Psychology Chapter 3 Textbook Notes PDF

TEXTBOOK NOTES Neurons: The Origin of Behaviour Components of the Neuron -​ Early philosophers (1880s) compared the brain to a loom - woven web of fine threads -​ Late 1880s, physician Santiago Ramon y Cajal discovered how to stain neurons in the brain, highlighting entire cells...

TEXTBOOK NOTES Neurons: The Origin of Behaviour Components of the Neuron -​ Early philosophers (1880s) compared the brain to a loom - woven web of fine threads -​ Late 1880s, physician Santiago Ramon y Cajal discovered how to stain neurons in the brain, highlighting entire cells, and revealing that they came in different shapes and sizes. -​ This technique is called a golgi stain -​ -​ Discovered that neurons are composed of three basic parts -​ 1. The cell body - the largest component of the neuron that coordinates the information-processing tasks and keeps the cell alive -​ Protein synthesis, energy production, and metabolism all take place here. -​ Contains a nucleus, which houses chromosomes that contain your DNA (your genetic blueprint). -​ Enclosed by a porous cell membrane that allows molecules to flow in and out of the cell. -​ 2. The dendrites -“branches” that receive information from other neurons and relay it to the cell body -​ 3. The axon - long, thin fibers that carry information to other neurons, muscles, or glands. -​ Can be up to a meter in length (base of spinal cord to big toe) -​ -​ Covered by a myelin sheath - insulating layer of fatty material​ -​ Myelin sheath is composed of glial cells - support cells found in the nervous system (latin word for glue). -​ Glial cells serve roles crucial to the function of the nervous system. -​ Some glial cells digest parts of dead neurons -​ Others provide physical and nutritional support for neurons. -​ They also help form the myelin that insulates axons of nearby neurons; allowing them to transmit information more quickly and efficiently. -​ Demyelinating diseases; e.g. multiple sclerosis; causes myelin sheath to deteriorate, slowing communication from one neuron to another. -​ Can lead to loss of feeling in limbs, blindness, and difficulties with movement and cognition.  -​ Dendrites and axons don’t actually touch. -​ Small gap between axon of one neuron and dendrites or cell body of another. -​ This gap is part of the synapse Synapse = the junction or region between the axon of one neuron and the dendrites or cell body of another. -​ Many of the billions of neurons in your brain have thousands of synaptic junctions each. -​ Adult brains have trillions of synapses. -​ Transmission of information across the synapse is fundamental to communication between neurons -​ Allows us to think, feel, and behave. Neurons Specialized by Function -​ 3 major types of neurons, each performing distinct functions Sensory neurons = neurons that receive information from the outside world and convey this information to the brain via the spinal cord. -​ Have specialized endings on their dendrites that receive signals for light, sound, touch, taste, and smell. -​ E.g. - the endings of sensory neurons in our eyes are sensitive to light. Motor neurons = neurons that carry signals from the spinal cord to the muscles to produce movement -​ Often have long axons that reach to muscles at our extremities. Interneurons = neurons that connect sensory neurons, motor neurons, or other interneurons -​ Comprise most of the nervous system -​ Work together in small circuits to perform simple tasks; e.g. identifying where a sensory signal is coming from, and more complex taste; e.g., recognizing a face. Neurons Specialized by Location Purkinje cells = type of interneuron that carries information from the cerebellum to the rest of the brain and spinal cord -​ Have dense, elaborate dendrites that look like bushes. Pyramidial cells = neurons with a pyramid (triangle) shaped cell body found in the cerebral cortex. -​ Have a single, long dendrite among many smaller dendrites Bipolar cells = a type of sensory neuron found in the retinas of the eye -​ Have a single axon and a single dendrite. -​ All different types of neurons exist to allow the brain to process different types of information. How much truth to the statement; we only use 10% of our brains? -​ Chabris and Simons (professors) broke down this statement and explained that it is false - the 10% myth. -​ The entire brain is put to use -​ Unused neurons always die, and unused circuits atrophy. -​ Myth arose from seeing areas “lighting up” in a brain scan, but the dark regions aren’t dormant or unused. -​ The 