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This 2 page Class Notes was uploaded by MelLem on Friday May 20, 2016. The Class Notes belongs to BIOL 225 at Simmons College taught by Dr. Lopilato in Fall 2016. Since its upload, it has received 7 views. For similar materials see Cell Biology in Biology at Simmons College.
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Date Created: 05/20/16
BIOL – 222 – Principles Animal Physiology Chapter 5: Neuron Structure and Function Chapter Outline Overview Cells use active transport of ions to maintain a voltage difference across their cell membranes termed – membrane potential Certain classes of cells termed – Excitable Cells – can rapidly alter their membrane potential by altering the distribution of ions across their membrane. These cells use the resulting changes in the membrane potential as communication signals. The best known excitable cells are neurons – cells that are specialized to carry electrical signals, often across long distances. Neurons vary in structure and properties, but all neurons use the same basic mechanisms to send signals. Motor neurons are neurons that communicate from the central nervous system to the muscles. The first functional zone of motor neuron consists of the dendrites and cell body (soma). Dendrites are fine, branching extensions of the neuron that originate from the cell body. They are responsible for sending incoming signals, converting these signals to an electrical signal in the form of a change in the membrane potential, and transmitting the signal to the cell body. The cell body contains the nucleus and the protein synthetic machinery of the cell, as well as most of the organelles, although mitochondria are also found in the dendrites and axon terminal. The plasma membrane of the cell body also contains receptors similar to the dendrites; therefore they can participate in detecting incoming signals. The second functional zone of a motor neuron consists of the axon hillock, which is specialized for signal integration. The axon hillock is located at the junction of the cell body and the axon. Incoming signals from dendrites and the cell body are conducted to the axon hillock, if the signal at the axon hillock is large, a specialized electrical signal termed – action potential is initiated. Action potentials occur in the axon a long slender extension leading off the cell body at the axon hillock. The third functional zone of the neuron is the axon, it is specialized for signal conduction. Each neuron only has one axon, although many may branch into several collaterals. Vertebrate motor neurons are wrapped in a myelin sheath that increases the speed of conduction of electrical impulses to the axon terminal. The fourth functional zone of the neuron is the axon terminals. They are specialized for signal transmission to target cells. Each axon terminal is a swelling of the end of the axon that forms a synapse with the target skeletal muscle cell. Signaling in a Vertebrate Motor Neuron The overall process of signaling in a vertebrate motor neuron involves receiving an incoming signal, converting that signal to a change in the membrane potential, triggering action potentials that conduct the signal across long distances, and then transmitting the signal to target cells in the form of a neurotransmitter. Electrical Signals in Neurons As excitable cells, neurons can rapidly alter their membrane potential in response to an incoming signal, and these changes in membrane potential can act as electrical signals. Like most animal cells, neurons maintain a coltage difference across their cell membranes. Excitable cells, when the cell is not involved in sending an electrical signal, this voltage difference is termed – resting membrane potential difference, or the resting membrane potential. The potential is approximately -70 mV (meaning the inside of the cell is about 70 mV more negative than the outside.
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