Nervous system development Flashcards
What is the diff b/w ganglion and nucleus?
Ganglion is a collection of cell bodies located outside of CNS (in PNS), while nucleus is located w/in the CNS
What does the brainstem consist of?
Medulla, pons, midbrain
The cerebellum has been largely viewed as a component of the __ sytem, but it has a wide range of functions including __ and __.
The cerebellum has been largely viewed as a component of the motor system, but it has a wide range of functions including learning and memory.
What does the diencephalon consist of?
What about the telencephalon?
Thalamus, Hypothalamus, and epithalamus;
striatum and cerebral cortex
What are the major lobes of the cerebral cortex/neo cortex?
occipital, parietal, temporal, frontal,
also post-central, orbito-frontal, cingulate
The neocortex is a 6-layered structure. In the sensory cortex, inputs from the thalamus largely target cells in what layer?
layer 4
The cerebral hemispheres are interconnected through what 3 major pathways?
Corpus callosum, anterior commissure, and posterior commissure.
In the 3rd wk, inductive factors from where cause the transformation of the surface ectoderm into the neural plate?
Notochord and paraxial mesenchyme.
What is primary neurulation and when does it happen?
Neural folds and a midline neural groove forms in the neural plate in the region of the 4th thru 6th somites. This happens in 4th wk days 22-23
Closure of the neural tube proceeds bidirectionally. When and where is the first closure?
Day 22 in the region of the 5th somite.
NOTE: neural tube closure occurs at up to 5 diff places and abnormal closure of different sites results in neural tube defects.
How is the caudal most portion of the neural tube formed?
When is this completed?
By secondary neurulation of the caudal eminence NOT the neural plate.
Secondary neurulation is completed by wk 8.
Failure of fusion of the neural rube and vertebral arches are defects collectively known as…
Spina bifida
Defects in the closure of the rostral neuropore results in what?
Defects in the closure of the caudal neuropore results in what?
Incomplete development of the brain, calvaria, and/or face;
Different types of spina bifida
What is microencephaly?
A severe form of rostral neural tube defect in which portions of the cranium fail to form w/ resulting defects in brain development.
Typically forebrain, midbrain, and portions of hindbrain fail to form.
Describe the different severities of spina bifida.
- Spina bifida occulta: failure of fusion of vertebral arches (L5 or S1). Indicated by a small dimple w/ a patch of hair
- Spina bifida cystica meningocele: spinal cord in normal position but a meningal sac protrudes thru the defect
- Spina bifida cystica meningomyelocele: spinal cord and nerve roots also protrude thru the vertebral defect
- Spina bifida myeloschisis: most severe form, the neural tube failed to fuse resulting in a flattened neural mass directly exposed to amniotic fluid.
Which neural crest cells migrate just deep to the ectoderm w/in the loose mesoderm?
Cephalic neural crest cells
What is neurofibromatosis?
What is neuroblastoma?
Peripheral nerve tumors;
Tumor of the adrenal medulla, autonomic ganglia
The ___ of the neural plate forms the spinal cord.
Caudal 1/3
What is the ventricular zone?
The neuroepithelial layer adjacent to the central canal (the lumen of the neural tube) and contains precursor cells that give rise to all of the neurons and macroglia of the spinal cord.
The primordial neurons migrate from ___ to ___.
the ventricular zone to the intermediate zone.
What is the sulcus limitans?
Where does it extend through?
It is a shallow longitudinal groove in the lateral walls of the neural tube that separate the developing gray matter into a dorsal alar plate and ventral basal plate.
The sulcus limitans extends the length of the spinal cord through the mesencephalon (midbrain).
Neuronal cell bodies in the alar plate form:
nuclei that constitute the dorsal gray matter that receive and relay input from afferent (sensory, somatic, and visceral) neurons
Neuronal cell bodies in the basal plate form:
The ventral gray matter or efferent neurons. Axons of these neurons project motor fibers to skeletal m. and form the ventral roots of the spinal n.’s
Describe how ventral and dorsal roots of the spinal nerves come about.
The ventral roots are motor fibers that extend from the basal plate. The dorsal roots arise from the developing spinal ganglia and join w/ the ventral roots.