10% myth and other neuromyths were presented to 242 primary and secondary school teachers in Netherlands and UK -​ 47% of teachers believed the 10% myth! -​ 76% believed that enriching children’s learning environments would “strengthen” their brains. - false! -​ 94% of teachers believed that students performed better when learning in their “preferred style” - this has little to do with how effectively they learn. -​ Neuromyths have widespread appeal, spread rapidly in fields like business and self-help. The Electrochemical Actions of Neurons: Information Processing -​ Our thoughts, feelings, actions depend on neural communication -​ Neurons use chemical and electrical signals to communicate -​ -​ First, an electric signal is conducted inside the neuron, from the dendrites to the cell body, then down to the axon. -​ Second, a chemical signal is transmitted from one neuron to another, across the synapse -​ These stages are called the electrochemical action of neurons Electrical Signaling: Conducting Information Inside a Neuron -​ A neuron’s cell membrane has pores that act as channels to allow ions to flow in and out of the cell. -​ Ions = molecules that carry a small positive (+) or negative (-) electric charge. -​ The flow of ions across a neuron’s cell membrane creates the conduction of electric current within the neuron. -​ How does this work? The Resting Potential: The Origin of the Neuron’s Electrical Properties. -​ When neurons are at “rest”, ions like positively charged potassium ions (K+) and negatively charged protein ions (A-) are more abundant inside the neuron than outside in the fluid-filled space between neurons (the synapse). -​ Positively charged sodium ions (Na+) are more abundant outside the neuron. -​ The resulting effect is that the inside of a neuron has a small negative charge, relative to the outside -​ This imbalance between the inside and the outside is called the resting potential. -​ -​ Resting potential = The different in charge between the inside and outside of a neuron’s cell membrane. -​ The resting potential is usually about -70 millivolts. -​ One reason for the different concentrations of ions inside and outside the cell membrane is channels in the cell membrane that restrict the movement of ions going in and out of the cell. -​ Like a dam, they can be opened, allowing ions to rush across the membrane in a fraction of a second. The Action Potential: Sending Signals Across the Neuron. -​ Biologists working with giant squid axon noticed that stimulating the axon with an electric shock set off a much larger electrical impulse; a spike in voltage that travelled down the axon in a wave while maintaining its intensity. -​ They used a squid because its axons are 100x larger than humans -​ Inserted a thin wire into the squid axon so it touched the jellylike fluid inside. -​ Placed another wire just outside the axon in the watery fluid that surrounds it -​ Found the electrical difference between charges = resting potential. This is called an action potential = an electric signal that is conducted along the length of neuron’s axon to a synapse -​ Action potentials are fundamental for everything we think, feel and do. -​ Only occur when the electric shock reached a certain level, or threshold. -​ Above that threshold, more electric shock did not increase the strength of the action potential. -​ The action potential is all or none. -​ Below the threshold, the electric shock will fail to produce an action potential. -​ Psychologists say a neuron “fires” because of the all-or-nothing nature of the action potential. The Action Potential Moves Across the Neuron in a Domino Effect -​ Action potential occurs due to changes in the axon’s membrane channels. -​ During resting potential, the membrane channels for sodium (Na+) ions are closed. -​ However, when the electrical charge across the cell membrane reaches the threshold, sodium channels in the cell membrane open up like floodgates, and Na+ ions from outside rush in almost instantaneously. -​ This inrush of positively charged ions surges electric charge from -70 mV to +40 mV in less than a millisecond. -​ Triggers a domino effect all the way down the axon, increasing electric charge in neighbouring areas, and causing all the Na+ channels to open up, letting more Na+ in and increasing the charge even more. - once again, this is called the action potential. -​ In many neurons, the action potential’s conductivity is increased by the myelin sheath around the axon. -​ Myelin sheaths prevent electric current from leaking out of the axon. -​ Keeps