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Chapter 3

Chapter 3

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McGill University
PSYC 100
Jens C Pruessner

3.1: How does nervous system operate? Basic units of nervous system: nerve cells/neurons: receive, integrate, transmit info in nervous system. Networks are basis of all psyc activity. Selective communication forms neural networks, develop permanent alliances through maturation/experience). Central: brain and spinal cord. Peripheral: all other nerve cells.  Neurons specialized for communication: excitable, powered by electrical impulses, communicate through chemical signals (reception, integration, transmission) o Types of neurons  Sensory (afferent) neurons detect physical info, pass to brain via spinal cord  Motor (efferent) neurons direct muscles to contract/relax, produce movement  Interneurons communicate locally, short-distance, only with other neurons o Neuron structure  Dendrites: short and branchlike, increase receptive field, detect nearby chemical signals  Cell body (soma): info from other neurons collected, integrated  Axon: narrow outgrowth of neuron by which electric info is transmitted to other neurons  Terminal buttons: at end of axon, release chemical signals from neuron to synapse  Synapse: site where chemical communication occurs between neurons  Synaptic cleft: gap between axon of sending neuron and dendrites of receiving neuron  Myelin sheath: glia/neuroglia that insulates axon, allows rapid electrical movement  Nodes of Ranvier: small gaps of exposed axon between segments of myelin sheath where action potentials are transmitted through ion channels o Resting membrane potential negatively charged: ratio of - to + ions greater inside than outside. Polarized resting stateelectrical energy necessary for firing o Na and K: ion channels allow specific ions through via gating mechanism, selective permeability. Na-K pumppolarization (more potassium than sodium)  Action potentialsneural communication; depends on ability to respond to stimulation by changing electrically, passing signal along. Action potential (firing): passes along axon, causes chemical release o Changes in electrical potentialaction. Neuron receives chem. signals via dendrites. Excitatory signals depolarize cell membranemore chance of fire. Inhibitory signals hyperpolarize cellless chance to fire. Total excitatory input > thresholdaction potential generated. When neuron fires, Na/K gates open; allow Na in, K out positive charge; later, negative restored. o Action potentials spread along axon: propagation: movement of depolarization along axon like wave, quick because of myelin sheath’s insulation, recharges at nodes of Ranvier.  Multiple sclerosis: demyelination slows down neural impulses, axons short-circuit o All-or-none principle: neuron either fires or not, same potency, depends on frequency of signals  Neurotransmitters (located in terminal button’s vesicles, chemical substances, carry signals across synaptic cleft) bind to receptors across synapse. Action potential at terminal button causes vesicles to attach to presynaptic membrane, release neurotransmitters to synaptic cleft; they bind to receptors on postsynaptic neuron. Receptors: specialized protein molecules on postsynaptic membrane, specifically respond to chemical structure of neurotransmitter in synapse. Binding of neurotransmitter with receptorexcitatory or inhibitory signal. o Neurotransmitters bind w/ specific receptors: when released, stimulates receptor until terminated  Reuptake: neurotransmitter taken back into presynaptic terminal buttons, cyclical  Enzyme deactivation: enzyme destroys neurotransmitter in synaptic cleft  Autoreception: autoreceptors signal presynaptic neuron to stop release when excess detected  Neurotransmitters influence mental activity, behavior: drugs and toxins alter how neurotransmitter is synthesized, raise/lower amount released from terminal buttons, or block reuptake, change how neurotransmitters are deactivated in synaptic cleft, affect concentration. Agonists enhance actions of neurotransmitters; antagonists inhibit. Receptors can’t differentiate between drugs and neurotransmitters. o Types of neurotransmitters  Acetylcholine (Ach): muscle motor control, learning, memory, sleeping, dreaming, botox inhibits  Epinephrine (adrenaline): burst of energy  Norepinephrine: arousal and vigilance  Serotonin: emotional states and impulsiveness, dreaming  Dopamine: reward and motivation, voluntary motor control, reduced in Parkinson’s  GABA: inhibition of action potentials, anxiety