Development of the neural tube including NTD

Question 1

hat is the weight of the brain in a newborn human?

Answer 1

350-400g (10% body weight)

Question 2

What is the weight of the brain in an adult human?

Answer 2

1,300-1,400g (2% body weight)

Question 3

How many neurons are in the brain of a newborn human?

Answer 3

100 billion

Question 4

How many neurons are in the brain of an adult human?

Answer 4

86 billion

Question 5

What does the difference in neuron count between newborns and adults mean?

Answer 5

14 billion neurons die (via apoptosis) before adulthood. Newborns have a larger number of neurons but fewer synaptic connections. The brain continues to grow and change throughout childhood and adolescence as new connections are formed, and existing connections are strengthened or weakened.

Question 6

What animal has the biggest brain?

Answer 6

Sperm whale (7-9 kg, 0.02% body weight)

Question 6

What animal has the highest brain-to-body ratio?

Answer 6

Small ant (1:7)

Question 7

What structural feature of the human brain is superior to any other animal?

Answer 7

Encephalization quotient (EQ)

Question 8

At what age does the human brain reach maximum functional capacity?

Answer 8

Females - 25 years, Males - 28 years

Question 9

What is the neural tube the primordium of?

Answer 9

The brain and spinal cord

Question 9

From which germ layer does the neural tube develop?

Answer 9

Ectoderm

Question 10

What are the five main stages in the synopsis of neural tube development?

Answer 10

1. Formation of the neural plate, 2. Formation of the neural fold and groove, 3. Fusion of the neural fold into a tube, 4. Detachment and migration of neural crest cells, 5. Defects in neural tube closure result in conditions such as spina bifida and anencephaly.

Question 10

What is neurulation?

Answer 10

The crucial process in embryonic development that forms the precursor to the central nervous system (brain and spinal cord). It’s also the process by which ectodermal cells respond to various GDFs (Growth Differentiation Factors) and produce the neural tube, neural crest, and epidermis.

Question 10

What three structures are produced during neurulation?

Answer 10

1. The neural tube (gives rise to brain and spinal cord), 2. The neural crest (migrates and gives rise to diverse cell types), 3. The epidermis (superficial layer of skin).

Question 11

What are some growth differentiation factors (GDFs) involved in neurulation?

Answer 11

Bone Morphogenetic Protein 4 (BMP4), Noggin, Chordin, Follistatin, WNT3a, FGF, and Retinoic acid.

Question 12

When does the neural plate form?

Answer 12

During the 3rd week of gastrulation.

Question 13

What forms from the elevated edges of the neural plate?

Answer 13

A neural groove bounded by neural folds.

Question 14

What happens to the neural groove as it continues to bend superiorly?

Answer 14

Its free edges meet and fuse to form the neural tube.

Question 15

What are some derivatives of neural crest cells (mnemonic: CA MOTEL ASS)?

Answer 15

Answer: Craniofacial structures, Arachnoid and pia mater (meninges), Melanocytes, Odontoblasts, Tracheal cartilage, Enterochromaffin (Suprarenal medulla), Laryngeal cartilage, All ganglia (sympathetic, sensory, parasympathetic), Schwann cells, and Spiral septum.

Question 16

When do the anterior and posterior neuropores close?

Answer 16

The anterior (rostral) neuropore closes first on day 26, and the posterior (caudal) neuropore closes 2 days later.

Question 17

What is Craniorachischisis?

Answer 17

A malformation resulting from the failure of the neural tube to close throughout most of the length of the body, affecting both the brain (anencephaly) and spinal cord (spina bifida).

Question 18

What is Anencephaly?

Answer 18

Failure of the cranial neuropore to close, resulting in variable degrees of brain deformity, from total absence to minor defects.

Question 19

What is Spina Bifida?

Answer 19

Failure of the caudal neuropore closure, involving variable defects of the arches of the vertebrae in the affected site.

Question 20

What maternal deficiency is associated with increased occurrence of Spina Bifida?