charge high along the axon - similar to insulation covering wires on power cord. -​ However, it doesn’t cover the entire axon - instead clumps around it with little break points between clumps (looks like sausage links). -​ Break points are called the Nodes of Ranvier (named after Louis Ranvier who discovered them). -​ Current jumps quickly from node to node - in a process called salatory conduction Action potential spreads onward, not backward -​ Because sodium channels in each region of the axon are temporarily inactivated after action potential passes over them - just like dominos knocked over cannot be knocked over until they are set up again -​ This inactive period is called a refractory period - the time following an action potential during which a new action potential cannot be initiated -​ -​ During this time the electrical/ chemical balance of the neuron is restored -​ Na+ channels briefly close, and K+ channels open, allowing excessive potassium ions to escape the cell -​ This returns the electrical charge inside the cell membrane to a negative state. -​ -​ To restore the chemical balance, special channels called ion pumps redistribute the ions -​ Pushing all excessive Na+ back out of the cell, pulling necessary K+ back in. -​ This rebalances concentrations and restores resting potential. -​ This serves as an analogy for setting the dominoes back up! -​ They are now ready to be knocked over again when triggered. Chemical Signaling: Transmission Between Neurons What happens when the action potential reaches the end of an axon? Especially since synaptic space makes neurons not actually touch each other? Axons have hundreds / thousands of branches that reach out to other neurons and organs. -​ Axons usually end in terminal buttons = knoblike structures that branch out from an axon. -​ Terminal buttons are filled with tiny “bags” that contain neurotransmitters = chemicals that transmit information across the synapse to a receiving neuron’s dendrites. -​ Receiving dendrites contain receptors = parts of the cell membrane that receive the neurotransmitter and either initiate or prevent a new electric signal. -​ Axon potential in the sending neuron - presynaptic neuron travels down the length of the axon to terminal buttons. -​ - Here, it stimulates the release of neurotransmitters from vesicles (bags) to synapses. -​ These quickly float across the synapse (fluid) and bind to receptor sites on the nearby dendrite of the receiving - postsynaptic neuron. -​ When postsynaptic neurons receive a neurotransmitter, they might activate nearby ion channels, raising or lowering the voltage across the cell membrane. -​ Depending on timing / combination of neurotransmitters acting on the receiving neuron, the voltage might reach a threshold, triggering a whole new action potential. -​ This is how neurotransmitter’s chemical “messages” create an electrical signal, and neuronal communication can continue from neuron to neuron. What tells the dendrites which neurotransmitters they should receive? -​ Neurons form pathways characterized by different types of neurotransmitters. -​ One kind of neurotransmitter might be prevalent in one part of the brain, whereas a different kind might be prevalent in another. -​ They also work as a lock and key system; certain neurotransmitters will only bind to specific receptor sites on a dendrite -​ Their molecular structures must fit each other. What happens to left over neurotransmitters in the synapse? -​ How do signals stop sending? -​ Neurotransmitters leave the synapse through 3 processes -​ 1. Reuptake = occurs when neurotransmitters are absorbed by the terminal buttons in the presynaptic neuron’s axon or absorbed by neighbouring glial cells. -​ 2. Enzyme deactivation = occurs when specialized enzymes break down neurotransmitters.  -​ 3. Diffusion = occurs when neurotransmitters drift out of the synapse, no longer able to reach receptors. Types and Functions of Neurotransmitters Important classes of neurotransmitters most common in the nervous system; Acetycholine - neurotransmitter involved in a number of functions, including voluntary motor control -​ Found in neurons of the brain and synapses where axons connect to muscles and body organs, like the heart -​ Helps activate muscle movements -​ Contributes to regulating attention, learning, sleeping, dreaming and memory -​ Alzheimers associated with the deterioration of Acetycholine producing neurons. Dopamine - neurotransmitter that regulates motor behaviour, motivation, pleasure, and emotional arousal. -​ Plays a role in