Week 4 - 1 Week 4 Notes 2/4/08 Synapses Knowledge of neuron...

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1 Week 4 Notes 2/4/08 Synapses Knowledge of neuron functions. - Understood muscle relaxers long before we knew what was going on at the neuromuscular junction - A major transduction event when the neurotransmitter is released. What is happening at the neuromuscular junction? NMJ is a special example of a synapse. The studies began with the neuromuscular junction. A NMJ is when a motor neuron is descending down (after the decision to twitch) and the motor neuron synapses at an NMJ. One motor neuron can synapse onto muscle end plates or multiple muscle fibers. What happens is: there is a motor neuron with Schwann cells then - Typical of many synaptic junctions: Invagination (motor end-plate on a muscle) – increasing the surface area to have a high resident population of receptors where the neurotransmitters will be released. - Consider: Scientists had no idea about this. Memorization of Neuromuscular Junction characteristics - Releases Acetylcholine into synapse - Acetylcholine manufactured in the axon terminal - Receptors for Ach on post-synaptic membrane (they exist in pre-synaptic and glial cells) - Glutamatic, Glycine, - ACh binds in a concentration dependent manner - there is always some ACh resident in the synapses - Increase in concentration in one end will bridge across and increase the likelihood that ACh will bind at the other end. - ACh is “cleared” by enzyme action o How to turn off the synapses. Destroy neurotransmitter inside
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2 Week 4 Notes take it back up into the pre-synaptic or the glial cells. change the concentration of the neurotransmitter present. o Acetylcholinesterase breaks down ACh to acetate and choline Choline is taken back into the terminal - Make more Acetylcholine is manufactured - Load into vesicles via an ACh transporter Consider: - How are you destroying the transmitter? - How do you load them in vesicles? unknown factor 50 years ago Most other cells in the body secrete their chemicals in indiscrete packages (“ooze”) not true - There is a discrete interaction between a motor neuron and a muscle fiber that it innervates . o This is called a motor unit – it is an all or none stimulus Those muscle fibers respond ______. The variance with muscle flex has to do with how many motor units are recruited. Bernard Katz - K of the GHK equation - Major protagonist behind voltage clamp - Studied the junction between the motor neurons and the target muscles 2 Theories 1. Quantal nature of neurotransmitter release a. Chemicals don’t ooze and for a stronger signal you don’t ooze out more i. There is a discrete amount oozing. 2. Ca++ dependent release of neurotransmitters.
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3 Week 4 Notes a. Even though the scientists were aware of Na+ , they didn’t think that another ion would be necessary. Consider
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This note was uploaded on 08/25/2008 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

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Week 4 - 1 Week 4 Notes 2/4/08 Synapses Knowledge of neuron...

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