Week 7, Thursday
Introduction to Embryology ppt - last few slides we didn’t finish Monday
Notochordal Development:
early 3rd week
Some of the mesodermal cells migrate cranially from the primitive node and pit, and form the notochordal process
The notochordal process develops between the ectoderm and endoderm
The notochordal process develops a lumen= notochordal canal
Openings develop in the floor of the canal, forming the notochordal plate
The notochordal plate infolds to form the notochord
The primordial axis around which the vertebral column forms
As the vertebral bodies form, The plate will degenerate and some portions with form the Nucleus Pulposus of each IVD
Neurulation:
the formation of neural plate, neural folds and neural tube
The neural plate appear as a thickening of the ectoderm
A longitudinal neural groove forms in the plate
The groove is flanked by neural folds
Fusion of these grooves form the neural tube (primordial of the CNS)
As the neural tube separates from the surface ectoderm, neural crest cells form the neural crest between the newly developed neural tube and the surface ectoderm
Then the neural crest soon separates into left and right parts that migrated to the Dorsolateral aspects of the neural tube
These 2 parts of the neural crest give rise to the sensory ganglia of the spinal and cranial nerves
Collection of CNS nerve cells is called a Nuclei
The neural tube becomes the spinal cord
Neural tube defects occur usually in the time period before a woman finds out they are pregnant
Women should start taking prenatal vitamins before they start trying to get pregnant
Condensation of the mesoderm:
at the time the notocaord is developing, the mesoderm is forming 3 distinct regions:
Paraxial mesoderm
Around the axis
Intermediate mesoderm
Lateral mesoderm
Each region is destined to be something different
Sacrococcygeal Teratoma
Germ cell tumor derived from remnants of the primitive streak
Contains tissue from all three germ layers in incomplete stages of differentiation
Most common tumor in newborns
Incidence of 1 per 35,000 live births (80% are females)
Most are benign
Usually surgically excised and prognosis is good
Chordomas
Benign and malignant tumors derived from vestigial remnants of notochoral tissue
1/3 occur at the base of the cranium
Slow growing
Malignant forms infiltrate bone
1/3 of boards is usually embryology
Embryology- the Somite system and vertebral column ppt
The notochord degenerates as the bodies of the vertebrae form, but portions of it persist as the nucleus pulposus of each IVD
This was already stated, but it is very important
Somite formation:
starts around Day 18
Paraxial mesoderm begins to form discrete segmented blocks (somites) in a cranial to caudal sequence
42-44 somites include:
4 occipital
8 cervical
12 thoracic
5 lumbar
5 sacral
8-10 coccygeal
The first occipital and last 5-7 coccygeal somites eventually disappear
Paraxial mesoderm condensing to form somite
3 types of mesoderm:
Paraxial
Intermediate
Lateral plate
Each Somite organizes into 3 parts:
Dermatome
Myotome
Sclerotome
Cells from sclerotome part migrate around the notochord and neural tube
They form the ribs and vertebrae
Dermatome cells migrate to form the dermis of the skin
Myotome cells migrate to form 2 parts:
epimere: a dorsal mass that gives rise to the deep back muscles - dorsal rami
Hypomere: a ventral mass that gives rise to trunk, limb, superficial back muscles - ventral rami
Folding lateral to medial creates abdominal and thoracic cavities
Folding into fetal position is cranium to caudal, and then we lose our tail
Clinical correlation:
The level at which a somite develops is retained in its Dermatome, Myotome and sclerotome throughout life
The deltoid by muscle is innervated by the auxiliary nerve
The axillary nerve contains fibers from the C5 & C6 spinal nerves
The deltoid is primarily innervated by C5 fibers but some C6 fibers also innervate the Deltoid
This indicates that the deltoid muscle primarily developed front he myotonic at the 5th cervical level
Formation of the vertebral column:
Axonal spouts grow into surrounding sclerotome mesenchyme and end in the Myotome mesenchyme
Sclerotome cells form vertebral bodies while Myotome cells migrate to form muscles, and the axon is right behind then to form neurons
As this occurs the cranial segment of each sclerotome recombines with the caudal segment of the next superior sclerotome to form a vertebral rudiment
This re-combination also places the myotomes BETWEN, as opposed to opposite. The sclerotome enabling the future muscles to act on the vertebral column
This also results in nerves exiting between the vertebrae
Normal vs blocked vertebrae:
if the cells dont migrate the way they are supposed to, they are called a “blocked vertebrae”.