motivated behaviours, like pleasure seeking, associated actions with rewards, etc.. -​ Plays an important role in drug additiction. -​ High levels of dopamine can be linked to schizophrenia -​ Low levels of dopamine can be linked to Parkinson’s Disease. Glutamate - the major excitatory neurotransmitter in the brain -​ Enhances the transmission of information between neurons GABA - the major inhibitory neurotransmitter in the brain -​ Slows the transmission of information between neurons -​ Too little glutamate, or too little GABA can cause neurons to become overactive, and induce seizures. Norepinephrine - neurotransmitter involved in states of vigilance, or heightened awareness of dangers in your environment. Serotonin - neurotransmitter involved in the regulation of sleep and wakefulness, eating and aggressive behaviour. -​ Norepinephrine and serotonin are related - both affect mood and arousal -​ Low levels of either are implicated in mood disorders like depression Endorphins - neurotransmitters that act within the pain pathways and emotion centres of the brain -​ Play a role in dulling pain and elevating moods -​ “Runner’s high” is caused by the release of endorphins in the brain. Each different neurotransmitter affects thoughts, feelings and behaviour differently -​ Need a delicate balance of all of them. -​ Sometimes, imbalances occur naturally, leading to mood disorders. -​ Other times, we seek things out that cause imbalances; drugs, alcohol, smoking, etc.. -​ For instance, LSD is similar to serotonin; binds easily with serotonin receptors in the brain - “tricking” receptor sites. How Drugs Mimic Neurotransmitters -​ Drugs can increase, interfere with, or mimic the function of neurotransmitters Agonists - drugs that increase the action of a neurotransmitter Antagonist - drugs that decrease the function of a neurotransmitter. -​ Other drugs alter a step in the production or release of neurotransmitters. -​ Some have a chemical structure so similar to neurotransmitters that they can successfully “fool” the receiving neuron’s receptors into binding successfully. -​ -​ EXAMPLE - L-dopa - drug used to treat Parkinson’s disease. -​ Parkinson’s caused by loss of neurons that make dopamine by modifying l-dopa already naturally present in the body -​ Taking L-dopa increases the concentration in the brain, engaging surviving neurons to produce more dopamine -​ Acting as an agonist. -​ EXAMPLE - Amphetamine - popular street drug -​ Stimulates the release of norepinephrine and dopamine -​ Creates an excess of neurotransmitters that flood the synapse, activating their receptors over and over - creating pleasurable effect. -​ Also agonists. -​ EXAMPLE - propanolol - a “beta blocker” -​ Obstruct receptor sites in the heart for norepinephrine -​ Causes heart rate to slow down -​ Helpful for conditions causing the heart to beat too fast. -​ This drug acts as an antagonist. The Organizaton of the Nervous System The Nervous System = an interacting network of neurons that conveys electrochemical information throughout the body. Divisions of the Nervous System Two major divisions 1.​ Central nervous system 2.​ Peripheral nervous system Central nervous system = composed of the brain and the spinal cord -​ Receives sensory information from the outside world. -​ Processes and coordinates this information -​ Sends commands to the skeletal / muscular systems for action. -​ Brain at the top - spinal cord branching down -​ Nerves that process sensory information and relay commands connect to the spinal cord. Peripheral nervous system = connects the central nervous system to the body’s organs and muscles -​ Composed of two major subdivisions -​ -​ The somatic nervous system = a set of nerves that conveys information between skeletal muscles and the central nervous system. -​ We use the somatic nervous system to consciously think, perceive, and coordinate our behaviour (e.g., reaching for an object). -​ -​ The autonomic nervous system = A set of nerves that carries involuntary and automatic commands that control blood vessels, body organs, and glands. -​ This system works on its own to regulate body systems outside of conscious control. -​ Two subdivisions within this subdivision -​ The sympathetic nervous system - a set of nerves that prepares the body for action in challenging / threatening situations. -​ The parasympathetic nervous system - helps the body return to a normal resting state -​ Reverses functions of the sympathetic nervous system -​ Constricts pupils, slows heart rate/respiration -​ Diverts blood flow -​ Decreases