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Chapter 2. Functional Regional Anesthesia Anatomy
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Which of the following descriptions is correct about the structure of the neuron?
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A. A typical neuron consists of a cell body, which is also called the soma, with a small or absent nucleus.
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B. Many dendrites branch out from the cell body; their main function is to spread out outgoing messages.
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C. A typical neuron consists of several axons, which carry outgoing messages. They can vary in length and are also called nerve fibers.
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D. Most neurons are incapable of dividing under normal circumstances and have limited ability to repair themselves after injury.
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D is correct. In adults, most neurons are incapable of dividing under normal circumstances and have limited ability to repair themselves after injury.
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A is incorrect. The cell body of the typical neuron has a large nucleus.
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B is incorrect. The function of dendrites is to receive incoming messages.
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C is incorrect. A typical neuron has only one axon.
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The structure of a typical peripheral nerve is as follows:
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A. The endoneurium is a resistant layer of connective tissue surrounding each axon; its main function is to deliver strength to the peripheral nerve.
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B. The nerve fascicle is surrounded by the perineurium. It protects the neural tissue from the surrounding tissue, functioning as a blood–nerve barrier.
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C. Fascicular bundles are continuous throughout the peripheral nerve. Because of this, axons starting in one quadrant of the nerve keep the same position distally.
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D. The peripheral nerve is composed of three parts: (1) somatosensory or efferent neurons, (2) motor or afferent neurons, and (3) autonomic neurons.
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B is correct. The nerve fascicle is surrounded by the perineurium, which imparts mechanical strength to the peripheral nerve. In addition to its mechanical strength, the perineurium functions as a diffusion barrier to the fascicle, isolating the endoneural space around the axon from the surrounding tissue. This barrier helps to preserve the ionic milieu of the axon and functions as a blood–nerve barrier.
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A is incorrect. The endoneurium is a thin and delicate layer of loose connective tissue surrounding each fiber.
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C is incorrect. The fascicular bundles are not continuous throughout the peripheral nerve. They divide and anastomose with one another as frequently as every few millimeters.
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D is incorrect. The peripheral nerve is composed of three parts: (1) somatosensory or afferent neurons, (2) motor or efferent neurons, and (3) autonomic neurons.
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