Neuroembryology Flashcards
What does the notochord help develop?
The spinal cord and spinal nerves via signaling molecules
Turns the caudal/inferior neuroectoderm physically into these structures
What does the prechordal mesoderm help produce?
Brain and cranial nerve development via signal molecules
The rostral/superior neruoectoderm turns physically into the Brain and cranial nerves
What is the process of neural induction/Neurulation mainly give rise to?
Differentiates the ectoderm into the neuroectoderm (neural plate)
- neuroectoderm eventually turns into Brain/spinal cord
Also gives rise to neural tube and neural crest cells
What does surface ectoderm (ectoderm that does differentiate into neuroectoderm) give rise to ultimately?
The skin
What are the signaling molecules secreted ventrally in the neural tube?
SHH
RA
Noggin
Chordin
are all secreted from the ventral floor plate
What are the signaling molecules secreted dorsally in the neural tube?
TDF-B
BMPs
Dorsalin
RA
Noggin
all are secreted from the dorsal roof plate
What are the signaling molecules secreted lateral to the neural tube ?
BMPs
these are secreted form the somites
Dysraphisms
Various neural tube defects (NTDs)
- usually in formation and fusion of the neural tube
Usually occur at or near anterior/posterior neuropores
Highly linked to low maternal folate/B9 levels in conception and early pregnancy
Most heavily associated defects include cranium or spinal bifida
Different types of cranial bifida
Meningocele
- contents include just CSF and meninges
Meningoencephalocele
- contents include CSF, brain tissue and meninges
Meningohydroencephalocele
- contents include CSF, Brian tissue, ventricles and meninges
- most severe
Different types of spina bifida
Spina bifida occulta
- unfixed neural arch that does NOT produce a cyst
- asymptomatic except sometimes tuffs of dark hair form in the area
Spina bifida cystic w/ meningocele
- cyst forms and includes meningitis and CSF only
Spina bifida cystic w/ meningomyelocele
- cyst forms and includes meningitis, CSF, Brain matter and spinal cord tissues
Myeloschisis
Posterior neurochord does not close
Leaves open spinal cord exposed.
Not compatable with life
Meroencephaly
Anterior neurochord does not close
Causes exposed Brain
Does not affect and bones
What do the neural crest cells give rise to?
All glial cells of the PNS
Most of the PNS nerves and ganglia
Where are the primary sensory neurons for CN 1 and 2 located?
CN1 = olfactory epithelium fund in the nasal cavity
CN2 = retina of the eye
both do NOT originate from neural crest cells
What do sensory ganglia of the true cranial nerves originate from?
Either cranial neural crest cells of neurogenic placodes (thickened surface ectoderm)
Sympathetic ganglia of PNS develop from what?
All arise from trunk crest neural crest cells
Parasympathetic ganglia of the PNS arise from what?
Postganglionic arise from neural crest cells
Parasympathetic ganglion and their associated Cranial nerve
Ciliary ganglion = CN 3
Pterygopalatine ganglion = CN 7
Submandibular ganglion = CN 7
Otic ganglion = CN 9
intramural ganglia = CN 10
Enteric ganglia = CN 10
What do apolar neuroblast cells give rise to?
All types of neurons in the body
- bipolar
- unipolar
- multipolar
- pseudounipolar
are derived from neuro-epithelium/ neuroectoderm
What do gllioblast cells give rise to?
All the glial cells in the CNS
- radial glial cells
- astrocytes
- oligodendrocytes
- are derived from neuroepothelium/ neuroectoderm*
What are the 1 group of glial cells that are NOT derived from neuroectoderm?
Microglia
- derived from monocytes/ bone marrow
How does the neural tube differentiate?
1) The original single layer of ectoderm gives rise to the ventricular zone
- contains the original precursors/ progenitor neuroblast/glialblasts that eventual move into ventricular zone
This layer elongates and forms a new layer called the marginal zone
- contains only neuro blasts and glialblasts projections. NO nuclei
- eventually, gives rise to all of the white matter
The last layer to develop is the intermediate zone (mantle zone)
- contains neuroblast and glioblasts that migrate from the ventricular zone
- eventually gives rise to all of the gray matter over time
Steps for differentiation of the intermediate zone
caused by gradient of signaling molecules
Alar plate (column) - house all dorsal neuroblasts that inevitably turn into all 2nd and 3rd sensory (both visceral and somatic) neurons and associated interneurons
Basal plate (column) - houses all ventral neuroblasts that inevitably turn into all lower motor neurons (somatic motor and presynaptic autonomic) and associated interneurons
- these plates are separated by the sulcus limitans (also called central canal in spinal cord)*
How are the motor and sensory columns aligned in both the alar and basal plate?
