Module 3 Unit 2 Flashcards
What is the paraxial mesoderm? What are the series known as?
Forms a segmented series of aggregated tissue blocks on each side of the neural tube
somitomeres - Loosely packed in the head region
Somites - more densely packed from the occipital to caudal region
How many pairs of somites are there for each region?
42 - 44 pairs of somites:
4 occiput
8 cervical
12 thoracic
5 lumbar
5 sacrum
8-10 coccyx
What are the differentiated parts of somites?
Dermatomes, Myotomes, Sclerotome
What is a dermtome? How does it relate to a clinical diagnosis?
Area is the skin innervates by sensory fibers from a single spinal nerve root. Relays sensation from a particular region of the skin to the brain.
Clinically to diagnose the level of the spinal cord or nerve root damage.
What are myotomes? How are there important for diagnosing?
Groups of muscles innervates by the motor fibers of a single spinal nerve root.
Important for assessing motor function and diagnosing neuromuscular disease.
What are the sclerotome? How is it clinically relevant?
The regions of bone or skeletal structures innervated by single spinal nerve roots.
Relevant in understanding patterns of referred pain in conditions affecting the skeletal system.
* Cells of sclerotome are mesenchymal that differentiate to become: chondroblasts, osteoblasts, fibroblasts
What does the paraxial mesoderm contribute to?
It contributes to the bones of the face and skull,and vertebrae and ribs.
What does the neural crest cells (NCC) contribute to?
It contributes to the bones of the face and skull.
What does the lateral plate mesoderm contribute to? What structures are the cells in the parietal mesoderm differentiated into?
It contributes to the viscerocranium in the pharyngeal arches. It is differentiated into parts of the appendicular skeleton such as, sternum, bones of the pelvic and shoulder girdles, and limb bones.
What are the two distinct processes involved in the formation of bones during embryonic and fetal development? What do they involve?
Intramembranous ossification - involves direct bone formation from mesenchymal tissue.
Endochondral ossification - the replacement of a cartilaginous template with bone tissue.
What is the intramembranous ossification process?
Mesenchymal stem cells —> Differentiate into osteoblasts —> Osteoblasts come together to form an ossification center —> Osteblasts gradually arrange in a circle around ossification center —> Osteoblasts secrete osteoid (unmineralized bone) —> Osteoid calcifies and hardens to form bone
What are the bone directly differentiated to in the intramembranous ossification process?
Flat bones of the skull (parietal, frontal, occipital etc.), clavicle
What does the endochondral ossification give rise to?
Mesenchyme (hyaline cartilage) —> Cartilage (scaffold) —> Primary ossification center formed in the center, blood vessels starts to enter (Osteoblasts and proliferating chondrocytes) —> Secondary ossification center formed on the two ends of the long bone
What does the brachial (pharyngeal) apparatus shape into?
The head and neck anatomy in vertebrate embryos
What does the pharyngeal cross-section consist of?
Mesenchymal core derived from mesoderm and neural crest cells, and each is lined internally by endodermis and externally by ectoderm.
What does the first pharyngeal arch (Meckel’s cartilage) give rise to?
Gives rise to the maxilla, mandible, and muscles of mastication innervated by CN 5
What does the secondary arch give rise to?
Contribute to the formation of the hyoid bone and muscles of facial expression innervated by CN 7
What does the third and fourth arches give rise to?
thyroid gland
Thymus
Parathyroid glands
Components of the middle ear and neck
What does arch/pouch 1 consist of?
Muscles of Mastication
Meckel’s Cartilage
Maxilla
Meatus
Middle ear
Mastoid air cells
Maxiallary artery
Mylohyoid
trigeMinal nerve (CN 3)
What does arch/pouch 2 consist of?
Staples
Styloid
Stylohyoid
Stapedius
Smiling (fascia nerve)
Stapedial artery
What does arch/pouch 3 consist of?
StyloPHARYNGEUS, glossoPHARYNGEAL nerve, Parathyroid glands, internal Carotid (Problem if severed), Common Carotid (Problems of severed)
What does arch/pouch 4 + 6 consist of?
everything from Vagus
4 - superior laryngeal
6 - Recurrent laryngeal
Arytenoids, Cricoid, Corniculate, Thyroid, Superior Parathyroid, Ultimobrachial body, Parafollicular Cells
Pulmonary arteries + ductus arteriosus (left)
What is the Neurocranium?
Forms a protective case around the brain
What is the Viscerocranium?
Forms the skeleton of the face
What is the neurocranium derived from?
Membranous and Cartilaginous/ Chondrocranium
How is the Viscerocranium formed?
From the first 2 pharyngeal arches
1st pharyngeal arch:
Maxillary process - extends beneath the eye - Maxilla, zygomatic and part of temporal bone
Mandibular process - Meckel cartilage - intramembranous ossification forms the mandible
Meckel cartilage along with the 2nd arch makes malleus and incus
2nd pharyngeal arch:
Stapes (3rd ossicle of mid ear)
Styloid process
Stylohyoid ligament
What are the fontanelles of the newborn skull? Where are they located? What order do they close in?
- Posterior fontanelle (back/ top of the head)- closes early @ 1 to 2 months
- Sphenoidal fontanelle (side of the head) - closes @ 6 months
- Mastoid fontanelle (back, bottom, side of the head) - closes in after sphenoidal and before anterior
- Anterior fontanelle (front/ top of head) - closes @ 18 months of age
What happens if the sagittal cranial sutures closes to fast?
Scaphocephaly - skull is long narrow shape with dominant frontal and occipital regions
What happens if the conornal cranial sutures closes to fast?
