Podcast
Questions and Answers
During which week of development do the somites begin to form?
During which week of development do the somites begin to form?
- 3rd week (correct)
- 1st week
- 2nd week
- 4th week
The notochord is derived from the mesoderm.
The notochord is derived from the mesoderm.
True (A)
What is the term for the phenomenon where the body is divided into repeating segments or units?
What is the term for the phenomenon where the body is divided into repeating segments or units?
Metamerization
The ______ migrates to surround the notochord and neural tube during axial skeleton formation.
The ______ migrates to surround the notochord and neural tube during axial skeleton formation.
From which embryonic structure do the vertebral bodies primarily develop?
From which embryonic structure do the vertebral bodies primarily develop?
The nucleus pulposus is derived from the sclerotome.
The nucleus pulposus is derived from the sclerotome.
What embryonic structure gives rise to the ribs?
What embryonic structure gives rise to the ribs?
The sternum forms from two ______ that fuse in the midline.
The sternum forms from two ______ that fuse in the midline.
Which of the following best describes spina bifida occulta?
Which of the following best describes spina bifida occulta?
In myéloméningocèle, only the meninges protrude through the vertebral defect.
In myéloméningocèle, only the meninges protrude through the vertebral defect.
In myéloschisis, what structure is exposed due to the vertebral defect?
In myéloschisis, what structure is exposed due to the vertebral defect?
Limb buds first appear during the ______ week of development.
Limb buds first appear during the ______ week of development.
What is the term for the complete absence of a limb?
What is the term for the complete absence of a limb?
Polydactyly refers to the absence of digits.
Polydactyly refers to the absence of digits.
What is the term for the condition involving fusion of digits?
What is the term for the condition involving fusion of digits?
Which of the following structures is derived from the para-axial mesoderm?
Which of the following structures is derived from the para-axial mesoderm?
The neural plate gives rise directly to the somites.
The neural plate gives rise directly to the somites.
What is the lécithocèle?
What is the lécithocèle?
Around the ______ week the embryo develops approximately 30 pairs of somites.
Around the ______ week the embryo develops approximately 30 pairs of somites.
Match each malformation with its description:
Match each malformation with its description:
Cells from the sclerotome migrate to which region?
Cells from the sclerotome migrate to which region?
The crête neurale forms into the spinal cord of the embryo.
The crête neurale forms into the spinal cord of the embryo.
Where do cells of the sclerotome migrate to?
Where do cells of the sclerotome migrate to?
The ossification of centres primitifs occurs during the ______ week of development.
The ossification of centres primitifs occurs during the ______ week of development.
What does the bourrelet ectodermique apical develop into?
What does the bourrelet ectodermique apical develop into?
Ectrodactylie involves having more than the normal number of digits.
Ectrodactylie involves having more than the normal number of digits.
What two embryonic tissue layers are involved in the movements leading to arm and leg development?
What two embryonic tissue layers are involved in the movements leading to arm and leg development?
The vertebral pre-cartilaginous body is developed by the ______ week of development.
The vertebral pre-cartilaginous body is developed by the ______ week of development.
The process costaux form into what?
The process costaux form into what?
Match the term with what it means:
Match the term with what it means:
Flashcards
Somite Formation
Somite Formation
The para-axial mesoderm differentiates into somites.
Metamerization
Metamerization
The process where the body is divided into repeating segments.
Sclerotome Migration
Sclerotome Migration
Cells migrate around the notochord and neural tube.
Vertebral Body Formation
Vertebral Body Formation
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Nucleus pulposus
Nucleus pulposus
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Primary Ossification Centers
Primary Ossification Centers
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Sternum Formation
Sternum Formation
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Spina Bifida Occulta
Spina Bifida Occulta
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Meningocele
Meningocele
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Myelomeningocele
Myelomeningocele
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Myeloschisis
Myeloschisis
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Limb Buds
Limb Buds
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Apical Ectodermal Ridge (AER)
Apical Ectodermal Ridge (AER)
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Amelia
Amelia
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Meromelia
Meromelia
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Micromelia
Micromelia
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Study Notes
- Formation of the skeleton
- Dr. Gallet Marlene, May 2022
Evolution of Somites (3rd Week)
- Para-axial mesoblast exists
- Dorsal cord is formed
- Amniotic cavity occurs
- Neural plate develops into the neural groove
- Neural crest arises
- Lecithocoele is present
- Somites are forming
Metamerization Phenomenon
- Metameres are present
- By the end of the 3rd week, somites form in 5 to 7 pairs
- By the end of the 4th week, 30 pairs of somites are present in the embryo
- These include occipital, cervical, dorsal, lumbar, sacral, and coccygeal somites
Differentiation of Somites
- Cells of the medio-ventral region are polymorphic and in contact with each other
- The sclerotome forms
- Cells migrate from each metamere to the axial region around the notochord
Formation of the Axial Skeleton
- Cells from the sclerotome migrate to the axial region of the embryo and surround the notochord
- This forms the mesoblastic column
Development of the Vertebrae (5th Week)
- Precartilaginous vertebral bodies form
- The zone near the head is called the cranial zone
- The zone near the tail is called the caudal zone
- Nerve root buds develop
- The intervertebral disc begins to develop
- Vertebral bodies begin to form along with the neural tube, cartilaginous differentiation, chorda regression and nucleus pulposus establishment
- Ossification of primary centers occurs and secondary centers are generated
Development of Ribs
- At 35 days, pre-cartilaginous ribs form
- By day 49, the cartilaginous sternum buds
Development of the Sternum
- At 42 days, costal buds and hemisternums form on the right and left
- At 49 days, fusion occurs on the midline
- By 56 days, the cartilaginous sternum forms
Spinal Dysraphism/Spina Bifida
- Spina bifida occulta has a tuft of hair in the lumbar region.
- Meningocele involves a protrusion of the meninges filled with cerebrospinal fluid
- Myelomeningocele involves protrusion of the spinal cord
Myeloschisis
- Myeloschisis involves an open spinal cord, not covered by skin
- Is often associated with neurological deficits
Development of Limbs
- At 26 days (4th week) limb buds of the upper and lower limbs form
- At 28 days (4th week) buds are also starting to form
- During the 5th-6th weeks, cartilaginous buds form and lengthen
- At the 8th week, limb segments become visible and have cartilaginous components, joints and furrows
Growth of the Limbs
- During the 4th week, the apical ectodermal ridge becomes flat, forming a palette
- This is when major movement begins for the mesoderm and ectoderm
- At the 12th week, ossification centers appear in the body
Limb Malformations
- Amelia: complete absence of a limb
- Phocomelia: limbs are absent or shortened but hands and feet are present
- Meromelia: a partial absence of a limb
- Micromelia: abnormally short limbs
- Achondroplasia: A disorder of bone growth that causes the most common type of dwarfism
- Syndactyly: fused or webbed fingers or toes
- Polydactyly: more than the usual number of fingers or toes
- Ectrodactyly: cleft hand or foot
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Description
Explore the formation of the axial skeleton, beginning with the evolution of somites during the third week. Learn about the metamerization phenomenon and the differentiation of somites. Discover how cells from the sclerotome migrate to form the mesoblastic column around the notochord, and see how vertebrae develop in the fifth week.