Patient wont have the same ROM as they could
You can adjust above and below it, but you can’t adjust it
Basically looks like two bodies that are fused with a large SP
Formation of the IVD
form from sclerotome cells and notochord
“Mesenchyme cells are like loosely packed cells”
Where the future vertebral body will form, the notochord degenerates and is replaced by sclerotome Mesenchymal. The centrum (body) of the vertebra is formed by sclerotome cells
Between vertebrae the notochord expands and becomes the nucleus Pulposus, which is the gelatinous center of the disc
The annulus Fibrosus forms from invading sclerotomal cells and consists of circular fibers that surround around the nucleus pulposis
“If it has to do wit the spine it will be on boards” - Gillam
Stages of Vertebral Development:
blastemal or pre-cartilaginous stage
Migration and organization of sclerotome mesenchyme forms a basic vertebral pattern around the notochord and neural tube; formation of the IVD
Cartilaginous Stage
Chondrification centers form as the sclerotome cells differentiate into chondroblasts and begin creating the cartilage vertebral model
Ossification stage
Bone replaces cartilage beginning around prenatal week 7-8 and continuing until the 25th postnatal year
Malformations:
Spina Bifida = unfused vertebral arch, can present with different severities:
Bulging area with displaced spinal cord
Open spinal cord
Ossification of the spine ppt
Stages of human development:
the developing human is called a Conceptus
The period of development or pregnancy is referred to as the gestation period which on average lasts for 280 days
There are 2 distinct period of gestation:
Embryonic Period:
From fertilization through week 8
Conceptus is called an embryo
Fetal period:
From week 9 through birth
Conceptus is called a fetus
Ossification of vertebrae:
vertebrae begin to develop during the embryonic period as mesenchymal condensations around the notochord
Later, these mesechymal bone models chondrify to form cartilaginous vertebrae
Vertebrae usually ossify towards the end of the embryonic period (8th week)
Ossification centers of typical vertebrae
begin at specific ossification centers within cartilaginous bone models
These centers can be classified as primary and secondary ossification centers
Typical vertebrae develop 3 primary and 5 secondary centers of ossification
Primary ossification centers:
1 for the vertebral body (centrum)
1 for each of the neural arches
Fuse with the body anteriorly, and in the midline posteriorly at the spinous process
With ossification, the cartilage begins to turn to bone from the primary center
Secondary ossification centers:
1 at the tip of each TP
1 at the tip of each SP
1 for each of the. 2 ring-shaped annular epiphysis that cap the superior and inferior aspects of the vertebral bodies
Epiphyseal Growth plate
Each secondary center is separated from the primary center by an epiphysial growth plate
Ossification Periods:
primary ossification centers for bodies appear first in the Lower T/S and upper L/S regions at 9-10 weeks in utero
These centers proceed cranially and cuadally from there
Primary centers for neural arches appear in the C/S and upper T/S segments during the 8th-9th week in utero
All 3 primary ossification centers are distinct at birth
The halves of the neural arches fuse wit each other during the st year of life, whining with the lumbar region
The arches fuse wit the bodies a few years later
The costal elements fuse with the neural arches, not the bodies
The 5 secondary centers appear after puberty and fuse with primary centers by the age of 21
In males, the superior and inferior annular epiphysis begin to fuse with eh body at ~17-18 y/o and is complete by age 25
T4 & T5 are the last to be completely ossified
Ossification of Atlas:
Has 2 primary ossification centers, one for each side
These form the arches and the lateral masses
The 2 sides fuse at ~ 4 years of age
Secondary ossification centers develop at the tips of both TPs, and on the anterior and posterior tubercles
Has the same ossification centers as all other typical vertebrae
Also has 2 primary centers for the dens
The body begins to ossify by the 3rd-4th month in utero
All primary centers fuse by the age of 6-7 years
An annular epiphysis for the inferior aspect of the body appears by puberty
Sacral Ossification:
The sacrum forms through the fusion of 5 sacral vertebrae, which ossify similar to other typical vertebrae
2 secondary centers form each Auricular surface
The 1st segment begins to ossify by the 9th week in utero, and this process proceeds caudally
IVDs exist between sacral segments until the bodies fuse beginning at ~20 years of age
Synostosis begins between S4 & S5, and proceed cranially
The process may not be completed until 33 years of age
Coccygeal Ossification:
4 primary center of ossification develop, one for each segment
1st segment begins to ossify soon after birth
2nd segment begins to ossify by age 5-10
3rd segment begins to ossify by age 10-15
