Development

Question 1

Alcohol and the fetal brain!

Effects during 1st, 2nd, and 3rd trimester?

Effects in frontal lobes, corpus callosum, basal ganglia, hypothalamus, hippocampus, cerebellum?

Answer 1

• 1st trimester→interferes with cell migration and organization
• 2nd trimester→definitive FAS traits
• 3rd trimester→hippocampus, problems encoding auditory and visual information (math and reading)
• Frontal lobes-impulsivity, executive functions
• Corpus callosum-attention deficits, psychosocial functioning
• Verbal learning
• Basal ganglia-spatial memory, perseveration, inability to switch modes, perception of time
• Hypothalamus-appetite, emotions, temperature, pain
• Hippocampus-chronic stress, anxiety, depression
• Cerebellum-balance, coordination, impacts learning and cognition

Question 2

Syringomyelia

What is it?

Inital signs?

Answer 2

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• Tubular cavitation of the spinal cord – generally cervical/upper thoracic
• Neural deficits begin with loss of pain & temperature sensation over shoulders and upper arms.
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Question 3

Dandy-Walker malformations

What is it?

Symptoms?

Answer 3

• Malformation of cerebellum, posterior fossa cyst, blockage of foramina of Magendie and Luschka -> hydrocephalus
• In infants - slow motor devel, irritability, vomiting,
• In older children - lack of muscle coordination and jerky eye movement

Question 4

Arnold-Chiari malformations

Type 1?

Type 2?

Answer 4

• Chiari type I: Milder variant of Type II. Many of these patients have syringomyelia and some have hydrocephalus. May be asymptomatic.
• Chiari type II: Syndrome or association of anomalies that includes a NTD such as a lumbosacral meningomyelocele, displacement of part of the cerebellum and brain stem into the cervical spinal canal, hydrocephalus.

Question 5

Hydrocephalus

Answer 5

• Dilation of the cerebral ventricles by CSF due to CSF overproduction, obstruction of flow or failure of CSF reabsorption.
• Often seen as part of other malformations such as Dandy-Walker or Chiari malformations

Question 6

Holoprosencephaly

Answer 6

Failure of the normal development of the forebrain such that it is not divided into two hemispheres

Question 7

How to detect NTD in utero?

Answer 7

AFP (alpha-fetoprotein) and acetylcholinesterase in amniotic fluid and maternal blood.

Question 8

Spina bifida occulta

Answer 8

Mildest form in which there is malformation of the vertebral arch

Question 9

Spina bifida cystica

1. Meningocele
2. Myelomeningocele

Answer 9

• Meningocele: Spinal cord is intact but meninges filled with CSF herniate through the defect in the vertebral arch and skin – usually in the lumbosacral region.
•

Myelomeningocele: Most severe form; malformed spinal cord and the meninges herniate through the opening – usually in the lumbosacral region.
o May be accompanied by an Arnold-Chiari malformation where the cerebellum and caudal brainstem are elongated and protrude caudally into the foramen magnum. In this situation, CSF is often obstructed resulting in hydrocephalus.

Question 10

Anencephaly and Meroanencepaly

Encephalocele

Answer 10

Failure of the rostral neuropore to close and subsequent failure of the cranial vault to form

Anencephaly = total absence of brain tissue
Meroanencephaly = remnants of brainstem tissue may be present

Protrusion of brain through a defect in the skull, often in the occipital area

Question 11

Craniorachischisis

Answer 11

Complete failure of the neural tube to close resulting in exposure of the malformed tissue to the outside of the head and body

Question 12

Hirschsprung’s disease

What?

Where?

Treatment?

Answer 12

NCC do not get into colon so peristalsis does not occur normally. Fecal retention with ballooning of colon and abdomen proximal to obstruction.

Usually involves sigmoid colon and rectum

Surgery includes removal of abnormal bowel.

Question 13

Waardenburg syndrome

What?

Symptoms?

Answer 13

Diffuse disruption of migration of neural crest cells.

• Abnormal appearance of face, deafness, due to head neural crest cell involvement
• Lack of pigmentation (melanocytes)
• Digestive problems (enteric ganglia) – chronic constipation

Question 14

Describe the formation of the Neural Tube and its segmentation into the developing brain (primary and secondary vesicles) and spinal cord.

