Where does the primitive streak first appear?
Click to see answer
At the caudal end of the embryo.
Click to see question
Where does the primitive streak first appear?
At the caudal end of the embryo.
During which week of development does the formation of the primitive streak occur?
During the 3rd week.
Which layer of the trilaminar embryonic disc is located between the ectoderm and endoderm?
Mesoderm.
Which layer of the bilaminar embryonic disc is located on the top?
Epiblast.
What is the definitive notochord?
A rod-like structure that starts in the middle of the embryo and proceeds in both cranial and caudal directions.
From which embryonic layer does the notochord arise?
Axial mesoderm.
Which parts of the nervous system are derived from the mesoderm?
Microglia and dura mater.
Which layer of the bilaminar embryonic disc is located on the bottom?
Hypoblast.
What forms at the cranial end of the primitive streak?
The primitive knot (primitive node) forms at the cranial end.
Where does the neural plate form in the embryo?
At the cranial ends of the embryo.
When is the notochord completely formed?
By the beginning of the fourth week.
What induces the ectodermal layer to form the neural plate?
The underlying notochord and paraxial mesoderm.
When does the nervous system begin to develop?
During the 3rd week.
From which germ layer is the nervous system derived?
Ectoderm (neuroectoderm).
What does the notochord define in the embryo?
The embryonic midline.
What is the mesoderm called when it remains thin on each side?
The lateral plate.
Where is the intermediate mesoderm located?
Between the paraxial mesoderm and the lateral plate.
What structure does the mesoderm cover as it moves to the midline?
The notochord.
What is the primitive streak?
A linear band of thickened epiblast cells that first appears at the caudal end of the embryo and grows cranially.
What are the edges of the neural plate called?
Neural folds.
What is the role of the notochord in embryonic development?
It provides signals that are essential for the development of surrounding tissues, including the neural tube and vertebral column.
What induces the ectodermal layer to form the neural plate?
The underlying notochord and paraxial mesoderm.
What flexure is located between the hindbrain and the spinal cord?
The Cervical flexure.
Which primary brain vesicle is also known as the forebrain?
Prosencephalon.
What are the three zones in the wall of the neural tube?
Ventricular zone, Mantle layer, and Marginal layer.
What is the function of the amnion in embryonic development?
The amnion is a membrane that surrounds and protects the embryo, forming the amniotic sac filled with amniotic fluid.
What is the connecting stalk and its significance?
The connecting stalk is the precursor to the umbilical cord, connecting the embryo to the placenta.
What forms the white matter of the spinal cord?
The marginal zone.
Which developed brain structures arise from the Telencephalon?
Cerebrum.
What does the basal lamina form in the spinal cord?
The ventral and lateral grey horns (motor).
In which direction does the primitive streak grow?
It grows cranially.
During which week of development does the formation of the primitive streak occur?
During the 3rd week.
What shape is the embryo during the 3rd week of development?
Pear-shaped.
What is the neural groove?
An invagination of the neural plate.
What is the neural crest?
The raised folds of the neural plate that disconnect from the epidermis.
What are the three primary brain vesicles formed from the neural tube?
Prosencephalon (forebrain), Mesencephalon (midbrain), and Rhombencephalon (hindbrain).
On which day does the rostral neuropore close?
The 25th day.
What structure is labeled as 'Neural groove' in the image?
The indentation that forms along the neural plate, which will eventually close to form the neural tube.
What is the presumptive gray matter layer in the neural tube called?
The Mantle layer.
What happens to the neural crest during the process shown in the image?
The neural crest disconnects from the epidermis.
What is the primitive streak?
A linear band of thickened epiblast cells that first appears at the caudal end of the embryo and grows cranially.
Which layer of the trilaminar embryonic disc is located dorsally?
Ectoderm (epiblast).
Which zone in the wall of the neural tube is devoid of cell bodies?
The Marginal layer.
Where is the intermediate zone located?
Between the ventricular zone and the marginal zone.
What is the 'Midbrain' and where is it located?
The midbrain is a portion of the brainstem located between the forebrain and the hindbrain.
What forms the grey matter of the spinal cord?
The mantle zone.
Where are the basal plates located in the neural tube?
Ventrally.
Which developed brain structures arise from the Metencephalon?
Pons and Cerebellum.
What is the primary defect in Neural Tube Defects (NTDs)?
Failure of neural folds to fuse in midline and form neural tube, and failure of neuropore to close.
What happens if the neural folds fail to fuse in the midline?
It results in a primary defect of Neural Tube Defects (NTDs).
What is seen over the defect in spina bifida with meningocele?
A bulge containing meninges and cerebrospinal fluid (CSF) in the subarachnoid space.
What are the two layers of the bilaminar embryonic disc?
Epiblast and Hypoblast.
What happens to the mesoderm as it moves to the midline?
