ABP Content Specs #2: A-C: Biological Mechanisms in Development and Behaviors Flashcards
Most common congenital malformation of CNS?
neural tube defects (improper closure of the embryonic neural tube)
Anencephaly
-underdeveloped brain and incomplete skull
-most common neural tube defects
-congenital absence of brain or parts of brain and cranium
-due to failure of cranial portion of neural tube
Spina bifida?
incomplete closing of spinal cord during 3rd nad 4th week of intrauterine development
4 types of spina bifida?
- myelomeningocele: both meninges and spinal cord in efect
- meningocele: the herniation has meninges
- myelocele: defect that has herniation with only CSF fluid
- spina bifida occulta
Arnold-Chiari malformation type II
combination of myelomeningocele (meninges + spinal cord in spina bifida defect) and cerebellar tonsil herniation
Encephalocele
-rare neural tube defect in which brain protrudes through an abnormal opening of cranium with or without meninges, leaving a projection of a bag-like structure on the head
-often with hydrocephalus
-might be result of aqueductal stenosis or torsion and may also be a post-surgical completion of ecnephalocele
What gestational week for these changes?
- Neuro-ectoderm induction
third week gestation
What gestational week for these changes?
- Neurulation?
3rd to 4th week gestation
What gestational week for these changes?
- Pro-encephalic and hemispheric formation?
5-12th week gestation
What gestational week for these changes?
- Neuronal proliferation
10-12th week gestation
What gestational week for these changes?
- neuronal migration
12-24th week gestation
What gestational week for these changes?
- Programmed neuronal cell death
28-41st gestation week
What gestational week for these changes?
- Neurogenesis
15th -20th week gestation to well into postnatal months or years
What gestational week for these changes?
- Synaptogenesis
20th week gestation to puberty
What gestational week for these changes?
- Gliogenesis
20-24th week gestation to well into postnatal years
What gestational week for these changes?
- Myelination
26th-28th week gestation to 2-3 years postnatal/post-birth
What gestational week for these changes?
- Angiogenesis
5th-10th week gestation to years after birth
Direction of closure of neural tube?
rostral to caudal
Conditions you get when you get failure of closure of rostral neural tube (anterior neuro-pore)?
anencephaly or encephalocele
condition you get when you get failure of closure of caudal (posterior neuropore) neural tube?
myelo-meningo-cele
3 parts/vesicles of primitive brain?
once neural tube closed then becomes 3 vesicle structure (primitive brain) with 3 parts:
- prosencephalon
- mesencephalon
- rhombencephalon
-happens 5-6th week gestation
5 parts of primitive brain?
- forebrain/prosencephalon –> telecephalon + diencephalon –> cerebral hemispheres, thamalus –> lateral ventricles & third ventricle
- midbrain/mesencephalon –> mesencephalon –> midbrain–> aqueduct
- Hindbrain/thombencephalon –> metencephalon + myelencephalon –> pons + cerebellum + medulla –> upper part of 4th ventricle + lower part of 4th ventricle
everything else becomes spinal cord
What causes primary microcephaly?
when you don’t et enough neurogenesis
What causes classic lissencephaly?
disorder of neuronal migration
What causes horizontal gaze palsy with progressive scoliosis?
disorder of axon outgrowth
How is folic acid and MTHFR related to neural tube defects?
-folate can help in methylation reactions in pureine and pyrimidine synthesis
-mutation in MTHFR gene (encodes enzyme methylene-tetra-hydro-folate reductase) is risk factor for NTD
-MTHFR gene enzyme regulates folate and homocysteine levels
-ppl with these defects have decreased folate levels which reduces conversion of homocysteine to methionine and increases risk of NTD
-thus give folic acid to help diminish effects of gene mutation
recommend dosing of folate during pregnancy?
400 IU/day maternal supplement of folic acid
-if mom had previous pregnancy with NTD then 4000 IU/day in month before becoming pregnant + during first 3 months of pregnancy
Microcephaly
abnormally small head and brain
-from progenitor cell proliferation and apoptosis
Macrocephaly
abnormally big head and brain
-from progenitor cell proliferation and apoptosis
Hemi-megalencephaly
overgrowth of part of a cerebral hemisphere
-from progenitor cell proliferation and apoptosis
Focal cortical dysplasia
disturbed lamination and dysmorphic neurons
-from progenitor cell proliferation and apoptosis
Lissencephaly type I
absence of normal convolutions/folds in brain (“smooth brain”)
-from neuronal migration issues (neurons didn’t reach their intended destination)
Periventricular heterotopic (PH)
neurons accumulating at the ventricles underneath a normal cortex
-from neuronal migration issues
Subcortical band heterotopia/double cortex
band of grey matter located between the lateral ventricular wall and the cortex
-from neuronal migration issues
Cobblestone lissencephaly/lissencephaly type II
overmigration of neurons to localize on the surface of a brain with reduced gyri
-from neuronal migration issues
-also assoc with hypo-plasia and malformation of cerebellum
-commonly in Walker-Walburg synrome, muscle eye brain disease, and Fukuyama-type congenital muscular dystrophy
Polymicrogyria
too many (usually small) folds/convolutions in brain; abnormal cerebral cortex with multiple small gyri
-due to neuronal organization issues
-usually due to phosphatidylinositol 3-kinase (PI3K/AKT)
-associated in conditions: chromosome 16q12-21 (polymicrogyria strongly associated with Aicardi, Delleman, DiGeroge 22q11.2 deletion, Sturge-Weber syndrome)
Schizencephaly
fluid-filled cleft from ventricles to pia lined by heterotopic grey matter
-like “split-brain” or cleft that goes between brain pia mater to ventricles
-from neuronal organization issues
Peri-ventricular heterotopic-associated most commonly with which conditions?
Afebrile seizures, EDS, Cri du Chat, and Williams syndrome
Megalencephaly
increased head size 2 SD above the mean; but technically 3 SD above mean to exclude ppl with familiar megalencephaly
Hemi-megaloencephaly?
one-sided cerebral hemisphere enlargement involving part of or whole cerebral hemisphere
-commonly seen in neurocutaneous syndromes like linear sebaceous syndrome, tuberous sclerosis, and NF-1
-often seen psychomotor retardation, intractable seizures, cranial nerve palsies, and hemiparesis
Synaptic pruning
process by which extra neurons and synaptic connections are eliminated to increase efficiency of neuronal transmissions
-get overproduction of synapses in first few years of life and then get pruning back the unused or overabundant synapses; 50% of synapses are pruned
-pruning occurs in late gestation and through adolescence
-pruning is experience driven
Synaptic plasticity
higher-level process in which the strenght of excitatory synapses is altered in response to the pattern of activity at the synapse
Neuro-plasticity?
biological capacity of nervous system to modify its structure and functioning to adapt to both physiological (learning and memory) and pathological (neuro rehab) variations in the environment
What does primary sensory area do?
-receives somesthetic, auditory, visual and gustatory stimuli from thalamus
-thalamus gets stimuli from specialized sensory organs and peripheral receptors
-olfactory pathways bypass thalamus and goes directly to specialized areas of cortex
-then sensory stimuli further processed in association areas that relate to one or more areas
What does primary motor cortex do?
-generates volitional body movements
-motor association areas help plan and execute complex motor activity
