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Chapter 3


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University of Toronto St. George
Ashley Waggoner Denton

CH3 – BIOLOGICAL FOUNDATION Nervous System Operations  NEURON – the basic unit of the nervous system; it operates through  Potassium easier in than sodium, cause polarization electrical impulses which communicate w/ other neurons through  Sodium-potassium pump, increase potassium, decreases sodium chemical signals, Neurons functions: received, integrate and transmit inside neuron information in the nervous system.  ACTION POTENTIAL (NEURAL FIRING) – the neural impulse that passes o Reception – intake information from neighboring neurons along the axon and subsequently causes the release of chemicals from the o Conduction – integration taken signals terminal buttons o Transmission – passing signals to other neurons o Changes in electrical potential lead to action  Types of Neurons: 3 major types  Chemical signal from nearby neuron through dendrite tell o SENSORY NEURONS – afferent neurons, detect information from the neuron fire/not physical world and pass that information along to the brain  Signals arrive at dendrites by the thousands  Usually via spinal cord  Excitatory signals – depolarize the cell membrane,  Afferent neurons – carry information to the brain increase likelihood neuron fire  Somatosensory –sensation experiences from w/i the body  Inhibitory signals – hyperpolarize cell, decrease o MOTOR NEURONS – efferent neurons, direct muscles to contract or likelihood neuron will fire relax, thereby producing movement  If total excitatory signal received surpass receiving  Efferent neurons – transmit signals from brain to muscles neuron’s threshold, action potential generated o INTERNEURONS – neurons communication only w/ other neurons, o Excitatory & inhibitory signal sum = positive voltage change typically w/i a specific brain region. exceeding neuron’s firing threshold, action potential generated  integrate neural activity w/i single area, communication w/i  Neuron firing: Sodium gates in cell membrane open  sodium local/short-distance circuits ion rush into neuron  cause inside neuron slightly positive o Sensory & Motor neurons together control movement than outside  potassium channels open, allow potassium ions  Neuron Structure – variety of shapes/sizes, share 4 structural regions out, now [+] inside, [-] outside  sodium channel close, sodium o DENRITES – short, branchlike extensions of the neuron that detect ion stop entering cell, potassium channel also close  information from neighboring neurons restoration, back to resting membrane potential o CELL BODY – information from thousands of other neurons is  Electrical charge inside cell starts slightly negative, becomes collected & processed positives, fires and allows more positive ions inside, natural o AXON – long narrow outgrowth of neuron by which information restoration to slightly negative (electrical impulses) is transmitted to other neurons  length varies few mm to 1m+, (longest = big toe to spinal cord)  Nerve – axons bundles, carry info btwn brain & bodily places  MYELIN SHEATH – A fatty material, made up of glial cells, insulates the axon in short segments  Allows for the rapid movement of electrical impulses along axon  NODES OF RANVIER – Small exposed axon gaps btwn myelin sheath segments  where action potentials are transmitted o TERMINAL BUTTONS – Small nodules, at the ends of axons, that release chemical signals from the neuron to synapse  SYNAPSE (SYNAPTIC CLEFT) – chemical communication site btwn neurons, contains extracellular fluid o Neuron’s membranes serves as boundary, regulates electrically charge molecule concentrations  RESTING MEMBRANE POTENTIAL – the electrical charge of neuron when it is not active, negative-positive ratio higher inside o Propagation – neuron fires, cell membrane’s depolarization move o Electrical charges inside neuron slight more negative than outside o Polarization – changing differential electrical charge inside/outside, along axon like waves  Sodium ions rush through ion channels, depolarization, case creates electrical energy necessary to power firing of the neuron adjacent sodium channels open successively moving down axon o Sodium & Potassium ions contribute to neuron’s resting membrane  b/c myelin sheath, action potential skips quickly along potential  Ion channels – specializes pores on Ranvier, specific to type of axon, recharge at each node ion (ex. Sodium channels and Potassium channels)  entire process = 1/1000 second  myelin sheath deterioration  multiple sclerosis, axons short-  Controlled by gating mechanism, open = ion flows in/out circuit  Ion flow also affected by cell membrane’s selective permeability, allow some ions pass easier o ALL-OR-NON PRINCIPLE – a neuron fires w/ the same