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Biology (Sci)
BIOL 111

Bio 111 Alanna Houston October 30, 2007 - All action potentials have the same magnitude for a given neuron - Depolarization, repolarization, hyperpolarization - Impulse travels along axon as ions channels open and close - At the end of the axon, there is a synapse (junction between the axon terminal and the next neuron) - 2 types: o Electrical Synapse o Chemical Synapse  Neurotransmitters are released (can have an excitatory synapse or inhibitory synapse) Neurotransmitters: - released into the synaptic cleft - Neurotransmitters bind to receptors: o On the next neuron o Or a muscle cell or gland - Can be excitatory (ex. Acetylcholine) o Cause depolarization - Can be inhibitory (ex. GABA) o Cause hyperpolarization Synapse: Bio 111 Alanna Houston - If acetylcholinesterase is lacking, with ATP muscle keeps contracting. Without ATP, it would only contract once Drugs interacting with excitatory neurotransmitters: - nerve gases (ex. Sarin) o inhibit acetylcholinesterase o acetylcholine is not broken down and remains in synapse o skeletal muscles contract uncontrollably causing paralysis - Antidepressants o Block the reuptake of excitatory neurotransmitters (ex. Seratonin) o Neurotransmitters remain in synapse longer o Impulses transmitted more frequently Drugs causing inhibitory effects at synapses: - anti-anxiety drugs (ex. Xanax) o mimic the actions of natural inhibitory neurotransmitters (ex. GABA) o Open Cl- channels causing hyperpolarization (more negative interior) o Greater stimulus needed to reach threshold - Tetrodoxin o Block Na+ channels and prevent depolarization o Found in a wide variety of animals Bio 111 Alanna Houston o Death by diaphragm paralysis - Anesthetics (ex. Novocain) o Inhibit local movement of Na+ through channels o Prevent depolarization Neuromuscular Junctions MUSCLE TISSUE - present in all animals except sponges - composed of proteins - contractions triggered by motor neuron depolarization - 3 types - Smooth muscle is found lining internal organs - Cardiac muscle is able to generate its own action potential (called the pacemaker) - - Skeletal muscle cells: o Contractile unit = sarcomere (actin – thin filaments, myosin – thick filaments) Bio 111 Alanna Houston o - H zone is only composed of myosin - During contraction, H zone shortens and the sarcomere shortens. Not actually shortening myosin or actin. “sliding filament theory” (overlap that is sliding) - Actin: o Globular protein o Composed of many monomers o Filamentous protein covering certain areas called tropomyosin (movement) and another globular protein called troponin o Have myosin binding sites (tropomyosin covers binding site so that it doesn’t contract all the time) o Troponin has monomers that bind to actin, tropomyosin, calcium ions o - Myosin: o Composed of many globular heads
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