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© Dr Mark Hill, 2003. |
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This Page covers Lab 8- Introduction to Musculoskeletal Development. Clicking on the small images below links to a large labelled image from the UNSW Embryology Program (more info?). For a comprehensive background in Embryology look at the UNSW Embryo Program available on the Web. Follow through the section descriptions as listed in your yellow practical book. This is an introductory class and you are not expected to understand all aspects of musculoskeletal development. Please also look at the Carnegie stages and identify changes in Limb development over this period as seen by external changes. There are 3 pages of Images and some Histology slides to work through in this class:
Remember that embryonic development can be divided into 23 Carnegie stages (fetal development starts after Carnegie stage 23). For terms in your Notes that you do not recognise, use the Glossary at the back of your yellow book or the brief description (Terms) on each or these page. For a comprehensive background in Embryology look at the UNSW Embryo Program available on the Web. Note- Use the back button at the top of
the Web Browser to return to this page. Bookmark
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This Page: Introduction | Stage13/14 Embryo | Terms | disclaimer | About Acrobat |
Dr Mark Hill |
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Other Pages: Pig (Stage 13/14) | Human (Stage 22) | High Power Human (Stage 22) | Musculoskeletal Development Lecture | Notes |
Email: m.hill@unsw.edu.au |
Lab 8- Development of the Musculoskeletal System |
Next Embryo notes: Lab 12 Pharynx and Face |
Early Human Carnegie StagesNote images are not all the same scale. |
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Stage 13/14 Embryo
Next Image Set- Human Stage 22
At this early stage the Musculoskeletal system consists of undifferentiated mesenchyme and early Limbbuds.
- Somites
- At the lower end of the embryo, somites are more immature and have somitocoeles still present.
- At the level of the forelimbbud and trunk, the
somites have differentiated into regions that can be
identified as sclerotome and dermamyotome.
- i.e. due to the sequential addition of somites in a single Carnegie stage you can see a range of somite developmental stages.
- Limbbud
- has surface ectoderm with core of mesenchyme.
- The forelimbbud is more prominant than the
hindlimb.
- as in the rostrocaudal addition of somites, the hindlimbs are more immature than the forelimbs.
- apical ectodermal ridge (AER) and blood vessels in the mesenchyme.
- Forelimbbud dorsal (extensor) and ventral (flexor) surfaces and axillary fossa (armpit).
- Note the position of the spinal cord and DRG with
spinal nerves relative to the limbbud.
- at both limbuds a nerve plexus will develop where segmental spinal nerves cross prior to entering the limb.
- brachial (arm) and lumbar (leg) plexus.
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Human Carnegie stage 13 |
Human Carnegie stage 14 |
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Next Image Set- Human Stage 22 |
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The vertebra of the spinal cord go through a lengthy period of maturation which I have briefly summarized below. A key aspect of development for vertebra (spinal cord) and skull (brain) is to create a flexible enclosure to allow continued growth of the neural components they enclose and that are relatively immature compared to the skeleton.
- Precartilaginous Stage (wk4 - wk6)
- shown in stage 13/14 embryo
- generated by the sclerotomal mesenchyme surrounding the notochord
- vertebra form out of register with the original somites
- each sclerotome has 2 components
- cranial loose cells
- fuses with next cranial segment
- caudal dense cells
- upper part of which forms annulus fibrosus of intervertebral disc (IVD)
- lower part fuses with next caudal segment (cranial+caudal=centrum)
- cranial loose cells
- notochord forms nucleus pulposus (surrounded by sclerotomal annulus fibrosus) of IVD
- Cartilaginous Stage (wk6 - )
- chondrification centers form in mesenchyme of centrum
- replaces mesenchyme with cartilage
- Bony Stage (wk7 - 25 years)
- shown in stage 22 embryo
- primary ossification centers form in cartilage
- 2 dorsal- each vertebral arch
- 1 ventral- centrum
- at birth vertebra is these 3 boney parts connected by cartilage
- postnatally 3-5 years- arch fuses
- puberty- secondary ossification centers form on body and facets
- acetabulum-
- alar plate- in the spinal cord is the afferent, dorsal horn region.
- amnion-
- anlage- (Ger. ) primordium, structure or cells which will form a future structure.
- annulus fibrosus- the circularly arranged fibers (derived from sclerotome)that together with the nucleus pulposus (derived from notochord) form the intervertebral disc (IVD) of the vertebral column.
- apical ectodermal ridge- (=AER) specialized region of ectoderm at the tip of the growing limbbuds that specifies
- aponeurosis-
- apoptosis- the process of programmed cell death. In development of the limbs occurs in the "paddle" if both the hand and foot, generating the separated digits. Occurs in many tissues of the embryo and adult.
