When are the axons of the coicospinal tracts fully myelinated?: (A) In the late embryonic period, (B) In the mid-fetal period, (C) At bih, (D) By the end of the second postnatal year
Answer is D. Axons of the coicospinal tracts are fully myelinated by the end of the second postnatal year *Babinski's sign (extensor plantar reflex) is usually elicitable before myelination of the coicospinal tracts -reflects poor coical control of motor function by the immature brain.