Basal plate
- ventral part = houses cell bodies of the somatic motor neurons (somatic efferent motor columns)
- dorsal part = houses presynaptic cell bodies for visceral motor neurons (visceral efferent motor columns)
Alar plate
- ventral part = houses cell bodies for visceral afferent/sensory neurons (visceral afferent sensory columns)
- dorsal part = houses cell bodies for somatic afferent/sensory neurons (somatic afferent sensory columns)
What do lower moter neurons do?
They are somatic motor neurons. They innervate skeletal muscles
Basal plate derivatives specifics
Medial motor column of the basal plate (MMC)
- controls somatic motor neurons that innervate the skeletal muscles of the trunk and limb girdles
- also called “anterior horn”
Lateral motor column of the basal plate (LMS)
- controls somatic motor neurons that innervate the skeletal muscles of the upper and lower limbs
- exception is accessory nerve bodies (these are found in the spinal accessory nucleus)
Intermediolateral (IML) nucleus of the basal plate
- controls presynaptic sympathetic visceral motor neurons within the T1-L2 Region
- controls presynaptic parasympathetic visceral motor neurons within the S2-4 region
- also known as “lateral horn”
Alar plate derivatives specifics
Dorsal region of the dorsal horns = secondary somatic afferent neurons and runs along the entire spinal cord length
Deeper regions of the dorsal horns = secondary visceral afferent neurons and runs only in the T1-L2 region and S2-4 region
Marginal zone of the mature spinal cord and the general concept of tract layouts
- note that the marginal zone contains the white matter, not gray*
1) sensory information from the trunk/limbs/viscera are carried up to the brain by ASCENDING axon fibers from all secondary afferent and some primary afferent neurons
2) signals from the brain to activate or inhibit firing of targeted lower motor neurons travel down spinal cord DESCENDING axon fibers
3) due to fibers of each pathway often decussing to the contralateral side, lesions that occur prior to decussations show signs/symptoms on contralateral side. Lesions after decussations show sings/symptoms on the ipsilateral side.
Teathered spinal cord
Abnormal attachment of the spinal cord to vertebra or surrounding tissues during growth and elongation
- stretches it to far and it goes past L2. Causes unwanted tension on spinal cord and nerves
Symptoms/signs
- often accompanies NTDs
- pain in back/lower extremities
- numbest of lower extremities
- muscular weakness of lower extremities/ back
- bowel and bladder issues
Development of the brain
Rostral/superior portion of the neural tube forms three swellings
Prosencephalon (forebrain)
- splits into telencephalon and diencephalon by the pontine flexure
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)
- splits into mesencephalon and myelencephalon by pontine flexure
once the 5 parts are split, the basal plate becomes medial to the alar plate (rotates clockwise 90 degrees due to cephalic and cervical flexures )
Myelencephalon and its basal plate associated derivatives
Forms the medulla oblongata
Basal plate derivatives associated:
- somatic efferent column (most medial) = somatic motor nucleus of CN12
- visceral efferent motor column (most lateral) = pre-synaptic parasympathetics for salivary nucleus of CN12 and dorsal motor nuclei of CN10
- special visceral/branchial efferent column = nucleus ambiguous which contains efferent motor neurons of CN10
Myelencephalon and its Alar plate associated derivatives
Visceral afferent (sensory) column = gives rise to secondary sensory neurons of solitary nucleus (taste and abdominal visceral for CN10). Also does carotid body and sinus visceral afferents (CN9/10)
Somatic afferent (sensory) column = gives rise to secondary sensory nuceli of CN5
Special somatic afferent column =gives rise to secondary sensory neurons to form vestibular and cochlear nuceli (CN8)
- also generates curate/gracile nuclei/ inferior Olivary nuclei
