Chapter 3: Nervous System Development

when does dorsal induction occur?

at 3-7 weeks gestational age

what happens during dorsal induction?

• neural plate is formed and becomes the neural tube

• brain and spinal cord develop out of the neural tube

what are neural tube defects?

• encephalocele

• anencephaly

• spina bifida

neural tube defects occur as a result of…

neural tube ends failing to close

encephalocele

when part of the brain protrudes from the skull

anencephaly

brain development ceases at brainstem; child without hemispheres

spina bifida

cyst on back that may or may not involve the spinal cord

when does ventral induction occur?

at 2-3 mos gestational age

what happens during ventral induction?

face and brain develop out of the neural tube; cerebral hemispheres divide

what are ventral induction defects?

• alobar form

• semilobar form

• lobar form

ventral induction defects occurs as a result of…

holoprosencephaly (failure of brain cleavage)

alobar form

no cleavage at all resulting in no distinct cerebral hemispheres; no corpus callosum

semilobar form

some cleavage and development of right and left hemispheres but incomplete; no corpus callosum

lobar form

least severe; brain looks normal but has abnormal connections between hemispheres

when does neural proliferation occur?

at 3-4 mos gestational age

what happens during neural proliferation?

• period of neurogenesis = birth of new neurons

• born out of spinal cord and brainstem

interruptions in neural proliferation may result in ______________

microcephaly

microcephaly

children have abnormally small heads/brains

when does neuronal migration occur?

at 3-5 mos gestational age

what happens during neuronal migration?

new neurons move to their correct position in the cerebral hemispheres

• chemical reeling signals neurons where to stop

what are neuronal migration defects?

• schizencephaly

• lissencephaly

neuronal migration defects occur as result of…

neurons failing to migrate to proper places due to a lack of reeling

schizencephaly

clefts in the cerebral hemispheres

lissencephaly

smooth brain that lacks characteristic sulci and gyri

when does cortical organization and synapse formation occur?

at 5 mos gestational age to years postnatal

what happens during cortical organization and synapse formation?

• neurons sprout dendrites and axons

• synaptogenensis

• synaptic pruning

what is synaptogenesis?

synapses begin to form between neurons

when does myelination occur?

occurs from the very beginning and continues as we grow

what happens during myelination?

neuron axons coated with myelin

when does myelination peak? what does this mean?

• peaks about 1 year postnatal

• gain greater control of body and begin to develop the ability to communicate verbally

what are myelination defects?

hypomyelination

hypomyelination

a reduced ability to form myelin resulting in intellectual disability