Normal and Abnormal Development of the Nervous System
Core concepts
Master the milestones: social smile, head control, sitting, walking, and language emergence, plus the red flags that signal delay or regression. Understand gross and fine motor, language, cognitive, and social-emotional streams and how they diverge. Know the primitive reflexes (Moro, rooting, palmar grasp, asymmetric tonic neck) and when they should integrate, and the postural reflexes that persist abnormally in cerebral palsy. Review brain growth, myelination timelines, and the emergence of handedness. Abnormal development includes microcephaly, macrocephaly, hypotonia, hypertonia, and regression. Recognize patterns of cerebral palsy (spastic, dyskinetic, ataxic), neural tube defects, and the distinction between static encephalopathy and progressive disease.
Traps
Questions love regression: loss of milestones is never normal and suggests a neurodegenerative or epileptic encephalopathy. Do not mistake a variant of normal (e.g., benign hypotonia, delayed but eventual walking) for pathology. Watch for persistent primitive reflexes being mislabeled as normal. Another trap is assuming a single delayed domain is global delay.
Rule of thumb
Use the sequence: does the child follow the expected trajectory, and is any milestone lost? Loss mandates urgent evaluation.
Worked example: A 9-month-old who sat at 6 months but now cannot sit and has lost babbling shows regression-not just delay-prompting metabolic and epilepsy workup.