CNS embryology 2006 anatomy
Terms
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- what is neurulation?
- process of neural induction and formation of neural tube
- what's a neural tube?
- is hollow tube made from the pear-shaped region of ectoderm called neurectoderm
- what are primary brain vesicles?
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formed by 4th week
are dilations of neural tube at anterior end
are 3 dilations;
1. prosencephalon = forebrain
2. mesencephalon = midbrain
3. rhombencephalon = hindbrain - what are secondary brain vesicles?
- divisions of primary brain vesicles
- what do the terms basal plate and alar plate refer to?
-
generally refer to developing CNS regions with
basal plate - motor and
alar plate - sensory neurons
in spinal cord
basal plate - ventral horn
alar plate - dorsal horn - what are the lateral ventricles?
- two ventricles in outpocketings of telencephalon
- what/where is the cerebral aqueduct?
- is small region between the 3rd and 4th ventricles
- what are the third and fourth ventricles?
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third ventricle - ventricle of diencephalon
fourth ventricle - ventricle of rhombencephalon - what is the ependymal layer?
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is layer of neural tube from which neuroblasts, or cells that give rise to neurons, first appear
near surface of ventricle - what's the mantle layer?
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future gray matter of spinal cord
from cells of ependymal lyaer that have differentiated and migrated short distance - where's the marginal layer?
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is cell-free zone with neurites - or long, thin processes from cells of mantle layer
near edge of spinal cord
will be white matter of spinal cord
becomes thick in dorsal and ventral spinal cord, thin in middle - what's the choroid plexus?
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from very vascularized roof of myelencephalon
invaginates into 4th ventricle - what do the cerebral hemispheres usually do in normal people?
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are centers of reasoning, memory, emotion
also are higher control of muscles - problem of paralysis with stroke - what does the diencephalon do?
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is relay center connecting sensory systems with cerebral hemispheres
regulates ANS - what does the midbrain do?
- is small region containing cell bodies of CN III and groups of neurons that interpret hearing/vision
- what's the hindbrain?
- includes cerebellum, pons, medulla oblongata
- what does the cerebellum do?
- is subconscious regulation of equilibrium, locomotion and posture
- what does the pons do?
- is bridge tween cerebral hemispheres, cerebellum and spinal cord
- what does the medulla oblongata contain?
- cell bodies of many of cranial nerves and other fiber tracts connecting the spinal cord with rest of the brain
- what's the neurectoderm?
- is pear-shaped region of ectoderm
- what makes up the neural plate?
-
is from thickening of neurectoderm at midline
3 week embryo - what are neural folds?
- are lateral margins of neural plate that elevate, move toward one another and fuse
- what's the neural tube?
- hollow tube of neurectoderm
- what are neuropores?
- are holes at either end of neural tube before they have fused
- what do the cells of the neural tube become?
- neurons and glia of CNS
- what does the hollow center of the neural tube become?
- is called the neural canal and stays hollow in adult brain as ventricles
- what's the neural canal?
- is the hollow center of the neural tube
- why is the anterior end of the neural tube larger than the posterior end? what do these ends eventually become?
-
anterior is larger because tube is made from pear-shaped ectoderm
anterior end becomes brain
posterior end becomes spinal cord - what process of the development of the CNS is particularly susceptible to mutation, or environmental insult? why?
-
neurulation
is problem because many women don't know they're pregnant at time, and can be taking prescription or recreational drugs - what's a result of abnormal neurulation?
- spinal bifida
- where do the primary brain vesicles form from?
- dilations at anterior end of neural tube at 4 weeks of develoment
- what are the names of the three primary brain ventricles?
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1. prosencephalon - forebrain
2. mesencephalon - midbrain
3. rhombencephalon - hindbrain - what are the flexures in embryonic CNS development?
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4th week of development
1. cephalic flexure = bend in neural tube at mesencephalon
2. cervical flexure = bend in neural tube between the rhombencephalon and spinal cord
3. pontine flexure
tween metencephalon and myelencephalon - what happens by 5 weeks in development of CNS?
- appearance of secondary brain vesicles
- what are the secondary brain vesicles are from what do they come from?
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prosencephalon becomes
anterior telencephalon
posterior diencephalon - what does the telencephalon become?
- the cerebral hemispheres
- what forms from the diencephalon?
- optic cups
- what secondary vesicles does the rhombencepholon become?
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anterior metencephalon
posterior myelencephalon - what does the metencephalon become?
