Nervous-Musculoskeletal Development and Limb Formation Flashcards
Describe somatic reflex (Hand touches flame)
Hand makes contact with flame, sensory afferents tract (pseudounipolar) conducted through dorsal root ganglion and then synapses at interneuron at dorsal horn. Another synapse into ventral horn, which flows through efferent tracts on ventral side and out to the same muscle
Where trilaminar embryonic disk came from. Describe dorsal and ventral side
Bilaminar embryo (the EPIBLAST layer, which underwent gastrultion at the primitive streak and ultimately becme ecotderm, mesoderm, endoderm). Dorsal side: amnionic cavity Ventral side: yolk sac
Describe destinies of Ectoderm, mesoderm, and ectoderm
Ectoderm: Communication with external environment (Nervous System, Epidermis, sensory receptors, some glands)
Mesoderm: Bones and muscles (support), skeletal, urogenital, muscular, cardio systems
Endoderm: Digestion, breathing, secreting ….glands fro dayz. Epithelia for urinary bladder, GI-respiratory, more glands
Describe organ formation
Comes from multiple germ layers and are made of multiple tissue types
What kind of matter makes up the cortex/horns layer? Where do you find the cortex?
Cortex is only found in the brain. After which, the grey matter transforms into the dorsal and ventral horns of the spinal cord
In PNS, where do you find schwann and where do you find satellite cells?
Schann cells: axons
Satellite cells: soma
When does neurolation start? What comes about from it?
Starts after gastrulation (so, after the 3rd week). Makes dorsal running neural tube, which makes brain and spinal cord. The cell bodies are in CNS but their axons extend through pns
Describe neural tube formation (neuralation)
- Ecoderm inducted by notochord factors (found in black dot aka midline rod of medoderm)
- Developing neuroectoderm cells organize in midline as thickening neural plate
- Proliferating neural plate “buckle” to form depression called neural groove with bilateral neural folds.
- Further buckling and folding or neural folds approximate and fuse in DORSAL midline to form neural tube.
- Neural tube detatches from epidermis-forming surface ectoderm
- Neural pore closes (anterior and posterior porse both close)
Neural tube defect
Defect associated with 4th week of development, where neural tube fails to close properly
Craniorachischisis
“Cleft skull and spine”
Defective closure of ENTIRE neural tube. Not compatible with life
Anencephaly
Screw up with the formation of cranial vault, exposing BRAIN to AMNIOTIC FLUID, leading to degeneration. Specifically involves defective closure of cranial neural pore. “Polyhydramnios” = too much amniotic fluid….the defect is of the brain, so the end result is a destruction of the swallowing reflex. Note that the embryo needs to swallow amniotic fluid…not compatible with life
Spina bifida…and describe difference between occulta and cystica
Screw up with lower lumbar-sacral region. Focused in the caudal region.
Occulta: mild defect involving defect in fusion of vertebral arches WITHOUT herniation of the underlying neural tissue.
Cystica: legitimate screw-up with fusion of vertebral arches WITH herniation of underlying neural tissue. 3 types, 2 of which focus on herniation of vertebral column and the other involves the subarachenoid space poring out of brain (head) area
Preventing neural tube defects
Increase intake of Folic Acid (type of vitamin B). Greens, plants, and such
What are neural crest cells? What do they do?
Arises from the DORSAL edges of neural tube (which makes cns). They detach from dorsal edges of the tube and form GANGLIA. Cells that remain closer to the tube = dorsal root ganglia. Cells that migrate further away = Sympathetic ganglia, enteric ganglia
Embryo development from week 2 to week 3
Week 2: EPIBLAST (bilaminar embryonic disk)
Week 3: ECTODERM (trilaminar emryonic disk, gastrulattion), neuroectoderm (neuroepithelium and neural crest). Focused on caudal region, which is the spinal cord and the central neural canal consisting of the 31 pairs of spinal nerves
Where is the central canal located?
Dead center point of the spinal card. GO back to the cross section of the ventral and dorsal roots. The point in the very center of the butterfly
Sulcan limitans
Line that marks polarity of neural tube (separates dorsal and ventral halves)
What lines neural tube lumen/neural canal? Describe these cells
Neuroepithelium…literally proliferates from the neual tube to the lateral side of the tube. These neuroepithelium cells proliferate and DIFFERENTIATE into CNS neuroblast cells (primitive neurons). Note that neuroblast cells CANNOT divide (amitotic). There for life.
Describe difference between mantle layer and marginal layer of spinal cord
Mantle layer: grey matter
Marginal (like the margin of word doc) layer: white matter
Importance of alar plate and basal plate
Alar plate = DORSAL thickening of neuroblast cells at the edge of the mantle.
Basal plate is the result fo neuroblast cells thickening a the VENTRAL side of the mantle layer
What do alar plate and basal plate become?
Alar plate: becomes dorsal horn
Basal plate: becomes ventral horn. Note that there are cell bodies in these horns.
What do neuroepithelial cells proliferate into?
CNS neuroblasts (primitive neurons) and glioblasts (primative neuroglia –> astrocytes, ependymal cells, oligodendrocytes, all of which develop here. Microglia are also present, but later…migrating during development)
Where are somatic motor neurons located?
Ventral horn
What’s a ganglia? Describe dorsal root ganglia (DRG) and autonomic ganglia
Aggregations of neuron cell bodies in PNS.
DRG: Sensory neurons. Peripherally-projecting processes from receptors and centrally-projecting processes pierce into spinal cord.
