Nervous System Flashcards
When does the process of neurolation occur?
~day 22
What is neuralation?
formation of neural plate and neural tube
What induces the formation of the neural plate?
notochord and paraxial mesoderm
Where does neural tube closure begin near?
somite pair 4
When does the cranial neuropore close?
day 25
When does the caudal neuropore close? And what does this establish?
day 27, establishment of neural tube vasculature
What will the neural canal form?
- ventricles of the brain
- central canal of SC
Where does the development of the spinal cord occur?
caudal to somite 4
What initially lines the neural tube?
pseudostratified columnar neuroepithelium
What does the ventricular zone refer to?
refers to the original neuroepithelium
What does the ventricular zone give rise to?
gives rise to spinal cord neurons, spinal cord astrocytes, oligodendrocytes and ependymal cells
How does the intermediate zone form?
forms by proliferation in the original ventricular zone
What does the intermediate zone form?
neuroblasts
- differentiate into spinal cord neurons
Where does the marginal zone form? what does it become?
- peripheral to the original ventricular zone
- becomes white matter as neuronal processes grow into it from spinal cord and brain
Where do glioblasts reside?
populate ventricular, intermediate, and marginal zones
What do glioblasts become?
- astroblasts => astrocytes
- oligodendroblasts => oligodendrocytes
What do ependymal cells persist as? what zone where they associated with?
- ependyma lining the central canal
- ventricular zone
What are microglial cells differentiated from?
mesenchyme
Where do microglial cels originate from?
bone marrow
What happens to the spinal cord as the neuroepithelial cells proliferate and differentiate?
spinal cord walls become think and roof and floor become thin
What is the sulcus limitans?
shallow longitudinal groove on either side of central canal lumen
What is the alar plate?
dorsal longitudinal bulge in the intermediate zone
What will the alar plate become?
dorsal columns in the grey matter
What are located in the dorsal columns of thee grey matter?
afferent neurons
When does the dorsal median septum form?
as alar plate enlarge bilaterally
What is the basal plate?
ventral longitudinal bulge in the intermediate zone
What will the basal plate become?
the ventral and lateral columns in the gray matter
What is located within the lateral columns in the gray matter?
efferent neurons
When does the ventral median fissure form?
as basal plates enlarge bilaterally
Where are pseudounipolar neurons derived from?
neural crest cells
What passes through the DRG to enter the spinal cord?
central processes
Primordial meninx is a membrane that develops from what?
mesenchyme surrounding the neural tube
What is dura mater?
thickened external layer (mesenchyme origin) or primordial meninx
What are leptomeninges?
Internal layer (neural crest origin) of the primordial meninx
What is subarachnoid space?
- separates leptomeninges into arachnoid and pia mater
- production begins week 5
What is the position of the SC in embryo?
SC extends entire length of vertebral canal
- spinal nn. exit intervertebral foramina opposite their level of origin
What is the position of the SC in a 6mo fetus?
SC conus medullaris extends to S1 vertebra
What is the position of the SC in a newborn infant?
SC conus medullaris extends L2 or L3 vertebra
What is the position of the SC in an adult?
- SC conus medullaris extends to inferior border of L1
- cauda equina
- dura and arachnoid end at S2 (filum terminale externum)
- pia extends as filum terminale internum to Cx1
CNS myelin is produced by what?
oligodendrocytes
Myelination of neuronal processes occurs when?
in late fetal period and continues through year 1 postnatally
Which are myelinated first, motor or sensory fibers?
motor
What does a spinal dermal sinus indicate?
Indicated site of closure of caudal neuropore
- last site of separation of surface ectoderm from neuroectoderm
What is spinal dermal sinus?
posterior median skin dimple in sacral region
What causes spina bifida occulta?
due to failure of embryonic halves of vertebral arch to grow and fuse in midlinw
Where does spina bifida occulta occur?
L5-S1 in ~10% of people
Does spina bifida occulta usually show clinical symptoms?
No
What evidence if any does spina bifida occulta show?
small dimple with a tuft of hair
What does spina bifida cystica involve?
protrusion of spinal cord and/or meninges through vertebral arch defect
What is present with spina bifida cystica?
a cyst-like sac
What is the occurrence/frequency of sspina bifida cystica?
1/1000
What neurological deficits accompany spina bifida cystica?
- dermatomal sensory loss
- complete or partial skeletal muscle paralysis
- lumbosacral defects => sphincter paralysis
What can be done to detect spina bifida cystica?
- amniocentesis to confirm Alpha Fetoprotein levels (will be high if cystica present) in amniotic fluid
- ultrasound can detect cyst 10-12weeks
What are 2 subtypes of spina bifida cystica? their occurence?
- spina bifida with meningocele (10%)
- spina bifida with meningomyelocele (90%)
What is present in cyst-like sac in spina bifida with meningocele?
meninges and CSF
What is in the cyst-like sac in spina bifida with meningomyelocele?
spinal cord and/or spinal roots
Is surgery and option with spina bifida with meningomyelocele?
surgery is possible but no functional restoration occurs
What is myeloschisis?
most severe type of spina bifida
- spinal cord is open caudal neuropore failed to close
What is the importance of Folic Acid supplements?
reduce the chance of neural tube deficits
Where does the brain develop?
cranial to somite pair 4
What are the 3 primary brain vesicles?
- Prosencephalon (forebrain)
- Mesencephalon (midbrain)
- Rhombencephalon (hindbrain)
What primary brain vesicles give rise to secondary brain vesicles in the 5th week?
prosencephalon and rhombencephalon
What 2 secondary brain vesicles does the prosencephalon form?
- Telencephalon
- Diencephalon
What 2 secondary brain vesicles does the rhombencephalon form?