activity in sweat glands The sympathetic and parasympathetic nervous systems control sexual behaviour in tandem. -​ Parasympathetic nervous system engorges blood vessels and causes erection -​ Sympathetic nervous system responsible for ejaculation  -​ Same in females for arousal / orgasm. Components of the Central Nervous System Spinal cord responsible for simple, but important tasks -​ Spinal reflexes = simple pathways in the nervous system that rapidly generate muscle contractions -​ For example, quickly pulling your hand away from a hot stove. -​ Sensory neurons sent inputs directly into spinal cord -​ THrough a few connections within the spinal cord, interneurons relay sensory inputs to motor neurons that connect to your arm muscles and force you to quickly retract your hand -​ This is the reflex arc = a neural pathway that controls reflex actions -​ Can include sensory neurons, interneurons, and motor neurons. Brain and spine both responsible for tasks more complex than simple reflexes -​ Peripherial nervous system sends messages from sensory neurons through the spinal cord to the brain. -​ Brain sends commands for voluntary movement through the spinal cord to motor neurons, who’s axons project out to skeletal muscles -​ Damage to the spinal cord severs the connection from the brain to the sensory and motor neurons that are crucial to sensory perception and movement. -​ This is why people with damage at specific places in the spinal cord lose motor function, sensation of touch, and pain below where the injury took place. -​ The higher up on your spinal cord you were injured, the more functions lost. -​ Christopher Reeves - actor for Superman who damaged his spinal cord in a horseback riding accident. -​ Loss of sensation and motor control everywhere below the neck. Investigating the Brain Studying the Damaged Brain -​ Research in neuroscience aims to link the loss of specific perceptual, motor, emotional, cognitive functions to a specific area of the brain. -​ From there, we can theorize about what functions these brain areas usually perform. -​ -​ Damaged brains are not the same as atypical brains - there are natural variations in structure/ function of brains that produce variations between individuals in how they function. History of neuroscience begins with Paul Broca (1824-1880). -​ Described patient who could no longer speak, but could still understand language due to small damage in the left frontal lobe. -​ Some of the earliest evidence that speech production and speech comprehension are separate in the brain; and that the left hemisphere is crucial to language abilities. The Emotional Functions of the Frontal Lobes Phineas Gage -​ Railroad worker from Vermont -​ Impaled by a 13 pound iron tamping rod after the explosive powder he was packing in a crevice accidentally exploded -​ Rod entered through his lower left jaw, and exited through the middle top of his head -​ Caused significant personality changes. -​ Went from “mild-mannered, quiet, conscientious hard worker” to “irritable, irresponsible, indecisive and profane”. -​ His case was extremely valuable, allowed researchers to investigate the hypothesis that the frontal lobe regulates emotion, planning, and decision making. The Distinct Roles of the Left and Right Hemispheres -​ Cerebral cortex divided into two hemispheres. -​ Usually act as one integrated unit, though some disorders prevent this. -​ For instance, people with epilepsy have frequent seizures that create a “firestorm” in the brain. -​ To alleviate their severity, doctors can sever the corpus callosum in a split-brain procedure. -​ Results in a seizure remaining isolated in one hemisphere of the brain. -​ Helps pain, but causes unusual behaviour. -​ Roger Sperry experimented with split-brain procedure patients. -​ Asked a person to look at a spot in the centre of a screen, tried projecting stimulus both left and right -​ When it was projected to the left visual field (left hemisphere control speaking), they could verbalize what they were seeing. -​ However, they couldn’t reach over with their left hand to pick it up! - the right hemisphere controls the left hand. But the right hemisphere had no clue what was happening because the two sides could not communicate -​ -​ When split-brain patients are shown a chimeric face (half one face, half another). They could only describe the left side, because speech is controlled by the left hemisphere.  -​ These studies show that the left and right hemispheres perform different functions, but work together in the presence of an intact corpus callosum. Studying the Brain’s Electrical Activity We can also study the link between brain structures by recording electrical activity of neurons. An electroencephalograph = a device used to record electrical activity in the brain. -​ Electrodes are placed on the outside of the head -​ EEG can amplify electric signals so they can be detected, even if they are occurring deep in the brain. -​ Using this technique, we can determine how much brain activity is happening during different experiences and states of consciousness. -​ Brain shows different patterns of activity while awake and while asleep. -​ EEG cannot read minds; but it can reveal abnormal activity patterns associated with brain injuries / disorders. -​ TOday, we use the EEG to understand brain processes involved with sleep, social interaction, and everyday activities. Another approach discovered by David Hubel and Torsten Weisel inserted electrodes into occipital lobes of anesthesized cats and observed action potential patterns in individual neurons. -​ Amplified signals through a loudspeaker -​ Flashed lights in front of animals eye -​ Discovered that neurons in the primary visual cortex are activated whena contrast between light and dark occurs in part of the visual field. -​ Since then, many studies have shown that neurons in the primary visual cortex respond to particular features of visual stimuli; contrast, shape, and colour for instance. -​ These neurons are called feature detectors - since they respond to only certain aspects of a visual image. Other studies have shown a variety of features detected by sensory neurons -​ Some visual processing neurons are only specialized for detecting faces -​ Damage to this area results in ability to perceive faces (face blindness!). Using Brain Imaging to Study Structure and to Watch the Brain in Action. -​ Third way to look into the human brain involves neuroimaging techniques -​ Using advanced technology to provide information about basic brain structure -​ Allows researchers to spot abnormalities or changes in brain structure -​ Functional brain imaging provides information about brain activity while people perform cognitive / motor tasks. Structural Brain Imaging -​ CT scan - rotates around a head and takes x-ray photographs of the brain at different angles -​ Computers combine images to get full 360, detailed view of brain -​ Used to locate lesions and tumors, which show up as darker in the scan because they are less dense than the cortex. -​ MRI scan - uses a magnetic field to line up nuclei of specific molecules in the brain tissue -​ Reveals brain structures with different molecular compositions -​ Produces images of soft tissue at a higher resolution than CT scans do. -​ Gives psychologists a clearer picture of the structure/ volume of the brain -​ Helps localize brain damage -​ Diffusion tensor imaging (DTI) - used to visualize white matter pathways (connecting regions of the brain to each other) -​ Measures rate/ diffusion of water molecules, which reveal the pathways of white matter. -​ Helps map connectivity in the human brain -​ Crucial to the Human Connectome Project - aims to provide complete map of neural pathways in the brain (availabe online) Functional brain imaging -​ Allows us to see the brain in action -​ Positron emission tomography (PET) - used to determine what parts of the brain are being activated during cognitive tasks. -​ Injects a harmless radioactive substance into bloodstream, then scans the brain by radiation detectors -​ Shows when more energy/ blood is flowing to a certain area. -​ Functional magnetic resonance imaging (fMRI) - most commonly used today - gives a picture of the level of activation in each brain area. -​ Detects difference between oxygenated hemoglobin and deoxygenated hemoglobin when exposed to magnetic pulses -​ Hemoglobin is the molecule in our bloodstream that carries oxygen to tissues like the brain -​ More hemoglobin at more active areas of the brain fMRI and PET scans can indicate functions like activity in the auditory cortex of a person listening to music! fMRI has advantages over PET -​ Can localize changes across briefer periods -​ Useful for analyzing process that occur quickly (reading a word, face, etc…). -​ Can also explore the relationship of brain regions with each other, using resting state functional connectivity -​ Participants can rest quietly while fMRI measurements are made. -​ Functional connectivity measures which brain activities are highly correlated/ connected with each other. Transcranial Magnetic Stimulation -​ Used to mimic brain damage -​ Delivers a magnetic pulse , passing through the skull to deactivate neurons in the cerebral cortex for a short period. -​ Can be directed to specific brain regions -​ Observe temporary changes in behaviour, and establish causal relationships. -​ Discovered that interfering with a particular region reduce the amount of details people remember from past experiences, and imagine in future experiences. Is a bigger brain a smarter brain? -​ Early studies showed that students with high honors had larger brains than others at the age of 19 - Sir Francis Galton. -​ A century later, a literature review exposed these earlier studies for having discrepancies, and failed to establish that such a relationship existed. -​ Methods have become more accurate over time, much old information is false. -​ Recent experiments with extremely large studies have shown between a +.19 and +.27 correlation between brain volume and intelligence. -​ Due to the diversity of the sample, we can deduce that this is a genuine correlation not caused by age, socioeconomic status, etc… -​ However, it is nonetheless small - and we don’t know if larger brain volume causes an increase in intelligence, or people with higher intelligence use their brain in a way that produces more volume. LECTURE NOTES (SOME REPEAT FROM TEXTBOOK NOTES) Genes Can a behaviour be genetically determined? -​ No -​ Genes code for proteins -​ You are made of proteins -​ -​ This means that behaviour is not governed by single proteins -​ This means that you can not have a “schizophrenia gene”, for example -​ You can have multiple genes related to schizophrenia, and still not develop schizophrenia -​ Most functions (and dysfunctions) require many many many proteins -​ The distance between genes and behaviour is very, very far. Is behaviour shaped by genetics? -​ Yes -​ Your cells, especially your nervous system, are the scaffold upon which you are built. -​ Differences in genes lead to differences in your nervous system, and this can lead to differences in your potential. -​ Some people’s gene combinations make them more predisposed to certain behaviours; lust, distraction, mental illnesses, etc… -​ Tryon’s experiment with “maze bright” (smart), and “maze dull” (dumb) rats; referring to rats that succeeded and failed at working through mazes. Nature and nurture -​ So what’s more important? -​ That’s the wrong question! Not VS, you can’t have one without the other. -​ Misconceptions like heritability estimate -​ “The heritability estimate for IQ is 0.5” -​ Describes variance not correlation. -​ Shows that 50% of variability in IQ is related to differences in genes. -​ Does not say anything about specific individuals. -​ E.G. - are arms 0% genetic? -​ Most people are born with two arms - but why some of us are born with fewer or no arms is due to environmental factors. -​ Heritability is a measure of how well differences in people's genes account for differences in their traits. -​ For arms, heritability is close to 0, since variance is environmental. Neuroscience LEARNING OBJECTIVES  1.​ Have a foundational understanding of basic brain facts. What aspect of the human brain is most likely responsible for our intelligence? 2.​ Name two general types of cells within the nervous system, and describe how their roles differ. 3.​ Name two general types of neurons, and describe how their roles differ. 4.​ Draw, label, and define the major features of a neuron, including understanding how information travels in the neuron. 5.​ Describe what is meant by the expression that “neuronal communication is electrochemical”. Phineas Gage: “Doctor, here is business for you”. -​ Got impaled through the skull by an iron rod. -​ Failed to put on blasting cap before tamping down explosives -​ Iron rod against stone causes a spark, explodes and shoots rod through his brain, through his head, and another 300 feet. -​ He never passed out, walked over to the hotel where the doctor was staying, and casually awaited an appointment. -​ Had a conversation with the doctor despite missing parts of his brain, vomited and lost more brain matter. -​ Story could’ve ended here, but the brain injury dramatically changed his personality. -​ Went from being a “shrewd, sharp, businessman” to becoming a “fitful, irreverent, indulging in “grossest profanity”, impatient, etc…” -​ Undoubtedly distorted account, partially temporary effects, but still interesting regardless. -​ Proves “mind” and brain are not separate - your brain Is your mind. Human brain facts -​ Despite being only around 