Musculoskeletal System Flashcards
Appendicular Skeleton
Pectoral girdle
Pelvic girdle
Limb bones
Axial Skeleton
Vertebrae
Ribs
Sternum
Skull
Mesoderm
Dev to Paraxial mesoderm (somites)
Lateral plate somatic mesoderm
origin for musculoskeletal system
Neural crest cells
Another origin for musculoskeletal system
Paraxial mesoderm –>
Mesenchyme –> Vertebral column, ribs, & neurocranium
Lateral plate mesoderm –>
Mesenchyme –> Pectoral girdle, pelvic girdle, limbs, & sternum
Neural crest cells–>
Mesenchyme–> Viscerocranium & hyoid bone
Sclerotome
forms all of the axial skeleton except:
Sternum & a portion of the skull
Paraxial Mesoderm Derivatives
Vertebrae
Annulus fibrosus of intervertebral discs
Ribs
Neurocranium
Vertebrae Development - 4th week
4th week: sclerotome cells surround neural tube & notochord
Each sclerotome segment has
Less dense cranial portion
Dense caudal portion
Dense portion (sclerotome
Annulus fibrosus of IV discs
Fuses with less dense portion of sclerotome immediately inferior to form the vertebral body
Sclerotomes Undergo Resegmentation
6th week: chondrification occurs
Ossification: Begins 7th week 3-5 years: vertebral arch halves fuse 3-6 years: vertebral arch fuses with body ~25 years: ossification complete
Dev of Annulus Fibrosus of IV Discs
Sclerotome–>
intersegmental mesenchyme –>annulus fibrosus
Rib dev.
Grow out as lateral extensions of costal processes developing from thoracic vertebrae & wrap around anteriorly
Synovial joint forms where costal process meets vertebra
Development of the Sternum
Induced to form by ribs at ventral midline from lateral plate somatic mesoderm
10th week:
Develops as two sternal bars that will fuse cranially to caudally
Later fuse to form manubrium, sternal body, and xiphoid process
Viscerocranium
anterolateral facial bones
Neurocranium
bones encasing the brain
Development of the Neurocranium
Occipital somites form a portion of the neurocranium
Cartilaginous Neurocranium
Base of skull
Sphenoid, petrous portion of temporal bone, portion of occipital bone
Form by endochondral ossification
All other parts of
Form by intramembranous
Membranous Neurocranium
Flat bones that surround the brain
Formed by intramembranous ossification
Fontanelles
Enlarged membranous spaces where more than 2 bones meet
Development of Appendicular Skeleton
Differentiates from mesenchyme of lateral plate somatic mesoderm
Endochondral Ossification
5th week: condensations of mesenchyme appear in limb buds
6th week: mesenchymal bone models undergo chondrification to form hyaline cartilage models
7th/8th week: ossification begins in long bones
Occurs initially in diaphysis from primary ossification centers
Skeletal muscle origin
Derived from paraxial mesoderm
Cardiac muscle origin
Cardiac muscle
Derived from intraembryonic splanchnic mesoderm surrounding developing heart
Smooth muscle origin
Smooth muscle
Of G.I. tract: Derived from intraembryonic splanchnic mesoderm surrounding gut tube
Somites differentiate into:
Sclerotome
Myotome
Dermatome
-skeletal muscle dev.
Somites give rise to:
Axial skeleton (most)
Associated musculature
Overlying dermis of back
Myoblasts
specialized mesoderm cells
Fuse together to form skeletal muscle
Actively contract by week 7
Progenitor cells for muscle tissues derived from
the ventrolateral and dorsomedial lips of the dermomyotome
Lateral somitic frontier
separates paraxial mesoderm from lateral plate somatic mesoderm
Primaxial domain
surrounds neural tube and contains only somite-derived cells **adjacent to the neural tube -very close to it.
Dorsomedial lip (DML) & a few Ventrolateral lip (VLL) cells left at the myotome will form the:
Musculature of the back
Shoulder girdle muscles
Intercostal muscles
Abaxial domain
parietal layer of lateral plate mesodem with somite-derived cells
Most Ventrolateral lip (VLL) myoblasts migrate across the frontier into lateral plate somatic mesoderm to form: Infrahyoid muscles Pectoralis major & minor muscles Abdominal wall muscles Limb muscles
Myotome
Each myotome divides into: Epaxial group (dorsal/posterior) Hypaxial group (ventral/anterior)
Each spinal nerve divides into:
Dorsal primary ramus
Ventral primary ramus:
Epaxial muscles –>
back muscles –>dorsal primary rami
Hypaxial muscles –>
muscles of the limbs + body wall –> ventral primary rami
Cardiac Muscle dev
Derived from intraembryonic splanchnic mesoderm
Gives rise to mesenchyme surrounding developing heart tube
Smooth Muscle dev
Derived from intraembryonic splanchnic mesoderm
Wall of gut & gut tube derivatives
Most large arteries (i.e., aorta)
Neuroectoderm
Sphincter pupillae m. & dilator pupillae m. of iris
-derived from ectoderm.
Surface ectoderm
Myoepithelial cells of mammary, salivary, & sweat glands
Limb Development
Limb buds emerge toward end of week 4 Upper limbs (UL) appear 1st Lower limbs (LL) appear 1-2 days later
Limb Bud
Core of mesenchyme, lined by surface ectoderm
Mesenchyme forms connective tissue of the limb
Cartilage, bone, dermis, blood vessels
Elongation of the Limbs
Apical ectodermal ridge (AER) sends signaling factors to nearby mesenchyme of progress zone
Keeps cells undifferentiated and rapidly dividing to form more limb tissue
Limb grows proximally to distally
Migratory Cells Invade Limb Bud
Melanocytes From neural crest Sensory axons & Schwann cells From neural crest Myoblasts From myotome of VLL Motor axons From neural
Outgrowth of Limbs, Weeks
4-8. Epaxial muscles
Dorsal primary rami
Hypaxial muscles
Ventral primary rami
Will divide to form dorsal & ventral branches to compartments
Limb buds initially grow straight out
laterally, followed by:
UL lateral rotation by 90° & LL medial rotation by 90 degrees
Week 6: “paddle stage”
End of week 6
Mesenchyme is condensing to form digital rays
Outlines of future digits
Organized apoptosis of cells in AER divides paddle into 5 digits
End of week 8
Mesenchyme will differentiate as hyaline cartilage in digits due to AER induction
Apoptosis in AER forms
Digits
Meromelia
absence of part of a limb
Amelia
absence of entire limb
Polydactyly
extra digits
Syndactyly
two or more fused digits
Sternum
Lateral plate mesoderm
Skull
Neural crest cells in origin
Portion of occipital somite
fuses with cranial portion of cranial 1. Bottom of spinal cord tapers off.
Manubrium
first to form, forms downward.
Each vertebral level will have
Ossification centers, begin to ossify from 12th week onward.
Bottom of skull with nerves
Endochondrial ossification
Rest of skull (flat bones)
Intermembranous ossification
Myogenic
Myoblasts on hold
Primaxial and abaxial
Helps determine dorsal and ventral ramus innervation.
Local molecular clues differentiate between
Cardiac and smooth muscle.
