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Pain Physiology

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Which of the following nerves conduct nociceptive stimuli?

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(A) A-δ fibers and C fibers

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(B) A-δ fibers and A-β fibers

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(C) A-β fibers and C fibers

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(D) B fibers and C fibers

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(E) A-α fibers and A-β fibers

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(A) Nociceptors transmit impulses mainly through the A-δ and C fibers to the spinal cord. A-β fibers carry impulses generated from low-threshold mechanoceptors. B fibers are mainly preganglionic autonomic (white rami and cranial nerves III, VII, IX, X).

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Arrange A-δ, A-β, B, C, and A-α nerves according to their conduction velocity (fastest to slowest):

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(A) A-α, A-β, A-δ, B, C

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(B) A-δ, C, B, A-β, A-α

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(C) C, B, A-δ, A-β, A-α

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(D) A-β, A-δ, C, B, A-α

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(E) B, C, A-β, A-α, A-δ

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(A) Conduction velocity is dependent on the size of the nerve fiber as well as myelination. Myelinated nerves conduct the impulse faster than unmyelinated nerves (C) due to jumping from one node to the next node of Ranvier (saltatory conduction).

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The impulse traveling through the C fiber terminates in the Rexed laminae:

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(A) Laminae 1 and 5

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(B) Laminae 1 and 2

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(C) Laminae 1, 2, and 5

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(D) Laminae 2 and 5

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(E) Laminae 3 and 5

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(C) Impulses C fibers and their collaterals terminate in the Rexed laminae L1, L2, and L5.

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Some of the naturally occurring chemicals involved in nociceptive input are hydrogen ions, serotonin (5-HT), and bradykinin. What effect do these have on the nociceptors?

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(A) Sensitize the nociceptors

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(B) Activate the nociceptors

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(C) Activate and sensitize the nociceptors

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(D) Block the nociceptors

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(E) Modify the nociceptors

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(B) The sensitization of nociceptors may be caused by prostaglandins and cytokines, whereas activation is caused by substance, such as hydrogen ions, serotonin, and bradykinin.

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Substance P release from the dorsal horn neuronal elements ...

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