When responding to stimulation of the outer margin of the sole of the foot,a 1-year-old infant extends her great toe without fanning of the other toes.This happens because:
A) the corticospinal fibers have become fully myelinated and the Babinski reflex becomes suppressed.
B) the corticospinal fibers have not yet become fully myelinated and the Babinski reflex is activated.
C) the sensory fibers in the ophthalmic branch of the fifth cranial nerve are mediated by reflex arcs.
D) a deep reflex is mediated by a two-neuron spinal arc.

Question

Quizplus · Accepted Answer

The described response is the Babinski reflex, which is a normal reflex in infants that disappears as the corticospinal fibers become fully myelinated. Therefore, choice B is correct, as it correctly describes that the corticospinal fibers have not yet fully myelinated, which results in the activation of the Babinski reflex. Choices A, C, and D are all incorrect, as they do not explain the specific phenomenon of the Babinski reflex.

When Responding to Stimulation of the Outer Margin of the Sole