Autonomic ganglia: motor neurons. Postsynaptic sympathetic and parasympathetic
Hirschsprung’s disease (congenital megacolon): Cause and prognosis
Defect in the migration of neural crest cells leads to AGANGLIONosis (no ganglions, leading to defective peristolsis) in the rectum (in almost all cases). Mainly effects large intestine. Distal. You will notice dilation of the gut UPSTREAM of the aganglionosis
Where does spinal cord end in adults? When, during development, did the length of the spinal cord start to differ from the length of the vertebral column?
Vertebral level of L1/L2 (Conduct a spinal tap at L3/L4). Difference started after the 3rd month of prenatal development. After the 3rd month, spinal cord stays in place, but the vertebral column keeps extending, dragging the spinal cord roots with it at an oblique angle (was horizontal at this point). This becomes cauda equina. Note that the roots at this point are exiting at a point that is more inferior than that of the conas medularis
Where does the conas medularis end in that of a newborn?
L3/L4
What does the paraxial mesoderm produce?
Produces the somite mesoderm, which makes somites along the neural tube
What does the parietal mesoderm produce?
Zeh Muszels. note that the parietal mesoderm comes from the LATERAL plate mesoderm
Name the mesoderm plates from medial to lateral:
Notochord mesoderm (has the factors that tell the plate to divide), paraxial mesoderm, intermediate mesoderm, lateral plate mesoderm
What is the job of the vacuole cells on the lateral plate mesoderm?
This is where the plate splits
Describe the somite mesoderm
Produces the sclerotome and dermatome (which work together to make mesenchyme…immature connective tissue arising from mesoderm and neural crest. Makes tendons, bones, ligaments, cartilage, dermis…essentially, the axial skeleton) and myotome (the skeletal muscles)
What does the lateral plate turn into and what is produced?
Lateral plate –> somatic/parietal mesoderm –> mesenchyme –> tendons,ligaments, cartilage, bone, dermis but all of which are for the APPENDICULAR skeletone
Parietal
somatic
Describe travel pattern of somites and neural crest cells
Travels laterally, becoming myoblasts (skeletal muscles for the arm) and melanocytes (sensory neurons for skin)
How does the neural plate go from 2d to 3d?
Cranial-caudal folding (like you bending to touch your toes) and lateral folding, where lateral edges of the embryo come down and meet together and fuse
Describe lateral folding
Lateral wing and visceral (associated with endoderm) wing fold together to make the body. meets at
Where did lateral wall fusion occur?
Anterior wall and midline
Abnormalities associated with screw ups during fusion of lateral region
Heart located outside of the body in the thoracic region.
Why are skeletal muscle cells large and multinucleated?
Formed from fusion of many immature myoblast cells (syncision). Satellite stem cells lye next to it.
Skeletal muscle anomalies
- Missing palmaris longus
- Poland’s sequence (lacking a pectoral muscle)
- Prune belly syndrome (lacking abdominal muscles)
Breakdown the types of cells that come from mesenchymal cells
chondroblasts: cartilage
osteoblasts: bone
fibroblasts: dermins, tendon, ligament
Where will you find the sclerotome in the body?
Posterior part of the skull, vertebral column, ribs
Job of notochord
Induces neurulation (spinal cord) and it induces sclerotome mesenchyme to form vertebra and intervertebral disk around the spinal cord
How do you get the erector spinae muscle to span the vertebrae instead of stay next to the particular vertebete?
The schleretome resegments itself, while keeping the future muscle in place. Note that the schleretome also produces intravertebral disks. In other words, the vertebraes form from sclerotome of somite segments
- Sclerotome segments split in half.
- Fusion between caudal end of superior sclerotome segment with cranial end of adjacent inferior sclerotome
segment. This resegmentation of mesenchyme results in muscle attachment between adjacent vertebrae to
allow for movement.
Where do ribs come from?
Schleretome
Where does sternum come from? Result if it screws up?
Parietal mesoderm (mesenchymal condensations). Mess up: Cleft Sternum…an indentation where the sternum is supposed to be
Describe skin formation from mesoderm
epidermis: surface ectoderm
dermis: dermatome or somatic mesoderm
Describe limb rotations
Upper limbs rotate 90 degrees outwards, lower limbs rotate 90 degrees inward. Upper limbs form at 24th week. Lower limb at 28th week
Job of apical ectodermal ridge
Ensures proximal to distal growth. has factors that induces the mesenchym cells in the limb bud to proliferate. As they proliferate, the limb bud extends. The apical ectodermal ridge gets farther away, losing influence. Upon losing influence, the cells left start to differentiate
Job of zone polarizing activity (ZPA)
Signals differentiation of digits in limbs (hand and feet). Close to zone = pinky. Farthest away = thumb. Note that there is polarity within the limbs too (anterior and posterior)
Limb defects
Amelia = no limbs formed
Meromelia = stubby limbs
Syndactyly: lack of apoptosis, conjoining digits as a result
Describe the two kinds of ossification
Endochondral/indirect ossification: utilizes intermediate (scleretome/somatic mesoderm/neural crest –> mesenchyme –> (chondroblasts…for cartilage…) —> osteoblasts, which makes bone).
Intramembranous/direct ossification: not use of chondroblasts
Go in detail about endochondral ossification
Starts prenatally. Starts in center of long bone (diaphysis). This is promary location of ossification…makes osteoid. . After birth, 2 secondary ossification centers (one at each end)
Growth plate
Where bone can grow. Cells in this region divide…chrondrocyte multiplication. Note: hyaline cartilage is cartilage that has not had the chance to become bone
Achondroplasia
Fibroblast receptor 3 screws up. Leads to problems with bond growth
