AN64.1-3 | Histology & Embryology (Neuroanatomy) — Glossary

Thickened neuroectoderm induced by the notochord at week 3 (days 18-19); the first stage of nervous system development

Structure formed by fusion of neural folds; gives rise to the entire CNS (brain and spinal cord); closes by week 4

Cells migrating from the junction of neural and surface ectoderm; form DRG, autonomic ganglia, Schwann cells, melanocytes, adrenal medulla, and pharyngeal arch cartilage

Anterior opening of the neural tube; closes on day 25; failure causes cranial NTDs (meningocele to anencephaly)

Posterior opening of the neural tube; closes on day 28; failure causes spinal NTDs (spina bifida occulta to myelomeningocele)

Absence of the skull vault and cerebral hemispheres from failure of cranial neuropore closure; incompatible with life

Most severe open spinal NTD; spinal cord and nerve roots herniate into a sac; causes paralysis and bladder dysfunction; >90% have Chiari II

Herniation of cerebellar tonsils, vermis, and medulla through the foramen magnum; causes hydrocephalus; associated with myelomeningocele

Large flask-shaped neuron forming a single layer in the cerebellar cortex; GABAergic inhibitory output; the only output neuron of the cerebellar cortex

Most numerous neuron in the CNS; located in the inner cerebellar cortical layer; excitatory (glutamate); sends parallel fibres to the molecular layer

Giant pyramidal neuron in layer V of the primary motor cortex; largest neuron in the CNS; gives rise to the corticospinal tract

Granular cortex with prominent layer IV rich in small granule cells; characteristic of primary sensory areas

Primary visual cortex (area 17); named for the line of Gennari, a visible stripe in layer IV from dense myelinated thalamocortical fibres

Elongated glial cells extending from ventricular zone to cortical surface; serve as scaffolds for migrating neurons during cortical development

Pattern of cortical development where earliest neurons settle in deepest layers and later neurons migrate past them to superficial layers

Smooth brain without gyri and sulci from failure of neuronal migration; causes severe intellectual disability and seizures

B-vitamin essential for DNA synthesis; 400 mcg daily periconceptional supplementation reduces NTD risk by 70%

Maternal serum alpha-fetoprotein; elevated in open NTDs (AFP leaks from exposed neural tissue); used as a screening marker

Secondary brain vesicle from the prosencephalon; develops into the cerebral hemispheres, basal ganglia, and hippocampus; cavity becomes the lateral ventricles

Embryonic midline structure that induces neural plate formation; remnants persist as the nucleus pulposus of intervertebral discs

Aggregations of rough endoplasmic reticulum in neuronal cell bodies; prominent in large motor neurons; absent in the axon and axon hillock

Dense area of small neurons at the tip of the posterior horn (Rolando); modulates pain transmission; site of action of endorphins and enkephalins