Development of Musculature and Limbs Flashcards
In embryology, anterior/posterior is a synonym for what other directional phrase?
cranial/caudal
What are th 4 requirements for normal muscle development?
- Mesenchymal cells
- Genetic signals
- Connective tissue framework
- fetal movement
Identify the components of the developing fetus at day 21 post fertilization
What cells are the “master inducers”? Where do they come from?
neural crest cells
originate at the neural fold
they are the “left over” from the formation of the neural tube; capable of ameboid movement and will disperse throughotut the embryo
Which direction do Myotomes split?
What is the name of the sections that split?
Does this happen before or after the somites differentiate?
Dorsal/Ventral
Epimere (dorsal)
Hypomere (ventral)
After the somites differentiate
What muscle is formed by the Epimere? What nerve is it innervated by? Where is it located with relation to the transverse process?
What muscle is formed by the Hypomere? What nerve is it innervated by?
- Epimere (
- epaxial muscle
- dorsal primary ramus
- dorsal to transverse process plane and plane of spinal nerve
- Hypomere (body wall and limbs)
- hypaxial muscle
- ventral primary ramus
- ventral (below) the plane of the spinal nerve
What is the name of the border of how far away the somite influence carriers? What is the name of the embryo lateral and medial to this border?
Lateal somitic frontier (down intermediate mesoderm)
lateral: abaxial
medial: primaxial
Identify the following characterisitc for the abaxial and primaxial portion each
origination of myogenic cells?
induction?
innervation?
derivation of connective tissue?
- Primaxial
- origination of myogenic cells?
- hypomere and epimere
- induction?
- neural tube and notochord
- innervation?
- dorsal and ventral rami
- derivation of connective tissue?
- somite
- origination of myogenic cells?
- Abaxial
- origination of myogenic cells?
- Hypomere
- induction?
- lateral plate mesoderm
- innervation?
- ventral ramus
- derivation of connective tissue?
- lateral plate
- origination of myogenic cells?
Myogenic cells differentiate from what type of progenitor cell?
What type of cells do Myogenic cells differentiate into?
Mesenchymal cells differentaite into myogenic cells
myogenic cells differentiate into postmitotic myoblasts
myoblasts fuse together to form a multinucleated syncytium (myotube), and once myofibrils are present the myotube is termed muscle fiber
What are the 3 populations of head muscles?
- Tongue: migrate similar to limb muscles
- Extraocular muscles: 3 condensations in 3 somitomeres, then migrate to orbit
- Brachial muslce: form very early complex with the neural crest cells
What type of signals specify limb development sites? What spinal segments are these located near?
a series of Hox genes creat activation gradients along the notochordal axis
forelimb C5-C8
Hindlimb L3-L5
initiated in the 4th week
What would happen if you placed the block of mesenchy for the “hindlimb” of a mouse near where the front limbs should be? Why does this happen?
What is the name of this expanding mesenchyme?
the hind limb would grow where the front limb should be
the block of mesenchyme has full limb identity; it develops with full polarity separate from each other and the rest of the embryo
limb bud
What groups forms the anterior-posterior axis of the limb?
group fo mesenchymal cell on the posterior edge of hte limb bud called the Zone of Polarizing Activyt (ZPA)
they create a morphogenic field of sonic hedgehog and retinoic acid
what group differentiates the proximal-distal axis of hte limb
a thickened strip of ectodermal cells termed the apical ectodermal ridge (AER). THey create a morphogenic field be secreting fibroblast growth factor (FGF), which stimulate proliferation of the mesenchyme
What region of limb undergoes mitotic proliferation?
Which region of limb undergoes differentiation?
The progress zone, underneath the apical ectodermal ridge undergoes rapid proliferation that does not differentaite
the more proximal mesenchyme differentiates but grows much solwer,so limbs develop form proximal to distal
By day 32, the progress zone flattens to form waht strucutre?
What happens around day 48?
flattened to forma hand or foot plate
around day 48, AER breks up into 5 distinct ridges & apoptosis begins to remove tissue betwteen to leave 5 distinct digits
What are the 3 distinct stages of muscle development that occur during week 5 of development?
durign week 5 mesenchymal cells from the hypomere migrate into the limb bud to form the appendicular musculature
- somite-specific stage
- gross functional grouping stage
- muscle specific stage
What is the name of the syndrome typefied by the unilateral absence of pectoralis major, disruption of the anterior axillary fold, reduction and lateral dislocation of the nipple, and reduction of the breast tissue?
Poland Syndrome
connective tissue does not form, so the muscle doesn’t form
What is the most common musculoskeletal defect?
What is the inheritance pattern of this defect?
Treatment?
Talipes Equinovarus (clubfoot)
multifactorial inheritance pattern
most cases, all anatomical components are present and normally formed, so therapeutic adjustment is adequate for complete reversal
What happens when there is a physical disruption or death of the AER?
Truncated Limb Syndrome
complete proximal segment of the limb, then an abrupt cessation of the limb development
What can happen if the ZPA is disrupted?
ZPA “mirror hand” defect
What are the major causes of major limb defects in neonates?
How common is this?
genetic conditions, physical environment, teratogens
thalidomide– blocks vascular perfusion of limb bud
1/500 neonates
