Embryology Muscle Development Flashcards
What are the three different germ tissues that give rise to the skeleton?
- Neural crest cells
- Mesoderm - somite - sclerotome
- Mesoderm - somatic lateral plate mesoderm
Neural crest cells become which structures?
- Bone
- cartilage associated with face and hyoid
- anterior cranial base and Vault
- clavicle
mesoderm - somite - sclerotome become which structures?
- Vertebrae
- Ribs
- Posterior cranial base and vault
mesoderm - somatic lateral plate mesoderm (LPM) become which structures?
- Sternum
- Scapula
- Pelvis
- Limb bones
Describe endochondral ossification.
Mesenchyme differentiates into hyaline cartilage which is then replaced by bone
Describe intramembranous ossification.
Mesenchyme differentiates directly into bone.
(mainly in the skull)
Where are the primary and secondary ossification centers located?
Diaphysis of the bone.
What is contained within the metaphysis of the bone?
Epiphyseal growth plate.
Which bones are formed by intramembranous ossification?
- Cranial Vault
- Facial bones
- Clavicles
Cranio-caudal patterning of the axial skeleton starts with what?
Expression of homeobox (hox) genes by the somites
What do Hox genes determine?
- Regional identities of the somites along the cranial - caudal access.
- Specify segment identity along the limbs
Describe vertebral development.
- The notochord signals sclerotome cells to migrate around the neural tube forming the vertebra.
- Notochord degrades except for the segmented portion that forms the nucleus pulposus of the intervertebral disc.
- Resegmentation occurs, forming the intervertebral foramina
Describe scull development.
- Develops from sclerotome and neural crest cells
- Through a mixture of endochondral and intramembranous ossification.
The ________ is the dividing line for germ layer contribution to the skull
hypophyseal or pituitary fossa of the sphenoid bone
The blue bones indicate development from which germ tissue? And the red?
Neural crest cells
sclerotome
Which structures of the skull are cartilaginous viscerocranium (chondrocranium/endocondral)?
- Mandibular condyle
- Ossicles
- Styloid process
In general neurocranium and viscerocranium, respectively, refer to what?
- Neurocranium refers to the bone that house the brain
- Viscerocranium refers to bones of the face
Which structures of the skull are considered membranous neurocranium?
Cranial vault (frontal, parietal, nasal, lacrimal bones)
Which structures of the skull are considered membranous viscerocranium?
- Maxilla
- Mandible
- Zygomatic Arch
When do limb buds appear? And when are they completed?
- 26 days
- 8 weeks
What determines where limbs will appear along the body’s access?
Hox genes
(Upper Limb buds are somites 8 - 12 lower limb buds are somites 24 - 29)
Somatic mesoderm cells migrate to form the ______ of the upper and lower limb buds approximately opposite segments _____.
- mesenchymal core
- C5 - T1 and L2 - S3
Define apical ectodermal ridge.
Thickened ectoderm at the distal border of the limb bud that induces adjacent mesoderm to remain undifferentiated and proliferate rapidly (progress zone). the more proximal mesoderm condenses and differentiates into hyaline cartilage models of limb bones
What is another name for Progress Zone.
Undifferentiated zone
Primary ossification centers are present by the ____week
12th
How are digits developed?
BMPs causes mesenchymal cells to either:
- Undergo apoptosis in interdigital tissue
- Become chondrocytes to form bone precursors of the hand
During week 6 the limbs lie in a _____ plane and in week 8 they are in a _____plane.
- coronal
- parasagittal
What produces the adult pattern of dermatome innervation in embryonic development?
Limb rotation from the sagittal to the parasagittal plane.
Upper Limb rotate 90 degrees posteriorly
Lower limb rotates 180 degrees anteriorly
(arm flexor m. go from being medial to anterior and leg flexor m. go from being anterior to posterior)
Somite (paraxial mesoderm) become which structure or tissue?
- myotomes, which diferentiate into skeletal muscle
- epimere = intrinsic back muscles, hypomere = limb & body wall msk
(splanchnic lateral plate mesoderm become smooth & cardiac msk)
What is myotome cell migration?
Each somite is associated with a single spinal nerve. Cells from the myotome of a single spinal nerve migrate outwards in a segmented manner.
(muscles also migrated during body development and this is why dermatomes and myotomes don’t line up with each other and most muscles have more than one myotome associated with them)
How are adult skin dermatomes formed in regard to muscle precursor cell migration?
Muscle precursor cells migrate into the mesenchyme of the hypaxial region and sensory fibers in the spinal nerve accompany them.
Describe myogenesis.
Embryonic muscle cells elongate & fuse to form multinucleated myotubes. Myofilaments (actin & myosin) form within the myotubes.
Anterior divisions of the anterior rami innervate the ___ compartment of the extremities and posterior divisions of the anterior rami innervate the ____ compartment of the extremities
- flexor
- extensor
(i.e. Musculocutaneous nerve, tibial nerve and radial nerve, common fibular nerve)
Sclerotome of the paraxial mesoderm become which structures?
vertebrae
annulus fibrosus
Ribs
Posterior skull
Syndetome of the paraxial mesoderm (somite) become which structures?
epaxial tendons
Describe somitogenesis.
At the end of the third week the paraxial mesoderm differentiates into somitomeres (paired on either side of the neural tube. These mature into mature somites in a cranial-caudal progression.