potency each time, although frequency can vary it either fires or not – it cannot partially fire  Ex. Neuron in visual system, fire frequency = brightness  Neurotransmitters Bind to Receptors across the Synapse o Action potential cause neuron release chemical from terminal buttons, travel across synapse, receive at other neuron’s dendrites  Presynaptic neurons – neuron that sends the signal  Postsynaptic neuron – neuron that receives the signal o NEUROTRANSMITTERS – A chemical substance that carries signal from one neuron to another, inside vesicles in terminal button o After action potential reaches terminal button, cause vesicles release neurotransmitters into synaptic clef  Neurotransmitter cross synaptic cleft, then bind to receptors  RECEPTORS – In neurons, specialized protein molecules, on the postsynaptic membrane that neurotransmitters bind to after passing across the synaptic cleft  binding btwn neurotransmitters & receptors creates excitatory or inhibitory signal for postsynaptic neuron o Monoamines – neurotransmitters, major functions = regulate state  All neurotransmitter trigger/inhibit action potentials  same neurotransmitter send excitatory or inhibitory of arousal, affect (feelings), motivate behavior postsynaptic singles, depending on receptor properties  EPINEPHRINE –responsible for adrenaline rushes, bursts of energy caused by its release throughout the body o Neurotransmitters bind w/ specific receptors  NOREPINEPHRINE –involved in states of arousal and awareness  60+ chemicals transmit information in brain/body  Important for vigilance, heightened sensitivity  Different transmitters influence emotion thought, behavior  Each receptor only receive one neurotransmitter  Inhibits responsiveness to weak synaptic inputs, strengths/maintains responsiveness to strong synaptic o Neurotransmitters release into synapse, fill & stimulate one receptor inputs type, block new signal until influence terminated by reuptake,  SEROTONIN –a wide range of psychological activity, including enzyme deactivation, autoreception  REUPTAKE – the process whereby a neurotransmitter is taken emotional states, impulse control and dreaming.  Low levels cause sadness, anxious mood, food craving, back into the presynaptic terminal buttons, thereby stopping its aggressive behavior activity  DOPAMINE –involved in reward, motivation, and motor control  Reuptake & release cycle repeats continuously  Enzyme deactivation – specific enzyme destroy specific  Communicates rewarding activities, ex. Eating when transmitter substance in synaptic clef hungry  Dopamine activation involved w/ motor control &  Autoreception – Neurotransmitter bind w/ receptors on planning, guiding behavior towards things (objects) and presynaptic neuron  Autoreceptors monitor how much neurotransmitter experiences (additional rewards) release into synapse  PARKINSON’S DISEASE (PD) – A neurological disorder that seems to be caused by dopamine depletion marked  If excess  autoreceptors stops neurotransmitter release by muscular rigidity, tremors and difficulty initiating in presynaptic neuron voluntary action  Neurotransmitters Influence Mind and Behavior o AGONISTS – Any drugs/toxins that enhances the actions of a specific  Monoamine oxidase (MAO) – enzyme interrupts monoamine activities neurotransmitter o GABA – the primary inhibitory transmitter in the nervous system o ANTAGONISTS – Any drugs/toxins that inhibits the action of a  Prevent synaptic excitation spread chaotically throughout brain specific neurotransmitter o Drugs/toxin also can mimic neurotransmitters, bind w/ receptors  GABA agonist treat anxiety disorder ex. Valium o GLUTAMATE – the primary excitatory transmitter in the nervous  Types of Neurotransmitters system o ACETYLCHOLINE (ACh) –responsible for motor control at the junction  Strengthen synaptic connections, aid learning & memory between nerves and muscles o ENDORPHINS – involved in natural pain reduction and reward  Binds w/ muscle cells, cause contract or relax  Also involved in mental processes such as learning, memory,  Prevent pain interfere w/ adaptive functioning sleeping, and dreaming  Alzheimer’s associated w/ diminished ACh functioning o SUBSTANCE P – A neurotransmitter involved in pain perception. Basic Brain Structures and Functions o At base of skull, spinal cord transforms into brain stem, contains:  Functional Units of the Nervous System  Medulla Oblongata, Pons, Midbrain o CENTRAL NERVOUS SYSTEM (CNS) – The Brain and spinal cord o Reticular Formation – network of neurons contained in brain stem, o PERIPHERAL NERVOUS SYSTEM (PNS) – All nerve cells in the body projects into cerebral cortex, affect general alertness, inducing & that are not part of the CNS terminating different sleep stages  Includes somatic and autonomic nervous system
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