- pons, cerebellum
- what does the myelencephalon become?
- medulla oblongata
- what are the secondary vesicles?
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telencephalon
diencephalon
metencephalon
myelencephalon - what's the third ventricle?
- ventricle of diencephalon
- what's the fourth ventricle?
- ventricle of rhombencephalon
- what's the central canal?
- is ventricle of spinal cord
- what's the neuroepithelium and what role does it play in CNS development?
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is epithelium of walls of neural tube
involved in formation of spinal cord
is pseudostratified epithelium - what are neuroblasts and where do they come from?
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are cells that make neurons
come from surface of ventricle, area called ependymal layer or germinal matrix - what's the ependymal layer or germinal matrix and what does it do?
- is surface of ventricle from which neuroblasts arise
- where does gray matter of spinal cord come from?
- from mantle zone or mantle layer, which is more differentiated layer of spinal cord with neurons showing up for the first time
- what are neurites?
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are long, thin processes extended from new neurons
grow toward outer edge of neuroepithelium - what makes the white matter of the spinal cord?
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the marginal layer - is cell-free zone where neurites are
near edge of spinal cord - where are most of the motoneurons in spinal cord development?
- ventral horn of spinal cord - with ventral gray matter
- what makes up the ventral and dorsal horns of the spinal cord? where do they come from?
- come from thickenings of mantle zones only in dorsal and ventral parts of spinal cord, middle is thin
- where do neurons that process sensory input hang out in the embryological development of the CNS?
- the dorsal horn with dorsal gray matter
- what area does the basal plate correlate with? why?
- the basal plate is an area where motor neurons are developing and correlates with the ventral horn
- what area does the alar plate correlate with and why?
- alar plate is area where sensory neurons are developing - this correlates with teh dorsal horn
- are congential malformations of the spinal cord common?
- yes
- what does spina bifida refer to?
- problem with fusion of vertebral arches
- what does spina bifida occulta refer to?
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problem with vertebrae fusing
occurs in 10% of population
usually goes undetected and doesn't cause problems - what does spina bifida cystica refer to?
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when there is a herniation of the meninges with or without the spinal cord
results from failure of vertebrae to fuse - what's spina bifida with meningocele
- when only the meninges bulge through opening in vertebral column
- what does the suffix -cele stand for?
- herniation
- what is spina bifida with mylomeningocele?
- is when spinal cord is included in herniation with meninges in bulging through opening in vertebral column
- what is rachischisis?
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is failure of neural folds to fuse
is accompanied by abnormal development of vertebrae
luminal surface of neuroepithelium left exposed - what specific spina bifida conditions are associated with neurological deficits that include partial or total paralysis of abdominal muscles and lower limbs as well as sphincter paralysis?
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1. spina bifida cystica with myelomeningocele AND
2. RACHISCHISIS - what divisions come from the rhombencephalon and when?
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myelencephalon and
metencephalon
5th week of development - where is the rhombencephalon located?
- most caudal primary brain vesicle
- where is the myelencephalon?
- is contiguous with the spinal cord
- what does the myelencephalon resemble?
- open book
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where are the basal plates located in the myelencephalon?
what do the basal plates contain? -
ventral surface near midline
basal plates contain motor neurons - where are the alar plates of the myelencephalon?
- dorsal
- what are in the alar plates of the myelencephalon?
- snesory interneurons
- where do primary sensory neurons come from and where are they located?
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primary sensory neurons are derived from neural crest cells
are located outside CNS in ganglia - what do the neurons of the basal plate of the myelencephalon eventually form?
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CN XII
motor parts of CN X and CN IX - what holes in the skull are formed near the myelencephalon?
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jugular foramen
hypoglossal canal - what does the choroid plexus form and where does it come from?
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is made from roof of myelencephalon
becomes 4th ventricle - what does the choroid plexus make?
- CSF - cerebrospinal fluid
- where is the choroid plexus and how many of them are there?
- are as many as there are ventricles, because there is one in every ventricle
- what's the path of CSF flow?
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from ventricles through openings in roof of myelencephalon
goes into subarachnoid space
is absorbed into venous blood through arachnoid villi - where are the basal plates in the metencephalon and what do they contain?
- like the basal plates in the myelencephalon, the basal plates in the metencephalon are located ventrally and contain motor neurons
- where are the alar plates of the metencephalon and what do they contain?