4th segment begins to ossify by age 14-20
All segments fuse with one another by 25-30 years of age
1st bone in the body to ossify is the Clavicle
The midterm will be on everything up to this point, and since we are caught up, we will discuss the midterm in length on Monday next week
Introduction to Embryology ppt - last few slides we didn’t finish Monday
Notochordal Development:
early 3rd week
Some of the mesodermal cells migrate cranially from the primitive node and pit, and form the notochordal process
The notochordal process develops between the ectoderm and endoderm
The notochordal process develops a lumen= notochordal canal
Openings develop in the floor of the canal, forming the notochordal plate
The notochordal plate infolds to form the notochord
The primordial axis around which the vertebral column forms
As the vertebral bodies form, The plate will degenerate and some portions with form the Nucleus Pulposus of each IVD
Neurulation:
the formation of neural plate, neural folds and neural tube
The neural plate appear as a thickening of the ectoderm
A longitudinal neural groove forms in the plate
The groove is flanked by neural folds
Fusion of these grooves form the neural tube (primordial of the CNS)
As the neural tube separates from the surface ectoderm, neural crest cells form the neural crest between the newly developed neural tube and the surface ectoderm
Then the neural crest soon separates into left and right parts that migrated to the Dorsolateral aspects of the neural tube
These 2 parts of the neural crest give rise to the sensory ganglia of the spinal and cranial nerves
Collection of CNS nerve cells is called a Nuclei
The neural tube becomes the spinal cord
Neural tube defects occur usually in the time period before a woman finds out they are pregnant
Women should start taking prenatal vitamins before they start trying to get pregnant
Condensation of the mesoderm:
at the time the notocaord is developing, the mesoderm is forming 3 distinct regions:
Paraxial mesoderm
Around the axis
Intermediate mesoderm
Lateral mesoderm
Each region is destined to be something different
Sacrococcygeal Teratoma
Germ cell tumor derived from remnants of the primitive streak
Contains tissue from all three germ layers in incomplete stages of differentiation
Most common tumor in newborns
Incidence of 1 per 35,000 live births (80% are females)
Most are benign
Usually surgically excised and prognosis is good
Chordomas
Benign and malignant tumors derived from vestigial remnants of notochoral tissue
1/3 occur at the base of the cranium
Slow growing
Malignant forms infiltrate bone
1/3 of boards is usually embryology
Embryology- the Somite system and vertebral column ppt
The notochord degenerates as the bodies of the vertebrae form, but portions of it persist as the nucleus pulposus of each IVD
This was already stated, but it is very important
Somite formation:
starts around Day 18
Paraxial mesoderm begins to form discrete segmented blocks (somites) in a cranial to caudal sequence
42-44 somites include:
4 occipital
8 cervical
12 thoracic
5 lumbar
5 sacral
8-10 coccygeal
The first occipital and last 5-7 coccygeal somites eventually disappear
Paraxial mesoderm condensing to form somite
3 types of mesoderm:
Paraxial
Intermediate
Lateral plate
Each Somite organizes into 3 parts:
Dermatome
Myotome
Sclerotome
Cells from sclerotome part migrate around the notochord and neural tube
They form the ribs and vertebrae
Dermatome cells migrate to form the dermis of the skin
Myotome cells migrate to form 2 parts:
epimere: a dorsal mass that gives rise to the deep back muscles - dorsal rami
Hypomere: a ventral mass that gives rise to trunk, limb, superficial back muscles - ventral rami
Folding lateral to medial creates abdominal and thoracic cavities
Folding into fetal position is cranium to caudal, and then we lose our tail
Clinical correlation:
The level at which a somite develops is retained in its Dermatome, Myotome and sclerotome throughout life
The deltoid by muscle is innervated by the auxiliary nerve
The axillary nerve contains fibers from the C5 & C6 spinal nerves
The deltoid is primarily innervated by C5 fibers but some C6 fibers also innervate the Deltoid
This indicates that the deltoid muscle primarily developed front he myotonic at the 5th cervical level
Formation of the vertebral column:
Axonal spouts grow into surrounding sclerotome mesenchyme and end in the Myotome mesenchyme
Sclerotome cells form vertebral bodies while Myotome cells migrate to form muscles, and the axon is right behind then to form neurons
As this occurs the cranial segment of each sclerotome recombines with the caudal segment of the next superior sclerotome to form a vertebral rudiment
This re-combination also places the myotomes BETWEN, as opposed to opposite. The sclerotome enabling the future muscles to act on the vertebral column
This also results in nerves exiting between the vertebrae
Normal vs blocked vertebrae:
if the cells dont migrate the way they are supposed to, they are called a “blocked vertebrae”.
