Development of the CNS

Question 1

Differentiation of the neuroepithelium (of the neural tube)

Answer 1

• Neuroblasts (all neurons with their cell bodies in the CNS)
• Glioblasts (glioblasts differentiate into astrocytes and oligodendrocytes)
• Ependymal cells (lining ventricles and central canal)

Question 2

Differentiation of neural crest cells

Answer 2

CELLS OF THE PERIPHERAL NERVOUS SYSTEM

• Sensory neurones of dorsal root ganglia and cranial ganglia
• Postganglionic autonomic neurons
• Schwann cells
• Non-neuronal derivatives (eg: melanocytes)

Question 3

Proliferation of neuroepithelium

Answer 3

-

Question 4

Differentiation of neuroepithelium

Answer 4

/

Question 5

Layers of the neural tube

Answer 5

• neural canal surrounded by ependymal layer (germinal layer)
• floor plate marks most ventral part of neural canal
• roof plate marks most dorsal part of neural canal
• ependymal layer surrounded by grey matter (mantle layer)
• grey matter surrounded by white matter (marginal layer)

Question 6

Control of neural tube differentiation

Answer 6

• controlled by selective signalling molecules secreted sequentially by surrounding tissues->interact with receptors on neuroblasts to control migration and axonal growth by attraction and repulsion
• dependent on concentration gradient and timing

Question 7

The developing spinal cord structure

Answer 7

• grey matter is split into the alar plate (more dorsal containing interneurons) and the basal plate (more ventral containing motorneurons and interneurons)
• neural crest cells form sensory neurons in dorsal root ganglion

Question 8

The mature spinal cord structure

Answer 8

• central canal shrinks
• the basal plate develops into the ventral horn (motor)
• the alar plate develops into the dorsal horn (sensory)
• the neural crest develops into the dorsal root ganglia

Question 9

The developing brainstem structure

Answer 9

• Early development is tubular, much like the spinal cord
• Lateral proliferation of the roof plate enlarges the neural canal to form the 4th ventricle-> causes basal plate containing motor nuclei to lie more medially in brainstem and alar plate containing sensory nuclei to lie more laterally in brainstem
• This arrangement of the plates dictates the pattern of cranial nerve nuclei
• sulcus limitans separates cranial nerve motor nuclei from the cranial nerve sensory nuclei (separates basal plate from alar plate)

Question 10

The 3 primary vesicles of the developing brain (~4 weeks)

Answer 10

• Prosencephalon (future forebrain)
• Mesencephalon (future midbrain)
• Rhombencephalon (future hindbrain) which is largely the cerebellum, pons and medulla oblongata

Question 11

The 5 secondary vesicles of the developing brain (~5 weeks)

Answer 11

• telencephalon (developing forebrain) containing the cerebral cortex
• diencephalon (developing forebrain) containing the thalamus and hypothalamus
• midbrain
• pons (developing hindbrain)
• medulla (developing hindbrain)

Question 12

The developing brain structure (~8 weeks)

Answer 12

• ventricular system arises
• development of individual brain hemispheres with lateral ventricles within (lateral ventricles drain into third ventricle)
• midbrain contains aqueduct (drains into fourth ventricle

Question 13

Folding of the developing brain

Answer 13

NAME OF FLEXURE DEPENDS ON POSITION

• cephalic flexure
• pontine flexure
• cervical flexure

Flexures become exaggerated as development occurs

Question 14

The developing cortex structure

Answer 14

• Neuroblasts formed from neuroepithelium migrate towards pial surface along radial glia
• successive waves of migration form the cortical layers (6 layers)
• myelination gradually occurs to term and beyond, producing the 6 discrete layers of the cerebral cortex
• highly convoluted structure as gyri and sulci=increases brains surface area and cognitive ability (higher complexity of activity)

Question 15

Developmental disorders

Answer 15

• Normal development depends on the coordinated completion of several complex processes (eg: proliferation, differentiation, migration, axon growth, synapse formation etc)
• Genetic mutation and environmental factors (eg: mother’s lifestyle, diet, teratogen exposure etc) can interfere with these processes
• developmental disorders largely relate to problems in the third trimester

Question 16

Neural tube defects

Answer 16

DEFECTS A TOP OR BASE OF NEURAL TUBE

• craniorachischisis
• anencephaly
• encephalocele
• iniencephaly
• spina bifida occulta
• closed spinal dysraphism
• meningocele
• myelomeningocele

FOLIC ACID SUPPLEMENTATION ADVISED TO REDUCE NEURAL TUBE DEFECT RISK

Question 17

Craniorachischisis

Answer 17

• most severe of the neural tube defects
• brain and spinal cord remain open
• presence of both anencephaly and spina bifida

Question 18

Anencephaly

Answer 18

• neural tube defect
• open brain and lack of skull vault
• partial or complete absence of bones of the rear of the skull, the meninges and the cerebral hemispheres of the brain

Question 19

Encephalocele

Answer 19

• neural tube defect

- herniation of the meninges and brain

Question 20

Iniencephaly

Answer 20

• neural tube defect

- occipital skull and spine defects with extreme retroflexion (backward bending) of the head

Question 21

Spina bifida occulta

Answer 21

• neural tube defect
• closed asymptomatic neural tube defect in which some of the vertebrae are not completely closed
• defect in the bony arch of the spine that has a normal skin covering

Question 22

Closed spinal dysraphism

Answer 22

• neural tube defect

- deficiency of at least two vertebral arches, here covered with a lipoma

Question 23

Meningocele

Answer 23

• neural tube defect

- protrusion of the meninges (filled with CSF) through a defect in the skull or spine

Question 24

Myelomeningocele

Answer 24

• neural tube defect
• type of spinal bifida
• open spinal cord with a meningeal cyst

Question 25

Radial glial cells

Answer 25

• astroglia (of astroglial lineage in the developing CNS)->type of macroglia
• develop vertically to act as scaffolding from the ventricles to the pial surface

Question 26

Neural stem cells

Answer 26

• apparent population in hippocampus but very few in number (not enough)->no programming to enhance neural circuitry (repairing damaged or lost neurons)->thus not used therapeutically
• Damaged/lost neurons from neuron apoptosis during development, neurodegenerative disease etc

Question 27

Developmental neurobiology in the repair of the nervous system

Answer 27

An understanding of the developmental mechanisms may lead to novel treatment of neurological disorders:

• neural stem cell use to replace lost neurons
• use of axonal guidance mechanisms to induce CNS regeneration

Question 28

The developing brain structure

Answer 28

• originally forms from the most anterior end of the neural tube
• the primary and then secondary vesicles develop by differential growth of the neural tube wall
• at the same time as the ventricle development, folding occurs to produce flexures so the developing brain fits into the cranial cavity
• the neural canal develops into the ventricular system

Question 29

The developing brain structure (~4 weeks)

Answer 29

• Flexure formation to define three levels of the embryonic brain
• Differential growth of neural tube wall to form primary vesicles

Question 30

The developing brain structure (~5 weeks)

Answer 30

Differential growth of neural tube wall to form secondary vesicles from the primary vesicles

Question 31

The developing brain structure (at term)

Answer 31

-growth continues with myelination of appropriate pathways post term (allows for functions such as standing up, walking etc)