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Chapter 3

Chapter 3 PSYA01 TEXTBOOK NOTES.docx

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University of Toronto Scarborough
Steve Joordens

PSYA01 – CHAPTER 3 : NEUROSCIENCE AND BEHAVIOR - David was brought into the emergency room by his friends as he was seeing people and things that weren’t really there - Doctors didn’t find any problems with his eyes but instead discovered he was suffering from hallucinations, a side effect of abusing methamphetiamines - His prolonged crystal meth habit had altered the normal functioning of some chemicals in his brain, distorting his perception of reality and fooling his brain into perceiving things that were not actually there - Although he complaining of problems with his vision, their symptoms were actually caused by disorders in the brain - Our ability to perceives the world around us and recognize familiar people depends not only on information we take in through our senses but, perhaps more importantly, on the interpretation of this information performed by the brain NEURONS: THE ORGIN OF BEHAVIOR: - There are approx. 100 billion cells in your brain that perform a variety of tasks to allow you to function as a human being - Humans have thoughts, feelings, and behaviors that are often accompanied by visible signals - Ex. when you see a good friend walk by: a smile on your face, walking toward her - All those visible and experimental signs are produced by an underlying invisible physical component coordinated by the activity of your brain cells - All your thoughts, feelings and behaviors spring from cells in the brain that take in information and produce some kind of output trillions of times a day - Neurons  cells in the nervous system that communicate with one another to perform information- processing tasks DISCOVERY OF HOW NEURONS FUNCTION: - In the late 1880’s a Spanish physicaian Ramon y Cajal learned about a new technique for staining neurons in the brain - The stain highlighted the appearance of entire cells, revealing that they came in different shapes and sizes - This technique of staining gave Cajal the idea that it could provide important new insights into the nature and structure of the nervous system - He used to this technique to see that each neuron was composed of a body with many threads extending outward toward other neurons - He also saw that the threads of each neuron did not actually touch other neurons - He arrived at the fundamental insight that neurons are the information-processing units of the brain and that even though he saw gaps b/w neurons, they had to communicate in some way COMPONENTS OF THE NEURON: - Cajal discovered that neurons are complex structures composed of three basic parts: the cell body, the dendrites and the azon - Cell body  the largest component of the neuron that coordinates the information-processing tasks and keeps the cell alive - Functions such as protein synthesis, energy production, and metabolism take place in the cell body - Cell body contains a nucleus --> the structure that houses chromosomes thajt contain your DNA or genetic blueprint of who you are - Cell body is surrounded by porous cell membrane that allows molecules to flow in and out of the cell - Neurons have two types of specialized extensions of the cell membrane that allow them to communicate: dendrites and axons - Dendrites  receive info from other neurons and relay it to teh cell body - Most neurons have many dendrites that look like tree branches - Axon  transmits info to other neurons, muscles or glands - each neuron has a single axon that sometimes can be very long, even stretching up to a meter from the base of the spinal cord down to the big toe - in many neurons axon is covered by myelin sheath  insulating layer of fatty material - myelin sheath is composed of glial cells  support cells found in the nervous system - some glial cells digest parts of dead neurons, others provide physical and nutitional support for neurons and other form myelin to help the axon transmit information more efficiently - like an insulated heater, an axon insulated with myelin can more efficiently transmit signals to other neurons, organs or muscles - in some demyelinating diseases, such as multiple sclerosis, the myelin sheath deteriorates slowing the transmission of information from one neuron to another - dendrites and azons of neurons do not actually touch each other...there is a gap b.w the axon of one neuron and the dendrites or cell body of another - this gap is part of the synapse  the junction or region b/.w the axon of one neuron and the dendrites or cell body of another MAJOR TYPES OF NEURONS: How do the three types of neurons work together to transmit information? - Sensory neurons, motor neurons and interneurons are the