BIO 365R lecture 10 - Autonomic nervous system: excitation...

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1 Autonomic nervous system: excitation or relaxation sympathetic parasympathetic
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2 Otto Loewi discovered neurotransmission (1873-1961) Nobel 1936
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3 Pharmacology of parasympathetic neurotransmission in the heart Antagonist (blocks the transmitter): Atropine (poison from Bella Donna plant). Acetylcholine (ACh) is the substance released by Vagus nerve stimulation; applying ACh to the heart slows down its beating. Agonist (acts like the transmitter): Muscarine (poison from a mushroom, Amanita muscaria ).
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4 Basal lamina The neuromuscular junction is the synapse made between a motor neuron and a muscle fiber and is a very large synapse. The synaptic region on the muscle fiber has a special name, the END-PLATE Bernard Katz (1911-2003) Nobel 1970
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5 nerve Axon that innervates muscle fiber end plate Muscle fiber
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6
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7 ACh always excites skeletal muscle fibers. It generates an EPP that is so large, that it exceeds threshold thereby generating an action potential in the muscle fiber End plate potential is generated by summation of many miniature end-plate potentials
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8 Nicotinic ACh receptors are found at the neuromuscular junction Nicotine acts as a substitute for ACh (it is an agonist) while curare blocks these receptors (it is an antagonist) Pipette filled with nicotine solution Pass current and eject nicotine RECORDINGS OF MEMBRANE POTENTIAL THROUGH PIPETTE Preparation bathed in low Ca++ to reduce transmitter release Stimulate nerve Pulse on nicotine
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9 ACh (acetylcholine) is always released from axon terminal. ACh opens channels that excite skeletal muscle fibers and generates an action potential in the muscle fiber Action potential recorded in muscle fiber End plate The excitatory post-synaptic potential in muscle fibers also has a special name: the end-plate potential or EPP
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10 Reversal potential is determined by voltage clamping the membrane to various membrane potentials while stimulating the motoneuron and causing it to release ACh. The membrane
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BIO 365R lecture 10 - Autonomic nervous system: excitation...

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