The spinal n.’s branch to form the dorsal and ventral primary rami.
At wk __, the spinal cord extends the full length of the vertebral column. In adults, the spinal cord ends at the level of __. This results in the formation of the __.
At wk 8, the spinal cord extends the full length of the vertebral column. In adults, the spinal cord ends at the level of L1-L2. This results in the formation of the Cauda equina (which consists of the long dorsal/ventral roots that descend to their original vertebral levels.
Where are SHH and BMP secreted?
SHH: by notochord and subsequently by the floor plate of the neural tube
BMP: by ectoderm over dorsal neural tube, which then sets up a secondary cetner in the roof plate of the neural tube
How do the opposing gradients of BMP and SHH control the fate of neuroblasts in the developing neural tube?
Neuroblasts exposed to hight SHH and low BMP will differentitate into motor neurons.
Neuroblasts exposed to low SHH and high BMP will differentiate into sensory neurons
What are the 3 primary vesicles of the brain and by what day are they apparent?
Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain);
Day 26
During the 5th wk, the prosencephalon (1,2)and rhombencephalon (4,5) each subdivide, contributing to 5 secondary vesicles. Name them and what the neural canal in each vesicle becomes definitively.
- Telencephalon: lateral ventricles
- Diencephalon: third ventricle
- Mesencephalon: aqueduct of Sylvius
- Metencephalon: (see 5)
- Myelencephalon: fourth ventricle (w/ 4)
What are the 3 main flexures and what do they become?
NOTE: They all appear during week 5.
- Cervical flexure: forms b/w rhomboencephalon and spinal cord: develops thru wk 8 but doesn’t persist in adule
- Cephalic flexure: forms at level of future midbrain: persists in adult as a bend b/w brainstem and forebrain
- Pontine flexure (AKA dorsal flexure): forms b/w metencephalon and myelencephalon: causes walls of myelencephalon to spread apart and results in the thinned roof of the 4th ventricle, doesn’t persist in adult, but plays an important role in the development of the cerebellum and pons.
A pair of dorsal root ganglia develops at every spinal segment, except at:
1st cervical, and 2nd & 3rd coccygeal levels
What are postganglionic parasympathetic neurons derived from?
from neural crest cells originating from the occipito-cervical region of the neural tube
Parasympathetic ganglion cells to the most inferior portion of the gut have 2 origins. What are they?
Occipito-cervical neural crest and sacral neural crest cells
What are the sympathetic chain ganglia derived from?
How many sympathetic ganglia are there in the cervical and coccygeal region?
From spinal neural crest cells that migrate to a position ventral to the developing dorsal root ganglia.
3 ganglia in cervical, 1 gangion in coccygeal region.
Which neurons are the first to send axons into the periphery?
Neurons in the ventral (motor) columns of the spinal cord
cells of the neuroepithelium differentiate into:
Where does this occur?
neurons, glia, and ependyma of the CNS;
Differentiation begins in the rhombocephalic region just after neural tube closure in that region
The layer of proliferating cells that line the central canal of the neural tube is called the __.
The first cells produced by the ventricular layer are the __ that migrate to from the __ layer. Processes that extend from this form a third layer, the __, which is a layer that contains no __ and becomes __.
The layer of proliferating cells that line the central canal of the neural tube is called the ventricular layer.
The first cells produced by the ventricular layer are the neuroblasts that migrate to from the mantle layer. Processes that extend from this form a third layer, the marginal__ zone, which is a layer that contains no cell bodies and becomes white matter.
After neuroblast formation __ differentiate from the epithelial lining of the neural canal.
What do they become?
Glioblasts; They become astrocytes and oligodendrocytes
After glioblast differentiation, the neuroepithelial layer will differentiate in place to form the __.
Ependymal cell lining of the ventricles and central canal of the spinal cord.
Initially neuroblasts are __, and once they differentiate into neurons they lose their ability to __.
non-polar; divide
What cells myelinate axons in the PNS and CNS?
Schwann cells; oligodendrocytes
What becomes of the ependyma (which is from the neuroepithelium)?
It becomes the epithelium of choroid plexus.