three major types of neurons - Sensory neurons  receive information from the external world and convey this information to the brain via the spinal cord - they have specialized ending on their dendrites that receive signals for light, sound, touch, taste and smell - motor neurons  carry signals from the spinal cord to the muscles to produce movement - these neurons have long axons that can stretch to muscles at our extremeties - interneurons  connect the sensory neurons, motor neurons and other interneurons - interneurons makes up most of the nervous system - some interneurons carry information from sensory neurons into the nervous system others carry information from the nervous system to motor neurons - interneurons work together in small circuits to perform simple tasks such as identifying the location of a sensory signal or recognizing a familiar face NEURONS SPECIALIZED BY LOCATION: - besides specialization for sensory, motor or connective functions, neurons can be specialized by where they are located - ex. purkinje cells are type of interneuron that carries info from the cerebellum to the rest of the brain and spinal cord - these neurons have dense, elaborate dendrites that resemble bushes (pg. 82 for picture) - ex. pyramidial cells, are found in the cerebral cortex and have a triangular cell body and a single, long dendrite among many smaller dendrites - ex. bipolar cells, a type of sensory neuron found in the retinas of the eye, have a single axon and a single dendrite THE ELECTROCHEMICAL ACTIONS OF NEURONS: INFORMATION PROCESSING - the communication and information within and between neurons proceeds in two stages: conduction and transmission - the first stage is the conduction of an electrical signal over relatively long distances within neurons, from the dendrites to teh cell body then throughout the axon - the second stage is the transmission of chemical signals between neurons over the synapse - together these are referred to as electrochemical action of neurons ELECTRICAL SIGNALIGN: CONDUCTING INFORMATION WITHIN A NEURON: - neurons cell membrane is porous and allows small electrically charges molecules (ions) to flow in and out of the cell ex. like a spaghetti strainer - just as flow of water out of a strainer enhances the quality of the pasta, the flow of molecules across a cell membrane enhances the transmission of info in the nervous system THE RESTING POTENTIAL : THE ORGIN OF THE NEURONS ELECTRICAL PROPERTIES: - neurons natural electric charge is called resting potential  difference in electric charge between the inside and outside of a neurons cell membrane - resting potential creates the environment for a possible electrical impulse - resting potential arises from the difference in concentrations of ions inside and outside the neurons cell membrane - ions carry positive and negative charge - in resting state, there is high concentration of a positively charged ion (K+) as well as negatively charged protein ions INSIDE the neurons cell membrane compared to outside it - by contrast, there is a high concentration of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-) OUTSIDE the neurons cell membrane - since both the inside and outside of the neuron contain one positively and one negatively charged ion, doesn’t mean the charges cancel out and the resting potential is neither positive or negative... THE RESTING POTENTIAL IS NEGATIVE - raising the concentration of K+ in the fluid outside the neuron to match the concentration of K+ inside the neuron causes the resting potential to disappear - differences in K+ concentration are the basis of the resting potential - the concentration of K+ inside and outside an axon is controlled by channels in the axon membrane that allow molecules to flow in and out of the neuron - in resting state, the channels that allow the flow of Na+ and the other ions noted earlier are generally closed - naturally there is a higher concentration of K+ molecules INSIDE the neuron but some K+ molecules move out of the neuron through the open channels, leaving the inside of the neuron with a charge of about -70 millivolts relative to the outside THE ACTION POTENTIAL: SENDING SIGNALS ACROSS THE NEURON: - producing a signal to stimulate the axon with a brief electric shock, results in the conduction of a large electric impulse down the length of the axon - this electric impulse is called action potential  an electric signal that is conducted along the length of a neurons axon to the synapse Why is an action potential an all-or-nothing event? - Action potential occurs only when the electric shock reaches a certain level or threshold - When shock is below the threshold, only tiny signals which dissipated rapidly - When shock reached threshold, a much larger signal (the action potential) was observed - Increase in the electric shock above the threshold did NOT increase the strength of the action potential - Action potential is all or none: electric stimulation below the threshold fails to produce an action potential whereas electric stimulation at or above the threshold always produces the action potential - The action potential always occurs with exactly the same characteristics and at the same magnitude regardless of whether the stimulus is at or above the threshold - Action potential occurs when there is a change in the state of teh axons membrane channels - During resting potential only K+ channels are open - BUT when electric charge is raised to the threshold value, the K+ channels briefly shut down and other channels that allow the flow of a positively charged ion Na+ are opened - Na+ is typically much more concentrated outside the axon than inside so when Na+ channels open, those positively charged ions flow inside, increasing the positive charge inside the axon relative to that outside - This flow of Na+ into the axon pushes the acton potential to its maximum value of 40 millivolts - After action potential reaches its maximum, the membrane channels return to their original state and K+ ions flows out until the axon returns to its resting potential of -70 millivolts - This leaves a lot of extra Na+ ions inside the axon and a lot of extra K+ ions outside the axon - During this period where the ions are imbalanced, the nuron cannot initiate another action potential so it is said to be in a refractory period  the time following an action potential during which a new action potential cannot be initiated - The imbalance is revered by an active chemical pump in the cell membrane that moves Na+ outside the axon and K+ inside the axon SUMMARY OF NEURON ACTIVITY 1) THE RESTING POTENTIAL : in the resting state, K+ molecules flow freely across the cell membrane but Na+ molecules are kept out, creating a difference in electric charge between the inside and outside of a neurons cell membrane. The inside of the neuron has a charge of about -70 millivolts relative to the outside, which is the potential energy that will be used to generate the action potential 2) THE ACTION POTENTIAL: electric stimulation of the neuron shuts down the K+ channels and opens the Na+ channels, allowing Na+ to rush in and increase the positive charge inside the axon relative to the outside, triggering the action potential 3) The imbalance in ions from the action potential is reverse by an active chemical “pump” in the cell membrane that moves Na+ outside the axon and moves K+ inside the axon. The neuron can now generate another action potential HOW DOES ELECTRIC CHARGE MOVE DOWN AXON: - When action potential is generated at the beginning of the axon, it spreads a short distance, which generates an action potential at a nearby location on the axon - That action potential also spreads, initiating another action potential at another nearby location and so on - Therefore, a charge is transmitted down the length of the axon - This ensures that the action potential travels the full length of the axon and that it achieves its full intensity at each step, regardless of the distance travelled - Myelin sheath which is made up of glial cells that coat and insulate the axon, facilitates the transmission of the action potential - Myelin doesn’t cover entire axon, rather it clumps around the axon with little break poins b/w clumps looking like sausage links - These break points are called nodes of Ranvier - When electric current passes down the length of a myelinated axon, the charge seems to “jump” from node to node rather than having to traverse the entire axon - This process is called salatory conduction and helps speed flow of info down the axon CHEMICAL SIGNALING: TRANSMISSION BETWEEN NEURONS: - When action potential reaches the end of an axon, the electric charge of teh action potential takes a form that can cross the relatively small synaptic gap by relying on a bit chemistry How does a neuron communicate with another neuron? - Axons usually end in terminal buttons  knoblike structures that branch out from an axon - A terminal button is filled with tiny vesicles (or “bags”) that contain neurotransmitters  chemicals that transmit information across the synapse to a receiving neurons dendrites - The dendrites of the receiving neuron contain receptors  parts of the cell membrane that receive neurotransmitters and either initiate or prevent a new electric signal - As K+ and Na+ flow across a cell membrane, they move the sending neuron, or presynaptic neuron from a resting potential to an action potential - The action potential travels downt he length of the axon to the terminal button where it stimulates the release of neurotransmitters from vesicles into the synapse - The