At approximately day 1

Notochord is completley formed.

Reference

Evans OB, Hutchins JB. 1997. Development of the Nervous System. Chapter 5 In: Haines DE, ed. Fundamental Neuroscience. New York: Churchill Livingstone.

At approximately day 1

Spinal cord, meningeal coverings, and vertebral arches are developed by the end of the first trimester.

Duration: 8 weeks

Reference

Evans OB, Hutchins JB. 1997. Development of the Nervous System. Chapter 5 In: Haines DE, ed. Fundamental Neuroscience. New York: Churchill Livingstone.

At approximately day 1

Nueroblasts that give rise to spinal cord neurons proliferate in the neural canal.

Duration: 16 weeks

Reference

Evans OB, Hutchins JB. 1997. Development of the Nervous System. Chapter 5 In: Haines DE, ed. Fundamental Neuroscience. New York: Churchill Livingstone.

At approximately day 1

Neurogenesis of amygdala, through week 16.9.

Duration: 12 weeks

Reference [PubMed Link]

Bayer SA, Altman J, Russo RJ, Zhang X. 1993. Timetables of neurogenesis in the human brain based on experimentally determined patterns in the rat. Neurotoxicology 14(1):83-144.

At approximately day 3

Pharyngeal arches begin to form.

Reference

Moore KL, Persaud TVN. 1998. The Developing Human: Clinically Oriented Embryology. 6th ed. Philadelphia: WB Saunders Co.

At approximately day 4

Primary brain vesicles form: prosencephalon (forebrain), mesencephalon (midbrain), and rhomencephalon (hindbrain).

Reference

Evans OB, Hutchins JB. 1997. Development of the Nervous System. Chapter 5 In: Haines DE, ed. Fundamental Neuroscience. New York: Churchill Livingstone.

At approximately day 4

Brain ventricular system forms: lateral ventricals (in telencephalic vessical cavities), third ventrical (in diencephalic cavity), and fourth ventrical (in rhombencephalic cavity).

Duration: 4 weeks

Reference

Evans OB, Hutchins JB. 1997. Development of the Nervous System. Chapter 5 In: Haines DE, ed. Fundamental Neuroscience. New York: Churchill Livingstone.

At approximately day 5

Forebrain can be identified.

Reference

Moore KL, Persaud TVN. 1998. The Developing Human: Clinically Oriented Embryology. 6th ed. Philadelphia: WB Saunders Co.

At approximately day 7

The cervical flexure forms, demarcating the hindbrain from the spinal cord.

Reference

Moore KL, Persaud TVN. 1998. The Developing Human: Clinically Oriented Embryology. 6th ed. Philadelphia: WB Saunders Co.

At approximately day 7

Brain stem cranial nerve motor nuclei are all distinguishable.

Duration: 1 week

Reference

Larsen WJ. 1997. Human Embryology. New York: Churchill Livingstone Inc.