First Aid: Neurology Embryology

Name the 3 primary and 5 secondary vesicles of the developing brain. Specify which primary vesicle forms each secondary vesicle.

1. (Forebrain) = Prosencephalon: telencephalon, diencephalon 2. (Midbrain) = Mesencephalon: mesencephalon 3. (Hindbrain) = Rhombencephalon: metencephalon, myelencephalon

The neuroectoderm gives rise to what?

1. CNS neurons 2. Ependymal cells (inner lining of ventricles, make CSF) 3. Oligodendroglia 4. Astrocytes

The origins of the CNS/PNS comes from what 3 cell types?

1. Neuroectoderm 2. Neural crest 3. Mesoderm

The neural crest cells become what part of the nervous system?

1. PNS neurons 2. Schwann cells

Neural tube defects are associated with elevated levels of what substance(s) in amniotic fluid and maternal serum?

1. α-fetoprotein 2. Acetylcholinesterase (AChE): amniotic fluid only

Neuropores fail to fuse during week ___, resulting in a connections between what structures? What is this called?

4th week; connection between amniotic cavity and spinal canal... this is called a neural tube defect.

What is the term for a malformation of the anterior neural tube, resulting in no forebrain and an open calvarium ("frog-like appearance")?

Anencephaly

Cranial nerve (CN) ____ mediates sensation in the anterior two thirds of the tongue; CN ____ mediates sensation in the posterior third.

Anterior 2/3 is CN V3 Posterior 1/3 is CN IX (extreme posterior is CN X)

Cranial nerve ____ mediates taste in the anterior 2/3 of the tongue; cranial nerve ____ mediates taste in the posterior 1/3.

Anterior 2/3 taste - VII Posterior 1/3 taste- IX

The 1st and 2nd branchial arches form what region of the tongue? The third and fourth arches?

Anterior 2/3; posterior 1/3

What other neurologic malformation is commonly associated with syringomyelia?

Chiari type I malformation (>3-5 mm cerebellar tonsillar ectopia)

Which cranial nerve supplies motor innervation to the tongue?

Cranial nerve XII

Which cranial nerves mediate the sense of pain in the tongue?

Cranial nerves V3, IX, and X

A patient has syringomyelia; which neuronal fibers of the spinal cord may be damaged?

Crossing anterior spinal commissural fibers are typically damaged first (spinothalamic tract carrying pain/temp).

The alar plate is ____ (dorsal/ventral) and contains ____ (sensory/motor) neurons.

Dorsal; sensory

A 43-year-old pregnant woman is found to have elevated α-fetoprotein. You order what other confirmatory test?

Elevated acetylcholinesterase (AChE) in amniotic fluid (fetal AChE in cerebrospinal fluid transudates across defect into the amniotic fluid)

The notochord induces _________ ________ to differentiate into neuroectoderm and form the neural plate.

Overlying ectoderm

What are the adult derivatives of the metencephalon in the developing brain? Specify derivatives from the walls vs. cavities.

Pons & cerebellum (walls), and upper part of the fourth ventricle (cavities)

What is the Dandy-Walker malformation?

Posterior fossa malformation: agenesis of cerebellar vermis with cystic enlargement of fourth ventricle (fills enlarged posterior fossa)

A neonate has a severe cleft lip and palate. Imaging shows holoprosencephaly. What signaling pathway mutation is implicated in this anomaly?

Sonic hedgehog signaling pathway

In the fetus, the failure of the bony spinal canal to close (without structural herniation) will result in what type of neural tube defect?

Spina bifida occulta

A patient has *"cape-like"* bilateral loss of pain and temperature in his arms. Imaging shows cystic enlargement of spinal cord central canal. Diagnosis?

Syringomyelia

Cranial nerves that mediate the sense of taste project to the ____ nucleus. Which CN's are they?

Taste projects to solitary nucleus: CN VII, IX, X

What are the adult derivatives of the diencephalon in the developing brain? Specify derivatives from the walls vs. cavities.

Thalamus (walls) and the third ventricle (cavities)

What adult structure is derived from the cavity in the embryonic mesencephalon?

The aqueduct

What is the adult derivative of the myelencephalon in the developing brain? Specify derivatives from the walls vs. cavities.

The medulla (walls) and the lower part of the fourth ventricle (cavities)

What happens to the amount of amniotic fluid if the fetus has anencephaly?

There is polyhydramnios due to the lack of a swallowing center in the brain; the fetus cannot swallow amniotic fluid

You see a patient who has developed loss of pain and temperature sensation in the hands, *but touch is intact.* Where is the lesion?

This describes the "cape-like" distribution of syringomyelia; this is most commonly at C8-T1

The neural plate gives rise to the neural ____ and neural ____ cells.

Tube; crest

What congenital abnormality usually occurs with a syringomyelia? How does it present in childhood/adulthood?

Usually asymptomatic in childhood, but manifests with headaches and cerebellar symptoms.

The basal plate is ____ (dorsal/ventral) and contains ____ (sensory/motor) neurons.

Ventral; motor

An neonate has a *tuft of hair* at his *lower spine.* Imaging shows failed closure of the bony spinal canal. Will the dura matter be intact?

Yes, *dura is intact*; the neonate has *spina bifida occulta* (associated with a tuft of hair or skin dimple at the level of bony defect); dura is intact

The alar and basal plates have ______ orientation as the spinal chord.

same: Dorsal (alar) is sensory, and Ventral (basal) is motor.

Syrinx means what?

tube, as in syringe

A cystic cavity within the spinal cord is called _________, but if in the central canal, it is called ______.

within spinal cord: syringomyelia within central canal: hydromyelia

In anencephaly, levels of which molecule are elevated in amniotic fluid?

α-fetoprotein

Neural tube defects are associated with low intake of what substance *before conception* and during pregnancy?

Folic acid

What adult structure is derived from the cavity in the embryonic metencephalon and myelencephalon?

Fourth ventricle

A(n) ____ is herniation of the *meninges only* through a spinal cord defect; a(n) ____ is herniation of *both meninges and spinal cord.*

Meningocele; meningomyelocele

What is the adult derivative of the mesencephalon in the developing brain? Specify derivatives from the walls vs. cavities.

Midbrain (walls) and aqueduct (cavities)

The spinal cord begins below what secondary embryological vesicle?

Myelencephalon

Describe the AFP levels during a meningocele.

Normal AFP

The notochord becomes the ____ of the intervertebral disk in adults.

Nucleus pulposus

Muscles of the tongue are derived from which myotomes?

Occipital myotomes

What are the adult derivatives of the telencephalon in the developing brain? Specify derivatives from the walls vs. cavities.

Cerebral hemispheres (walls) and lateral ventricles (cavities)

An infant has significant cerebellar tonsillar and vermian herniation through the foramen magnum with aqueductal stenosis and hydrocephalus. Diagnosis? Other findings?

Chiari II (Arnold-Chiari malformation); often presents with thoracosacral myelomeningocele and paralysis below the defect

What is the term for failure of separation of the cerebral hemispheres across the midline in a fetus?

Holoprosencephaly

An infant has cyclopia; what neural defect are you worried about?

Holoprosencephaly (most severe form)

Failure of the left and right hemispheres to separate usually occurs during what weeks? What is this called?

Holoprosencephaly usually occurs during weeks 5-6

An infant has a Dandy-Walker malformation. What other associated malformations might you find?

Hydrocephalus and spina bifida

A baby is born with anencephaly. What maternal illness increased the risk for this? Supplementation with what may have prevented it?

Maternal type I diabetes; Maternal folate supplementation decreases risk.