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PSY1101 Chapter 2

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University of Ottawa
Najwa Haddad

PSY1101 Section I Chapter 2 The Biology of the Mind ∑. The Nervous System I. Function and structure Why are we studying it? Because everything psychological is biological – everything we think, feel, and therefore do is from the nervous system Nervous System Peripheral Nervous Sytem Central Nervous System (all the nerves outside of (brain and spinal cord) the CNS) Function: think of this as a complex communications system – receives info from the environment, analyzes, organizes, and integrates it, then uses this to send out messages to muscles and glands – also responsible for conscious experience (no idea how this happens, people are trying to figure it out) II. Neurons A. Basic Function and Structure Neurons are the basic unit of communication 3 types: sensory (receiving info from the environment), motor (carrying messages to muscles, etc), interneurons (has the most complex job – analyze, organize, integrate – only in central nervous system, we have billions of them) Basic structure – come in a variety of shapes and sizes, share same structure Soma – the cell body, control centre of the neuron, has DNA, produces everything the neurons need to survive, grow repair, function Dendrites – 2 main functions: increase surface area of the soma, receive messages from other neurons Axon – carries out messages is the main job, carries out action potential, electrical/nerve impulse Axon/Terminal Branches - allow the flow of information for one neuron cell to more than one cells Terminal Buttons/Axon Terminals – releases neurotransmissions Myelin Sheath – some axons are covered with it – insulates them from other chemicals/messages speeds up transmission of action potential (multiple sclerosis destroys the myelin sheath) Synapse – where neurons meet to communicate PSY1101 Section I Synaptic Cleft/Gap – space between two neurons at the synapse Presynaptic Neuron – sending out a message Postsynaptic Neuron – receiving a message B. Communication B1. Communication with a Neuron The brain is 80% water Water inside neurons is called cellular fluid, outside it is called extracellular fluid PSY1101 Section I This water has dissolved chemicals such as sodium ions (Na +), chloride ions (I-) and potassium ions (K+) found both inside and outside of the neurons, however they are found in different concentrations, concentration changes depending on what goes on with neurons Membrane of the neuron is porous, materials can go in or out – however, it is selectively permeable – ions have rules and regulations about when they can move in or out Neurons at rest (not firing): Inside the cell Outside the cell Higher K+ Higher Na + More negative Ions More positive ions Negative Positive Electrical charge of -70mV Polarized – resting potential of the neuron Even at rest it is receiving messages from other neurons, which changes concentration of ions and the electrical charge – 2 types of messages – inhibitory: ‘you cannot fire’ (hyperbolize = more negative, eg from -70mV to 76mV – membrane becomes more negative than at rest making it less likely to fire) and excitatory: ‘fire’ (concentration of ions changes as a number of sodium ions go into the cell, increasing # of positive ions, leading to the depolarization of the membrane – less negative than at rest, eg. From 70mV to -63mV, making it more likely to fire) ~the more salt and less bananas, the colder the water- the colder the water, the more likely to fire~ When will it fire? When the depolarization reaches about -50mV, the threshold of excitation – at this point a huge number of positive ions will rush into the cell and it will depolarize to 40+ mV – at this point, potassium starts leaving the cell in large numbers, serious decrease of positive ions, and the membrane repolarizes, becoming more negative than at rest, then the neuron goes through a refractory period where it cannot fire and because of this, during this period the sodium – potassium pump kicks in, pumping K+ in and Na+ out and it goes into resting potential because of this polarizing again Keep in mind: action potential is an all or none phenomenon, so every time a neuron fires, it is of the same strength B2. Communication between Neurons Neurotransmitters – chemical molecules made by neurons, used for communication Synaptic vesicles – like little bags that contain neurotransmitters Receptors – structures found on the membrane of post synaptic neurons, neuron attach to them to send messages and specific transmitters have specific receptors The presynaptic neuron fires, so the action potential travels down the axon, reaches the