Exam 1 NS Development Flashcards
The two simultaneous processes in development
~morphogenesis
~histogensis
Morphogenesis
process by which the normal shape of the adult nervous system is formed
Histogenesis
the processes by which nerve cells proliferate and develop form, chemical composition, arrangement, and connections
Morphogensis begins with
Gastrulation
Gastrulation
~occurs during 3rd week of development
~produces the 3 layered embryonic disc from a single layer of blastula
The three layers formed during gastrulation are
~ectoderm- outer
~mesoderm- middle
~endoderm- inner
Mesenchymal cells (during gastrulation)
~these cells migrate
~the cells the migrate cranially in the embryo form a structure called a notochord
The phase after gastrulation during morphogenesis is
Neurulation
Neurulation is
~begins during the 4th week of development
~the notochord formed by the dranially migrated mesenchymal cells induces specialization of the overlying ectoderm to form the neural plate
~ectoderm proliferation produces infolding of the neural plate and formation of neural groove
Neural groove in neurulation
~the neural groove deepens with upper cells referred to as neural crest cells
~the neural groove seals off forming the neural tube with separate neural crest cells
~surrounding or peraxial mesoderm forms somites
Central lumen of neural tube forms (during neurulation)
~neural (ependymal) canal, which becomes ventricular system
thickening wall of neural tube becomes (during neurulation)
brain and spinal cord
Neural crest cells develop into
~peripheral ganglia (autonomic and dorsal root)
~cells of adrenal medulla
~peripheral glia- Schwann and satellite cells
Neural tube cells develop into:
~CNS neurons (pyramidal, stellate, purkinje, spinal motor neurons)
~CNS glia cells (astrocytes, oligodendroglia, microglia, ependymal cells)
Neurons will migrate to their final position in the neural structure by two principal mechanisms of migration:
~Radial migration
~Tangential migration
Radial migration
~occurs from the “inside-out” from ventricular germinal zone to pial layers (meninges)- cortical plate
~the first migration to deeper layer with later migration passing early migration to end more superficially
Radial migration (3 forms)
~somal (perikaryal)
~glial-guided
~branching
Radial migration- Somal translocation
~the neuron first sends apical dendrite to pial surface
~cell pulls its cell body up behind the apical dendrite t final level to which the cell body migrate
~generally occurs in early migration to lower layers
Radial migration- Glial-guiding translocation
~form of radial migration the glial cells link the germinal zone to the cortical plate (outer level)
~neuron then pull itself up along the glial path
~by this mechanism that the later migration to more superficial layers
Radial migration- Branching translocation
~only recent been describe and differentiated as specific form of somal translocation
~neuron apical dendrite branches and the neuron soma follows one branch while others degenerate
Neurulation- openings
~Neural canal rostral opening
~Posterior opening
Neurulation- Rostral openings
~anterior (rostral) neuropore
~close on day 25
Neurulation- Posterior openings
~posterior (caudal) neuropore
~closes on day 27
Neural Tube Defects (3)
~Spina Bifida
~Arnold-Chiari Malformation
~Anencephaly
Spina Bifida
~Defective closure of the caudal neural pore
~often occurs with other congenital anomalies
~incidence declining with early prenatal detection and dietary supplement folic acid
Spina Bifida (severity)
~Spina bifida oculta
~Spina bifida cystica
~Spina bifida with meningocele
~Spina bifida with myelomeningocele
Spina bifida oculta
~defect is confined to the vertebral arch
~no clinical symptoms
~it may be marked by tuft of hair on overlying skin
Spina bifida cystica
~occurs when there is a herniation through the vertebral defect
~in 2 forms (spina bifida with meningocele and myelomeningocele)
Spina bifida with meningocele
~herniation of the meninges but no neural structures through the vertebral defect
~may be without symptoms or the symptoms might be quite mild
Spina bifida with myelomeningocele
~when there is a protrusion of both spinal cord and meninges through the vertebral deficit
~symptoms may include (saddle anesthesia, paralysis of bladder and bowel sphincters, paralysis of lower limbs)
Arnold- Chiari Malformation
~associated often with spina bifida with meningomyelocele
~congenital anomaly with medulla and posterior cerebellum
~may be asymptomatic
~may result in hydrocephalus and other symptoms
Anencephaly
~congenital anomaly that results from a failure of rostral neuropore closure
~large portion of scalp, cranial bones, and cerebral hemisphere are absent
~most die in utero, virtually all by first postnatal week; some cases that survive into childhood
The next stage of morphogenesis after neurulation is
vesiculation
What three primary vesicles are formed during vesiculation and what week are they formed?
~prosencephalon
~mesencephalon
~rhombencephalon
*week 6
What are the 5 secondary formed during vesiculation and what week are they formed?
