What is the critical period for development of the CNS?
Weeks 3-16
When during gestation is the nervous system sensitive to teratogens?
Almost all of gestation
Neurulation is the process of…
Forming the neural tube
Gastrulation occurs during which week of gestation?
Week 3
Gastrulation begins with the appearance of the ______________________
Primitive streak
During gastrulation, cells of the epiblast migrate towards the ____________________. What happens once it gets there?
Primitive streak
Cells of the epiblast
All three germ layers are derived from ____________________
Epiblast
Where is the notochord found?
Between ectoderm and endoderm
The notochord gives rise to the __________________
Nucleus propulsus
The ___________________ gives rise to the nucleus propulsus
Notochord
How is the neural plate derived?
The ectoderm overlying the notochord thickens into the neural plate
The dorsal view of the trilaminar embryo shows the ____________________ superiorly
Neural plate
_________________ is the name of the process of folding that results in a closed tube of neuroectoderm
Neurulation
What is neurulation?
Process of folding that results in a closed tube of neuroectoderm
What happens 16-18 days post-fertilization?
Formation of neural plate
When in gestation does formation of neural plate occur?
16-18
What happens 19-20 days post-fertilization?
Neural folds elevate
When in gestation does neural folds elevate?
19-20 days
What happens 21-24 days post-fertilization?
Fusion of neural folds
When in gestation does fusion of neural folds?
21-24 days
What happens 25 days post-fertilization?
Cranial neuropore closes
When in gestation does cranial neuropore close?
25 days
What happens 27 days post-fertilization?
Caudal neuropore closes
When in gestation does caudal neuropore close?
27 days
The closure of the neural tube begins at the level of the __________________
First five somites
Neurulation commences as the neural plate begins to crease and the…
Lateral lips of the neural tube (neural folds) begin to approximate each other
What causes anencephaly?
Failure of the cranial neuropore to close
What is the most common neural tube defect?
Spina bifida
What is spina bifida?
A cleft in the vertebral column with a corresponding skin defect and possible exposure of the spinal cord
Spina bifida is most commonly seen in which region of the back?
Lumbar
What causes spina bifida?
Failure of the caudal neuropore to close
What is the most common form of spina bifida?
Spina bifida occulta
What is the difference between spina bifida vs spina bifida occulta?
Spina bifida occulta has a cleft in vertebral column but without skin and neural structure defects
What is meningocele?
Severe form of spina bifida
Sac containing the meninges pushes through the vertebral column defect
What is meningomyelocele?
Severe form of spina bifida
Sac contains meninges and neural tissue
Which form of spina bifida has tissues and nerves exposed and is more prone to infection?
Meningomyelocele
Which form of spina bifida is known as complete spina bifida?
Rachischisis
In this variation of spina bifida, the cleft may extend through the entire spine from the cervical region to the sacrum
Rachischisis
How do you prevent neural tube defects?
Folic acid
The forebrain is aka ___________________
Prosencephalon
The midbrain is aka ___________________
Mesencephalon
The hindbrain is aka __________________
Rhombencephalon
Where is the cephalic flexure located?
Midbrain
Where is the cervical flexure located?
Inferior border of the rhombencephalon
What encephalons make up the prosencephalon?
Telencephalon
Diencephalon
What encephalons make up the mesencephalon?
Mesencephalon
What encephalons make up the rhombencephalon?
Metencephalon
Myelencephalon
What structures make up the diencephalon?
Thalamus and hypothalamus
Thalamus and hypothalamus make up the _______________________
Diencephalon
What structures make up the telencephalon?
Cerebral hemispheres
Cerebral hemispheres make up the ______________________
Telencephalon
What structures make up the mesencephalon?
Midbrain
Midbrain makes up the _______________________
Mesencephalon
What structures make up the metencephalon?
Pons and cerebellum
Pons and cerebellum make up the ______________________
Metencephalon
What structures make up the myelencephalon?
Medulla
Medulla makes up the ___________________
Myelencephalon
All the encephalons appear during which week of gestation?
Week 5
Neural tube is aka _______________________
Myelon
Neural tube will become the ________________________
Spinal cord
At what month of gestation does the brain develop sulci and gyri?
30 weeks/6 months
When during gestation do ventricles start to form?
Week 5
What is hydrocephalus?
Accumulation of CSF
Why does accumulation of CSF cause hydrocephalus?
Skull bones are not fused so it expands
What is the first evidence of eye formation in the embryo?