- axial mesoderm- (=notochord)
- axillary fossa- the future "armpit" region
- basal plate- in the spinal cord is the efferent, ventral horns.
- brachial plexus- mixed spinal nerves innervating the upper limb form a complex meshwork (crossing).
- brain- general term for the central nervous system formed from 3 primary vesicles.
- buccopharyngeal membrane- (=oral membrane) at cranial (mouth) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet. (see also cloacal membrane)
- cardinal vein-
- cartilage- connective tissue from mesoderm in the embryo forms initial skeleton replaced by bone. In adult, found on surface of bone joints.
- centrum- the primordium of the vertebral body formed initially by the sclerotome.
- clavicle- (L. little key) bone which locks sholder to body.
- cloacal membrane- at caudal (anal) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet forms the openings for GIT, urinary, reproductive tracts. (see also buccopharyngeal membrane)
- connective tissue-
- costotransverse-
- costovertebral-
- dermatome-
- dermomyotome- dorsolateral half of each somite that forms the dermis and muscle.
- dorsal aorta-
- dorsal root ganglia- (=spinal ganglia) sensory ganglia derived from the neural crest lying laterally paired and dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord.
- dura mater-
- dystrophy-
- ectoderm- the layer (of the 3 germ cell layers) which form the nervous system from the neural tube and neural crest and also generates the epithelia covering the embryo.
- ectodermal ring- the thickened ring of ectoderm seen dorsally in the early (stage13/14) embryo adjacent to the dermatome. Ectoderm ventrally is relatively thin, gaining its dermatome component at a later stage.
- endochondrial ossification- the process of replacement of the cartilagenous framework by osteoblasts with bone.
- endoderm- the layer (of the 3 germ cell layers) which form the epithelial lining of the gastrointestinal tract (GIT) and accessory organs of GIT in the embryo.
- epaxial myotome- the dorsal portion of the myotome that generates dorsal skeletal muscles (epaxial muscles).
- epimysium-
- erector spinae-
- external oblique m.-
- extracellular matrix- material secreted by and surrounding cells. Consists if fibers and ground substance.
- ependyma-
- epiblast- the layer (of the bilaminar embryo) that generates endoderm and mesoderm by migration of cells through the primitive streak. The remaing cells form ectoderm.
- extensor-
- fascia-
- fascicle- (=bundle)
- femur-
- fibroblast growth factor-
- flexor-
- fossa-
- gracilis m.-
- growth factor- usually a protein or peptide that will bind a cell membrane receptor and then activates an intracellular signaling pathway. The function of the pathway will be to alter the cell directly or indirectly by changing gene expression. (eg shh)
- hox- (=homeobox) family of transcription factors that bind DNA and activate gene expression. Expression of different Hox genes along neural tube defines rostral-caudal axis and segmental levels.
- humerus-
- hypaxial myotome- the ventral portion of the myotome that generates ventral skeletal muscles (hypaxial muscles).
- inguinal fossa- the region of the lower limb ajacent to flexor surface (exuivilant to the axillary fossa of the upper limb).
- intercostal- the region between adjacent ribs, usually comprising intercostal muscles and connective tissue.
- intervertebral disc- (IVD) the annulus fibrosus+nucleus pulposus together form the intervertebral disc (IVD) of the vertebral column. This is the flexible region between each bony vertebra that allows the column to be bent.
- intervertebral foramina-
- ischium-
- lumbar plexus- mixed spinal nerves innervating the lower limb form a complex meshwork (crossing).
- mesenchyme-
- mesoderm- the middle layer of the 3 germ cell layers of the embryo. Mesoderm outside the embryo and covering the amnion, yolk and chorion sacs is extraembryonic mesoderm.
- metacarpal cartilage-
- muscle- 3 main types of muscle (smooth, cardiac and skeletal) all derived from mesoderm but different regions.
- myotome-
- myoblast- the undifferentiated mononucleated muscle cells that will fuse together to form a multinucleated myotube, then mature into a muscle fibre.
- MyoD- transcription factor involved in the determination of muscle cells in the somite. A basic helix-loop-helix factor which binds DNA.
- myotome- the portion of the dermamyotome that generates skeletal muscle. Has 2 components epaxial (dorsal muscles ) hypaxial (ventral muscles).
- neural crest- cell region at edge of neural plate, then atop the neural folds, that remains outside and initially dorsal to the neural tube when it forms. These paired dorsal lateral streaks of cells migrate throughout the embryo and can differentiate into many different cell types(=pluripotential). Those that remain on the dorsal neural tube form the sensory spinal ganglia (DRG). Neural crest cells migrate into the somites.
