embryology of the nervous system

ectoderm

sensory organs

epidermis layer

nervous system

mesoderm

dermis

muscle

skeleton

circulatory

excretory structures

endoderm

gut

liver

internal organs

respiratory system

what is the critical period when the neural tube starts to develop

week 3

neurulation

process by which the neural tube is formed

what is the order of devlopment for the neural tube

neural plate

neural groove

neural folds

neural tube

when does the neural tube develop into the brain and spinal cord

about 3 weeks

what do neural crest cells form

the peripheral nervous system

become sensory dermatomes at each level

somites

part of mesoderm

neural crest cells follow them while fetus develops

form vertebral column bodies

what are the 3 layers of the neural tube

mantle layer

marginal layer

epithelial / ventricular layer

mantle layer of neural tube

gray matter

layer of cell bodies

marginal layer of neural tube

white matter

myelinated fibers, axons

alar plate

dorsal aspect of neural tube

location of sensory info

basal plate

ventral aspect of neural tube

location of motor info

when does closure of the neural tube occur

3-3.5 weeks

what is the critical period that occurs at week 4

superior and inferior pores must close

if not there will be developmental issues

when does brain formation begin

day 28

3 primary brain vesicles

prosencephalon

mesencephalon

rhomboencephalon

when does the brain change from 3 to 5 vesicles

around 4 weeks

5 secondary brain vesicles

telencephalon

diencephalon

mesencephalon

metencephalon

myelencephalon

what 2 secondary brain vesicles are formed from the prosencephalon (forebrain)

telencephalon

diencephalon

what 2 seconday brain vesicles are formed from the rhombencephalon (hindbrain)

metencephalon

myelencephalon

what 2 brain vesicles form the brain stem

mesencephalon

rhombencephalon

when is the brain formed

~11 weeks

glial cells

support cells that nerves attach to until they find their final destination

oligodendrocytes

in CNS

create myelin

can send out arms to myelinate multiple axons / branches of axons

schwann cells

in PNS

create myelin

attach to axon and replicate

at what point of development does myelination start

4-5 months

when is myelination complete

when toddler is 2-3 years old

(part of why toddlers are still so clumsy)

anencephaly

superior neuro pore defect which causes bony defects of skull and malformation of cerebral hemispheres

typically results in miscarriage, stillbirth

spina bifida

associated with lack of closing of inferior neuro pore

varying degrees of involvement

three types of spina bifida

spina bifida occulta

meningocele

myelomeningocele

spina bifida occulta

MILD bony defect

generally lower (lumbar spine)

small gap because vertebral column did not close fully

nervous system fully in tact so no deficits associated

meningocele

bony defect with fluid filled sac on outside of infant’s back containing CSF and dura

myelomeningocele

MORE SEVERE bony defect

nerve tissue involvement as spinal cord / peripheral nerves extend into sac

dysfunction varies on level involved

typically utilize an assistive device

a lack of ______ can cause a failure of the inferior pore and lead to spina bifida

folate (vitamin B9)

microcephaly

smaller head size = smaller brain

at what point in development does microcephaly typically occur

about 4 months

toxoplasmosis

can be caused by changing cat litter, radiation, zika virus

hydrocephalus

accumulation of CSF in ventricles of the brain

clogging of cerebral aqueduct

increased pressure on brain tissue

hydrocephalus and chiara malformation

abnormal development of hindbrain

causes extension of structures into spinal canal which blocks CSF flow in vnetricles

CSF collects and builds up

causes abnormal growth of head, lethargy, difficulty feeding, cranial nerve deficits

what are 5 examples of intellectual or developmental disbalities

fetal alcohol syndrome

drug exposure in utero

cerebral palsy

down syndrome

fragile x syndrome

characteristics associated with fetal alcohol syndrome

small head

small eyes

thin upper lip

smooth philtrum

cerebral palsy

result of varying pre birth problems or time of birth problems

NOT PROGRESSIVE

down syndrome

born with additional copy of chromosome 21

affects development of brain and body

fragile X syndrome

genetic condition

causes change in protein essential to brain development

results in intellectual disability

epigenetics

impact of environmental things on gene expression

(diet, chemicals, toxins)