Answer 20

Folate (Vitamin B9) deficiency.

Question 21

What are some variations of Spina Bifida?

Answer 21

Occulta, SB with meningocoele, SB with meningomyocoele, SB with myeloschisis.

Question 22

What are some anomalies of the brain mentioned?

Answer 22

Meroanencephaly, Meningo-encephalocoele, Microcephaly, Hydrocephalus.

Question 23

How is the Mantle layer (future Grey matter) formed in the spinal cord?

Answer 23

By the cell bodies of primitive neurocytes.

Question 24

How is the Marginal layer (future White matter) formed in the spinal cord?

Answer 24

By cell processes extending from primitive neurocytes.

Question 25

Which two neuroglial cells are produced by theneuroectoderm after primitive neurocytes?

Answer 25

Oligodendrocytes and astrocytes.

Question 26

What are the cells called that the neuroectoderm transforms into after producing oligodendrocytes and astrocytes?

Answer 26

Ependyma.

Question 27

What do ependymal cells line?

Answer 27

The central canal of the spinal cord and ventricles of the brain.

Question 28

Where do microglia (the 4th neuroglial cell) differentiate from?

Answer 28

Mesenchyme.

Question 28

Where does the spinal cord terminate at birth and in adults?

Answer 28

At birth, it terminates at L3. In adults, it terminates at L1 At birth, it terminates at L3. In adults, it terminates at L1

Question 29

What are the three primary brain vesicles that form from cranial to caudal? What are the three primary brain vesicles that form from cranial to caudal?

Answer 29

Prosencephalon, Mesencephalon, and Rhombencephalon.Prosencephalon, Mesencephalon, and Rhombencephalon.

Question 30

What two structures does the Prosencephalon form by Week 5?

Answer 30

Cranial Telencephalon and Caudal Diencephalon. Cranial Telencephalon and Caudal Diencephalon.

Question 31

What do the lateral diverticula of the Telencephalon become?

Answer 31

Cerebral hemispheres.

Question 32

What do the smaller diverticula of the Diencephalon become?

Answer 32

Optic Vesicles.

Question 33

What two structures does the Rhombencephalon form?

Answer 33

Cephalic Metencephalon and caudal Myelencephalon.

Question 34

What does the ventral part of the Metencephalon develop into, and what does the dorsal part develop into?

Answer 34

The ventral part develops into the Pons, and the dorsal part develops into the cerebellum.

Question 35

Which cranial nerves originate from the Pons?

Answer 35

CNV, CNVI, CNVII, and CNVIII.

Question 36

What does the Myelencephalon develop into, and which cranial nerves originate from it?

Answer 36

The Myelencephalon develops into the Medulla Oblongata, from which CNIX, CNX, CNXI (cranial part), and CNXII originate.

Question 36

What are the five basic processes of brain development?

Answer 36

Neurogenesis, Neural migration, Myelination, Synaptogenesis, and Pruning.

Question 37

What is Neurogenesis?

Answer 37

The process of forming neurons, completed before birth with about 100 billion neurons produced.

Question 38

What is Neural Migration?

Answer 38

The process of organizing the brain by moving neurons to specific areas based on their functions. It begins prenatally and continues for at least 8 to 10 months after birth, using neuroglial processes as scaffolding.

Question 39

What is Myelination?

Answer 39

The process of coating the axon of each neuron with a fatty coating called myelin, which protects the neuron and helps it conduct signals more efficiently. Oligodendrocytes are responsible for myelination in the brain, while Schwann cells myelinate peripheral nerves. It begins before birth in the brain stem and cerebellum but is not completed in the frontal cortex until late adolescence. Breastfeeding contributes to more rapid myelination.

Question 40

What is Synaptogenesis?

Answer 40

The process of forming networks of specialized connections (synapses) in the brain. It begins prenatally and continues throughout life, facilitated by exogenous cues like classical music, reading, and peaceful surroundings.

Question 41

What is Pruning?

