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Chapter 2

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Langara College
PSYC 1115
Troy Chenier

Chapter 2: The Biology of Mind Biology, Behaviour and Mind 2-1 why are psychologists concerned with human biology? -in the early 1800s, German physician Franz Gall proposed that phrenology, studying bumps on the skull, could reveal a person’s mental abilities and character traits -although its mental popularity faded, phrenology succeeded in focusing attention on the localization of function-the idea that various brain regions have particular functions -by studying the links between biological activity and psychological events, those working from the biological perspective are announcing discoveries about the interplay of our biology and our behaviour and mind at an exhilarating pace -the body is composed of cells - among these are nerve cells that conduct electricity and “talk” to one another by sending chemical messages across a tiny gap that separates them -specific brain systems serve specific functions (though not the functions Gall supposed) -we integrate information processed in these different brain systems to construct our experience of sights and sounds, meanings, pain and passion -our adaptive brain is wired by our experience -we realized that we are each a system composed of subsystems that are in turn composed of smaller subsystems -tiny cells organize to form body organs -these organs form larger systems for digestion, circulation, and information processing -and those systems are part of an even larger system the individual who in turn is a part of a family, culture, and community Neural Communication -humans and animals operate so similarly-so similarly that you could not distinguish between small samples of brain tissue from a human and a monkey -similarity allows researchers to study relatively simple animals, such as squids and sea slugs to discover how our neural systems operate -it allows them to understand the organization of our own -animals differ yet their nervous systems operate similarly -though the human brain is more complex than the rat’s, both follow the same principles Neurons 2-2 What are neurons, and how do they transmit information? -our body’s natural neutral information system is complexity built from simplicity -its building blocks are neurons, or nerve cells -neurons differ but are similar in some ways -the bushy dendrite fibers receive information and conduct it toward the body - cell’s lengthy axon fiber passes the message through its terminal branches to other neurons or to muscles or glands; dendrites listen, axon speak -much as home electrical wire is insulated, some axons are encased in a myelin sheath, a layer of fatty tissue that insulates them and speeds their impulses -as myelin is laid down to about age 25, neural efficiency, judgement, and self-control grows -if the myelin sheath degenerates, multiple sclerosis results: Communication to muscles slows, with eventual loss of muscle control -in response, a neuron fires an impulse called action potential- a brief electrical charge that travels down its axon - in the neuron’s chemistry-to-electricity process, ions (electrically charged atoms) are exchanged -fluid outside an axon’s membrane has mostly positive charged ions; a resting axons’s fluid interior has mostly negative ions - this positive-outside negative state is called the resting potential -like a tightly guarded facility, the axon’s surface is very selective about what it allows through the gates; we can say that the axon’s surface is selectively permeable - when a neuron fires however, the security parameters change: The first section of axon opens its gates, like sewer covers flying open, and positively charged sodium ions flood through the cell membrane -this depolarizes that axon section, causing another axon channel to open, and then another, like a line of falling dominos, each tripping the next -during the resting phase (the refractory period, rather like a web page pausing to refresh), the neuron pumps the positively charged sodium ions back outside; then it can fire again - this process repeats up to 100 or even 1000 times a second -each neuron is itself a miniature decision-making device performing complex calculations as it receives signals from hundreds, even thousands, of other neurons -most signals are excitatory, somewhat like pushing a neuron’s accelerator -some are inhibitory, more like pushing its brake -if excitatory signals minus inhibitory signals exceed a minimum intensity or threshold, the combined signals trigger an action potential -the action potential then travels down the axon, which branches into junctions with hundreds or thousands of other neurons or with the body’s muscles and glands -increasing the level of stimulation above the threshold will not increase the neural impulse’s intensity -the neuron’s reaction is an all-or-none response: Like guns, neurons either fire or they don’t - a strong stimulus can trigger more neurons to fire, and to fire more often, but it does not affect the action’s potential’s strength or speed - squeezing a trigger harder won’t make a bullet go faster How Neurons Communicate 2-3 How do nerve cells communicate with other nerve cells? -scientists once believed that the axon is fused with dendrites of another in an uninterrupted fabric -inferring that there must be a brief