terminal button, then the synaptic vesicles attach to the membrane of the terminal button, then they burst open, the neurotransmitters release into the synaptic gap, bind to the receptor sites, then everything starts all over again Fate of the neurotransmitter – they deliver the message, then they detach themselves and sometimes reuptake happens – they go back to the neuron that released them where they PSY1101 Section I are recycled, or degradation happens – an enzyme breaks it down while it is the gap – must do one or the other or else it will deliver the message over and over again and either overstimulate or over inhibit the nervous system C. Neurotransmitters Healthy levels (balanced) needed in order to function properly, eg dopamine – healthy levels = good mood, motivation, motor function, but if levels go down – Parkinson’s disease can happen, bad mood, etc, and too high – some cases of schizophrenia Neurotransmitter Function Examples of Malfunction Acetylcholine (Ach) Enables muscle action, learning, Alzheimer’s disease – Ach-producing and memory neurons deteriorate Dopamine Influences movement, learning, Oversupply linked to schizophrenia. attention, and emotion Undersupply linked to tremors and decreased mobility in Parkinson’s disease Serotonin Affects mood, hunger, sleep, Undersupply linked to depression. Some and arousal antidepressant drugs raise serotonin levels Norepinephrine Helps control alertness, and Undersupply can depress mood arousal GABA (gamma- A major inhibitory Undersupply linked to seizures, tremors, aminobutyric acid) neurotransmitter and insomnia Glutamate A major excitatory Oversupply can overstimulate brain, neurotransmitter; involved in producing migraines or seizures (which is memory why some people avoid MSG, monosodium glutamate, in food) The brain produces its own naturally occurring opiates – eg. When in pain, our body releases neurotransmitter molecules similar to morphine called endorphins – the runner’s high, etc D. How Drugs and Other Chemicals Affect the Brain Eg. Pesticides, cocaine, etc in general for now Effects at the synapse, in 3 major ways  Presynaptic neuron – At this level a drug can inhibit (block it completely or reduce its signature) eg. Botox or facilitate the release of the neurotransmitters eg. Coffee  Activity in the cleft – Affecting reuptake (blocking, speeding up or down) or interfering with degradation  Postsynaptic level – Drug locks and mimics the neurotransmitter: drug does what the neurotransmitter does, delivers messages, or locks and blocks: attaches and does nothing, so no messages, or locks and enhances or diminishes the activity of the neurotransmitter Drugs – agonist or antagonist – Agonist: drugs mimics or enhances or facilitates activity of the neurotransmitter, Antagonist: drug blocks or reduces its affects PSY1101 Section I III. The Brain (CNS) A. Introduction The ancient Greeks first try to figure out what body art did what and were not impressed with the brain – Aristotle decided the heart was the source of feeling and thinking and that the brain only cooled blood – Hippocrates is considered the father of modern medicine: saw the brain as the source of feelings and movement, etc B. Tools of Discovery B1. Clinical observation The oldest method to study the brain, was the only way before technology eg. Watching someone with a brain injury – other way was brain dissection – a lot of data collected this way B2. Brain manipulation Several ways – 1. Surgical (done without medical needs on animals) take out parts or cut off connections, then observe, or PSY1101 Section I 2. Inject chemicals that will activate or deactivate part of the brain and observe, eg. Saw left hemisphere as responsible for language, or 3. Electrical stimulation by inserting electrodes, sending weak currents to manipulate the area, observing, or 4. Magnetic stimulation, exposing area to a magnetic field to activate or deactivate, then observing, or 5. Optogenetics, targeting neurons eg. Rats addicted to cocaine, shine light on different pathways of brain caused addiction to go away, gave and then healed them of Parkinson’s B3. EEG Created in 1929 (one of the oldest technologies, still useful), place electrodes on the skull, those electrodes can see electrical activity of the brain can see brain waves – allows us to see the brain in action – can see if you are dreaming, etc – can now pick up activity of a single neuron B4. Neuroimaging Techniques 1. CT or CAT Scan – is a super sophisticated x-ray, fast and multiple x-ray images from multiple angles that are later put together to make a full image – does not show the brain in action, only the structure 2. MRI – not invasive
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