1. At 3 weeks

2. Two longitudinally oriented ridges formed by thickenings of ectoderm and induced by underlying notochord

3. In the region where the brain will be, neural folds more widely separated

The raised plateau between the two neural folds

1. Ectoderm with neural folds

2. Cells destined to become nervous system

1. Located in neural crest (the top of neural folds)

2. Differentiate and begin long migrations to distant parts of the body

3. Give rise to PNS

1. Formed after neural crest cells have departed

2. Formed from neural folds at the 5th somite (future neck) that fuse outward-cranially and caudally

3. Is the future brain and spinal cord (CNS)

4. Crainal neuropore closes ~25 days, and caudal neuropore closes ~27 days

6. Neural tube is dominant structure from 3-6 weeks of development, and its growth causes cephalocaudal folding of embryo during 4th week

Neuroectodermal cells that form the inner layer of the neural tube that becomes the grey matter of the spinal cord

1. Neuroectodermal cells that form the outer layer of the neural tube

2. Comprised of the nerve fibers emerging from the cells of the mantle zone and the glial cells (astrocytes and oligodendrocytes)

3. Becomes the white matter of the spinal cord

A longitudinal groove, or furrow, formed by the thickenings of the the dorsal and ventral regions of the mantle zone that develops along the right and left lateral walls of the developing spinal cord

1. Region of the spinal cord dorsal to sulcus limitans

2. Neurons developing in this region will all be sensory nerves

1. The region of the spinal cord ventral to sulculs limitans

2. Neurons developing in this region will all be motor neurons

The most cranial dilation of the neural tube destined to be the brain

1. Develops from prosencephalon

2. The pineal gland, thalamus, hypothalamus, neurohypophysis, and most of the eye develops from this region

1. Develops from two lateral outpouchings from the prosencephalon

2. These regions develop into the cerebral hemispheres

1. Caudal to the telencephalon

2. Midbrain develops from this region

1. Develops caudally to the mesencephalon

2. Forms the pons and cerebellum

Forms the medulla oblongata

A ventral bending of the brain tube causing the diencephalon to lie adjacent to the proximal metencephalon

A dorsal folding of the brain tube causing the distal metencephalon to lie adjacent to the mesencephalon

1. Ancephaly

2. Spina bifida

3. Hirschprung's disease

1. No brain, no cranial bones,     2. Occurs once in about 1000 births

3. Multifactoral inheritance

1. Focal opening of the spinal cord to the skin surface

2. Secondary to failure of neural tube to close

3. Multifactoral inheritance

1. Severe intractable constapation with massive bowel dilation

2. Secondary to failure of neural crest cells to migrate to the colon

3. Lack of innervation causes spasms of bowel, with marked dilation of the proximal, normally innervated bowel