- neural tube- neural plate region of ectoderm pinched off to form hollow ectodermal tube above notochord in mesoderm.
- neuropore- opening at either end of neural tube: cranial=rostral=anterior, caudal=posterior. The cranial neuropore closes (day 25) approx. 2 days (human) before caudal.
- nucleus pulposus- central region of intervertebral discs of the spinal cord derived from the notochord.
- notochord- rod of cells lying in mesoderm layer ventral to the neural tube, induces neural tube and secretes sonic hedgehog which "ventralizes" the neural tube and may influence somite development.
- otocyst- (=otic vesicle) sensory placode which sinks into mesoderm to form spherical vesicle (stage 13/14 embryo) that will form components of the inner ear.
- patella-
- Pax- name derived from Drosophila gene 'paired' (prd) with a box domain. Transcription factor of the helix-turn-helix structural family, DNA binding, and activating gene expression. In human, nine member proteins from Pax-1 to Pax-9.
- pedicle-
- perichondrium-
- perimysium-
- phalangeal cartilage-
- pharyngeal arches- (=branchial arches, Gk. gill) form structures of the head. Six arches form but only 4 form any structures. Each arch has a pouch, membrane and cleft.
- pharynx- uppermost end of GIT, beginning at the buccopharyngeal membrane and at the level of the pharyngeal arches.
- phocomelia-
- quadratus lumborum m.-
- quadriceps m.-
- rectus abdominal m.-
- sacrum-
- scapula-
- sclerotome- ventromedial half of each somite that forms the vertebral body and intervertebral disc.
- segmentation- to break a solid structure into a number of usually equal size pieces.
- serosa-
- spinal canal- the mature space in the core of the spinal cord (filled with CSF) formed from the original lumen of the neural tube.
- spinal cord- caudal end of neural tube that does not contribute to brain. Note: the process of secondary neuralation contributes the caudal end of the spinal cord.
- spinal ganglia- (=dorsal root ganglia, drg) sensory ganglia derived from the neural crest lying laterally paired and dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord.
- spinal nerve- mixed nerve (motor and sensory) arising as lateral pairs at each vertebral segmental level.
- somatic mesoderm- derived from lateral mesoderm closest to the ectoderm and separated from other component of lateral mesoderm (splanchnic, near endoderm) by the intraembryonic coelom.
- somite- segmental block (ball) of mesoderm formed from paraxial mesoderm adjacent to notochord (axial mesoderm). Differentiates to form initially sclerotome and dermamyotome (then dermotome and myotome).
- somitic mesoderm-
- somitocoel- a transient cavity that appears within each of the the early forming somites then is lost.
- somitogenesis- the process of segmentation of the paraxial mesoderm to form "mesoderm balls" beginning cranially (humans day20) and extending caudally at 1 somite/90 minutes until approx. 44 pairs have been formed.
- sonic hedgehog- (=shh) secreted growth factor that binds patched (ptc) receptor on cell membrane. SHH function is different for different tissues in the embryo. In the nervous system, it is secreted by the notochord, ventralizes the neural tube, inducing the floor plate and motor neurons. In the Limb it is secreted by the zone of polarizing activity (ZPA) organizing limb axis formation.
- sternum-
- syndactyly-
- tarsal-
- Tbx- T-box genes (transcription factor)
- tibia-
- transcription factor- a factor (protein or protein with steroid) that binds to DNA to alter gene expression, usually to activate. (eg steroid hormone+receptor, Retinoic acid+Receptor, Hox, Pax, Lim, Nkx-2.2).
- transverse abdominal m.-
- trochanter-
- vertebral body- formed by centrum, vertebral arch, facets for ribs. It is the mature vertebral structure formed by the 5 secondary ossification centers after puberty.
- vertebral column- name given to the complete structure formed from the alternating segments of vertebra and intervertebral discs which support the spinal cord.
- vertebral foramen- the dorsal cavity within each vertebra, generated by the vertebral arch that surrounds the spinal cord.
- vertebral canal-
- Wnt7a-
- zone of polarizing activity- (zpa) dorsal region with forming limbbud mesenchyme that secretes shh and regulates limb axis formation.
The serial Embryo sections (stage 13/14, 22, Carnegie stages) used in practical class on computers and available on the Web are also available on the UNSW Embryo CD ($15) from the Anatomy School office on the First Floor. This CD was made in 1997 and so the current Web Version has additional content. A newer CD Version 2.0 will be available at a later date this year but all serial images are also on the original Version 1.0 CD.
The document is for educational purposes and personal use only and should not be reproduced for other purposes. This document and attached pages © Dr M. Hill, 2003.
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Date Last Modified: 29/07/2003
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