3208Ch7lec - MCB32F08

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Chapter 7: Neuronal action potentials and synaptic transmission Outline Basic anatomy of nerve cells; sensory and motor nerves, support cells Action potential: Threshold Depolarization Overshoot Repolarization Refractory period Na and K channels: activation and inactivation, voltage-dependent Propagation of action potential: myelin and salutatory conduction Synaptic function and integration: excitatory and inhibitory synapse Overview: Nerves allow rapid, long distance communication for integrated control of a variety of functions ranging from thinking to sensing to control of heart and other organs etc. This communication requires rapid changes in membrane potential due to the activation of voltage-sensitive Na and K channels in the membranes of the nerves. These ion channels turn on and off by changing their structures, depolarizing and then repolarizing the membrane voltage of the nerves. One nerve triggers the next in series by releasing a chemical transmitter that depolarizes the next neuron, which then becomes triggered to generate its own action potential. Due to their anatomic organization and the one- way conduction of action potentials, the nerves transmit action potentials only in one direction, from one nerve axon to its end plate and synapse with the next neuron at its dendrites and then to the axon of the second cell. Since the action potential is all or none, information processing occurs in terms of action potential frequencies and connections, not in terms of the magnitude of the action potentials triggered. Anatomy Central nervous system (brain and spinal cord) and peripheral nervous system (nerves outside the CNS). Sensory nerves transmit AP’s from sensory organs to the CNS Motor nerves transmit AP’s from CNS to organs; somatic motor nerves go to skeletal muscles and autonomic nerves go to organs. Neurons have the following key structures: dendrites, cell bodies, axon hillock, axons, end plates or boutons at the synapse with next dendrites. Many but not all axons are surrounded with a coating or sheath, myelin generated by cells (Schwann cells or oligodendrocytes depending on where the cells are located, peripheral or central nervous system) that wrap themselves around the axon. Myelin provides some protection but main function is to speed neuronal conduction along the axon. The supporting cells can serve metabolic functions too. Glial cells are also present for metabolic support . 1
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This note was uploaded on 01/23/2009 for the course MCB 57703 taught by Professor Machen during the Fall '08 term at Berkeley.

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3208Ch7lec - MCB32F08

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