reduction, alcohol intoxication  Glutamate: enhancement of action potentials, learning and memory  Endorphins: pain reduction, reward  Substance P: pain perception, mood and anxiety 3.2 What are basic brain structures and functions? Brain weighs 3 pounds / 1.4 kg, collection of interacting neural circuits that have accumulated and developed throughout human evolution. Brain has evolved specialized mechanisms; life experiences “prune” connections. Phrenology: assessing personality traits and mental abilities by measuring bumps on human skull. Equipotentiality: all areas equally important in cognitive activities Broca’s area: small portion of left frontal region of brain, crucial for production of language, first evidence that brain regions perform specialized functions through 1861 autopsy on “tan” Leborgne.  Brain stem houses basic programs of survival: spinal cord is neural tissue, made of gray (neurons’ cell bodies), white matter (axons and myelin sheaths). Spinal cord becomes brain stem: houses structures for survival– medulla oblongata, pons, midbrain, also contains neuron network (reticular formation)  Cerebellum essential for movement: “little brain,” coordinated movement, balance, motor learning, motor memory. “Trained” but independent of nervous system, unconscious –e.g., planning while biking.  Subcortical structures control emotions, appetitive behaviors: forebrain has L/R cerebral hemispheres. Limbic*: border between evolutionary older parts (brain stem, cerebellum) and newer (cerebral cortex). o Hypothalamus: regulates bodily functions (temp, pressure, glucose), influences basic motivated behaviors (thirst, aggression, lust). Receives input and influences almost everywhere o Thalamus: gateway to brain/cortex, receives incoming sensory info, organizes, sends to cortex (except smell). Partially shuts gate on incoming sensation during sleep o Hippocampus and amygdala*: stores new memories by creating new interconnections within cerebral cortex, grows larger with use (London taxi drivers). Amygdala in front; vital role in associating things w/ emotional responses, processing emotional info, esp. fear and expressions o Basal ganglia: subcortical structures for planning, movement, receive input from cerebral cortex and project it to motor centers of brain stem, motor planning area of cerebral cortex. Nucleus accumbens: experiencing reward and motivating behavior  Cerebral cortex underlies complex mental activity: outer layer of cerebral hemispheres, wrinkled. Site of thoughts, perceptions, behaviors, comprehension, culture, communication. Corpus callosum connects hemispheres and allows flow of info. Each cerebral hemisphere has four lobes: o Occipital: back portion, devoted to vision, including primary visual cortex o Parietal: devoted partially to touch, divided between hemispheres – left vs. right. Info directed to primary somatosensory cortex, groups nearby sensations, somatosensory homunculus (little man, distorted representation of entire body). Also conceptualizing space.  hemineglect: damage to right parietal region; patients don’t notice left side o Temporal: processing auditory info (primary auditory cortex), memory, object, face perception (houses hippocampus and amygdala). Fusiform face area at intersection temporal/occipital o Frontal: planning, movement. Primary motor cortex has neurons that project to spinal cord to move muscles, left vs. right control. Prefrontal cortex: 30% of brain, complexity and organization of neural circuits may separate humans from animals. Responsible for attention, keeping ideas in mind, making plans, rational activity, social life, sense of self, empathy, etc. o Prefrontal cortex in close-up: Phineas Gage’s prefrontal cortex damaged, associated with social phenomena. Lobotomy: damaging prefrontal cortex to make mental patients easier to manage. 3.3 How does brain communicate with body? Nervous system includes CNS (brain and spinal cord) and PNS (all other nerves). PNS transmits info to CNS, responds to messages from CNS to perform behaviors, make adjustments. In production of psyc activity, both systems interact with endocrine system.  Peripheral nervous system includes somatic and autonomic nervous systems: SNS transmits sensory signals to CNS via nerves. Specialized receptors send sensory info to spinal cord, which sends to brain. CNS sends signals through SNS system to muscles/joins/skin to initiate/modulate/inhibit movement. ANS regulates body’s internal environment by stimulating glands, maintain internal organs. Nerves in ANS carry
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