It covers the notochord and proliferates to form the paraxial mesoderm.
What does the notochord persist as in the adult body?
The nucleus pulposus of the intervertebral discs.
What does the neural tube give rise to after it is completely closed?
The brain and spinal cord.
What is the anterior (rostral) end of the neural tube responsible for forming?
The primary brain vesicles.
Which zone in the wall of the neural tube is also known as the ependymal layer?
The Ventricular zone.
What are the two parts of the neural tube before it is completely closed?
A large cranial part and a caudal tubular part.
What does the forebrain prominence indicate in the developing embryo?
The forebrain prominence indicates the early development of the forebrain, which will give rise to the cerebral hemispheres.
What forms the ependymal lining of the central canal?
The ependymal zone.
What is the part of the mantle layer ventral to the sulcus limitans called?
The basal plate.
What is the teratogenic effect of carbamazepine?
It acts as a folate antagonist.
Which antihistaminic drug is mentioned as a teratogen?
Chlorpheniramine.
What is the subarachnoid space in the context of spina bifida?
The space between the arachnoid mater and the pia mater, containing cerebrospinal fluid.
What does the Prosencephalon develop into?
Telencephalon and Diencephalon.
What are the three germ layers in the embryonic disc?
Ectoderm, mesoderm, and endoderm.
What does the notochord define in the embryo?
The longitudinal axis of the embryo.
What are the derivatives of the neural crest in the sensory ganglia?
Spinal (DRG) and autonomic ganglia (sympathetic and parasympathetic).
What is the posterior (caudal) end of the neural tube responsible for forming?
The spinal cord.
What is the intermediate zone also known as?
The mantle layer.
Into what do cells in the intermediate zone differentiate?
Neuroblasts, which form neurons.
What role does folate (folic acid) play in the body?
Folate plays an important role in forming red blood cells and maintaining brain health.
What is the embryonic brain region derived from the midbrain?
Mesencephalon.
What nutritional issues can act as teratogens?
Nutritional deficiencies and hypervitaminosis A, as well as deficient or inadequate maternal vitamin B12.
What diagnostic marker is increased in maternal serum and amniotic fluid in cases of anencephaly?
Alpha-fetoprotein (AFP) levels are increased in maternal serum and amniotic fluid in cases of anencephaly.
What is a characteristic of spina bifida occulta regarding the bony defect?
There is no bulge over the bony defect.
What is the spinal ganglion in the context of spina bifida?
A cluster of nerve cell bodies in the spinal nerve roots.
What does the Mesencephalon develop into?
The midbrain of the brain stem.
At what stage of development does the notochord begin to form?
At about 16 days.
What is the significance of the trilaminar embryonic disc?
It marks the formation of the three primary germ layers: endoderm, mesoderm, and ectoderm.
What are the derivatives of the neural crest in the muscle tissue?
Ciliary muscles.
Which primary brain vesicle is also known as the hindbrain?
Rhombencephalon.
What structures are involved in the development of the skull?
Lateral plate mesoderm, paraxial mesoderm, and neural crest cells.
What is the role of the yolk stalk in embryonic development?
The yolk stalk connects the yolk sac to the midgut of the developing embryo, providing nutrients during early development.
What is the result of the thickening of the mantle zone in the neural tube?
The lumen becomes rhomboidal.
What is one environmental factor that can act as a teratogen during early pregnancy?
Hyperthermia.
What causes anencephaly?
Anencephaly occurs when the neural tube fails to close at the base of the skull, specifically due to the failure of the rostral neuropore to close.
Is survival possible for individuals with anencephaly?
No, survival is not possible for individuals with anencephaly.
What does the mesoderm form in relation to NTDs?
The mesoderm forms skeletal structures (vertebrae and ribs) and muscular structures (back muscles) that cover neural structures.
What are the two types of spina bifida shown in the image?
Occulta and With meningocele.
What does the subarachnoid space contain in spina bifida with meningocele?
Meninges and cerebrospinal fluid (CSF).
What are the two types of spina bifida shown in the image?
With meningomyelocele and with myeloschisis.
What does the Rhombencephalon develop into?
Metencephalon and Myelencephalon.
Where is the 4th ventricle located?
In the Rhombencephalon.
In which direction does the neural plate grow?
In a cranio-caudal direction.
What structure is formed when the neural folds fuse together in the midline?
The neural tube.
Which layer of the trilaminar embryonic disc is located ventrally?
Endoderm.
Where does the fusion of the neural groove begin?
Cervically, and it proceeds both cranially and caudally.
When does the anterior neuropore close?
On the 25th day.
What are the derivatives of the neural crest in the endocrine tissue?
Adreno-medullary cells, calcitonin C cells of the thyroid gland, and carotid body.
What structure is labeled as the 'Dorsal root ganglion' in the developing brain?
The Dorsal root ganglion.
