anatomy 14.8

Nervous tissue development start

Begins during the third week of embryonic development.

Embryonic tissue for nervous development

Portion of the ectoderm overlying the notochord.

Thickened ectoderm for nervous system development

The neural plate.

Cells of the neural plate

Collectively called neuroectoderm.

Neurulation

A series of dramatic changes in the neuroectoderm that form nervous tissue structures.

Structure forming in the center of the neural plate

A longitudinal indentation called the neural groove.

Cell changes along lateral margins of the neural plate

They proliferate and become thickened neural folds.

Location of neural crest cells

At the tips of the neural folds.

Position of neural crest cells during early neurulation

At the highest points of the neural folds surrounding the neural groove.

Changes in neural folds as the neural groove deepens

They elevate and move toward one another.

Fate of neural crest cells during neurulation

They pinch off from the neural folds and form other structures.

Outcome for neural folds by end of the third week

They meet and fuse at the midline.

Transformation of the neural groove after fusion

Becomes the neural tube.

Internal cavity of the neural tube

The neural canal.

Formation process of the neural tube by neural folds

They ‘zip’ together by fusing at the midline and continuing to fuse superiorly and inferiorly.

What are neuropores

Temporary openings at both ends of the developing neural tube.

Closure timing of the neuropores

Normally closes during the end of the fourth week.

Cranial neuropore definition

The neuropore closest to the future head.

Caudal neuropore definition

The neuropore closest to the future buttocks region.

Consequences of neuropores failing to close

A neural tube defect can develop.

Outcome of the developing neural tube

Forms the central nervous system (CNS).

Cranial portion development from neural tube

Develops into the brain.

Caudal portion development from neural tube

Develops into the spinal cord.

Definition of neural tube defects (NTDs)

Serious developmental deformities of the brain, spinal cord, and meninges caused by localized failure of the neural tube to close.

Basic categories of neural tube defects

Anencephaly and spina bifida.

Anencephaly definition

Substantial or complete absence of the brain and the bones forming the cranium.

Spina bifida definition

A neural tube defect caused by failure of the caudal portion of the neural tube to close, often in the lumbar or sacral region.

Severe spina bifida form

Spina bifida cystica, where almost no vertebral arch forms.

Less serious spina bifida form

Spina bifida occulta, involving a partial defect of the vertebral arch.

Method to reduce risk of neural tube defects

Increased intake of folic acid (folate) during pregnancy is associated with a decreased incidence of neural tube defects.