Embryology: Development of Spinal Cord & NTD

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Questions and Answers

What induces the ectodermal layer to form the neural plate?

The underlying notochord and paraxial mesoderm induce the ectodermal layer to form the neural plate.

What structures are formed from the edges of the neural plate?

The edges of the neural plate form the neural folds.

What two parts does the ectoderm differentiate into during neurulation?

The ectoderm differentiates into surface ectoderm and neuroectoderm.

What occurs simultaneously as the neural folds approximate during tubulation?

The neural crest disconnects from the epidermis simultaneously. Signup and view all the answers

What do the cranial and caudal parts of the neural tube ultimately give rise to?

The cranial part develops into the brain, while the caudal part forms the spinal cord. Signup and view all the answers

What are the derivatives of the neural crest related to the nervous system?

The derivatives include nervous tissue such as leptomeninges (pia & arachnoid) and Schwann cells. Signup and view all the answers

How does the neural groove develop and where does fusion begin?

The neural groove begins fusion cervically and proceeds cranially and caudally. Signup and view all the answers

What role do neural crest derivatives play in the endocrine system?

Neural crest derivatives contribute to endocrine tissues such as adreno-medullary cells and calcitonin C cells of the thyroid gland. Signup and view all the answers

Name two connective tissue structures that originate from the neural crest.

Bone and cartilage of the facial skeleton are connective tissues derived from the neural crest. Signup and view all the answers

What is the significance of the anterior and posterior neuropores in neural development?

The anterior and posterior neuropores remain patent during development and close later, playing a crucial role in the formation of the central nervous system. Signup and view all the answers

What is the significance of the primitive streak during embryonic development?

The primitive streak is important for establishing the body plan by forming the trilaminar embryonic disc and defining the midline. Signup and view all the answers

Describe the role of the notochord in embryonic development.

The notochord defines the longitudinal axis of the embryo and contributes to the formation of the vertebral column. Signup and view all the answers

What structures arise from the ectoderm during the development of the nervous system?

The nervous system develops from the ectoderm, specifically neuroectoderm, except for microglia and dura mater which are mesodermal. Signup and view all the answers

During which week of embryonic development does gastrulation primarily occur?

Gastrulation primarily occurs during the third week of embryonic development. Signup and view all the answers

What are the three germ layers formed during gastrulation?

The three germ layers formed are ectoderm, mesoderm, and endoderm. Signup and view all the answers

How does the mesoderm contribute to embryonic structure?

The mesoderm contributes to the formation of structures like the vertebrae and muscles, surrounding and covering the notochord. Signup and view all the answers

When is the notochord completely formed in the embryo?

The notochord is completely formed by the beginning of the fourth week of embryonic development. Signup and view all the answers

What happens to the mesoderm as it moves to the midline of the embryo?

As the mesoderm moves to the midline, it proliferates to form the paraxial mesoderm and creates lateral plates. Signup and view all the answers

What is the primary defect associated with Neural Tube Defects (NTDs)?

The primary defect is the failure of neural folds to fuse in the midline and form the neural tube. Signup and view all the answers

Name two medications that can alter folate metabolism and potentially contribute to Neural Tube Defects.

Valproic acid and carbamazepine can alter folate metabolism. Signup and view all the answers

What clinical condition results from the failure of the rostral neuropore to close?

Anencephaly results from the failure of the rostral neuropore to close. Signup and view all the answers

Describe the appearance and cause of a sacral spinal sinus.

A sacral spinal sinus appears as a skin dimple in the mid sacral region caused by focal failure of dysjunction between the cutaneous ectoderm and neuroectoderm. Signup and view all the answers

What is spina bifida and where is it most commonly located?

Spina bifida is a condition due to the failure of fusion of the two vertebral arches, most commonly located in the lumbosacral region. Signup and view all the answers

On which days do the rostral and caudal neuropores close?

The rostral neuropore closes on the 25th day and the caudal neuropore closes on the 27th day. Signup and view all the answers

What is the role of the cranial part of the neural tube in development?

The cranial part of the neural tube develops into the brain. Signup and view all the answers

Which flexures are mentioned in connection with brain development?

The midbrain flexure and cervical flexure are mentioned. Signup and view all the answers

Which parts of the brain derive from the prosencephalon?

The forebrain and specific vesicles like the lateral and third ventricles derive from the prosencephalon. Signup and view all the answers

What are the layers formed from the neural tube during spinal cord development?

The ventricular zone, intermediate zone (mantle layer), and the marginal zone are formed. Signup and view all the answers

What forms after the primitive neuroepithelial cells multiply?

Newly formed cells migrate out to create the intermediate zone. Signup and view all the answers

What is the relationship between somites and the neural tube?

Somites are associated with the development of mesodermal structures alongside the neural tube. Signup and view all the answers

Identify the derivative of the rhombencephalon.

The rhombencephalon contributes to the brainstem and cerebellum. Signup and view all the answers

What are the main characteristics of spina bifida occulta?

Spina bifida occulta is characterized by no bulge over the bony defect, the presence of a skin dimple or tuft of hairs, and the absence of neurological symptoms. Signup and view all the answers

Describe the key differences between spina bifida with meningocele and meninomyelocele.

In meningocele, a bulge is present that contains meninges and cerebrospinal fluid; in myelomeningocele, the bulge contains meninges, spinal cord, and nerves. Signup and view all the answers

What is myeloschisis and how does it differ from other types of spina bifida?

Myeloschisis is characterized by an open defect where the spinal cord is exposed as a mass of neural tissue, differing from other types where the spinal cord is contained within a sac. Signup and view all the answers

What symptoms are typically absent in cases of spina bifida occulta?