interruption in the transmission, Sherrington called the meeting point between neurons a synapse - the axon terminal of one neuron is in fact separated from the receiving neuron by a synaptic gap (or synaptic cleft) less than a millionth of an inch wide - Spanish anatomist Santiago Ramon y Cajal described the near-unions of neurons as “protoplasmic kisses” - “like-elegant ladies air-kissing so much as not to muss their makeup, dendrites and axons don’t quite touch”-poet Diane Ackerman -when an action potential reaches the knoblike terminals at an axon’s end, it triggers the release of chemical messengers, called neurotransmitters th -within 1/10,000 of a second, the neurotransmitter molecules across the synaptic gap, and bind to receptor sites on the receiving neuron as precisely as key fits a lock -for an instant, the neurotransmitter unlocks tiny channels at the receiving site, and electrically charged atoms flow in, exciting or inhibiting the receiving neuron’s readiness to fire - then in a process called reuptake, the sending neuron reabsorbs the excess neurotransmitters How Neurotransmitters Influence Us 2-4 How do neurotransmitters influence behaviour, and how do drugs and other chemicals affect neurotransmission? -a particular brain pathway may use only one or two neurotransmitters and particular neurotransmitters may affect specific behaviours and emotions - Acetylcholine (Ach) which plays a role in learning and memory, is one of the best-understood neurotransmitters - In addition, it is the messenger at every junction between motor neurons (which carry information from the brain and spinal cord to the body’s tissues) and skeletal muscles -When Ach is released to our muscle cell receptors, the muscle contracts -If Ach transmission is blocked, as happens during some kinds of anesthesia, the muscles cannot contract and we are paralyzed -researchers soon confirmed that the brain does indeed produce its own naturally occurring opiates -our body releases several types of neurotransmitter molecules similar to morphine in response to pain and vigorous exercise -these endorphins help explain good feelings such as the “runner’s high,” the painkilling, effects of acupuncture, and the indifference to pain in some severely injured people How Drugs and Other Chemicals Alter Neurotransmission -drug and other chemicals affect brain chemistry at synapses, often by either exciting or inhibiting neurons’ firing -agonist molecules may be similar enough to a neurotransmitter to bind to its receptor and mimic its effects -some opiate drugs are agonists and produce a temporary “high” by amplifying normal sensations of arousal or pleasure -antagonists also bind to receptors but their efforts is instead to block a neurotransmitter’s functioning -botulin, a poison that can form in improperly canned food, causes paralysis by blocking Ach release -these antagonists are strong enough like the natural neurotransmitter to occupy its receptor site and block its effect, but are not similar enough to stimulate the receptor (rather like foreign coins that fit into, but won’t operate, a candy machine) -curare, a poison some South American Indians have applied to hunting-dart trips, occupies and blocks Ach receptor sites, causing paralysis in animals struck by darts The Nervous System 2-5 What are the functions of the nervous system’s main divisions, and what are the three main types of neurons? -to live is to take in information from the world and the body’s tissues, to make decisions, and to send back information and orders to the body’s tissues -this happens thanks to our nervous system -the brain and spinal cord from the central nervous system (CNS), the body’s decision maker -the peripheral nervous system (PNS) is responsible for gathering information and for transmitting CNS decisions to other body parts -nerves , electrical cables formed if bundles of axons, link the CNS with the body’s receptors, muscles, and glands -the optic nerve, for example, bundles a million axons into a single cable carrying the messages each eye sends -our nervous system enables voluntary control of our skeletal muscles -our autonomic nervous system (ANS) controls our glands and the muscles of our internal organs, influencing such functions as glandular activity, heartbeat, and digestion - autonomic nervous system serves two important basic functions -the sympathetic nervous system arouses and expends energy -if something challenges you (such as a longed-for-job-interview), your sympathetic nervous system will accelerate your heartbeat, raise your blood pressure, slow your digestion, raise your blood sugar, and cool you with perspiration, making you alert and ready for action -when the stress subsides (the interview is over), your parasympathetic nervous system will produce the opposite effects, conserving energy as it calms you by decreasing your heartbeat, lowering your blood sugar, and so forth -in everyday situations, the sympathetic and parasympathetic nervous systems work together to keep you in a steady internal state The Central Nervous System -it is the brain that enables our humanity- our thinking, feeling and acting - tens of billions of neurons, each communicating with thousands of other neurons, yield an ever- changing writing diagram -with some 40 billion neurons, each connecting with roughly 10,000 other neurons, we end up w
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