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Chapter 45 - Chapter 45 Electrical Signals in Animals Key...

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Chapter 45: Electrical Signals in Animals Key Concepts Neurons are cells that transmit electrical signals used in communication. Neurons have a membrane potential, which is an electric potential difference, or voltage, across the plasma membrane. A voltage exists due to differences in the concentrations of ions on the two sides of the plasma membrane. Electrical signals are transmitted as graded or all-or-none changes in membrane voltage. All-or-none changes are called action potentials. During an action potential, an inflow of sodium ions is followed by an outflow of potassium ions. At synapses, an electrical signal from one neuron is converted to a chemical signal in the form of a neurotransmitter. When it arrives at an adjacent neuron, the neurotransmitter causes a change in that cell's membrane potential. Animals have a central nervous system (CNS) and a peripheral nervous system (PNS). PNS neurons receive sensory information and transmit it to the CNS for processing. The CNS then sends signals to muscles, glands, or other target tissues via other PNS neurons. Section 45.1 Outline: Principles of Electrical Signaling The Anatomy of a Neuron An Introduction to Membrane Potentials The Resulting Potential Using the Nernst and Goldman Equations Using Microelectrodes to Measure Membrane Potentials What Is an Action Potential A sensory receptor transmits the information it receives from the environment by means of a nerve cell called a sensory neuron . In vertebrates, the sensory neuron sends the information to neurons in the brain or spinal cord via nerves —long, tough strands of nervous tissue, containing thousands of neurons. The central nervous system (CNS) , made up of the brain and spinal cord, integrates information from many sensory neurons. Cells in the CNS called interneurons make connections between sensory neurons and motor neurons , which are nerve cells that send signals to effector cells in glands or muscles. All of the components of the nervous system outside the CNS are part of the peripheral nervous system (PNS) . Sensory information from receptors in the PNS is sent to the CNS, where it is processed. Then a response is transmitted back to appropriate parts of the body.
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Some information from a sensory neuron results in a reflex —a direct response to a signal that bypasses the brain. The Anatomy of a Neuron o Most neurons have a cell body, dendrites, and one or more axons (Figure 45.3). o A dendrite receives electrical signals from the axons of adjacent cells. o The axon then sends the signal to the dendrites of other neurons. o The cell body , or soma , which includes the nucleus, integrates the incoming signals and generates an outgoing signal in the axon. An Introduction to Membrane Potentials o A difference of electrical charge between any two points creates a difference in electrical potential , or a voltage .
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