9. Development of the Nervous System Flashcards
Gastrulation occurs during week 3 and a primitive streak forms with a primitive node, groove, and pit along with the notochordal process. What does this become? (2)
Template for formation of vertebral column
Induce formation of the neural plate
Neurulation begins day 22-23 and notochord release sonic hedge hog which induces formation of neural plate (ectoderm), including?
Neural groove, folds, and NEURAL TUBE (primary neurulation)
As primary neurulation continues, the rostral and caudal neuropore form and fuse at what times?
Rostral at day 25
Caudal at day 28
Closure forms definitive neural tube
Secondary neurulation occurs days 20-42, and is when the caudal eminence fuses with ________ to form what?
Caudal neuropore to make sacral/coccyx regions
What will the neural tube/primary neurulation produce?
From brain to lumbar spinal cord
The neural tube from neuroectoderm forms many things, including neurons, astrocytes, oligodendrocytes and ependymal cells/epithelium of choroid plexus. What is the only cell of the nervous system not made from this?
microglial cells, which is phagocytic and is made from mesoderm and derived from monocytes/mesenchymal cell
The brain forms from the neural tube caudal to the fourth somite (mesoderm). What are the three primary brain vesicles?
Prosencephalon- forebrain
Mesencephalon - midbrain
Rhombencephalon - hindbrain
During the 5th week, the prosencephalon and rhombencephalon (fore/hindbrain) will divide into?
Fore: telencephalong and diencephalon
Hind: metencephalon and myelencephalon
The cervical flexure divides the hindbrain from the spinal cord, what does the pontine flexure divide?
the hindbrain into caudal myelencephalon and rostral metencephalon
What does the cephalic flexure bend between?
midbrain and forebrain
The basal ganglion and cortical structure inside is developing between what weeks?
6 to 32
What forms the following: cerebral cortex, subcortical white matter (internal capsule), olfactory bulb and tract, basal ganglia, amygdala, and hippocampus?
telencephalon
What forms the following: thalamus, hypothalamus, epithalamus, subthalamic nucleus and eyes (optic nerve)?
diencephalon
What forms the following: cerebral peduncles, superior and inferior collilculus, and CN II?
Mesencephalon/Midbrain
What forms the following: cerebellum and pons?
metencephalon
What forms the following: medulla oblongata, olive, pyramid?
myelencephalon
What results from incomplete separation of cerebral hemispheres, associated with facial abnormalities, reduction of FNP (frontonasal prominence) and hypotelorism (eyes close together)?
holoprosencepahly (HPE)
What are the three main causes of holoprosencephaly?
genetic AND environmental factors
maternal diabetes
teratogens (alcohol)
What are some of the common clinic features of HPE? 6
microcephalu, micropthalmia, cleft palate/lip, intellextual disability, epilepsy and hydrocephalus
The pituitary gland is formed from first arch of surface ectoderm from the roof of the mouth. Which contributes to what part?
anterior lobe known as rathke’s pouch (hypophysial diverticulum)
The posterior lobe of the pituitary gland is from neuroectoderm and is from the diencephalic floor. How do anterior and posterior meet?
Rathke’s pouch migrates up and fuses with neurohypophysial diverticulum, stalk of rathke’s pouch degrades
The neural tube caudal to 4ths somite will form the neural/central canal as well as the sulcus limitans which separates what?
alar plate from basal plate
What do the alar and basal plate form?
alar: dorsal horn/sensory neurons in CNS
Basal: motor neurons to skeletal M, presynpatic autonomics
The neural/central canal has three different zones, ventricular (directly around canal), intermediate and marginal. What are the main contents of each?
Ventricular Zone: Stem cell, ependymal, choroid plexus cell
intermediate: neurons, glioblast, astrocyte (gray matt)
Marginal: Oligodendrocyte
Sulcus limitans separates alar and basal plate, at the pontine flexure, it pushes what?
the alar laterl and basal plate medial
*this is why GVE/GSE/SVE are medial and GVA/SVA/SSA/GSA (sensory) are lateral
Where do the hypoglossal nucleus, dorsal motor vagal nuclesu and nucleus ambiguus in the myelencephalon are from what?
basal plate
the vestibular, cochlear nuclei, spinal trigeminal tract and nucleus, and solitary nucleus in the myelencephalon are from what plate?
Alar plate
The facial, trigeminal, and superior salivatory nuclei and abducens nucleus in the metencephalon are from what?
basal plate
Within the mesencephalon where do the red nucleus, oculomotor nucleus, trochlear nucleus and edinger westphal nucleus come from what plate?
Basal plate
Where do the lateral ventricle, 3rd, 4th ventricles, and cerebral aqueduct come from?
lateral ventricle: telencephalon
3rd ventricle: diencephalon
4th ventricle: metencephalon AND myelencephalon
Cerebral aqueduct: mesencephalon
Choroid plexus lines all the ventricles and produces CSF, how does CSF leave the 4th ventricle?
