139.A 22-year-old male receives a severe, traumatic compression injury
to his radial nerve after a motorcycle crash. He shows an advancing Tinel’s
sign. Which of the following is true about regeneration of axons after his
nerve injury?
a. It occurs in the absence of motor unit potentials
b. It occurs at a rate of 100 mm/day
c. It occurs by a mechanism that is dependent on the proliferation of Schwann
cells
d. It occurs in conjunction with degeneration and phagocytosis of endoneurial
tubes
e. It occurs in the segment distal to the damage
140.The nodes of Ranvier increase the efficiency of neural transmission
by means of which of the following?
a. Decelerating the closing of Na+-gated channels
b. Enhancing myelination of the internodal segment
c. Sequestration of Na+entry into the axon
d. Multiple firings due to local ionic currents around the node
e. Decreasing threshold for the action potential
141.The blood-brain barrier is formed by which of the following?
a. Fenestrations between brain capillary endothelial cells
b. Occluding junctions between brain capillary endothelial cells
c. Astrocytic foot processes surrounding blood vessels entering the brain
parenchyma
d. The basement membrane associated with the glia limitans
e. Microglial activity
142.At the neuromuscular junction, action potentials are coupled to neu-
rotransmitter release by which of the following?
a. Ca^2 +-gated channels
b. Na+-gated channels
c. K+-gated channels
d. Cl−-gated channels
e. Gap junctions
232 Anatomy, Histology, and Cell Biology