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Chapter 3- OCT EXAM.doc

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Psychology 1000

CHAPTER 3- Biological Foundations of Behaviour NEURONS · Plasticity: changing in neurons in response to new experiences · Neurons: basic building blocks of the nervous system o Linked together in circuits o Birth--> 100 billion neurons o Communicate through electrical signals: ACTION POTENTIALS · 3 main parts: cell body, dendrites and an axon 1. CELL BODY (soma): o Biochemical structures that keep the neuronalive o Carries genetic information that determines how the cell developsand functions 2. DENDRITES: o Branch like fibres emerge from cell body o Collectmessages from other neurons and send them to the cell body (1000+ neurons) o Information is combined and processed 3. AXON: o Extending from one side of the cell body is a single AXON o Sends electrical impulses: from cell body  neurons, muscles or glands (generate action potential) o Branches at the end= axonterminals · Neurons vary greatly in size & shape--> more that 200 different types have been viewed · Glial cells: surroundand hold neurons in place o Make food for neurons (nutrient chemicals) o Absorb toxins o During prenatal brain development--> glial cells send long fibres that guide newly divided neurons to their target place in the brain o Glial cells outnumber neurons 10:1 o Blood brain barrier: prevents substances & toxinsfrom entering the brain (made of glial cells) ELECTRICAL ACTIVITY OF NEURONS 1 · Neurons do 2 important things: 1. Communicate through electrical signals called actionpotentials 2. Release chemicals that allow them to communicatewith other neurons/muscles/glands · Action potential involves 3 steps: 1. Resting Potential: at rest, the difference in charge between the inside and outside of a neuron is -70 millivolts= state of polarization o Protein on the inside are – charged, sodium that surrounds it is + charged 2. When stimulated, a flow of ions in and out through the cell membrane reverses the electrical charged of the resting potential, producing an action potential 3. The original distribution of ions is restored, and the neuron is again at rest · Neurons are surrounded by body fluids and separated from this liquid environment by a protective membrane · This membraneallows certain substances to pass through ion channels(passageway) into the cell while refusing or limiting passage to other substances · Outside the neuron(NA+) and (CL-) · Inside the neuron(A-) and (K+) o High concentration of (NA+) & (A-) = negativeresting potential THE ACTION POTENTIAL · Action potential: sudden reversal in the neuron’s membrane voltage called depolarization (-7040mv) o Absolute refractory period: membrane is not excitable and cannot generate another action potential · Limit of impulses for humans = 300/second · All-or-none law: action potentials mustoccur at a uniform & maximum intensity, or they will not occur · Action potential threshold: The - potential insidethe axon HAS to be changed from -70  -50 mv in order to travel · Graded potentials: when it does not reach -50 action potential threshold · For a neuron to function properly, NA and K ions must enter and leave the membrane at the right rate THE MYLEIN SHEATH · Fatty, whitish insulation layer derived from glialcellson some axons 2 · Make action potentials travel down the axon FASTER · Interrupted at regular intervals by the NodesofRanvier, where it is either extremely thin or absent · Unmyelinated axons= action potential travels down the axon like a burning fuse (slower) · Myelinated axons= electrical conduction “great leaps” highconductionspeedsof 300+km/hr · Multiple sclerosis: damage to the myelin coating o Person’s immune system attacks the myelin sheath (damage=jerky, uncoordinated movements) HOW NEURONSCOMMUNICATE: SYNAPTIC TRANSMISSION · Synapse: functional connection between a neuron and its target · Otto Loewi--> neurons released chemicals that carried the messaged from one neuron to the next cell in the circuit · Synapticcleft: tiny space between the axon of one neuron and the dendrite of the next neuron · What carries the message?... NEUROTRANSMITTERS · Process of chemical communication involves 5 steps: 1.Synthesis: chemical molecules are formed inside the neuron 2.Storage: molecules stored in synapticvesicles  Each neurotransmitter is stored within one axon i.e dopamine and seratonin= separate 3.Release: when the action potential comes down axon--> vesicles move to the surface of the axon terminal and the molecules are releasedinto the presynaptic and the postynaptic (membrane of receiving neuron) 4.Binding: bind to receptor sitesof receiving neuron  Each receptor site conforms to 1 neurotransmitter only (dopamine + serotonin=separate) 5.Deactivation: the receiving neuron either: a) Is excited by excitatory (inflow of + ions) depolarization (EPSP) b) Is hyperpolarized (IPSP) by inhibitory transmitters (outflow of + ions, inflow of – ions) o This makes the membrane potential more negative= harder to reach action potential (-70 to -72) 3 o A balance of hyperpolarization and depolarization must be maintained if the nervous system is to work properly ExcitatorySeizures are caused by large amounts of neurons firing off action potential Neurotransmitt s neuron’s likelihood of action er membrane potential Deactivation occurs in 2 ways: Inhibitoryctivated by either other Hyperpolarizeshe synaptic space (neutraDecreases Neurotransmitt neuron’s likelihood of 2. Byreuptake: reabsorbed into thmembraneaptic cleft and reused er action potential SPECIALIZED TRANSMITTER SYSTEMS · Transmitter molecules can assume many shapes: o 100-150 are known to be transmitters but may be many more o Each substance has specific excitatory or inhibitory effect on certain neurons -----------------------> -----------------------> -----------------------> -----------------------> ******page 11&12****** THE NERVOUS SYSTEM 1. Sensory neurons: sends messages from sense organs  brain 2. Motor neurons: sends messages from the brain  muscles/organs 3.Interneurons: most abundant neurons, have a connective function  EX: allow us to recognize a tune by linking the sensory input from the song with the memory of that song stored elsewhere in the brain 1) THE PERIPHERAL NERVOUSSYSTEM · Outside the brain & spinal cord · Neurons that connect muscles, glands and sensory receptors o Necessary for us to sense what is going on inside/outside our bodies and how to respond with our muscles and glands THE SOMATIC NERVOUSSYSTEM o Sensory neurons that transmit messages from eyes, ears o Axons group together (like a rope) to form sensorynerves o Motor neurons send messages from the brain & sp
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