2 lateral foramina of luschka
1 medial foramen of magendie
How does fluid go from lateral ventricle to 3rd ventricle?
interventricular foramen of monroe
The lateral ventricle is split into 3 horns, what are they?
frontal/anterior horn
temporal/inferior horn
occiptal/posterior horn
What abnormality is associated with chiari type 1 malformation, where there is excess fluid in the central canal, most commonly WITHIN the SC between C2-T9?
Syringomyelia
What is characteristic of spastic cerebral palsy, due to excess fluid?
toe walking with a scissor gait, often with forearms out to gaurd from falling
What is characteristic of athetoid cerebral palsy?
slow writhing movements of the extremities/trunk
What is ataxic cerebral palsy?
incoordination, weakness and shaking during voluntary movement (drunken sailor)
What malformation occurs when there is deformity of the hindbrain where herniation of cerebellar tonsils go through the foramen magnum, commonly seen with syringomyelia?
Arnold Chiari Type 1 malformation
What malformation occurs when there is herniation of the medulla and cerebellum through the foramen magnum, ALWAYS has hydrocephalus (and spina bifida)?
Arnold Chiari Type II malformation
Type 1 chiari is associated with head and neck pain and lower cranial nerve problems. What about Chiari type II?
Lower cranial nerve problems (tongue, facial M, lateral eye movement, decreased hearing, dizziness, sternocleidomastoid paralysis, and coordinating movements)
What is most commonly seen with Chiari type I?
syringomyelia which is excess CSF within the SC in the spinal canal
Chiari type II can be diagnosed via MRI, by herniation seen through the foramen magnum and what else?
Myelomeningocele (spina bifida with spinal cord and tissue)
Dandy Walker Malformation (Cyst) is a large posterior fossa cyst continuous with the 4th ventricle, hypoplasia and atresia of what can be seen?
Hypoplasia of the cerebellum, and sometimes vermis
Atresia of foramina of luschka and magendie
What has an unknown cause but is thought to be due to the obstruction of blood flow to the areas supplied by internal carotid arteries?
hydranencephaly (no cortex, SC in tact)
Up until 5months, the brain is smooth and there are no sulci or gyri. What is the reason for gyri and sulci?
to increase SA while decreasing size
What is the insula covered by?
operculum = frontal parietal and temporal lobes
Lamina IV of the cerebrum receives the majority of what?
inputs from the thalamus (SENSORY)
Lamina V of the cerebrum projects mostly to subcortical structures such as?
brainstem, spinal cord, and basal ganglia (MOTOR)
Cytodifferentiation of the cerebrum is done from the inside-out. first neurons are produce in the ventricular zone. what are the next two steps?
- From VZ, a superficial layer is formed called the Preplate
- Axons from these neurons in VZ form intermediate zone
Once the VZ, intermediate and preplate are made, neurons that are to be born migrate into the middle of the preplate and divide into three parts known as ?
marginal zone
cortical plate
subplate
The to be born neurons migrate radially from VZ and intermediate zone using radial glial cells. What is the order of formation of the laminae of the cerebrum?
VI , V then IV , III , II, one is from the marginal zone
Lissencephaly or agyria (smooth brain) is due to what?
incomplete or failure of neuronal migration during weeks 12-24
What is characterized by microcephaly, ventriculomegaly, large sylvian fissures and agenesis of the corpus callosum?
Lissencephaly/agyria
What sign has two major mechanisms of abnormal or lack of brain development or injust or insult to a previously normal brain?
microcephaly (SIGN NOT DX)
What are some things that cause microcephaly? 4
genetic
prenatal/perinatal brain injury
craniosynostosis
Postnala brain injury
The cerebellum is old so there are only three layers. Cells from the ventricle migration and proliferate to form deep cerebellar nuclei and purkinje cells. What happens at the external germination center of the cerebellum during cytodifferentiation?
migrate over purkinje/deep cerebellar nuclei, then cells from external germ center migrate back in and form the granule cells, making the cerebellum
What are the layers of the cerebellar cortex?
molecular layer purkinje cell layer granular layer white matter cerebellar nuclei
While the alar plate gives sensory in the CNS via surface ectoderm, what gives rise to spinal ganglion cells and sensory neurons in the periphery?
Neural Crest cells
What is the difference between length of spinal cord between newborn and adult?
Newborn: L2/L3
Adult: L1/L2
Neural crest and ectodermal placode form the?
PNS
What do these develop from: neurons of dorsal root ganglia, sensory ganglia of cranial nerves, schwann cells, and sympathetic ganglia?
NEURAL CREST
preganglionic in CNS from Neuroectoderm
Myelination forms during late fetal period and continues through first postnatal year. What myelinates the CNS and PNS?
CNS: oligodendrocytes, starting in lower brain stem at mo 6
PNS: schwann cells, motor roots first at 4mo
Spina bifida is due to failure of closure of caudal neuropore = no formation of vertebral lamina. What is characteristic of the following: Spina bifida oculta meningocele meningomyelocele myelocele
Spina bifida oculta: tuft of hair
meningocele: sac with dura mater
meningomyelocele: sac with dura mater and spinal cord outside the body
myelocele: spinal cord is open to the back
Anencephaly (no closure), encephalocele with brain tissue, encephalocele without brain tissue are all caused due to?
failure of the rostral neuropore to fuse/close during day 25
