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18 Cards in this Set
- Front
- Back
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What is the sensory impact of a single nerve root lesion?
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Seldom in significant sensory loss and never in anesthesia.
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Describe teh arrangement of the three types of nerve coverings.
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Endoneurium between individual axons, perineurium around nerve fascicles, perineurium around the entire nerve.
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What is the typical tensile strength of a nerve? Where is this the weakest and what is it's tensile strength there?
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Between 20-30 kg. Weakest at the root where tensile strength is only 2-3kg.
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What are the main anions and cations at the axonal membrane that lead to its charge?
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Anion: Cl-, cation: Na+ and K+.
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At a resting electrical state, what is the relative concentration of sodium and potassium intracellularly and extracellularly
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Potassium is greater in the cell, sodium outside the cell.
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What is the resting potential of the neuron soma? The axon? (inside compared to outside)
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-70mV, -90mV
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Describe the act of depolarization
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Positive charge down the axon (~30 mV change) causes opening of voltage gated sodium channels (threshold), allowing Na in, leading to the action potential.
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Describe the two mechanisms by which the membrane goes into a refractory period
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1) Inactivation gate of the sodium channel turns on after 2ms. 2) K+ channels open, driving the membrane more negative.
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Describe the positive and negative aspects of saltatory conduction.
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More current is needed (typically larger axon) but speed is much faster.
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What's the fastest speeds of unmyelinated fibers? What's the speed range of myelinated fibers?
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3-5m/s, 35-75m/s.
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What is a motor unit?
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The anterior horn cell, the axon, and all myocytes innervated by it.
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What is a MUAP?
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The collective depolarization of a single motor unit.
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Briefly describe the mechanism of the terminal bouton to the muscle.
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Voltage is carried down the axon, causing Ca2+ release at the bouton, which causes vesicles of Ach to be released.
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What's the problem with A delta, B, and C fibers and NCS?
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They typically transmit autonomic and pain signals. They are small and unmyelinated and thus not recordable on NCS.
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What are the largest and fastest cutaneous nerve fibers? What's their speed range?
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A beta. 35-75 m/s.
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What are the largest and fastest nerve fibers? When are they recorded?
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A alpha afferents. They originate from the muscle spindle. Mixed nerve studies.
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What is volume conduction?
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The process of an intracellular electrical potential being transmitted through extracellular fluid and tissue.
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Give examples of near field and far field volume conducted potentials
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Near field: MUAPs, SNAPs, MNAPs; Far field: stimulus artifact
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