neurotransmitters float across the synapse adn bind to receptor sites on a nearby dendrite or the receiving neuron, or post-synaptic neuron - A new electric potential is initiated in that neuron and the process continues down that neurons axon to the next synapse and the next neuron - This electrochemical action is called synaptic transmission  allows neurons to communicate with one another and ultimately underlies your thoughts, emotions and behavior HOW DOES DENDRITES KNOW WHICH NEUROTRANSMITTER TO RECEIVE? - Neurons tend to form pathways in the brain that are characterized by specific types of neurotransmitters...so one neurostransmitter might be prevalent in one part of the brain whereas a different neurotransmitter might be prevalent in a different part of the brain - Also, neurotransmitters and receptor sites act like a lock and key system - Only some neurotransmitters bind to specific receptor sites on a dendrite (like a lock and key) - The molecular structure of the neurotransmitter must fit the molecular structure of teh receptor site WHAT HAPPENS TO THE NEUROTRANSMITTERS LEFT IN THE SYNAPSE AFTER CHEMICAL MESSAGE IS RELAYED TO POSTSYNAPTIC NEURON? - Neurotransmitters leave the synapse through three processes - 1) reuptake  occurs when neutrotransmitters are reabsorbed byt he terminal buttons of the presynaptic neurons axon - 2) enzyme deactivation  neurotransmitters can be destryoyed by enzymes in this process. Specific enzymes break down specific neurotransmitters - 3) autoreceptors  detect how much of a neurotransmitter has been rleased into a synapse and signal the neuron to stop releaseing neurotransmitters when an excess is present ( neutransmitters bind to receptor sites called autoreceptors) TYPES AND FUNCTIONS OF NEUROTRANSMITTERS: - About 60 chemicals play a role in transmitting information throughout the brain and body and that they differentially affect thought, feeling and behavior 1) ACETYLCHOLINE o is a neurotransmitter involved in a number of functions including voluntary motor control o is found in neurons of the brain and in the synapses where axons connect to muscles and body organs such as the heart o activates muscles to initiate motor behavior o also contributes to the regulation of attention, learning, sleeping, dreaming and memory o alzheimers disease, a medical condtion involving severe memory impairments, is associated with the deterioration of acetylcholine producing neurons 2) DOPAMINE o Is a neurotransmitter that regulates motor behavior, motivation, pleasure and emotional arousal o It has a role in basic motivated behaviors such as seeking pleasure or associating actions with rewards and therefore also plays a role in drug addiction o High levels of dopamine have been linked to schizophrenia o Low levels of dopamine have been linked to parkinsons disease 3) GLUTAMATE o Is a major excitatory neurotransmitter involved in information transmission throughout the brain o It enhances the transmission of information o Too much glutamate can overtimulate the brain causing seizures o GABA (gamma-aminobutyric acid) in contrast, is the primary inhibitory neurotransmitter int he brain o Inhibitory neurotransmitters stop the firing of neurons o Too little GABA just like too much glutamate can cause neurons to become overactive 4) NOREPINEPHRINE o A neurotransmitter that influences mood and arousal o Is involved in states of vigilance or heightened awareness of dangers in the environment o Similarily, serotonin  is involved in the regulation of sleep and wakefulness, eating and aggressive hevaior o Because both neurotransmitters affect mood and arousal, low levels of each have been implicated in mood disorders 5) ENDORPHINS o Are chemicals that act within the pain pathways and emotion centers of the brain o Morphione is synthetic drug that has a calming and pleasurable effect o An endorphin is internally produced substance that has similar properties such as dulling the experience of pain and elevating moods o The “runners high” experience by many athletes as they push their bodies to painful limits of endurance can be explained by the release of endorphins in the brain How do neurotransmitters create the feeling of a “runners high”? - Each neurotransmitter affects thought, feeling and behavior in different ways so normal functioning involves a delicate balance of each - Too much of one neurotransmitter or not enough of another can dramatically affect behavior - Sometimes these imbalances can occur naturally - For example, if the brain doesn’t produce enough serotonin, this can contribute to depressed or anxious moods - Sometimes, people actively seek to cause imbalances - People who smoke, drink alcohol or take drugs are altering the balance of neurotransmitters in their brains - For example, the drug LSD is