Nerve Tissue Flashcards
Week 1 & 2 Development Key Points
- gametogenesis: eggs & sperm form at 2 weeks
- fertilization
- day 6-12 implantation to the uterine wall
- trophoblast becomes cyto and syncytiotrophoblasts at day 7
- Day 8: differentiate into epiblast and hypoblast
- Day 12: Mom’s blood enters lacunae - starts circulation
- Day 14: prechordal plate forms: the nervous sytem is forming here; the mouth and anus will arise from this plate
when is the “key” time period for CNS development in utero
when is the “danger period”
Week 3 : the start of CNS development
Week 6: all primordial CNS structures are formed
Week 16: Commisures are formed
Month 7-9: gyri and sulci are formed
week 5 is ther highest risk week of birth defects occurring
KEY CNS Developmental processes to know
Day 15
Day 16
Day 17
Day 15: Formation of the Primitive Streak
- the epiblast cells move to dorsal aspect and form the streak: adding cells to the caudal end & at the cranial end: there is a primitive node of cells
- primitive streak: essential for signaling for futher development
- secreted factors initiated the formation of the primitive streak
- node = the signaler for the gasturlation processes of gene expression
- PS = establisheds cranial, caudal orientation & laterality of the embryo
Day 16: Formation of the Trilaminar Disc
- endoderm
- mesoderm
- ectoderm
- the CNS is composed of the ectoderm outer most layer
- epitherlial tissue is made of all 3 layers
Day 17: Notochord Formation
- a solide rod of mesoderm from the primitive node to the perchordal plate
- made from the factors released by the primitive node : CNS and axial skeleton formation from this
KEY CNS Formation points to know
Days 18-23
Days 18-23:Neurulation
18-19: neutochord overlays of ectoderm = formation of the neural plate
day 20: the neural plate envaginates and creates the neural groove and then neuroal folds appear on eitehr side of the groove
day 21: the folds approach each other and fuse into the neural tube
Day 25: cranial nerupore closes
Day 28: caudal neuropore closes
inability to close the cranial neurpore ends in what? what about caudal neuropore?
Cranial Neuropore failure to close = death or anencephaly
Caudal Neuropore failure to close = Spina Bidida or myelomeningocele
- lumbar spinal cord injury: can be repaired surgically in utero or post-natally
folic acid supplementation can help prevent most NTD
what is the neural crest
- how is it formed
- what tissues are formed from neural crest
- while the neural folds are forming the neural pore, pieces break off whiel the circle comes together and these peices undergo cellular changes
- change to mesenchymal transformation: mesoderm and neural crest tissue
Neural Crest Tissue is…
- all the PNS ganglia (DRG, ANS, cranial nerve)
- schwann cells
- pia and arachnoid mater
- adrenal medulla cells
Weeks 4-6 Development CNS Keys
Week 4: forebrain, midbrain, hindbrain are formed
Week 4: cranial nerves form
Week 5: differentiation of the telenecephalon, diencephalon, mesencephalon
Week 5: ventricles and brachial plexus
Week 6:blood supply to the brain forms & nuceli forming
all the precursor structures to most of the CNS structures exist at the end of week 6
how does cell differentiation in the embryo happen to create the CNS
cell proliferation (mitosis) allows for growth and differentiation occurs through specialization via gene expression
- location and timing are theindicators for when cells are to become specialized in a specific locations
- gene expression: Rhombencephalon : helps govern the right differentaion of the CNS and its specifi areas/cells
for spinal cord developement: think anterior and posterior horns
- the 4th week is when the dorsal and ventral pattern of teh SC occurs
how is the pattern of cranial to caudal and dorsal/ventral and laterality decided in the embryo?
what are the Transcription factors to know which are assocaited wtih signaling development in neural tissue fomration
the first siganl is the formation of the prechordial plate: through the primitive streal, the notochorid and the neural tube
- this is all regulated by the signalling molecules and transcription factrs: gene expression & temporalspatial sequencing
Neural Transcription Factors
- Sonic Hedgehog & Bone Morphogenic Protein
- SHH = ventral (motor) patterning (motor becasue sonic if fast!)
- BMP = dorsal (sensory) patterning
- Hox = for anterior/posterior planning and limb development
what is polyneuronal innervation
how is this differnet in neonates than older humans
Polyneuronal Innervation
- the idea that there are many more neurons per 1 muscle fiber (multiple neurons sending signals to the muscel cell)
- as the neonate is processing motor function; the motor circuits of the brain adjust and prune these neurons; so that there is only 1 neuron per fiber, knowing there could be multiple synpases still but only one motor axon per muscle fiber
what is the nervous tissue: from what layer
types of stian
Nervoud Tissue: arises from the ectoderm layer
(epitherlial = from ectoderm and endoderm, connective = mesoderm, muscle tissue = mesoderm)
Staining: help to differentiate the tissue and cell structures
- H&E stain: nuceli blue & tissue pink : MC
- Luxol Fast-blue: stains mylein dark
- Silver and Gold
- Electronmicroscopy: to see close
Histology of the Cerebellum: how many layers
- what are the layers (important 1 to know)
Cerebellum: has 6 layers of cells visable on histolgy slices
1 = molecular/plexiform layer : neruons from thalamus
II = External Granular :
III = external pyramidal :corticocortical out
IV = interal granular : thalmus C-fibers in
layer V:the iNternal Pyramidal layer: scatter betx cells= this is where the CELL BODIES OF THE CORTICOSPINAL TRACT ARE
VI: multiform/polymorphic layer: in and out of thalamus
Neuron Types by Region and Function
mutlipolar
pseudounipolar
bipolar
Multipolar = those most commony throughout the nervous system; in the brain and spinal cord
- effernt (motor: somatic and autonomic) and interneurosn
- two or more dendrites with one axon
Pseudounipolar = in the PNS; afferent senesory neurons with cell bodies located in the DRG
- have two axon-like processes
Bipolar Neurons = special sense nerouns; small and sight
- classic dendrtie, cell body and axon arangement
Multipolar Neurons + Cerebellum
input and output tracts
- complex multipolar tracts of efferent and afferent fibers for the cerebellum to communicate to many different areas of the brain to coordinate movement
Middle Peduncle: afferent fibers (coming INTO the cerebellum) from the contralateral cortex thorugh pointine nucli
- Mossy Fibers: go to the granular cells in the cerebellum
Inferior Peduncle: afferent fibers (coming INTO the cerebellum)
- from the ipsilateral spinal cord = mossy fibers: go to granular cells
- from the contralateral spinal cord through the inferior olive: Climbing fibers: go to purkinje cell layer in cerebellum
Multipolar Neruons + Cerebellum
- deep cerebeullar nuclei
- most all efferent neurosn of teh cerebellum go to the deep nuceli then leave
- these are multpolar neruons: and are much more intricately shaped: more complex function ability than other primates
