Module 3: Unit 1/2 Flashcards
What is the length of the Embryonic Period?
3-8 weeks
What are the three germ layers and in what layers are they?
Ectoderm (outer later)
Mesodderm (Middle layer)
Endoderm (Deepest layer)
The skeleton is split into what two divisions?
Axial skeleton
And
Appendicular skeleton
Define Somitomeres. What germ layer do they abide?
Loosely packed in the head region — Bones of skull
Paraxial mesoderm
Define somites. How many pairs of somites are there in paraxial mesoderm?
42-44 pairs of somites:
4 occipital
8 cervical
12 thoracic
5 lumbar
5 sacrum
8-10 coccyx
What are the three somite differentiations? Briefly describe each.
Dermatomes - These are areas of skin innervates by sensory fibers from a single spinal nerve root. Each spinal nerve relays sensation from a particular region of skin to the brain. Dermatome maps are used clinically to diagnose the level os spinal cord or nerve root damage.
Myotomes - Thesse are groups of muscles innervates by the motor fibers of a single spinal nerve root. Myotomes are important for assessing motor function and diagnosing neuromuscular diseases.
Sclerotome - These are regions of bone or skeletal structures innervates by a single spinal nerve root. Sclerotomes are used less frequently in clinical practice but are relevant in understanding patterns of referred pain in conditions affecting the skeletal system.
Cells of sclerotome are mesenchymal that differentiate to become what?
Chondroblasts
Osteoblasts
Fibroblasts
*review summary slide #10 on MOD 3 UNIT 2 for mesodermal origin gas of most osseous structures
What are the 2 main types of ossification?
Intramenbranous ossificication
Endochondral ossification
Describe endochondral ossification.
Involves the replacement of a cartilaginous template with bone tissue
Describe intramembranous ossification.
Involves direct bone formation from mesenchymal tissue
Name the steps of intramembranous ossification, and give examples of the bones they form.
- Mesenchymal stem cells
- Differentiate into osteoblasts
- Osteoblasts come together to form an ossification Center
- Osteoblasts gradually arrange in a circle around the ossification Center
- Osteoblasts secrete esteoid (unmineralized bone)
- O steroid calcifies and hardens to form bone.
*Picture on slide 14.
Formation of flat bones of the skull (parietal, frontal, occipital, etc.) clavicle
Name the steps of endochondral ossification, and give examples of the bones formed.
- Mesenchymal stem cells come together to form cartilage.
- at 8 weeks (embryo has cartilage skeleton)
- Primary ossification Center formed in the Center, blood vessels starting to enter.
- Secondary ossification Center formed on the two ends of the long bone
*Slide 16 for reference
Ex: bones of the limbs and the base of the skull
What does the Branchial (Pharyngeal) apparatus do?
Shapes the head and neck anatomy in vertebrate embryos.
REVIEW Branchial apparatus, pouches, and groupings on slides 19 and 20
What two parts does the skull consist of? What are the two ossification processes of the neurocrainuim?
Neurocranium and Viscerocranium (forms the skeleton of the face)
- The neurocranium (which forms a protective cause around the brain)
*Derived from a mixed population of cells, neural crest cells, and parochial mesoderm via both methods of bone formation.
1st method of bone formation: Membranous —> intramembranous ossification (Flat skull bones, EX: frontal, parietal)
2nd method of bone formation: Cartilaginous/Chondrocranium —> Endochondral ossification, (basal skull bones, EX: Sphenoud ethmoid, etc)
The viscerocranium (forms the skeleton of the face) is formed mainly from the first two pharyngeal arches. Name name these arches and the division of formation with these arches.
1st pharyngeal arch: maxillary process - extends beneath the eye - MAXILLA, ZYGOMATIC and part of the TEMPORAL BONE.
- mandibular process - MECKEL CARTILAGE- intramembranous ossification format the MANDIBLE
2nd pharyngeal arch: STAPES (3rd ossicle of mid.ear) STYLOID PROCESS, STYLOHYOID LIGAMENT
*look at reference picture on slide 28 unit 2
How many arches (keys to cranial facial development) are there in a 4 week old developing embryos?
There are five well developed arches numbered one through six because the fifth is vestigial (non-functional)
OBJECTIVE:
Understand the origin and development of the axial skeleton, appendicular skeleton, and muscles.
*COME BACK AND NOTE
OBJECTIVE:
Understand the embryonic origins of the skeletal system
*COME BACK
OBJECTIVE: Understand the two types of ossification processes.
Come back
OBJECTIVE: Understand the Axial Skeleton
— Development of the head and neck, parts of the skull
— Neurocranium, Viscerocranium
— Formation of the vertebral column, ribs and sternum
Come back
OBJECTIVE: Understand the appendicular skeleton
— Development of limbs
Come back
What are fontenelles and what are the four types of fontanelles?
*locations on slide 31 unit 2
IN ORDER OF CLOSER
- Posterior fontanelle - closes early @ 1 and 2 months of age
- Sphenoidal fantanelle - closes @ 6 months
- Mastoid fontanelle - closes after sphenoidal but before Anterior fontanelle
- Anterior fontanelle - closes @ 18 months of age
What are the developmental anomalies (abnormalities) of the skull? Name and briefly describe.
Craniosynostosis: early closure of cranial sutures
— Scaphocephaly caused by early closure of the sagittal suture
— Brachycephyaly cause by early closure of coronal sutures - tall shape of skull
— Plagiocephaly results from premature closure of the coronal suture on one side of the skull
Abnormalities:
Anencephaly - cranial neuropore open fails to close. The skull never forms and the brain tissue is exposed to amniotic fluid, thus tissue degenerates.
Microcephaly - A small head due to the brain failed to grow to its normal size.
Vertebrae are formed form the ___________ of the somites which are derived from paraxial mesoderm.
Sclerotome,
These cells migrate around the neural tube and notochord to merge with sclerotome cells of the state on the other side of the neural tube (forming the primitive membranous vertebrae)
Review Diagram on Slide 38 unit 2
Growth of each intersegmental sclerotome occurs in which 3 directions?
Medial- surrounds the notochord, forms membranous vertebral body
Dorsally - surrounds the neural tube, forms the posterior arch
Anterolaterally - into space between Myotomes, forms the costal processes (ribs and TP’s)
What is the segmentation/re-segmentation process?
Each vertebra is formed from the combination of the caudal half of one somite and the cranial half of its subjacent somite.
*diagram and further explain on slides 40-45
What happens as a result of resegmentation?
The Myotomes bridge the intervertebral discs - giving them the capacity to move the spine
The intersegmental arteries, that mere initially present between the sclerotomes, now pass over and into the vertebral bodies.
The spinal nerves lie near the intervertebral discs. Nerves exit that vertebral column through the intervertebral foramen.
*Diagram 43-45 for reference
What three directions do the growth of each intersegmental sclerotome occurs in?
Medial - surrounds the nontochord, forms membranous vertebral body
Dorsally - surrounds the neural tube, forms the posterior arch
Anterolarterally - into space between Myotomes, forms the costal processes (ribs and TP’s)
What 4 chondrification centers appear a the 7th week?
2 for the vertebral body (left and right) - enlarge and unite at the center
2 for the posterior arch (left and right) - Unite posteriorly at approximately 3 months, enclose the spinal cord