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		1. Acetylcholine Acteylcholineis the neurotransmitter released at synapses with skeletal muscle(excitatory) and with smooth and cardiac muscle(inhibitory). This discrepancy results from the use of different receptors in the two muscle systems. Many toxic substances interfere with the action of acetylcholine at neuromuscular junctions. Several snake venom toxins and curare used on poisoned arrows irreversible bind to acetylcholine receptors on skeletal muscle. Q. Are they acting as an agonist or antagonist? - antagonist Q. What do you think will happen? - paralysis because muscles can't be stimulated Q. Would you expect these poisons to affect the heart? - no, different type of receptor 2. Biogenic amines The biogenic amines norepinephrine, epinephrine, dopamine, and serotonin are derived from modified amino acids. Norepinephrineis the neurotransmitter produced by the effector neurons of the sympathetic nervous system. Serotonin and dopamine are used in the synapses in the brain. Serotonin activates pathways leading to control of muscles; it inhibits pathways that mediate sensations and plays a role in controlling mood. Dopamineappears to be important in a region of the brain that helps to control body movements. These neurons degenerate in Parkinson's disease causing tremors and progressive motor dysfunction. Several therapeutic strategies have been tried or suggested: - supplementation with L-DOPA (the dopamine precursor) - transplanting fetal tissue into affected regions of brain - implanting genetically-altered cells producing dopamine - rescuing affected neurons with new growth factor (GDNF) Q. What are the advantages and disadvantages of these strategies? Mood-altering drugs often mimic the effects of neurochemicals (opiates) or alter their release or reuptake (nicotine, cocaine) in the brain.