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DOI: 10.1055/s-0035-1557162
Functions of the corticospinal and corticobulbar tracts in the human newborn
Subject Editor:
Publication History
16 May 2003
06 June 2003
Publication Date:
29 July 2015 (online)
Abstract
The corticospinal and corticobulbar tracts (CST, CBT) are immature at birth, in neuroanatomical terms of myelination and terminal axonal sprouting for multiple synaptic contact; these developmental features are not mature until 2 years of age. Physiologically, the CST is mainly inhibitory. Nevertheless, these pathways have an important role to play in normal neurological function at this age, though different from their functions in the older child and adult. They are important in the neonate by 1) inhibition of the monosynaptic stretch reflexes at spinal cord levels, beginning at 25 weeks gestation or earlier; 2) influence upon muscle tone, hence posture, by mediating proximal flexion in axial and limb girdle muscles and distal extension of the fingers and toes and abduction of the thumbs; 3) antagonism of the proximal extension and distal flexion and adduction from the medial subcorticospinal pathways of Lawrence and Kuypers; 4) reinforcement of tactile reflexes, the most important of which are suck and swallow; 5)early individualization of finger movements; 6) transmission of epileptic activity from the cerebral cortex. Understanding the unique roles of the CST at birth provide rational, physiological explanations of such neonatal phenomena as clonus, opisthotonus, strong distal flexion and adduction ("cortical thumb") and fisting), and poor suck and swallow in affected neonates, regardless of the cause of cerebral cortical impairment or its reversibility or irreversibility. In summary, the CST and CBT are indeed important functional pathways in the neonate, but many of their functions are very different than in the adult. (J Pediatr Neurol 2003; 1(1): 3-8).