Development of the Nervous System

Development of the Nervous System

1. Human somatic cells are diploid - have two sets of chromosomes

   • MALE: 46 (XY) FEMALE: 46 (XX)
     • A missing chromosome changes the number and causes a trisomy to occur
       • Three common chromosomal trisomys are: Chromosome 13 – Patau Syndrome Chromosome 18 – Edwards Syndrome Chromosome 21 – Down Syndrome
         • Trisomy 13 – 1 in 25,000 births. Severe central nervous system malformations, bilateral cleft lip and palate, malformed ears and cognitive delays.
         • Trisomy 18 – 1 in 8,000 births. Cognitive delays, growth retardation, low set malformed ears
         • Trisomy 21 – 1 in 800 births. Cognitive delays, flat nasal bridge, protruding tongue, simian crease.

2. WEEK 3 of Gestation: Development of the brain and spinal cord begins.

   • The Neural Tube closes at approximately day 22.
     • Days 22-23 the rostral two thirds of the neural tube represents the future brain.
     • The caudal one third represents the future spinal cord.
     • Three primary brain vesicles form during week 4 Prosencephalon - telencephalon, diencephalon Rhombencephalon - metencephalon, mylencephalon Mesenecephalon does not divide

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