2-3% of your body weight, it consumes a lot of resources -​ Over 20% of your energy! -​ Slightly larger in men than women -​ Huge individual variation -​ Composed of neurons, glia, stem cells, blood vessels -​ soma -> axon -> terminals -​ 3 important types to remember -​ A. Pyramidal B. Stellate C. Purkinje -​ Stellate found in areas under the cortex (star shape) - single axon emerges. -​ Purkinje cells comprised of rich dendritic branching. Important for coordination, motor control etc. -​ All cell types converge on a cell body, axon as output, axon heads to terminal. Two basic types of neurons -​ Projection neurons  -​ Long axons that project somewhere else in the brain -​ -​ Interneurons -​ Small, star shaped -​ Small axons that project nearby. -​ Projection neuron projects axon into brain area -​ Synapses with another projection neuron, projects an axon into another part of the brain -​ Populated with interneurons -​ The brain is a whole bunch of projection neurons that regularly stop and synapse. -​ At synapse points, one neuron sends a message to a target neuron—another cell Glial cells -​ Four glial cell types -​ Microglia -​ -​ Very small - play the role of the brain’s immune system. -​ Brain is protected from the rest of your body by a blood-brain barrier -​ When microglia detect something that isn’t supposed to be into your brain, they take on a different form, “crawling around” in a passive state to determine the source of a signal of a foreign element. -​ They then grow into an “active state”, blowing up to an enormous size, swallowing bacteria and destroying them to protect your brain. -​ -​ Macroglia -​ -​ Ogliodendrocyte -​ Myelinate several axons at a time in the brain or spinal cord. -​ Central nervous system (CNS) -​ -​ Schwann Cell -​ Myelinates one axon at a time in the peripheral nervous system (PNS). -​ Myelination speeds up our action potentials as they travel -​ -​ Astrocytes -​ Are half of your blood brain barrier -​ Play a key role in providing all that is needed for your neurons’ -​ Any oxygen, glucose, amino acids, etc.. pas through astrocytes before reaching neurons. -​ Not only playing a support role - are a team player in the tripartite synapse -​ Glia have receptors, transmitters. -​ Pre-synaptic axon, post-synaptic axon, and astrocytes interact (3). -​ Glia shapes conditions at this synapse. Neuronal communication (contd.)  -​ Healthy neuron - when a neuron is doing nothing at all = resting membrane potential (or membrane voltage) between -60 and -80 mV (the voltage inside the neuron is 60-80 mV less than outside the neuron. -​ Similar to potential energy at the top of a hill example (from physics). -​ Potential energy measured from the inside of the cell. -​ Outside is negative with respect to the inside. Neuronal communication is chemical -​ Communicating in a neuron revolves around two ions, sodium (Na+) and potassium (K+) -​ Both positively charged ions -​ As they move into or out of cell, they change the potential (voltage) at the membrane. -​ Note: absence of positive indicates negative. Chemical and electrical gradients -​ Ions want to flow from high concentration to low concentration. -​ Moving from a “swimming pool” to cells -​ If there are a lot of ions in a cell, a chemical force tries to push the ions outside of the cell. -​ If there are a lot of ions outside a cell, the same chemical force tries to push the ions inside the cell. -​ Nature wants everything to be balanced. The cell membrane - guardian -​ Lipid bylayer is tightly packed - both hydrophobic (water repellant) and hydrophilic (likes water), keeping out dangerous entities. -​ Ensures that everything in the cell stays in the cell, and everything outside the cell stays outside the cell. Channels and pumps -​ Only certain molecules and ions permitted to enter through the cell membrane via channels and pumps. -​ Channels: allow passive diffusion (i.e. along chemical gradient) -​ Pumps: actively push ions against their chemical gradient -​ Requires energy (ATP). The resting membrane potential -​ Sodium/potassium pump is always working -​ Sodium exits the cell (3 Na+ out), potassium enters the cell (2 K+ in) -​ K+ “leak” channel (always open) -​ As potassium leaves the cell, the charge of the cell becomes more negative -​ Na+ channel (closed). -​ This means that there is more sodium outside of the cell, and a chemical force trying to push it inside the cell, but it cannot enter. -​ At the same time, there is a chemical force trying to push the potassium inside the cell -​ There is also a force -​ -70 mV