- Metencephalon
- Myelencephalon
What primary brain vesicle doesnt dived?
mesencephalon
What are the 3 flexures?
- midbrain flexure
- cervical flexure
- pontine flexure
Where is the midbrain flexure?
- ventral fold in the midbrain region
Where is the cervical flexure?
ventral fold at the junction of the hindbrain and the spinal cord
Where is the pontine flexure located?
dorsal fold between the midbrain and the cervical flexures
What is the function of the pontine flexure?
divides the brain into its 2 respective parts
- metencephalon (rostrally)=> pons & cerebellum - myelencephalon (caudally)=> medulla oblongata
The pontine flexure produces a cavity which becomes what?
the IV ventricle
What does the caudal region of the developing myelencephalon resemble?
resembles the developing spinal cord
- closed part of the medulla
What nuclei are present in the myelencephalon?
- gracile nuclei
- cuneate nuclei
What white tract is present in the myelencephalon?
pyramids
What will the walls of the metencephalon form?
cerebellum and pons
What spreads the lateral walls of the metencephalon?
pontine flexure
- spreads gray matter in the floor of the IV ventricle
What is the pons and where is it located in the developing brain?
It is a bridge of large tracts connecting cerebral cortex and cerebellar cortex and it is located within the metencephalon
What is choroid plexus and where is it developed?
- developed in roof of IV, III ventricle and medial walls of the lateral ventricles
- produces CSF
What are the outpouchings from the IV ventricle called?
median and lateral aperatures
Does the mesencephalon undergo a lot of change?
comparatively little change
What happens to the neural canal in the mesencephalon?
narrows to become the cerebral aqueduct
What are the three swellings in the diencephalon?
- epithalamus
- thalamus
- hypothalamus
Where is the pineal gland?
median growth of caudal part of diencephalon roof associated with the epithalamus
What is melatonin and from what is it secreted from?
regulates circadian rhythm and is secreted from the pineal gland
How often do the thalamus sides fuse in midline?
70% of brains
What is the function of the thalamus?
relay station for afferent information heading to cerebral cortex
What is the function of thee hypothalamus?
coordinates many endocrine activities in the body
What does the hypothalamus regulate?
autonomic nervous system
- BP, body temp, fluid/ion balance, body weight, appetite, etc.
What does the pituitary gland work with?
works with the hypothalamus as a major controller of the endocrine system
The Neurohypophysial diverticulum is a downgrowth of what?
diencephalon
What does the neurohypophysial diverticulum form?
The posterior lobe (nervous part)
What is the name of the posterior lobe of the pituitary?
neurohypophysis
What does the connection of the pituitary to the diencephalon persist as?
infundibulum
What do neurosecretory cells secrete?
oxytocin & ADH
What is the upgrowth from the roof of the stomodeum?
hypophysial diverticulum
What does the hypophysial diverticulum form?
anterior lobe (glandular part)
What is the name of the anterior lobe of the pituitary?
adenohypophysis
What does the adenohypophysis secrete?
TSH, ACTH, FSH, LH, PRL, GH
Cavities in the primordial cerebral hemispheres become what?
lateral ventricles
What do the lateral ventricles interact with? and how?
III ventricle and through the interventricular foramen
Where is the choroid plexus located in the lateral ventricles?
the medial walls
What grows more rapidly in the cerebral hemispheres?
the walls and roof grow more rapidly than the floor
Trapped mesenchyme in the midline becomes what?
falx cerebri
How does the temporal lobe form?
caudal end of cerebral hemispheres turn ventrally and rostrally
Which commissure forms first?
anterior commissure
The cortical surface is smooth or bumpy initialy?
smooth
What happens to the surface area of the brain as the cortex grows? what causes this?
Increases surface area due to gyri and sulci
What is the medullary center?
large volume of myelinated processes in the “core” of the brain
What bony landmarks are usually associated with cranium bifidum?
squamous occipital bone and/or posterior foramen magnum
What is cranial meningocele?
small defect with only meninges herniated
What is cranial meningoencephalocele?
large defect with brain and meninges herniated
What is cranial meningohydroeencephalocele?
large defect with brain, ventricular components and meninges herniated
What is meroencephaly?
severe anomaly due to failure of rostral neuropore to close
- brain and calvarium (acrania) don’t develop normally
What is exencephaly?
brain is exposed or extruding from cranium
What is anencephaly?
misnomer for rostral neuropore closure defects
What is microcephaly?
brain and calvarium are small; face is normal
What is hydrocephaly?
imbalances between CSF production and absorption => accumulation in ventricular system
Congenital aqueductal stenosis is a common form of what?
Hydrocephalus
What is congenital aqueductal stenosis?
narrowing and blockage primarily of lateral and III ventricles
- genetic and environmental causes
What happen to cranial bones when ventricular fluid accumulates in the cranium?
expand and thin
What is Arnold-Chiari malformation?
Inferior displacement of vermis of cerebellum through foramen magnum
What are sensory neurons derived from?
neural crest cells
In the regions of the DRG sensory neurons start out as what? and become what later?
bipolar neurons => unipolar
Where does the peripheral process terminate?
sensory endings
What aspect of a sensory neuron terminates in the SC or extends up to the brain?
central process
What are satellite cells?
ganglion support cells derived from neural crest cells
- modified schwann cells
What emerges from the ventrolateral aspect of SC as ventral root?
motor neurons
What do dorsal primary ramus supply?
skin, muscles etc on back
What do ventral primary ramus supply?
skin, muscles etc in limbs and ventrolateral body wall
What are Schwann cells?
neural crest cells that migrate into position to myelinate sensory and motor neurons
