Exam #1: Development--Self Study

Question 1

What is neurulation?

Answer 1

Process by which the trilaminar embryo internalizes its developing nervous system (ectoderm)

Question 2

Describe the process of neurulation.

Answer 2

Gastrulation= formation of the trilaminar disc

Neurulation=

1) Mesoderm forms the notochord
2) Notochord induces the overlying ectoderm to proliferate & become the neural plate
3) Induction causes the neural plate to fold & become a central neural groove/ lateral & raised neural folds
4) Neural folds approximate & fuse, forming the neural tube

Question 3

What is the embryological defect that causes spina bifida?

Answer 3

Incomplete fusion of the neural tube (opening into the ectoderm)

Question 4

What are the three sources of nervous tissue in the body?

Answer 4

1) Neural tube
2) Neural crest cells
3) Ectodermal placodes

Question 5

What tissue & cell types are derived from the neural tube?

Answer 5

CNS
Somatic motoneurons
Preganglionic ANS neurons

Question 6

Where do most neural crest cell migrate?

Answer 6

Pharyngeal arches of the developing head & neck

Question 7

What tissue & cell types are derived from ectodermal placodes?

Answer 7

Lens of the eye
Inner ear
Pituitary gland
Some somatic sensory ganglia of cranial nerves

Question 8

What are neural crest cells?

Answer 8

• A narrow strip of cells at either edge of the neural plate

- Do NOT fuse with the neural tube; instead, lie ontop of it forming “neural crest”

Question 9

What are the derivatives of neural crest cells? Specifically, what are the neural crest derivates of the head/ neck & body?

Answer 9

Head & Neck

• Bones, cartilage, & muscles in the head / neck
• Neurons of sensory ganglia in CN: V, VII, VIII, IX, X
• Odontoblasts
• Parafollicular cells of the thyroid gland
• Cells of aortic & carotid bodies
• PNS ganglia of CN

Body

• Ganglia (ANS & DRG)
• Schwann cells
• Adrenal medulla
• Melanocytes)

Question 10

During early development, what are the three divisions of the neural tube?

Answer 10

1) Prosencephalon (forebrain)
2) Mesencephalon (midbrain & cerebral aqueduct of Sylvius)
3) Rhombencephalon (hindbrain)

Question 11

When in gestation are the three major division of the neural tube further divided?

Answer 11

Week 5

Question 12

Which of the three major divisions further divide?

Answer 12

Prosencephalon

Rhombencephalon

Question 13

What does the prosencephalon divide into?

Answer 13

Telencephalon–>cerebral hemispheres & lateral ventricles

Diencephalon–>thalami & 3rd ventricle

Question 14

What does the Rhombencephalon divide into?

Answer 14

Metencephalon= pons & cerebellum/ upper 4th ventricle
Mylencephalon= medulla oblongata/ lower 4th ventricle

Question 15

What are the three flexures in the brain?

Answer 15

1) Cephalic flexure
2) Cervical flexure
3) Pontine flexure

Question 16

What is the Cephalic Flexure?

Answer 16

Bend in the region of the mesencephalon

Question 17

What is the Cervical Flexure?

Answer 17

Bend between the Rhombencephalon & future spinal cord

Question 18

What is the Pontine Flexure?

Answer 18

Bend in the Rhombencephalon that forms the two distinct:

• Metencephalon (pons & cerebellum)
• Myelencephalon (medulla oblongata)

Question 19

What are CNS neurons & neuroglia derived from?

Answer 19

Neuroepithelium of the neural tube

Question 20

What is the neuroepithelium?

Answer 20

Cells of the neural tube that form three distinct layers:

1) Ventricular
2) Intermediate/ Mantle
3) Marginal

Question 21

Describe the formation of neurons in the CNS.

Answer 21

During weeks 4-20:

1) G1 ventricular
2) Migration to marginal & S-phase
3) Return to ventricular G2
4) Mitosis in ventricular
5) Migration to mantle & differentiation into neurons
6) Axon growth into the marginal layer

*****Migratory neurons that establish synaptic contacts remain; those that don’t undergo apoptosis

Question 22

Describe the formation of neuroglia in the CNS.

Answer 22

Following the same general process as neuroblasts, glioblasts migrate into the marginal layer

Question 23

How do the three zones of the neural tube translate into the mature spinal cord?

Answer 23

Ventricular= ependymal cells that line the ventricles 
Mantle= gray matter 
Marginal= white matter

Question 24

How do microglia differ from other glial cells in the CNS?

Answer 24

Derived from bone marrow i.e. hematopoietic stem cells that migrate to the CNS; these are the macrophages of the CNS

Question 25

How does the development of the PNS differ from the CNS?

Answer 25

All PNS cells are derived from neural crest cells i.e. neurons & neuroglia of the PNS are neural crest in origin

Question 26

How do the meninges differ in their development?

Answer 26

Pia & arachnoid mater= neural crest

Dura= mesoderm

Question 27

Describe the process of myelination. Specifically address: start & end/ cell types.

Answer 27

• Myelination begins at 16 weeks gestation
• Ends 3 years, except frontal lobes that continue till 20s
• CNS= oligodendrocytes
• PNS= Schwann cells

Question 28

What is Spina Bifida Occulta?

Answer 28

• Incomplete closure of the neural tube in 1st month of gestation
• Overlying bone (L5/ S1) will have subtle defects
• Mildest form that is typically asymptomatic–maybe tuft of hair on skin in lumbar region

Question 29

What is Spina Bifida Cystica?

Answer 29

• Incomplete closure of the neural tube in 1st month of gestation
• Herniate of nervous tissue through the bony defect causes a visible cyst-like structure in the individuals back i.e. “cystica”
• Two subtypes:
  1) Meningocele
  2) Meningomyelocele

Question 30

What is Spina Bifida Meningocele?

Answer 30

• Herniation of meninges through body defect

- Spinal cord intact in spinal canal

Question 31

What is Spina Bifida Meningomyelocele?

Answer 31

Herniation of meninges & spinal cord through defect

Question 32

What is Spina Bifida Myeloschisis?

Answer 32

This is the most severe form of Spina Bifida that involves an externally open & flattened spinal cord

Question 33

What supplement in early pregnancy can reduce the risk of Spina Bifida?

Answer 33

Folic acid