Development of the Muscular & Skeletal Systems Flashcards
When is the critical period in development?
weeks 3 - 8
When do the upper limbs and lower limbs begin development
week 4 (lower limbs start after)
Where does myotome come from and what comes from it
1) Somites (paraxial)
2) ALL MUSCLE
What are the three types of somites and what do they give rise to
myotome - muscle
sclerotome - axial skeleton
dermatome - dermis (some)
Describe the process of vertebral body formation starting with Somite division
1) The somite divides diagonally into the dorsal later part (myotome and dermatome) and the ventral medial part (sclerotome)
2) The sclerotome from the ventral medial part migrates down to surround the notochord to form the vertebrae
3) The Caudal Dense part of the sclerotome from the superior sclerotome A migrates down to merge with the inferior Cephalic Loose part of sclerotome B.
4) Merging of these parts leads to the creation of the vertebral body
What forms along with the vertebral body and by what week
WEEK 5
1) Muscle movement (joints become crossed by muscles – myotome connect to vertebrae/neural tube)
2) Motor Nerves (sensory n. form later using motor as a template)
When does the vertebral column form by
week 5
Where do the following derive from:
1 - PNS sensory neurons
2 - PNS motor neurons
3 - PNS preganglionic neurons
1 - Neural Crest
2 & 3 - Neural Ectoderm
Where do nerves come out in the cervical spine
Above the vertebrae whose number they share (i.e. second number rule) — different in the rest of the body
What do motor nerves do by week 5
migrate between the vertebrae to innervate myotomes
What parts of the adult vertebrae derive from A) Caudal Dense part and B) Cephalic Loose part
What about the spinous process?
Superior parts = Caudal Dense (superior articular process, pedicle, transverse process)
Inferior parts = Cephalic Loose (inferior articular process)
Spinous process = BOTH!!
Where does the nucleus pulposus come from
notochord remnant – mesoderm
mucoid substance/jelly
where does the annulus fibrosis come from
sclerotome
fibrous tissue/fibrocartilage
Rib origin
from sclerotome cells that migrate out from the costal processes of thoracic vertebrae
sternum origin
somatic lateral plater mesoderm
Mesenchymal condensation cells migrate to midline from the ribs to ossify as the sternum
Hox genes (what parts of spine to they impact)
group of genes that determine bone shape and control the body plan on a cranial-caudal axis
Hox 4 + 5 = cervical Hox 6 = Ribs (thoracic) Hox 9 = Floating Ribs (thoracic) Hox 10 = lumbar Hox 11 = sacral
Caudalization (and Hox genes affected)
aka gain of function
leads to vertebrae transformation where vertebrae take on characteristics of vertebrae INFERIOR to it (i.e cervical become thoracic w/ ribs)
Hox 6 - cervical to thoracic (w/ ribs)
Hox 10 - thoracic to lumbar (no ribs)
Cranialization (and Hox genes affected)
aka loss of function
leads to transformation of vertebrae to take on characteristics of vertebrae SUPERIOR to it
Hox 4 = C2-C3 will look like C1
Hox 5 = C4-T2 will look like C2
Hox 10 = look like thoracic vertebrae (with ribs)
Cervical Rib abnormality
Rib development in cervical vertebrae (VERY RARE - lumbar more common)
Caused by gain of function (caudalization)
Contributes to THORACIC OUTLET SYNDROME —- subclavian A is compressed, causes issues in limbs
Pectus carinatum
aka Pigeon chest
unusual growth of rib that makes chest jut out (sternum protrusion)
males more than females
noticed at age 11
no known causes
Pectus excavatum
sternum depression (excavated chest) aka funnel chest
Heart displaces almost entirely to the left side
Patients often have exercise intolerance
noticed by age 1
What are the subclassifications of myotome (explain them)
1) epimere
- epaxial muscles — deep back muscles (LAYERS 4,5,6)
- dorsal/posterior rami innervated
2) hypomere
- hypaxial muscles —- flexor muscles of the trunk and limbs/all other skeletal muscles
- ventral/anterior rami innervated
What part of the somite does epaxial, hypoaxial and dermatome derive from?
epaxial — dorsal part of the Dermomyotome
hypoaxial —- ventral part of the dermomyotome
dermatome – central part of the dermamyotome
How does the migration of hypomere cells from the dermomyotome determine what skeletal muscles they become?
Some migrate to the Doral side of the limb bud, creating the anterior compartment muscles (triceps, extensors —- radial and axillary n.)
The others go to the ventral side of the limb bud to make the anterior compartment (flexors, pronators — lateral and medial cords)
Poland syndrome
SEE TANK 26 in lab for an example!!!
- No pectoral major or minor present
- Ipsilateral breast hypoplasia (different musculature on each breast)
-Absence of 2-4 ribs (severe cases)
Prune-Belly Syndrome
Partial or complete absence of abdominal muscles
- primarily affects males
- associated with:
- cryptorchidism (failure of testicular drop)
- poor formation of bladder/urinary tract