structurally very similar to serotonis so it binds very easily with serotonin receptors in the brain, producing similar effects on thoughts, feelings or behavior HOW DRUGS MIMIC NEUROTRANSMITTERS: - Many of the drugs that affect the nervous sytem operate by increasing, interfering with or mimicking teh manufacture or function neurotransmitters - Agonists  are drugs that increase the action of neurotransmitters - Antagonists  are drugs that block the function of a neurotransmitter - Some drugs alter a step in the production or relasea of the neurotransmitter whereas others have a chemical structure so similar to a neurotransmitter that the drug is able to bind to that neurons receptor - If by binding to a receptor, a drug activates the neurotransmitter, it is a agonist - If it blocks the action of the neurotransmitter, it is an antagonist HOW DOES GIVING PATIENTS L-dopa ALLEVIATE SYMPTOMS OF PARKINSONS DISEASE: - Parkinsons disease is a movement disorder characterized by tremors and difficulty initiating movement and caused byt he loss of neurons that use the neurotransmitter dopamine - Dopamine is created in neurons by a modification of a common molecule called L-dopa - Injesting l-dopa will elevate the amount of L-dopa in the brain and spur the surviving neurons to produce more dopamine - L-dopa acts as an agonist for dopamine OTHER STREET DRUGS ALTER THE ACTIONS OF NEUROTRANSMITTERS - 1) METHAMPHETAMINE o Affects the pathwasy for dopamine, setotonis and norepinephrine at the neurons synapses making it difficult to interpret exactly how it works o The combination of its agonist and antagonist effects alters the functions of neurotransmitters that help us perceive and interpret visual images o Ex. David who’s paranoid hallucinations were induced by his crystal meth habit o - 2) AMPHETAMINE o Popular drug that stimulates the rlease of norepinephrine and dopamine o Both amphetamine and cocaine prevent the reuptake of norepinephrine and dopamine o Combination of increased release of norepinephrine and dopamine and prevention of their reuptake floods the synapse with those neurotransmitters, resulting in increased activation of their receptors o Both these drugs are strong agonists o Norepinepherine and dopamine play a crucial role in mood control such that if you increase any of the two neurotransmitter it results in euphoria, wakefulness and a burst of energy o It also increases heart rate so an overdose of amphetamine or cocaine can cause the heart to contract so rapidly that heartbeats do not last long enough to pump blood effectivbely leading to fainting and sometimes to death o The size of the brain strcutre known as the amygdale, which plays an important role in recognizing expressions of fear is reduced in regular cocaine users (they are unable to recognize facial expression compared to recreational users of cocaine) - 3) PROZAC o Drug commonly used to treat depression is an example of a agonist neurotransmitter o It blocks the reuptake of teh neurotransmitter serotonin making it part of a category of drugs called selective serotonin reuptake inhibitors o Patients suffering from depression have reduced levels of serotonin in their brains o By blocking reuptake more of the neurotransmitter remains in the synapse longer and produces greater activation of serotonin receptors o Serotonin elevates mood which can help relieve depression - 4) PROPRANALOL o Part of the call of drugs called beta blockers that obstruct a receptor site for norepinephrine in the heart o Because norepinepherine cannot bing to these receptors, hear rate slows down which is helpful for disorders in wich the ehart beats too fast or irregularly o Beta-blockers are also prescribed to reduce the agitation, racing heart, and nervousness associated with stage fright - Agonists  drugs that increase the action of a neurotransmitter - Agtanonists  drugs that block the function of a neurotransmitter THE ORGANIZATION OF THE NERVOUS SYSTEM: - Neurons work by forming circuits and pathways in the brain, which in turn influence circuits and pathways in the other areas of the body - Nervous system  interacting network of neurons that converys electrochemical information throughout the body DIVISIONS OF THE NERVOUS SYSTEM: - Two major divisions: central and peripheral nervous system - Central nervous system  composed of the brain and spinal cord - It receives sensory information from the external world, processes and coordinates this info and sends commands to the skeletal and muscular system for action - At the top of the CNS is the brain, which contains structures that support the most complex perceptual, motor, emotional and cognitive functions of the nervous system - Spinal cord branches down from brain and nerves that process sensory info and relay commands to the body connect to