- alar plates are located dorsaly and contain sensory interneurons
- what do the motor neurons of basal plates of metencephalon form?
- MOTOR parts of CN VII, VI, V3
- where is the motor nucleus of CN IV located?
- near border of metencephalon and myelencephalon
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what's the cerebellar plate?
when does it form? -
is projection of alar plates of metencephalon
forms around week 8 - what brain region is one of the last to mature?
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cerebellum
continues to develop new neurons and grow even after birth - again, where are and what are found in the basal plates of the mesencephalon?
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ventrally
motor nuclei has motor neurons of CN III - where are alar plates of mesencephalon?
- alar plates are always dorsally
- what does the alar plate of the mesencephalon become?
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superior (anterior) and
inferior (posterior) colliculi - what are the superior and inferior colliculi?
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superior - serves visual system
inferior - serves auditory system - what cranial nerve is also associated with the mesencephalon?
- CN IV
- what's the shape of the ventricle of the mesencephalon? what's another name for it?
- is long and narrow; called cerebral aqueduct
- what happens if the cerebral aqueduct becomes obstructed during development?
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CSF from choroid plexus in laterl ventricles of cerebral hemispheres can't go to fourth ventricle where it normally leaves
CSF accumulates in lateral ventricles forming hydrocephalus - how do we treat hydrocephalus?
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place oe end of shunt into ventricle where CSF accumulates
other end of shunt into peritoneal cavity - what are the origins of the trochlear nerve CN IV?
- cell bodies are in basal plates of metencephalon near mesencephalon
- what's the path of the CN IV in development?
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all other motor nerves exit ventrally, but trochlear nerve travel dorsally in mesencephalon
cross roof
exit dorsaly on opposite side from basal plate of origin - what does the development of CN IV have to do with visual deficits?
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if problem is with movement of left eye, lesion could be in left superior oblique
left cranial nerve IV or
RIGHT side of midbrain
CN IV can be damaged by stretching midbrain (from buildup of CSF) - what structures come from the diencephalon?
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1. retina
2. optic stalk
3. pineal body - helps regulate behavioral rhythms
4. infundibulum - fuses with stomodeum to make pituitary gland
5. thalamus, hypothalamus
6. choroid plexus of third ventricle comes from roof of diencephalon - what are the primary regions of the alar plates of the diencephalon?
- thalamus and hypothalamus
- what does the hypothalamus do?
- regulates sleep, emotions and body temperature
- where do the cerebral hemispheres come from?
- lateral outpocketings of telencephalon
- a newborn is diagnosed with hydrocephalus resulting from an obstruction of cerebral aqueduct during development. where is the cerebral aqueduct of an embryo?
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A. inside telencephalon
B. inside diencephalon
C. inside mesencephalon
D. inside the metencephalon
E. inside the myelencephalon - a newborn has asymmetric eye movements. examination reveals right oculomotor nerve palsy and left trochlear nerve palsy. a lesion associated with what part of the developing brain is consistent with this observation?
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A. right mesencephalon
B. left mesencephalon
C. right telencephalon
D. right myelencephalon
E. left myelencephalon - what does a cross section of the spinal cord look like?
- labia major
- what are cells around the middle of the cross section of the spinal cord called?
- ependymal layer
- what is the mantle layer in the cross section of the spinal cord?
- dorsal and ventral horns
- where is the marginal layer of the cross section of the spinal cord?
- everywhere else outside mantle layer
- what's the reflex arc with the cross section of the spinal cord?
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1. starts with basal plate - motor neurons
2. goes to spinal nerves - mix of afferent and efferent nerves
3. ends with sensory ganglia leading to alar plate - what's the cross section look like of the myelencephalon?
- smile
- what's the top of the cross section of the myelencephalon?
- the 4th ventricle
- which side of myelencephalon is roof?
- top of smile
- what comes out of the basal plates of the myelencephalon?
- hypoglossal - motor
- where does the third ventricle come from?
- prosencephalon
- what do the optic cups become?
- retina
- what is the optic stalk?
-
is root of optic cup
from prosencephalon
becomes optic nerve - where's the cerebral aqueduct?
- center of mesencephalon
- where's the 4th ventricle?
- center of myelencephalon
- what does the cross section of the metencephalon look like?
- smile curled upwards, almost touching at dorsal side
- what is at the center, back of the metencephalon?
- 4th ventricle
- what is at the ventral side of the metencephalon?
- what becomes pons