chapter45%20Electrical%20Signals%20in%20Animals-[1] -...

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Electrical Signals in Animals 1 BLY122 A. Hunter from C. S. Major Chapter 45 Electrical Signals in Animals I. Principles of Electrical Signaling A. Neurons transmit information through electrical impulses. 1. The speed of transmission may be as rapid as 100 m/sec (225 mph). 2. Sensory receptors receive information about the external environment and body interior. a. Sensory cells on the periphery of the body transmit information about the external environment. b. Sensory cells inside the body monitor conditions that are important in homeostasis. 3. The pathway of information flow in the nervous system in vertebrates: a. Sensory neurons send information to the central nervous system (CNS). b. The CNS integrates information from many sensory neurons. c. The CNS stimulates a motor neuron, which sends signals to effector cells in glands or muscles. 4. The peripheral nervous system (PNS) consists of all components of the nervous system that are outside the CNS. 5. A reflex bypasses the brain and travels directly to an effector. a. The reflex makes it possible to have rapid automatic responses. b. A connection is made between a sensory neuron and a motor neuron in the spinal cord. B. The Anatomy of a Neuron 1. Neurons are small, transparent, and morphologically complex. 2. C. Golgi discovered that silver nitrate solution makes some neurons visible. a. Most neurons have dendrites, a cell body, and one or more axons. b. Dendrites are highly branched but are generally no more than 2 mm long. c. Axons can be over 1 meter long. d. The number and arrangement of dendrites varies in different neurons. e. Many brain neurons have only dendrites and lack axons. 3. Hypothesis: Dendrites receive electrical signals and axons pass them on. a. Golgi—Neurons are directly connected to each other; they form a continuous network. b. Cajal—Neurons are distinct, and the membranes of axons and dendrites meet at synapses. c. 1950s—Electron microscopy showed that, for most neurons, Cajal was correct. C. An Introduction to Membrane Potentials 1. Cells are inherently electrical in nature. a. Ions carry an electric charge, and extracellular fluids contain ions. b. If an imbalance of ions occurs across the membrane, a voltage, or electrical potential, is created. c. Membrane potential is a separation of charge across a membrane. d. Membrane voltage is large if the charge difference across the membrane is large. 2. If a membrane potential exists, the ions on either side of the membrane have potential energy. a. Ions move across membranes in response to charge and concentration gradients, that is, an electrochemical gradient. b. A flow of charge is called an electric current. D.
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This note was uploaded on 11/11/2009 for the course BLY 459 taught by Professor Obrien,j during the Spring '08 term at S. Alabama.

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chapter45%20Electrical%20Signals%20in%20Animals-[1] -...

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