the spinal cord - Peripheral nervous system  connects the CNS to the bodys organs and muscles - PNS is composed of two subdivisions: somatic nervous system and autonomic nervous sytem - Somatic nervous system  set of nerves that conveys info into and out of the CNS - We have control over this system and use it to perceive, think and coordinate behavior - Ex. when reaching for cup of coffee: info from the receptors in your eyes travels to your brain, registering that a cup is on he table and then signals from your brain travel to the muscles in your arm and hand and feedback from those muscles tells your brain that the cup has been grasped - Autonomic nervous system  set of nerves that carries involuntary and automatic commands that control blood vessels, body organs and glands (works on its own out of conscious control) - it has two major subdivisions: sympathetic and parasympathetic nervous system - sympathetic nervous system  set of nerves that prepares the body for action in threatening situations What triggers the increase in your heart rate when you feel threatened? - Your sympathetic nervous sytem kicks into action - dialating your pupils to let in more light, - increases your heart rate and respiration to pump more oxygen to muscles - divers blood flow toy our brain and muscles - activates sweat glands to cool your body - to conserve energy sympathetic nervous system inhibits salivation and bowel movements - suppresses the bodys immune response - suppresses responses to pain and injury - parasympathetic nervous system  helps the body return to a normal resting state - after you get away from the attacker, your body doesn’t need to reamin on red alert - parasympathetic nervous system kicks in to reverse and effects of the sympathetic nervous system and return body back to normal state - ex. constricting your pupils, slows heart rate, diverts blood flow to digestive system, decreases activity in sweat glands COMPONENTS OF THE CENTRAL NERVOUS SYSTEM: What important functions does the spinal cord perform on its own? - Spinal cord does important tasks including keeping you breathing, responding to pain, moving your muscles, allowing you to walk - Connections b/w sensory inputs and motor neurons in the spinal cord mediate spinal reflexes simple pathways in the nervous system that rapidly generate muscle contractions - Ex. if you touch a hot stove, sensory neruosn that register pain send inputs directly to spinal cord - Through just a few synaptic connections within the spinal cord, interneurons relay these sensory inputs to motor neurons that connect to your arm muscles and direct you to quickly retract your hand - The brain sends commands for voluntary movement through the spinal cord to motor neurons, whoses axons project out to skeletal muscles and send the message to contract - Different regions of the spinal cord control different systems of the body STRUCTURE OF THE BRAIN: - Brain can be divided into three parts: hindbrain, midbrain, and forebrain HINDBRAIN: - Spinal cord is continuous with the hindbrain area of the brain that coordinates info coming into and out of the spinal cord - Controls most basic functions: respiration, alertness and motor skills - 3 autonomical structures that make up hindbrain: medulla, cerebellum and pons - Medulla  an extension of the spinal cord into the skull that coordinates heart rate, circulation and respiration - Inside medulla is a small cluster of neurons called reticular formation regulates sleep, wakefulness and levels of arousal - Behind medulla is the cerebellum  a large structure of the hindbrain that controls fine motor skills - Celebellum orchestrates the proper sequence movements when we ride a bike play the piano or maintain balance while walking/running and contributes to fine tuning of behavior, smoothing our actions to allow their graceful execution - Pons  structure that relays information from the cerebellum to the rest of the brain - It acts as bridge between the cerebellum nd other structures of the brain MIDBRAIN: - two main structures of midbrain : tectum and tegmentum - tectum orients an organism in the environment - it receives stimulus input from the eyes, ears and skin and moves the organism in a coordinated way toward the stimulus - ex. when you hear a click behind you, your body will swivel and orient to the direction of the click - tegmentum  involved in movement and arousal and also helps orient an organism toward sensory stimuli - you can survive with just midbrain and hindbrain: structures in hindbrain would take care of all the bodily functions necessary to sustain life and structures in midbrain would orient you toward or away from pleasurable or threatening stimuli in the environment FOREBRAIN: - forebrain  cont
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