Brachycephaly - tall shape of skull
What happens if one of the coronal cranial sutures closes to fast?
Plagiocephaly
What is anencephaly?
Cranial neuropore open fails to close causing the skull to not form and brain tissue is exposed to amniotic fluid
What is microcephaly? Why does it happen?
Small head doe to the brain failing to grow to its normal size.
Alcohol consumption during gestation
What are the 3 directions for each intersegmental sclerotome? What does it surround? What does it form?
Medial - Surrounds the notocord/ forms the membranous vertebral
Dorsal - surrounds the neural tube/ forms the posterior arch
Anterolateral - into space between myotomes/ forms the costal processes
Which half of the sclerotome is dense and loose?
Top half of the sclerotome is loose cranial half
Bottom half of the sclerotome is dense caudal half
After resegmentation, where are the sclerotome?
The dense caudal end above migrates and merges with the loose cranial end below.
What is the result of the resegmentation?
- The myotomes bridge the intervertebral discs which gives them the capacity to move the spine.
- The intersegmental arteries, that were initially present between the sclerotome, now pass over and into the vertebral bodies.
- The spinal nerves lie near the intervertebral discs. Nerves exit the vertebral column through the intervertebral foramen.
What are the 4 chondrification centers that appear at the 7th week?
2 for the vertebral body
2 for the posterior arch
What is it called if the vertebral body and posterior arch do not fuse until ossification occurs?
Synchondrosis
When does ossification begin?
7-9 weeks
When do the primary ossification and the union of vertebral arch and body occur?
3 years for cervical spine
6 years for the lumbar spine
When does the primary ossification and the union of vertebral arch and body occur in the cervical and lumbar spine?
3 years for cervical spine
6 years for the lumbar spine
When does the secondary ossification occur?
Around 7-15 years
When does the skeletal immaturity occur around?
20 years of age
What are the 9 secondary ossification centers?
1 for the development of epiphyseal plate on cranial surface of segment
1 for the development of epiphyseal plate on caudal surface of segment
2 for the superior zygapophyseal processes
2 for the inferior zygapophyseal processes
1 spinous process
When do the end plates ossified?
15-17 years of age
How many primary ossification centers in the prenatal period? How many does each vertebra have?
3 primary ossification centers
3 bony parts connected by cartilage
When does the vertebral arches fuse halves to the vertebral body? When does the second ossification center seen?
Between 3-6 years
Puberty
How do we apply embryology in the real world?
The process of formation and rearrangement of segmental sclerotome into vertebrae is complicated.
When does neural tube defects happen? How does these defects occur?
4th week of embryologic development
Caused by nutritional, environmental, or drugs
What does deflects in formation and segmentation results in? List examples
Absence of a structural element, causing an alternation in normal growth patterns.
Examples: Hemivertebra (formation) and block vertebra (segmentation)
What does deflects in formation and segmentation results in? List examples
Absence of a structural element, causing an alternation in normal growth patterns.
Examples: Hemivertebra (formation) and block vertebra (segmentation)
What are some congenital anomalies seen regularly in clinical practice?
Hemivertebrae, Block vertebrae, spina bifida occulta, butterfly vertebrae
When do limb buds appear and grow out from the ventrolateral body wall?
4th week
What do limb buds consist of?
A mesenchymal core that forms the bones and the connective tissue of the limb and a layer of ectoderm
What does the terminal end of the limb bud do?
The ectoderm thickens and forms the apical ectodermal ridge (AER)
What are 3 components are formed in the proximodistal manner?
1) Stylopod (humerus and femur)
2) Zeugopod (radius/ ulna and tibia ibula)
3) Autopod (carpals, metacarpals, tarsals, metatarsals)
What flattens to form hand or foot plates?
Autopods
What direction does limb rotation occur?
Upper and lower limbs rotate in opposite direction.
Adult elbow pointing posteriorly and adult knee pointing anteriorly.
When does limb rotation occur?
6-8 weeks
What do the muscular system consist of?
Skeletal, Cardiac, Smooth
What mesoderm is the skeletal muscle in?
Paraxial mesoderm
What mesoderm is the cardiac muscle in?
Visceral/ splanchnic mesoderm
What derms layers is the smooth muscle in?
Visceral/ splanchnic mesoderm
Ectoderm
Neural crest cells
How is the head muscularture derived from?
The first 7 somitomeres (paraxial)
What is derived from somites?
Muscles of axial skeleton, body wall, and limbs
What is derived from somites?
Muscles of axial skeleton, body wall, and limbs
What do myoblasts fuse to? What do they produce?
They fuse to form a single, multinucleated skeletal muscle cell. They rapidly start producing actin and myosin of fibrils.
How is the cardiac muscle developed? What does it surround?
Cardiac muscles develops from visceral/ splanchnic lateral plate mesoderm. It is surrounded by the endothelial heart tube.
How does the heart adhere to one another?
Intercalated discs
What do the myotomal cells differentiate into?
- Dorsomedial muscle cells = Epimere
- Ventrolateral muscle cells = Hypomere
What are the epimere layers migrate into?
Erector Spinae Group:
1. Ilicostalis
2. Longissimus
3. Spinalis
4. Deep spinal intrinsic muscles
What are the hypomere layers migrate into?
- Sub vertebral muscles
- 4 layered lateral body wall muscles
- Suprcostal or outmost muscles
- External muscles
- Middle muscles
- Innermost muscles - Ventral muscles
What is prune belly syndrome?
Partial or complete absence of abdominal musculature
What is the Poland sequence?
The pectoral is minor and part of the pectoralis major muscles are missing on the patient’s left side.