~telencephalon ~diencephalon ~mesencephalon ~metencephalon ~myelencephalon *week 8
Prosencephalon forms:
~telencephalon
~diencephalon
Rhombencephalon forms:
~metencephalon
~myelencephalon
Telencephalon forms:
~cerebral hemispheres
~the lateral parts of the basal nuclei (ganglia)
Diencephalon forms:
thalamus and hypothalamus along with the more medial aspects of the basal nuclei
Mesencephalon forms:
midbrain
Metencephalon forms:
~pons
~cerebellum
Myelencephon forms:
medulla
The brain flexures into (4)
~Cervical flexures
~Pontine flexures
~Cephalic flexures
Cervical flexure
~the junction of spinal cord and rhombencephalon
~disappears as head becomes upright
Pontine flexure
~the junction of metencephalon and myelencephalon widens brainstem shape
~forms the rhomboencephalic sulcus on dorsum of brainstem which forms 4th ventricles
Cephalic flexure
~the junction of metencephalon and mesencephalon
~persists in mature CNS
~represents the bend of the forebrain on the brainstem
Development of Lateral and 3rd Ventricles
~obvious in their form n the 12th week
~3rd shrinks with medial expansion of diencephalon and flattens
Development of 4th Ventricle
~forms is seen as rhombencephalon
~widens and flattens from the pontine flexture
~forms between the thickened brainstem and thin membranous rook
Development of Cerebral Aqueduct
~pinched down into a thin tube through the mesencephalon with the development and thickening of the midbrain
basis of development has _ layers (and what are they)
3
~ependymal
~mantle
~marginal
Ependymal layer during development
germinal layer
Mantle later during development
neuroblasts and glioblasts migration and for differentiation into different types of neurons and glia respectively
Marginal layer during development
cells sparse layer into which axon grow forming ascending tracts
What are the two plates that are best seen during development?
Alar and Basal plate
What separates the alar and basal plates?
the lateral longitudinal groove called the sulcus limitans
Alar Plate
develops into sensory neurons
Basal Plate
develops into motor neurons
basis of development of the spinal cord
~sensory neurons of alar plate develop into dorsal horn
~axons from these cells project out into the marginal zone and ascend
~motor neurons of basal plate develop into ventral horn (somatic efferents) and lateral horn (autonomic efferents)
~ Axons from both form the ventral root of the spinal cord
In the medulla and pons, the Alar and Basal plates are pushed (dorsally or ventrally) by _____ producing the _________
Alar and Basal plates pushed ventrally by the developing rhomboid fossa which produces the 4th ventricle and a thin ependymal layer dorsally
In the medulla, neurons in the alar plate become
somatic and visceral sensory nuclei
In the medulla, neurons in the basal plate become
somatomotor and visceromotor nuclei and inferior olivary nucleus (motor related)
In the pons, neurons in the alar plate become
develop into dorsolateral sensory “tegmentum” (sensory nuclei)
In the pons, neurons in the basal plate become
develop more medial and ventral basilar region again forming motor nuclei of the motor components of the cranial nerves and the pontine nuclei (motor related)
Development of the cerebellum- if formed by thickening of
thickening of rostral metencephalon to form rhombic lips
Development of the cerebellum- projects
projects above the roof plate (extraventricular) and partly into the 4th ventricle (intraventricular)
Development of the cerebellum- Extraventricular
Extraventricular portion of the cerebellum from each side fuse – with the Unpaired central portion forms the vermis and the bilateral portions forming the cerebellar hemispheres
Development of the Mesencephalon- the alar plate forms…
the “tectum” with the superior colliculus and periaqueductal gray regions
*sensory functions
Development of the Mesencephalon- the basal plate forms…
forms the tegmentum which contains the oculomotor nucleus, red nucleus, and substantia nigra (motor nuclei)
Development of the Mesencephalon- the cerebral peduncle develops..
develops from marginal layer of the mesencephalon as axons from the cerebral cortex pass through this area
Diencephalon arises from
the alar plate
*most of the thalamic nuclei are sensory relay nuclei
Hypothalamus and Subthalamus arise from
the basal plate
*they are automonic and somatic motor in function
Epithalamus arises from
the thin roof plate
Development of the Telencephalon- the cerebral cortex is formed by
the great expansion of the dorsal component of the telecephalic vesicles
Development of the Telencephalon- The insula, temporal lobes, and basal nuclei are formed by
formed by ventral expanse of this growth of the dorsal component
Development of the Telencephalon- what is the only connection between the right and left developing hemispheres?
the lamina terminalis (site of closure of anterior neuropore)
*axons forming all connecting commissures project through the lamina terminalis
Development of the Telencephalon- the basal nuclei grow around …
diencephalon
Development of the Telencephalon- axons forming internal capsule project through the …
~basal nuclei separating the caudate nucleus form the lentiform nucleus (putamen and globus pallidus)
~between the diencephalon and the expanding telencephalic basal nuclei to become the cerebral peduncle
Development of the Telencephalon- sulci and gyri (details)
~infolding of sulci and gyri form because rapid growth and limited space within forming skull
~sulci and gyri apparent about 7 months
Somites
~during 3rd week, the mesoderm just lateral to neural tube differentiates into somites that relate to developing neural tube
3 parts of somites
~dermatome
~myotome
~scleromtome
Somite- dermatome
develops into dermis of the skin
Somite- myotome
develops into striated muscle
Somite- Sclerotome
develops into vertebrae and ribs