What are the derivatives of the neural crest in the pigment cells?
Melanocytes.
What zone does the neuroepithelium form in the neural tube?
The ventricular zone.
What happens to primitive neuroepithelial cells in the ventricular zone?
They multiply and newly formed cells move out to form the intermediate zone (mantle layer).
What is the structure labeled as 'Forebrain' in the development of the spinal cord?
The forebrain is the anterior part of the brain that develops from the neural tube.
What are the four regions where the mantle zone thickens in the wall of the neural tube?
Why is it challenging to ensure ingestion of preconception folic acid?
Because less than 50% of pregnancies are planned.
What forms the central canal of the spinal cord?
The cavity of the neural tube.
What does the 'Spinal cord' develop from?
The spinal cord develops from the narrow caudal part of the neural tube.
From which embryonic structures do the bones of the skull develop?
The bones of the skull develop from neural crest cells and paraxial and lateral plate mesoderm.
Does spina bifida occulta typically present with neurological symptoms?
No, it does not present with neurological symptoms.
What is the dura mater in the context of spina bifida?
A tough membrane that surrounds the spinal cord.
What adult brain structures arise from the Diencephalon?
Thalamus, hypothalamus, epithalamus, and retina.
What is the function of the cerebral aqueduct?
It connects the 3rd and 4th ventricles.
Where is the 3rd ventricle located?
In the Diencephalon.
What is the main difference between Spina bifida with meningomyelocele and Spina bifida with myeloschisis?
In meningomyelocele, the spinal cord and meninges protrude through a defect, while in myeloschisis, the spinal cord is exposed and not covered by skin or meninges.
What are the three germ layers formed during the formation of the trilaminar embryonic disc?
Definite Endoderm, Intraembryonic Mesoderm, and Ectoderm.
What structure develops from the primitive streak and is crucial for the formation of the axial skeleton?
The notochord.
What is the paraxial mesoderm?
The mesoderm that proliferates and forms on either side of the notochord.
In which week of embryonic development does the formation of the neural tube (neurulation) occur?
In the 3rd week.
What are the three layers of the trilaminar embryonic disc?
Ectoderm (epiblast) dorsally, Endoderm ventrally, and Mesoderm in between.
What are the cranial and caudal ends of the neural groove called?
The cranial and caudal ends of the neural groove are called the anterior (ant.) and posterior (post.) neuropores.
What are the three primary regions of the developing brain?
Forebrain, Midbrain, and Hindbrain.
What happens to the neural folds during neurulation?
They approximate and fuse together in the midline to form the neural tube.
What are the two parts the ectoderm differentiates into during neurulation?
Surface ectoderm and neuroectoderm.
What does the neuroectoderm form?
The nervous system of the embryo.
What is the function of the 'Optic vesicle' in embryonic development?
The optic vesicle is an outgrowth of the forebrain that eventually forms the eyes.
When do Neural Tube Defects (NTDs) typically occur post-fertilization?
NTDs occur 26 days post-fertilization.
What is the 'Hindbrain' and its significance in development?
The hindbrain is the posterior part of the brain that develops into structures such as the cerebellum, pons, and medulla oblongata.
What structure is found in the lateral walls of the neural tube?
Sulcus limitans.
What does the alar lamina form in the spinal cord?
The dorsal grey horn (sensory).
What are teratogens?
Substances that cause congenital disorders in a developing embryo or fetus.
What structures are affected by the maldevelopment of mesoderm in NTDs?
The skeletal (vertebrae and ribs) and muscular (back muscles) structures that cover neural structures.
What is a characteristic of spina bifida occulta?
No bulge over the bony defect.
What is the role of the dura mater in the context of spina bifida?
It is a protective membrane surrounding the spinal cord.
What is seen over the defect in spina bifida with meningomyelocele?
A bulge containing meninges, cord, and nerves.
What are the primary brain vesicles?
Prosencephalon, Mesencephalon, Rhombencephalon.
What adult brain structures arise from the Myelencephalon?
Medulla oblongata.
What role does the notochord play in the orientation of the vertebral column?
It determines the orientation of the vertebral column.
Where is the ectoderm thickened to form the neural plate?
In a median area on the dorsal aspect of the embryonic disc.
What are the edges of the neural plate called?
Neural folds.
Which primary brain vesicle is also known as the midbrain?
Mesencephalon.
What does the paraxial mesoderm form?
The axial skeleton (vertebral & ribs).
What does the surface ectoderm give rise to?
Tissues on the outer surface of the body like epidermis, hair, and nails.
What is the presumptive white matter layer in the neural tube called?
The Marginal layer.
What is the 'Midbrain flexure'?
The midbrain flexure is a bend in the neural tube that occurs in the midbrain region during development.
How do sulfonamides act as teratogens?
They competitively inhibit enzymes that function in the synthesis of folic acid.