Answer 41

The process of weeding out underutilized connections and strengthening more frequently utilized ones based on experiences. Rapid pruning occurs between ages 3 and 16, with specific localized pruning during infancy, adolescence, and advanced age.

Question 42

What is the primary germ layer from which the neural tube develops?

Answer 42

Ectoderm. (Crucial for understanding early embryology and congenital anomalies).

Question 43

What are the three primary structures formed during neurulation?

Answer 43

Neural tube, neural crest, and epidermis. (Essential to remember for comprehensive understanding of neurulation outcomes).

Question 44

What is the critical maternal deficiency linked to neural tube defects like Spina Bifida, and what is the preventative measure?

Answer 44

Folate (Vitamin B9) deficiency. Supplementation with folic acid before and during early pregnancy is key. (High-yield for public health, obstetrics, and pediatrics).

Question 45

When do the anterior (rostral) and posterior (caudal) neuropores typically close, and what is the clinical significance of their failure to close?

Answer 45

Anterior neuropore closes on day 26; Posterior neuropore closes on day 28. Failure to close leads to Anencephaly (anterior) or Spina Bifida (posterior). (Key timeline and associated clinical conditions).

Question 46

What are the five basic processes of brain development that continue into adolescence/adulthood?

Answer 46

Neurogenesis, Neural migration, Myelination, Synaptogenesis, and Pruning. (Understanding these processes is fundamental to developmental neuroscience and clinical observations).

Question 47

A newborn presents with absence of most of the brain and skull, with the neural tissue exposed. What is this condition, and what was the embryological defect?

Answer 47

Anencephaly (specifically Meroanencephaly if some brainstem tissue is present). It results from the failure of the cranial (anterior) neuropore to close.

Question 48

A child is diagnosed with a sac-like protrusion on their lower back containing cerebrospinal fluid and meninges, but no neural tissue. What is this form of Spina Bifida called?

Answer 48

Spina Bifida with Meningocoele. (Differentiate from meningomyocoele which includes neural tissue).

Question 49

In a neonate, imaging reveals an abnormally small head and brain. What is this condition, and what developmental process is likely impaired?

Answer 49

Microcephaly. This often involves impaired neurogenesis or neural migration.

Question 50

A child shows signs of increased intracranial pressure and an enlarged head circumference due to excessive CSF accumulation. What is the most likely diagnosis, and what common embryological factor can contribute?

Answer 50

Hydrocephalus. Obstruction of CSF flow, potentially due to aqueductal stenosis (a developmental anomaly of the cerebral aqueduct, derived from the mesencephalon).

Question 51

A severe neural tube defect involves the entire length of the neural tube failing to close, affecting both the brain and spinal cord. What is this condition?

Answer 51

Craniorachischisis. (Important to recognize as the most severe form of neural tube defect).

Question 52

While most neuroglial cells (Oligodendrocytes, Astrocytes, Ependyma) differentiate from neuroectoderm, what is the mesenchymal derivative among them?

Answer 52

Microglia. (A common trick question to test understanding of germ layer origins).

Question 53

Name at least three Growth Differentiation Factors (GDFs) involved in the formation of the forebrain and midbrain.

Answer 53

Chordin, Noggin, and Follistatin (all are BMP4-inhibitory GDFs). (Specifics on regional brain development)

Question 54

What specific brain vesicle gives rise to the Pons and Cerebellum?

Answer 54

The Metencephalon (from the Rhombencephalon). (Detailed knowledge of brain vesicle derivatives).

Question 55

The spinal cord terminates at L3 at birth. Where does it terminate in an adult, and why does this change occur?

Answer 55

L1 in adults. This is due to the differential growth rate between the vertebral column and the spinal cord. (Anatomical detail with clinical relevance for lumbar punctures).

Question 56

At what specific ages do human brains reach their maximum functional capacity for females and males?

Answer 56

Females - 25 years, Males - 28 years. (An easy-to-miss detail that highlights gender-based differences in brain maturation).