Affiliations: Departments of Pediatrics and Pathology, David Geffen
School of Medicineat UCLA and Cedars-Sinai Medical Center, Los Angeles,
California, U.S.A.
Note: [] Correspondence: Harvey B. Sarnat, M.D., F.R.C.P.C., Cedars-Sinai
Medical Center, Departments of Pediatrics (Neurology) and Pathology (Neuropat
hology), 4221 North Tower, 8700 Beverly Blvd. Los Angeles, CA 90048, U.S.A.
Tel: (310) 423-1299; fax: (310) 423-4131; E-mail: [email protected]
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).
Keywords: corticospinal tract, muscle tone, neonate, post ure, st retch reflexes, suck, swallow, tactile reflexes