What might be present over the unfused vertebral arches in spina bifida occulta?
A skin dimple or a tuft of hairs.
What structure is unfused in spina bifida occulta?
The vertebral arch.
What structures are contained in the bulge seen in spina bifida with meningomyelocele?
Meninges, cord, and nerves.
What is the difference between spina bifida with meningomyelocele and with myeloschisis?
In meningomyelocele, a bulge containing meninges, cord, and nerves is seen over the defect, while in myeloschisis, the open spinal cord is seen as a mass of neural tissue over the bony defect.
What adult brain structures arise from the Telencephalon?
Cerebrum: cerebral hemispheres (cortex, white matter, basal nuclei).
What is Spina bifida with myeloschisis?
A severe form of spina bifida where the spinal cord is exposed through a gap in the spine and is not covered by skin or meninges.
When does the posterior neuropore close?
On the 27th day.
From which part of the neural tube does the brain develop?
The cranial part of the neural tube.
What flexure is located between the midbrain and hindbrain?
The Midbrain flexure.
What is shown in the cross section of the trilaminar embryonic disc?
Neural plate, neural fold, neural crest, neural tube, surface ectoderm, paraxial mesoderm, notochord, yolk sac.
What are the embryonic brain regions derived from the forebrain?
Telencephalon and Diencephalon.
When is folic acid protective against Neural Tube Defects (NTDs)?
Folic acid is protective only if ingested during the preconception period.
What are the two plates found in the neural tube apart from the alar and basal plates?
Roof plate and floor plate.
Which developed brain structures arise from the Myelencephalon?
Medulla oblongata.
At what embryonic stage does the brain start to show distinct regions?
At 3 weeks.
At what embryonic stage do the Pons and Cerebellum start to develop?
At 7 weeks.
Where are the skin features of spina bifida occulta typically located?
Over unfused vertebral arches.
What adult brain structures arise from the Metencephalon?
Pons and cerebellum.
Where are the lateral ventricles located?
In the Telencephalon.
What are the derivatives of the neural crest in the connective tissue?
Bone and cartilage of the facial skeleton.
What lines the neural tube during spinal cord development?
A thick layer of neuroepithelium.
Where is the marginal zone located in relation to the ventricular zone?
Superficial to the ventricular zone.
What is the heart prominence in the developing embryo?
The heart prominence is the early formation of the heart, which will eventually develop into the fully functional heart.
What is the 'Cervical flexure'?
The cervical flexure is a bend in the neural tube that occurs between the hindbrain and the spinal cord.
Which developed brain structures arise from the Diencephalon?
Thalamus.
Which developed brain structures arise from the Mesencephalon?
Parts of the brainstem.
Which epilepsy medication is known to alter folate metabolism and act as a teratogen?
Valproic acid (sodium valproate, e.g., Depakine).
What skin features may be present in spina bifida occulta?
A skin dimple or a tuft of hairs may be present.
What are the derivatives of the neural crest in the nervous tissue?
Leptomeninges (pia & arachnoid) and Schwann cells.
What structure is labeled as the 'Optic vesicle' in the developing brain?
The Optic vesicle.
On which day does the caudal neuropore close?
The 27th day.
What is the significance of the somites in embryonic development?
Somites are blocks of mesoderm that segment the body of the embryo and give rise to the vertebrae, ribs, and skeletal muscles.
From which part of the neural tube does the spinal cord develop?
The narrow caudal part of the neural tube.
What are two main causes of Neural Tube Defects (NTDs)?
Genetic factors and folate deficiency.
Where are the alar plates located in the neural tube?
Dorsally.
What are the embryonic brain regions derived from the hindbrain?
Metencephalon and Myelencephalon.
What is the consequence of the failure of the neuropore to close?
It leads to Neural Tube Defects (NTDs).
What is the 'Dorsal root ganglion' and its role in development?
The dorsal root ganglion contains the cell bodies of sensory neurons and is crucial for transmitting sensory information to the spinal cord.
What is the part of the mantle layer dorsal to the sulcus limitans called?
The alar plate.
What is anencephaly?
Anencephaly is one of the most common neural tube defects (NTDs) characterized by the absence of the calvarium, posterior bone elements (skull), and deficiency in the brain (prosencephalus) and meninges.
Are there any neurological symptoms associated with spina bifida occulta?
No, there are no neurological symptoms.
What is seen over the bony defect in spina bifida with myeloschisis?
An open spinal cord seen as a mass of neural tissue.
What is Spina bifida with meningomyelocele?
A form of spina bifida where the spinal cord and meninges protrude through a defect in the vertebral column.
At what embryonic stage is the brain more developed with distinct structures like the Cerebrum and Thalamus?
At 11 weeks.
What is the membranous sac in spina bifida with meningomyelocele?
A sac that contains the displaced spinal cord and roots of the spinal nerve.