In cases of spina bifida occulta, neurological symptoms are typically absent. Signup and view all the answers

What anatomical structures are involved in spina bifida with myelomeningocele?

Spina bifida with myelomeningocele involves the meninges, spinal cord, and nerves within a membranous sac. Signup and view all the answers

How do spina bifida conditions generally affect the skin over the defect?

In spina bifida occulta, the skin may show a dimple or tuft of hairs, while in other types, a bulge may be visible. Signup and view all the answers

What is the general embryological basis of spina bifida?

Spina bifida occurs due to failure of the embryonic neural tube to close properly during development. Signup and view all the answers

Why is it important for healthcare providers to differentiate between types of spina bifida?

Differentiating between types of spina bifida is crucial as it influences treatment options, prognosis, and management of potential complications. Signup and view all the answers

Study Notes

Development of Spinal Cord & NTD

Spinal cord development originates from the caudal portion of the neural tube.
The neural tube develops from the ectoderm during the third week of gestation.
Ectoderm thickens to form the neural plate, induced by the notochord and paraxial mesoderm.
Neural plate edges fold to form neural folds.
Neural folds fuse, forming the neural tube.
The neural crest detaches from the epidermis concurrently.
The neural tube differentiates into the brain and spinal cord.
Three primary brain vesicles form: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).
These vesicles further develop into secondary brain vesicles and eventually into adult brain structures.

Embryonic Disc

The early embryo is a bilaminar embryonic disc.
It consists of the epiblast and the hypoblast.

Gastrulation (3rd Week)

Primitive streak forms at the caudal end of the embryo.
Cells of the primitive streak migrate cranially.
Primitive knot forms at the cranial end of the primitive streak.
Trilaminar embryonic disc develops (ectoderm, mesoderm, endoderm).
Notochord develops from axial mesoderm.

Definitive Notochord

A rod-like structure that starts in the middle of the embryo.
Proceeds in both cranial and caudal directions.
Arises from axial mesoderm around day 16.
Is fully formed by the beginning of the fourth week.

Notochord Remnants

The notochord persists as the nucleus pulposus of intervertebral discs.
Determines the longitudinal axis of the embryo.
Determines the vertebral column's orientation.

Mesoderm Development

Mesoderm moves to the midline to cover the notochord.
It proliferates to form paraxial mesoderm.
Mesoderm on each side remains thin (lateral plate).
The intermediate mesoderm lies between paraxial and lateral plate.

Nervous System Development

The nervous system begins to develop in the third week.
It's derived from the ectoderm (neuroectoderm).
Microglia and dura mater are exceptions, being mesodermal.

Neural Tube Formation (Neurulation)

In the third week, the embryo is a trilaminar pear-shaped disc.
The three layers are ectoderm (epiblast) dorsally, endoderm ventrally, and mesoderm in between.
Ectodermal layer is induced to form neural plate by underlying structures.
Neural plate edges form neural folds.
Neural folds fuse, forming the neural tube.

Neural Plate Formation

The neural plate thickens in the median area of the embryonic disc.
Forms the neural plate.
Its edges become neural folds.

Neural Tube Closure

Neural groove starts fusing in the cervical region.
Cranial and caudal neurpores (openings) are formed.
Cranial neuropore closes around day 25.
Caudal neuropore closes around day 27.

Closure of Neuropores

The rostral neuropore closes on the 25th day.
The caudal neuropore closes on the 27th day.

Brain Development

Brain develops from the cranial part of the neural tube.
The brain develops flexures (midbrain and cervical).
Primary brain vesicles form (prosencephalon, mesencephalon, rhombencephalon).
Secondary brain vesicles form (telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon).
Brain vesicles further develop into adult brain structures.

Spinal Cord Development

Spinal cord develops from the caudal part of the neural tube.

Spinal Cord Zones

Neural tube is lined by a neuroepithelium (ventricular zone).
Marginal zone forms superficially to the ventricular zone.
Primitive neuroepithelial cells multiply.
Newly formed cells migrate to form the intermediate zone.

Spinal Cord Layers

The mantle zone thickens in four regions.
Forms alar plates dorsally and basal plates ventrally.
Exhibits a sulcus limitans.
Shows a roof plate and a floor plate.
Marginal zone is formed.

Gray and White Matter

Marginal zone forms white matter.
Mantle zone forms gray matter.
Ependymal zone forms ependymal lining of the central canal.
Cavity of neural tube forms central canal.
Alar plates form the sensory horns.
Basal plates form the motor horns.

Neural Tube Defects (NTDs)

Primary defect: Failure of neural folds to fuse in the midline.
Secondary defect: Maldevelopment of mesoderm.
Causes include genetic predisposition, folate deficiency, and teratogens.

Clinical Notes (Specific NTDs)

Anencephaly: Absence of the skull and brain, non-survivable.
Spina bifida: Failure of vertebral arches to close.
Spina bifida occulta: No bulge, skin dimple, or tuft of hair.
Meningocele: Bulge containing meninges and CSF.
Myeloschisis: Open spinal cord visible.
Meningomyelocele: Bulge containing meninges, spinal cord, and nerve roots.

Causes of NTDs

Genetic factors.
Folate deficiency (important in early pregnancy, need for ingestion prior to conception)
Teratogens (e.g., hyperthermia, hypervitaminosis A, vitamin B12 deficiency, drugs)

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Description

Explore the intricate process of spinal cord development and neural tube formation in early embryology. This quiz covers key stages from neural tube formation to brain vesicle differentiation, emphasizing the role of the ectoderm and primitive streak in gastrulation.