brain Size and Guts  Bigger brains require extra energy o Brain uses 16% of basal metabolic rate o Digestion uses 15% (get net increase in energy)  Could reduce digestion to give brain more energy, but there’d be a decrease in net energy  Inverse relationship between brain size and stomach size o Reduce digestive tract by eating meat; easier to digest  Meat is easier to digest than the fiber of plants (don’t need digestive tract to be so long) o Humans have small intestine – protein rapidly broken down  Small intestine  evolved for the digestion of meat (chimps don’t have it) o Divert energy surplus to brain  Large brain is very expensive! What forces selected for it? o Social Brain Hypothesis Brain Evolution  Allometric Changes: o Olfactory bulb: PI = 1/40  Sense of smell (gotten smaller) o Neocortex: PI = 156 (chimp PI = 58)  Outer part of brain (uniquely human cognitive functions) o Amygdala: PI = 3.9 o Hippocampus: PI = 4.2  Progression of memory o Enlarged Basal Ganglia  Involved in selection of motor actions o Enlarged Cerebellum and Ne
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