Answer 14

Neurulation begins on day 18 with thickening of the neuroectoderm due to influce from the the notochord - neural plate forms

Neural folds develop by day 19 and the cells on the lateral bord become NCC

Fusion begins in week 4 on the 5th somites and the neuropores are formed. Rostral closes on day 24, caudal on day 26.

Question 15

List the adult derivatives of the Primary and Secondary Brain Vesicles.

Answer 15

Primary: Pro-, mes-. rhomb-encephalon

(Forebrain, midbrain, hindbrain)

Secondary

Forebrain: Tel- (cerebral hemisphere) and Di- (thalamus, hypothalamus, epithalamus, subthalamus)

Midbrain: midbrain (tectum, tegmentum, basis pedunculi)

Hindbrain: Met- (pons and cerebellum) and Myel- (medulla)

Question 16

Describe the development of the neural tube into the Gray and White Matter of the CNS in the adult.

Answer 16

Cell layers in the neural tube:

Ventricular layer-lines neural canal
Rapidly dividing neuroepithelial cells that cause the wall of the tube to thicken.
Source of neuroblasts (neurons) and glioblasts (glial cells).
After all neurons and glia are formed, this ventricular layer becomes the ependyma, i.e. a single layer of cells lining the central canal of the spinal cord.

Intermediate layer
Becomes populated by neuroblasts formed in the ventricular layer.
Will become the gray matter of the spinal cord (dorsal, ventral, lateral horns); containing all spinal cord nerve cell bodies.

Marginal layer
Includes the axons of neuroblasts whose cell bodies are in the intermediate layer and in the spinal ganglia.
Becomes the white matter of the spinal cord.

Question 16

Describe the relationship of the Alar and Basal Plates to the organization of the adult nervous system.

Answer 16

Within the intermediate layer (gray matter), the rapidly forming neuroblasts form two mirror image accumulations of cells – the alar and basal plates divided by the sulcus limitans.

The alar plate forms the dorsal horn – neurites with synapse within gray matter or enter the marginal layer and ascend or descend. They will also recieve primary synaptic input from DRG.

The basal plate forms the ventral and lateral horn – neurites will form synaptic terminals on skeletal muscles or peripheral autonomic ganglia

Question 17

Describe the development of the Ventricular System.

Answer 17

Tel – Lateral - forms with cerebral folding

Dy – Third - with choroid plexus in its thin roof

Mes – Cerebral aquaduct

Met – Fourth

My – Fourth ventricle with choroid plexus extending from the very thin roof of the ventricle

Question 18

Describe the development of the Cranial Nerve Nuclei and how they are related to the motor and sensory cranial nerves.

Answer 18

Tel – CN 1

Dy – CN 2

Mes – (Ros to Caud) - Superior colliculus, mesencephalic nucleus CN V (alar), oculomotor nucleus (basal), red nucleus, substantia nigra (basal) – CN 3, 4

Met – Contains the pons, consisting of fiber tracts.

My – In the caudal portion, the basal plate forms the pyramids (composed of corticospinal fibers). In the rostral portion, some of the alar plate moves ventrally. – CN 5 and 12 (both met and my)

Question 19

Describe the development of the Hypophysis or pituitary gland.

Answer 19

Pituitary (hypophysis) has a dual ectodermal origin from the neuroectoderm and the oral ectoderm.

Infundibulum = downward extension from the floor of the diencephalon

Neuroectoderm
• gives rise to the neurohypophysis
• makes up most of the posterior lobe of the pituitary
• this is the neural tissue of the pituitary – retains connections to hypothalamus
b. Rathke’s pouch = outgrowth from the ectodermally lined roof of the stomodeum (primitive oral cavity)

**Oral Ectoderm **
• gives rise to the adenohypophysis
• makes up most of the anterior lobe of the pituitary
• this is the glandular tissue of the pituitary

Located in sella turcica of the sphenoid bone.

Question 20

Describe the neural crest: origin and adult derivatives

Answer 20

1. Schwann cells
2. Enteric ganglia and nerves
3. Autonomic ganglia
4. Most sensory neurons in the spinal and cranial ganglia
5. Satellite cells
6. Arachnoid and pia mater
7. Connective tissues of the aorta
8. Merkel cells-pressure sensitive cells in skin
9. Chromaffin cells of adrenal medulla that secrete adrenaline (epinephrine)
10. Odontoblasts
11. Various cartilages and bones of the head and neck
12. Melanocytes

Question 21

Describe the development of the Sympathetic and Parasympathetic Nervous Systems.