5.1 Nerve Trunks

Question 1

conduction velocity is directly proportional to _________

Answer 1

axon diameter

Question 2

the ________ of an extracellularyly recorded action poteential is _______ proportional to axon diameter or neuronal cell size

Answer 2

amplitude, directly

Question 3

threshold for depolarization (external stimulus) is __________ related to axon diameter, larger then smaller axons recruited

Answer 3

inversely

Question 4

threshold for depolarization (natural stimulus) is _______ then _________, known as orderly recruitment

Answer 4

small, large

Question 5

local anesthetics, such as lidocaine, block ________ diameter axon first

Answer 5

small

Question 6

in a whole nerve recording, increasing the current gives larger ________ action potentials, and peaks represent _________ of axons

Answer 6

compound, populations

Question 7

the largest axons in the dorsal root are the _______ afferents

Answer 7

1A

Question 8

the ventral root has mostly _____, ______ and ______ fibers for muscle spindles and golgi tendon organs

Answer 8

B, A-alpha, A-gamma

Question 9

studies of motor nerve conduction have two stimulation points, where conduction velocity determined by _________

Answer 9

distance between

Question 10

exception to Bell Magendie law?

Answer 10

some sensory fibers for pelvic viscera (pain and temp) go to ventral root from dorsal root ganglion, problem for intractable pain treatment

Question 11

muscle wave, direct activation of alpha motor axon leading to muscle contraction, short latent period, orthodromic direction (physiologic), amplitude proportional to stimulus intensity

Answer 11

M wave

Question 12

maximal intensity stimulation of alpha motor neuron, antidromic AP (non-physiologic) causes another firing of alpha motor neuron cell body, second muscle twitch after M wave, not seen at low intensity stimulus, abnormal in Guillan Barre

Answer 12

F wave

Question 13

orthodromic AP in 1a afferent, alpha motor neurons lead to second contraction following small M wave contraction, seen with LOW intensity stimulus only, antidromic AP is of no consequence, tests same thing as deep tendon reflex, artificially activating 1a reflex

Answer 13

H reflex

Question 14

abnormal firing of a motor unit, ex eyelid twitch, not disease related if in isolation

Answer 14

fasciculation

Question 15

acute denervation of a single muscle fiber, spontaneous depolarization, seen as tiny repetitive spikes

Answer 15

fibrillation

Question 16

chronic denervation and reinnervation with recruitment of other fiber, seen as messy motor unit wave

Answer 16

motor unit change