Appearance of the optic nerve
The future lens will develop from the ____________________
Lens vesicle
The optic cup is connected to the brain by the _____________________
Optic stalk
The inferior part of the optic vesicle invaginates creating the ______________________
Choroid fissure
What are the layers of the eye?
Neural retina
Inner layer
__________________ is the part of the retina that contains the photoreceptors
Neural retina
Most congenital eye defects involve what part of the eye?
Inferior aspect of the eye
Choroid fissure fuses during which week?
Week 7
What is coloboma? What is it caused by?
Gap on inferior portion of the iris
Portions of the choroid fissure remain open
What are the three layers of the neural tube from innermost to outermost?
Ventricular layer
Mantle layer
Marginal layer
When the neural tube closes, it produces primitive nerve cells called ____________________
Neuroblasts
Neuroblasts develop from the ____________________ layer of the neural tube then they migrate into the __________________ layer
Ventricular
Mantle
The ___________________ of the neural tube contains nerve fibers emerging from the neuroblasts in the mantle layer
Marginal layer
The white matter of the spinal cord is made up of which neural tube layer?
Marginal layer
The gray matter of the spinal cord is made up of which neural tube layer?
Mantle layer
What is the sulcus limitans?
Separates grey matter (mantle layer) into ventral and dorsal
What separates grey matter (mantle layer) into ventral dorsal?
Sulcus limitans
Dorsal root of spinal cord comes from the ________________
Alar plate
Ventral root of spinal cord comes from the _________________
Basal plate
What happens in week 8 in the spinal cord?
Vertebral column grows faster than spinal cord resulting in conus medullaris
Where do you insert needle for lumbar puncture?
After conus medullaris
The conus medullaris ends at ___________ in newborns and at ____________ in adults
L3
L1
The PNS largely develops from _________________ cells
Neural crest
During _________________, folds of neuroectoderm approximate each other in the midline
Neurulation
Neural crest cells are derived from _________________ that are initially at a zone between the neural plate and surface ectoderm
Ectodermal cells
How does the PNS develop from the neural crest?
Folds of neuroectoderm approximate each other
Neural crest cells detach from the neural tube and migrates to regions around the body
What are neurocristopathies?
Pathologies that arise from defects in the tissues that contain cells of the neural crest
What is the genetics behind DiGeorge’s syndrome?
Deletion on chromosome 22
DiGeorge’s syndrome is a type of ____________________
Neurocristopahy
What PNS structures are developed from the neural crest? (6)
Dorsal root ganglia
Sympathetic postganglionics
Parasympathetic postganglionics
Cranial nerve sensory ganglia
Adrenal medulla
Schwann cells
_________________ is formed from clusters of neural crest cells located along future spinal cord and they grow processes that extend into the alar plate. These processes will become fibers that will convey __________________ information into the CNS
Dorsal root ganglia
Afferent
Nerve fibers in the dorsal root are formed from the ____________________
Neural crest
Since some visceral afferent neurons and somatic afferent neurons use the same DRG, some information can be confused, such as pain in the arm during an MI. What can this cause?
Referred pain
Sympathetic fibers travel to the heart from which spinal level?
T1-T4
Nerve fibers in the ventral root are formed from the ____________________
Neural tube
Preganglionic sympathetics are found at which spinal level?
T1-L2
Postganglionic parasympathetics are found at which spinal level?
S2-S4
Which cranial nerves have sensory ganglia derived from the neural crest?
V: trigeminal
VII: facial
VIII: vestibulocochlear
IX: glossopharyngeal
X: vagus
True or false. Preganglionic neurons are neural crest cell derived.
False! They are derived from neural tube
True or false. Postganglionic neurons are neural crest cell derived.
True
Which ganglia make up the paravertebral ganglia?
Sympathetic trunk ganglia
Which ganglia make up the prevertebral ganglia?
Celiac ganglion
Superior mesenteric ganglion
Are the paravertebral and prevertebral ganglia sympathetic or parasympathetic?
Sympathetic
Which ganglia make up the intrinsic ganglia?
Ganglia in target organ
Which ganglia make up the head/neck ganglia?
Ciliary ganglion
Otic ganglion
Pterygopalatine ganglion
Submandibular ganglion
Neural crest cells migrate in what direction? Because of this, what is the last region they colonize?
Proximodistally
Rectum
What causes Hirschprung’s disease?
Failure of neural crest cell migration to the distal gut tube
What would a biopsy show in a patient with Hirschsprung’s disease?
Absence of ganglia in the lower colon
How is Hirschprung’s disease usually treated?
Surgical resection of part of the bowel lacking ganglia
