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Chapter 2

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Nigel Desouza

Chapter 2: The Biology of Mind • Everything psychological is simultaneously biological • Every idea, every mood, every urge is a biological happening • To think, feel, or act without a body would be like running without legs • Greek philosopher Plato located the mind in the spherical head – his idea of the perfect form • Aristotle believed the mind was in the heart • We have come further in knowledge by learning that: o The body is composed of cells o Among these are nerve cells that conduct electricity and ‘talk’ to one another by sending chemical messages across a tiny gap that separates them o Specific brain systems serve specific functions o We integrate information processed in these different brain systems to construct our experience of sights and sounds, meanings and memories, pain and passion o Our adaptive brain is wired by our experience • Biological psychology – a branch of psychology concerned with the links between biology and behaviour; also called behavioural neuroscientists, neuropsychologists, behaviour geneticists • By studying links between biological activity and psychological events, biological psychologists expand our understanding of sleep, dreams, depression, schizophrenia, hunger, sex, stress and disease • We are each a system composed of subsystems that are composed of smaller subsystems o Tiny cells form organs like the stomach, heart, etc., which form the digestion, circulation, etc. systems, which form humans who are part of a family, culture and community  We are biopsychosocial systems • Psychologists examine how we process information Neural Communication  • Information systems of humans and other animals operate very similarly NEURONS • Neuron – a nerve cell; the basic building block of the nervous system • Sensory neurons – neurons that carry incoming information from the sensory receptors to the brain and spinal cord • Motor neurons – neurons that carry outgoing information from the brain and spinal cord to the muscles and glands • Interneurons – neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs o Our complexity resides mostly in our interneuron systems • Nervous system has a few million sensory and motor neurons, and billions of interneurons • Each consists of a cell body and its branching fibres • Dendrites – the bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body; short • Axon – the extension of a neurons, ending in branching terminal fibres, through which messages pass to other neurons or to muscles or glands; sometimes very long • Axons speak, dendrites listen • Myelin sheath – a layer of fatty tissue segmentally encasing the fibres of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next • Multiple sclerosis is an effect of the myelin sheath degenerating; communications to muscle slows, causing the eventual loss of muscle control • Neural impulse travels at speeds from 2-200+ miles per hour • Action potential – a neural impulse; a brief electrical charge that travels down an axon • Neurons generate electricity from chemical events • Chemistry-to-electricity process involves the exchange of ions (electrically charged atoms) o Fluid interior has excess of negatively charged ions, fluid outside has more positively charged ions  Called the resting potential o Axon’s surface is selectively permeable; very selective about what is allowed in • Each neuron is a mini decision making device that receives signals from thousands of neurons o Excitatory signals; pushing a neuron’s accelerator o Inhibitory signals; pushing a neuron’s brake • Threshold – the level of stimulation required to trigger a neural impulse • If excitatory signals minus the inhibitory signals exceed a minimal intensity (threshold), the combined signals trigger an action potential • Action potential travels down the axon, which branches into other neurons, muscles and glands HOW NEURONS COMMUNICATE • British psychologist Sir Charles Sherrington (1857-1952) noticed neural impulses were taking a long time to travel a neural pathway • Inferred there must be a brief interruption in the transmission o Called the meeting point between neurons a synapse  Synapse – the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at the junction is called the synaptic gap or synaptic clef • There must be a way that neurons send information across the tiny synaptic gap • When action potential reaches knoblike terminals, chemical messengers are released o Neurotransmitters – chemical messengers that cross the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse • Reuptake – a neurotransmitter’s reabsorption by sending the neuron HOW NEUROTRANSMITTERS INFLUENCE US • Acetylcholine is one of the best understood neurotransmitter o Enables muscle action, learning and memory o Alzheimer’s disease, Ach-producing neurons deteriorate • Dopamine is another well understood neurotransmitter o Influences movement, learning, attention and emotion o Schizophrenia caused by excess dopamine, Parkinson’s disease caused by lack of dopamine • Serotonin is also a well understood neurotransmitter o Affects mood, hunger, sleep, and arousal o Depression caused by undersupply • Body also produces its own naturally occurring opiates • Endorphins – ‘morphine within’; natural, opiatelike neurotransmitters linked to pain control and pleasure (endogenous morphine) How Drugs and Other Chemicals Alter Neurotransmission • Why not flood the brain with artificial opiates, intensifying the brain’s own ‘feel-good’ chemistry? • When flooded with opiate drugs like heroin, brain may stop producing its own natural opiates • Once the drug is withdrawn, the brain will have no opiates at all • Drugs and other chemicals affect at synapses, either amplifying or blocking a neurotransmitter’s activity • Agonist molecule may be similar enough to a neurotransmitter to mimic its effects, or it may block the neurotransmitter’s reuptake • Antagonist molecule blocks a neurotransmitter’s functioning o Ex. Botulin causes paralysis by blocking Ach release (botox) The Nervous System • Nervous System – the body’s speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous system o Peripheral nervous system – the sensory and motor neurons that connect the central nervous system to the rest of your body; two components  Somatic – the division of the PNS that controls the body’s skeletal muscles (voluntary)  Autonomic – the part of the PNS that controls the glands and the muscles of the internal organs; also has two parts • Sympathetic – arouses the body, mobilizing its energy in stressful situations • Parasympathetic – calms the body, conserving its energy o Central nervous system – the brain and spinal cord • Nerves – bundled axons that form neural ‘cables’ connecting the central nervous system to the rest of the body CENTRAL NERVOUS SYSTEM • Grain-of-sand sized speck of your brain contains some 100,000 neurons and one billion ‘talking’ synapses • Brain’s neurons cluster into work groups called neural networks • Spinal cord is an information highway connecting the PNS to the brain o Ascending neural fibres send up sensory information, and descending fibres send back motor-control information • Reflex – a simple, automatic response to a sensory stimulus, such as the knee-jerk response • A spinal reflex pathway is compose
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