12a - Neuro: embryology

Alar plate, basal plate

Alar plate = dorsal, sensory Basal plate = ventral, motor

Tongue: sensory, taste

Anterior 2/3 taste = CN VII (facial) Anterior 2/3 sensory = CN V3 (trigeminal) Posterior 1/3 taste + sensation = CN IX (glossopharyngeal) Extreme posterior taste + sensation = CN X (vagus)

Syringomyelia

Cystic cavity within central canal of spina cord. Fibers crossing the anterior white commissure are typically damaged first. Will result in cape-like bilateral loss of pain and temp sensation in upper extremities. Associated with Chiari malformations.

NCC - adult derivatives in nervous system

PNS neurons, Schwann cells

NT defects

Persistent connection between amniotic cavity and spinal canal d/t neuropore failure to close. Associated with low folic acid levels. Dx: will see inc AFP in amniotic fluid and maternal serum; inc AChE in amniotic fluid (fetal AChE flow through defect from CSF)

Metencephalon: adult derivative

Pons, cerebellum; upper part of fourth ventricle

Primary vesicles of the developing brain

Prosencephalon (forebrain): telencephalon, diencephalon Mesencephalon (midbrain) Rhombencephalon (hindbrain): metencephalon, myelecephalon

Diencephalon: adult derivative

Thalamus, hypothalamus; third ventricle

Spina bifida occulta

Failure of bony spinal cord to close, but no herniation. Seen at lower vertebral levels. Dura is intact. Associated with tuft of hair, skin dimple at the level of the bony defect. Normal AFP (no direct opening).

Holoprosencephaly

Failure of left and right hemispheres to separate; occurs during weeks 5-6. May be related to mutation in sonic hedgehog pathway. Moderate form has cleft lip/paalte. Most severe form is cyclopean. Seen in Patau syndrome (trisomy 13) and FAS.

Meningocele

Meninges (but not neural tissue) herniate through bony defect.

Meningomyelocele

Menings and neural tissue herniate through bony defect.

Mesoderm - adult derivatives in nervous system

Microglia (macrophages in CNS)

Mesencephalon: adult derivative

Midbrain, aqueduct

Neural development

Notochord induces overlying ectoderm to differentiate into neurectoderm and form neural plate. Neural plate gives rise to neural tube and NCC. Notochord becomes nucleus pulpous of intervertebral dic in adults

Tongue: motor innervation

CN XII (hypoglossal) = hyoglossus, genioglossus, styloglossus mm CN X (vagus) = palatoglossus (elevates posterior tongue, initiates swallowing)

Neuroectoderm - adult derivatives in nervous system

CNS neuron, ependymal cells, oligodendroglia, astrocytes

Chiari I malformation

Cerebellar tonsillar ectopia > 3-5 mm. Congenital; usually asymptomatic in childhood; manifests w headaches and cerebellar sx in adulthood. Will present LATER than Chiari II.

Telencephalon: adult derivative

Cerebral hemisphere, lateral ventricles

Dandy-Walker syndrome

Genesis of the cerebellar vermis with cystic enlargement of 4th ventricle. Fills the enlarged posterior fossa. Associated with noncommunicating hydrocephalus, spina bifida.

Chiari II malformation (Arnold-Chiari)

Herniation of low-lying cerebellar vermis through foramen magnum with aqueduct stenosis = hydrocephalus. Usually associated with lumbosacral meningomyelocele. (Presents earlier than Chiari I and is more severe.)

Anencephaly

Malformation of anterior NT - leads to no forebrain, open calvarium. Findings: inc AFP, polyhydramnios (can't swallow it, so it builds up!). Associated with maternal type I diabetes.

Myelencephalon: adult derivative

Medulla, lower part of fourth ventricle.