Lec 11 Overview of CNS Development Flashcards
What are the two exceptions to the rule that entire nervous system develops from the ectoderm?
- microglia and dural mater
- both develop from mesoderm
What is gastrulation?
- induction of neural ectoderm from general ectoderm
- forms neural plate
What are the steps of CNS development?
- gastrulation [formation neural plate]
- neurulation [formation of neural tube]
- histogenesis [3 tissue layer formation]
- end neurulation [closure neural tube]
- vesicle formation
When does gastrulation happen in embryo growth?
at approximately 16 days
What is neurulation?
- development of neural tube and neural crests from neural ectoderm
What are the steps in neurulation?
- cell proliferation at margins of neural plate, created neural groove between neural folds
- cells lining groove give rise to cells of CNS
- margins of neural folds grow toward each other and fuse in midline to form neural tube
What do neural crest cells become?
PNS
- sensory ganglia of cranial and spinal nerves
- spinal sensory + motor nerves
- ANS [parasymathetic, sympathetic, enteric nervous systems]
- schwann cells
- leptomeninges [pia + arachnoid]
What does the cavity of the neural tube become?
the ventricular system
When does neural tube closure begin? finish? Does anterior or posterior end of neural tube close first?
begins ~22 days, done anterior first (26 days) then posterior (28 days)
When does neurulation start?
~ 20 days
What marks cephalic closure of the neural tube?
lamina terminalis
What does neural tube become?
CNS
- brain [cerebrum and brainstem]
- spinal cord
What is histogenesis?
- formation of 3 layered tube consisting of
1. internal ependymal layer
2. middle layer of mantle cells that will become gray matter
3. external layer that will become white matter
neurons develop from neuroblasts and migrate into the middle mantle layer
What is the lamina terminalis? Its fate?
- marks the closure of the cephalic end of neural tube
- becomes the anterior wall of 3rd ventricle
What are the 3 cephalic vesicles formed after neural tube closure?
- forebrain [prosencephalon]
- midbrain [mesencephalon]
- hindbrain [rhombencephalon]
When does neural tube formation occur in development [in wks]?
3-4 wks
What are the 5 cephalic vesicles formed at the end of wk 4 in development from the initial 3 vesicles?
from prosencephalon [fore]
- telencephalon
- diencephalon
from mesencephalon [mid]
- mesencephalon
from rhombencephalon [hind]
- metencephalon
- myelencephalon
What is the fate of the telencephalon?
becomes cerebral hemispheres
What is the fate of the metencephalon?
pons and cerebellum
What is the fate of the myelencephalon?
medulla
What are the 3 main flexures in the 5 vesicle brain?
- mesencephalic
- pontine [delineates metencephalon from myelencephalon aka pons from medulla]
- cervical [ delineates myelencephalon aka cerebellum from spinal cord]
When does procencephalic development occur in gestation [wks]?
wks 5-6
When does cortical formation occur in gestation [wks]?
wks 8-24
What is the sulcus limitans?
- shallow longitudinal groove along length of neural tube
- separates alar [sensory] and basal [motor] plots
What is the alar plate?
the dorsal half of the mantle
What is the basal plate?
the ventral half of the mantle
What does the alar plate give rise to?
- neuronal cell bodies that form nuclei that receive/relay sensory
What does basal plate give rise to?
- origin of motor neurons of spinal cord
- axons of basal plate derivatives form ventral roots of spinal nerves
Which cranial nerves are recognizable in embryo at 5-6 wks?
all but CN 1 and CN 2
How does the organization of basal and alar plates in brainstem differ from in spinal cord?
- in medulla and pons: alar plate is lateral to basal plate [rather than dorsal]
- migration of neuroblasts of both plate from ventricular floor to other locations
- special sensory + motor structures of head require new/different cell groups for innervation
Which plate do structures that are rostral to midbrain develop from?
alar plate
Which plate does the cerebellum develop from?
alar plate
What does the sulcus between telencephalon and diencephalon develop into?
horizontal transverse cerebral fissure
What does the sulcus limitans develop into?
hypothalamic sulcus
When does myelination occur in development?
- begins early in 3rdt rimester, most rapid period of myelination occurs in first 2 years of life
- ocurs early for motor-sensory roots, special senses, and brainstem
What are the 3 main stages of CNS development that can be disrupted?
- neuration [wks 3-4]
- prosencephalic development [wks 5-6]
- cortical formation [wks 8-24]
What are adult derivative of telencephalon [wall and cavities]
wall: cerebral hemispheres
cavity: lateral ventricle
What are adult derivative of diencephalon [wall and cavities]
wall: thalamus
cavity: 3rd ventricle
What are adult derivative of mesencephalon [wall and cavities]
wall: midbrain
cavity: cerebral aqueduct
What are adult derivative of metencephalon [walls and cavities]
wall: pons and cerebellum
cavity: upper part of 4th ventricle
What are adult derivative of myelencephalon [wall and cavities]
wall: medulla
cavity: lower part of 4th ventricle
What does the notorchord become?
nucleus pulposus of intervertebral disc in adalt
