Embryology and Congenital Malformations Flashcards by Robbie Pollock

Nervous system develpos form the embryonic __________

ectoderm

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CNS appears at the beginning of the _____ week

3rd

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Thickening of ectoderm anterior to the primitive node leads to the formation of what?

neural plate

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edges of the neural plate thicken and move upwards to form what?

neural folds

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Neural folds migrate towards each other and fuse at midline forming the _________

neural tube

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Where does the neural tube originally remain open at?

anterior and posterior ends

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When do the anterior and posterior ends close?

Anterior (cranial/rostral) neuropore closes 18 – 20 somite stage (~25 days)

Posterior (caudal) neuropore closes ~ day 27

(neuropore - either of the openings to the exterior at the anterior and posterior ends of the neural tube of a vertebrate embryo)

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The neural plate goes on to form what?

neural tube

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What is closure of the neural tube essential for?

normal development and function

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What is the process of the neural tube closing?

Initiated at several points along A-P axis

Proceeds in cranial and caudal directions

Begins day 18

Completed by end of 4th week (~day 27)

Up to 5 closure sites in humans

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Failure of neural tube to close properly results in neural tube defects (NTDs), what are some examples?

Anencephaly
Encephalocoele
Spina bifida

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What is Anencephaly?

Failure of anterior neuropore to close

Skull fails to form

Brain tissue degenerates

Incompatible with life

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How common is Anencephaly?

1:1500 births (~4x more common in females)

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What is Craniorachischisis?

failure of neural tube closure along entire neuroaxis

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What is Encephalocoele?

Herniation of cerebral tissue through a defect in the skull

Failure in closure of rostral neural tube

Most frequent in occipital region

Variable degree of neurological deficits

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How common is Encephalocoele?

1:4000 births

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What is Spina Bifida?

Defective closure of the caudal neural tube

Affects tissues overlying the spinal cord

Spina bifida = non-fusion of vertebral arches

Neural tissue may or may not be affected

Severity ranges from minor abnormalities to major clinical symptoms

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What is spina bifida occulta?

Most minor form of spina bifida

Failure of embryonic halves of vertebral arch to grow normally and fuse

Occurs in L5 and L6 vertebrae of 10% of otherwise healthy people

Usually no clinical symptoms

May result in dimple with small tuft of hair

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What is spina bifida cystica?

Protrusion of spinal cord and/or meninges through the defect in the vertebral arches

1:1000 live births

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What is spina bifida with meningocele?

rarest form

protrusion of meninges and cerebrospinal fluid

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What is spina bifida with meningomyelocle?

Nerve roots and/or spinal cord included in the sac

Neurological deficits - loss of sensation and muscle paralysis

Area affected determined by level of lesion

Often associated with hydrocephalus (a condition in which excess cerebrospinal fluid (CSF) builds up within the ventricles)

Most severe form is myeloschisis. Spinal cord in affected area open due to failure of neural folds to fuse

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How are neural tube defects prevented?

Folic acid supplements (400 µg/day - 50-70% decrease in risk)

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How is a prenatal diagnosis made of neural tube defects?

Maternal blood screening - Indicated by high levels α-fetoprotein (AFP) in serum – AFP from foetal liver leaks into amniotic fluid then into maternal blood. Best detected 16 - 20 weeks

Amniocentesis (high levels AFP in amniotic fluid)

Ultrasound (Anencephaly from 12 weeks, spina bifida from 16-20 weeks)

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What are the risk factors for neural tube defects?

Genetic predisposition

Nutritional (e.g. too little folate, too much vitamin A)

Environmental (e.g. hyperthermia; taking certain drugs - e.g. sodium valproate)

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What is A?

Prosencephalon

What is B?

Mesencephalon

What is C?

Rhombencephalon

Telencephalon

Diencephalon

Metencephalon

Myelencephalon

How many primary and how many secondary brain vesicles are there?

3 primary and 5 secondary

What are the 3 flextures seen in the developing embryo, when do they develop and where are they?

Cephalic flexure - End of 3rd week. Between midbrain (mesencephalon) and hindbrain (rhombencephalon) Cervical flexure - End of 4th week. Between hindbrain and spinal cord Pontine flexure - 5th week. In hindbrain (between metencephalon and myelencephalon)

Prosencephalon

Diencephalon

telencephalon

Mesencephalon

Rhombencephalon

metencephalon

myelencephalon

What does the telencephalon form

cerebral hemispheres, hippocampus, basal ganglia

What does the Diencephalon form?

thalamus, hypothalamus, pituitary gland, pineal

What does the Mesencephalon form?

superior and inferior colliculi

What does the metencephalon form?

cerebellum, pons

What does the myelencephalon form?

medulla

The lumen of the neural tube forms the ventricular system, what does the Telencephalon form

lateral ventricles

The lumen of the neural tube forms the ventricular system, what does the Diencephalon form

3rd ventricle

The lumen of the neural tube forms the ventricular system, what does the Mesencephalon form

cerebral aqueduct

The lumen of the neural tube forms the ventricular system, what does the Metencephalon and Myelencephalon form

4th ventricle

When is CSF formed, what is it made by, and where does it drain?