Patient wont have the same ROM as they could
You can adjust above and below it, but you can’t adjust it
Basically looks like two bodies that are fused with a large SP
Formation of the IVD
form from sclerotome cells and notochord
“Mesenchyme cells are like loosely packed cells”
Where the future vertebral body will form, the notochord degenerates and is replaced by sclerotome Mesenchymal. The centrum (body) of the vertebra is formed by sclerotome cells
Between vertebrae the notochord expands and becomes the nucleus Pulposus, which is the gelatinous center of the disc
The annulus Fibrosus forms from invading sclerotomal cells and consists of circular fibers that surround around the nucleus pulposis
“If it has to do wit the spine it will be on boards” - Gillam
Stages of Vertebral Development:
blastemal or pre-cartilaginous stage
Migration and organization of sclerotome mesenchyme forms a basic vertebral pattern around the notochord and neural tube; formation of the IVD
Cartilaginous Stage
Chondrification centers form as the sclerotome cells differentiate into chondroblasts and begin creating the cartilage vertebral model
Ossification stage
Bone replaces cartilage beginning around prenatal week 7-8 and continuing until the 25th postnatal year
Malformations:
Spina Bifida = unfused vertebral arch, can present with different severities:
Bulging area with displaced spinal cord
Open spinal cord
Ossification of the spine ppt
Stages of human development:
the developing human is called a Conceptus
The period of development or pregnancy is referred to as the gestation period which on average lasts for 280 days
There are 2 distinct period of gestation:
Embryonic Period:
From fertilization through week 8
Conceptus is called an embryo
Fetal period:
From week 9 through birth
Conceptus is called a fetus
Ossification of vertebrae:
vertebrae begin to develop during the embryonic period as mesenchymal condensations around the notochord
Later, these mesechymal bone models chondrify to form cartilaginous vertebrae
Vertebrae usually ossify towards the end of the embryonic period (8th week)
Ossification centers of typical vertebrae
begin at specific ossification centers within cartilaginous bone models
These centers can be classified as primary and secondary ossification centers
Typical vertebrae develop 3 primary and 5 secondary centers of ossification
Primary ossification centers:
1 for the vertebral body (centrum)
1 for each of the neural arches
Fuse with the body anteriorly, and in the midline posteriorly at the spinous process
With ossification, the cartilage begins to turn to bone from the primary center
Secondary ossification centers:
1 at the tip of each TP
1 at the tip of each SP
1 for each of the. 2 ring-shaped annular epiphysis that cap the superior and inferior aspects of the vertebral bodies
Epiphyseal Growth plate
Each secondary center is separated from the primary center by an epiphysial growth plate
Ossification Periods:
primary ossification centers for bodies appear first in the Lower T/S and upper L/S regions at 9-10 weeks in utero
These centers proceed cranially and cuadally from there
Primary centers for neural arches appear in the C/S and upper T/S segments during the 8th-9th week in utero
All 3 primary ossification centers are distinct at birth
The halves of the neural arches fuse wit each other during the st year of life, whining with the lumbar region
The arches fuse wit the bodies a few years later
The costal elements fuse with the neural arches, not the bodies
The 5 secondary centers appear after puberty and fuse with primary centers by the age of 21
In males, the superior and inferior annular epiphysis begin to fuse with eh body at ~17-18 y/o and is complete by age 25
T4 & T5 are the last to be completely ossified
Ossification of Atlas:
Has 2 primary ossification centers, one for each side
These form the arches and the lateral masses
The 2 sides fuse at ~ 4 years of age
Secondary ossification centers develop at the tips of both TPs, and on the anterior and posterior tubercles
Has the same ossification centers as all other typical vertebrae
Also has 2 primary centers for the dens
The body begins to ossify by the 3rd-4th month in utero
All primary centers fuse by the age of 6-7 years
An annular epiphysis for the inferior aspect of the body appears by puberty
Sacral Ossification:
The sacrum forms through the fusion of 5 sacral vertebrae, which ossify similar to other typical vertebrae
2 secondary centers form each Auricular surface
The 1st segment begins to ossify by the 9th week in utero, and this process proceeds caudally
IVDs exist between sacral segments until the bodies fuse beginning at ~20 years of age
Synostosis begins between S4 & S5, and proceed cranially
The process may not be completed until 33 years of age
Coccygeal Ossification:
4 primary center of ossification develop, one for each segment
1st segment begins to ossify soon after birth
2nd segment begins to ossify by age 5-10
3rd segment begins to ossify by age 10-15
4th segment begins to ossify by age 14-20
All segments fuse with one another by 25-30 years of age
1st bone in the body to ossify is the Clavicle
The midterm will be on everything up to this point, and since we are caught up, we will discuss the midterm in length on Monday next week