Begins to form during 5th week Produced predominately by choroid plexus (in 3rd, 4th, lateral ventricles) Drains into subarachnoid space via openings in roof of 4th ventricle Absorbed into venous system

What is an accumulation of cerebral spinal fluid called?

Hydrocephalus

What does hydrocephalus, reason for it happening and its causes

Results in enlarged brain and cranium Frequently due to blocked aqueduct Prevents CSF from lateral and 3rd ventricles passing into the 4th ventricle - can’t drain properly Causes: genetic, prenatal viral infection or intraventricular haemorrhage, spina bifida cystica

Cellular differentiation happens in the neural tube, itially what is formed?

Initially a single layer of rapidly dividing neuroepithelial cells Pseudostratified epithelium Divide at ventricular surface

What produces most cells of the CNS?

neuroepithelium

What cells do neuroepithelial cells make?

Microglia are the exception as they are not made by the neuroepithelium, what makes microglia?

What are neural crest cells?

Cells of PNS, Autonomic nervous system (neurons and glia) Non-neuronal cells: e.g. melanocytes, adrenal medulla, meninges, facial bones/cartilage Located at the dorsal tip of the neural tube and migrate off the neural tube and give rise to a whole host of structures in the embryo

What are some neural crest derivatives?

Sensory neurons Autonomic neurons (sympathetic and parasympathetic ganglia) Schwann cells + satellite cells of ganglia Aortic plexuses (nerves surrounding the aorta) Endocrine cells (chromaffin cells of adrenal medulla; calcitonin producing cells of carotid body; parafollicular cells of thyroid). Enteric nervous system Pigment cells (melanocytes) – all pigment except RPE Leptomeninges of anterior brain (prosencephalon and part of mesencephalon) Non-neural head structures (including bone, cartilage and connective tissue). Teeth (dental papilla; odontoblasts) Iris muscle and pigment; ciliary muscles Corneal stroma Inner ear development Regions of the heart + walls of large arteries

Neural crest forms ___ neurons and \_\_\_\_

Neural crest forms PNS neurons and glia

The dorsal root ganglia (DRG; spinal ganglia) – sensory component, is formed form what?

neural crest

The motor component - motor neurons of spinal cord is formed by what?

the neural tube

What do the elongated spinal nerves form?

cauda equina

What does the piat mater form at the end of the spinal cord?

terminal filum

Surface of cerebral hemispheres is initially ______ then you develop ______ (grooves) and ____ (elevations)

smooth sulci gyri

What is the reason for the sulci and gyri developing?

space saving - minimises brain volume Brings together brain regions that would otherwise be far apart – optimises brain wiring and functional organisation

What is Lissencephaly?

also known as "smooth brain" Rare brain disorder Caused by defective neuronal migration Gyri and sulci fail to develop Results in severe mental impairment, failure to thrive, seizures, and abnormal muscle tone Many affected children die before age 10

What is Polymicrogyria?

Excessive number of small gyri Variable degree of neurological problems (e.g. mental retardation, seizures, motor deficits etc)

Other congenital abnormalities (all very rare): What is Microcephaly?

Genetic, drugs, infection (e.g. Zika virus) Intellectual impairment, delayed motor functions/speech, hyperactivity, seizures, balance/co-ordination problems etc smaller head than normal

Other congenital abnormalities (all very rare): What is Aegenesis corpus callosum?

a complete or partial absence of the corpus callosum Alone or with other cerebral abnormalities Effects range from subtle – severe Cognitive and social difficulties - intellectual impairment, seizures, hypotonia etc

Other congenital abnormalities (all very rare): What is Porencephaly?

Other congenital abnormalities (all very rare): What is Schizencephaly?

characterized by abnormal slits or clefts in the cerebral hemispheres of the brain

What is diastematomyelia (split cord malformation)?

a congenital disorder in which a part of the spinal cord is split (sagittal), usually at the level of the upper lumbar vertebra Spinal cord split longitudinally into 2 parts Usually associated with vertebral anomalies Bony or cartilaginous process “fixes” cord in place Scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation

What are causes of intellectual impairment?

genetic (e.g. Down’s syndrome) Radiation Infectious agents (e.g. rubella, toxoplasmosis, cytomegalovirus) Birth trauma postnatal insults (e.g. head injury, infections (e.g. meningitis), lead exposure) Common cause – maternal alcohol abuse

in intellectual impairment there is often ________ gross brain defects

no obvious

Development of the nervous system begins in week \_

Neural tube develops from \_\_\_\_\_\_\_\_\_\_\_\_\_\_

embryonic ectoderm

Neural tube closed by end of \_th week. Defects in closure result in ____ (e.g. spina bifida

4th NTDs

Neural tube forms _______ and ____ of CNS

neurons and glia of CNS

•Neural crest cells form neurons and glia of _____ (plus non-neuronal cells)

PNS

Expansion and bending of neural tube forms _ primary and _ secondary brain vesicles.

3 5

Lumen of neural tube forms \_\_\_\_\_\_\_\_\_\_\_\_

ventricular system

Embryology and Congenital Malformations Flashcards

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