Unit 1.L4-Development of the Skeletal and Muscular System Flashcards
(104 cards)
1
Q
What occurs on day 18?
A
formation and early differentiation of somites
2
Q
On day 18, The Intraembryonic mesoderm is organized into what 3 sections?
A
paraxial(medial),intermediate and lateral mesoderm(laterally).
3
Q
on day 18 3 mesoderms flank what?
A
the notochord and the neural groove
4
Q
On day 18 what becomes segmented into bead like blocks called somites?
A
“dorsolateral columns” of paraxial mesoderm in the trunk
5
Q
what occurs on day 22?
A
differention of 3 bead like somites
6
Q
What do the 3 bead like somites differentiate into on day 22?
A
- The Ventromedial part: Sclerotomes (forms vertebrae and ribs).
- The Dorsolateral part: Dermomyotomes (myoblasts& fibroblasts).
-Myotomes (Myoblasts) –> Muscle cells
-Dermatome (Fibroblasts) –> Dermis/Skin
7
Q
What does the dermis use?
What does the epidermis use?
A
Dermis: mesodermal
Epidermis: ectodermal
8
Q
How are the somites: sclerotome, myotome and dermatome organized?
A
Sclerotome: medial
Myotome: center
Dermatome: outside
9
Q
What occurs on day 24?
A
Folding of the embryo & movement of Somite Cells
10
Q
on day 24, Folding makes the Embryo ____, allowing what movement?
A
- cylindrical
- Sclerotomes to move Ventromedially
- Dermomyotomes to move Dorsolaterally
11
Q
What occurs on day 26?
A
The embryo has folded further to form the Dermatome, Myotome & Sclerotome.
12
Q
What is the Dermatome, Myotome & Sclerotome (D26)?
A
- dermatome: dorsal-most; skin.
- myotome: intermediate; muscle.
- sclerotome: ventromedial; vertebrae & ribs (bones) regions of a somite have become distinct. (sclerotome is precursor for all bone formation)
13
Q
What occurs on day 28 (4th week)?
A
development of bone and cartilage
14
Q
On day 28, what does the sclerotome form?
A
forms a loose tissue, the mesenchyme (embryonic connective tissue)
15
Q
What does the condesation of loose mesenchym form?
A
Bones
16
Q
Day 28 include the developement of bone, what are the 2 mechanisms of bone formation (osteogenesis)?
A
- Flat bones: Develop in mesenchyme in the membrane –> Intramembranous bone formation.
- Undergo oss. after the sclerotomes condense
- Remain membranous+soft
- Limb bones: Mesenchyme –> Cartilage bone -> Ossified–>2. Endochondral bone formation.
17
Q
Fill in the blanks for the 6 steps of intramembranous bone formation.
1. Intramembranous ____ occurs in ____
2. Mesenchyme forms “_______” _____ prior cartilage formation.
3. The mesenchyme ____ and becomes highly ____.
4. Mesenchymal cells ____ and deposit ____ to form ____
5. ____ deposited in osteoid matrix organize to form ____.
6. Bone osteoblasts “____ in the matrix” become ____
A
- Intramembranous Ossification occurs in mesenchymal membranous sheath. -> tighten and condense
- Mesenchyme forms “Osseous tissue” WITHOUT prior cartilage formation.
- The mesenchyme condenses and becomes highly vascular.-> to evade the area to bring in osteoblasts
- Mesenchymal cells differentiate and deposit unmineralized matrix (osteoid) to form “Osteoblasts” (bone-forming cells).
- Calcium phosphate (meschemyal cells) deposited in osteoid matrix organize to form Bone Osteoblasts.
- Bone osteoblasts “trapped in the matrix” become Osteocytes.
Example: Maxilla, Clavicle, Mandible, Cranium, Flat bones (Craneofacial region).
1. ossification in membranous sheath
2. osseous tissue witn no cartilage
3. condensed vascularized mesenchyme
4. osteoid deposited to form osteoblasts
5. Ca2+ phospahete–> matrix–> osteoblasts
6. Blasts trapped in matrix-> cytes
18
Q
What are examples of intramembranous bones?
A
Maxilla, Clavicle, Mandible, Cranium, Flat bones (Craneofacial region).
19
Q
What occurs in stage 1 of intramembranous ossification?
What appears?
A
An ossification center appears in the fibrous CT membrane
- Selected centrally located mesenchymal cells cluster and differentiate into osetoblasts forming an ossification center
20
Q
What occurs in stage 2 of intramembranous ossification?
What is secreted?
A
Bone matrix (osteoid) is secreted within the fibrous membrane.
- osteoblasts begin to secrete osteoid which is mineralized within a few days.
- trapped osteoblasts become osteocytes
21
Q
What occurs in stage 3 of intramembranous ossification?
What is fomed?
A
Woven bone and periosteum form
- accumulating osteoid is laid down b/w embryonic blood vessels which form a random network. The result is a network (instead of lamellae) of trabeculae
- Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum
22
Q
What occurs in stage 4 of intramembranous ossification?
What forms and appears?
A
Bone collar of compact bone forms and red marrow appears
- trabecular just deep to the periosteum thicken forming a woven bone colalr that is later replaced with mature lamellar bone.
- spongy bone (diploe) consisting of distinct trabecular, persists internally and its vascular tissue becomes red marrow
23
Q
During intramembranous ossification what do osteoblasts form? What happens to osteocytes and what begins to form? What does this contain?
A
Osteoblasts lining their surface(arrows), form trabeculae.
Osteocytes trapped in lacunae(arrowheads),and primordial osteons (canals) begin to form.
The osteons (canals) contain blood vessels (BV) & capillaries
24
Q
What is stage 1 of ossification (endochondral bone formation)?
A
Mesh. cell-> Chondroblasts –>Chondrocytes
25
In stage 1 of ossification fill in the blanks or answer the questions
1. Formation of all other bones in the body occurs by?
2. Endochondral ossification occurs in ____ to form bones
3. Chondroblasrs convert to what?
4. Where does bone collar. formation occur?
5. What has its 1st breakdown?
1. endochondral ossification
2. Endochondral ossification occurs in preexisting hyline cartilage models to form bones
3. chondrocytes
4. Bone collar formation begins at the primary ossification center: the Diaphysis (shaft of a long bone)
5. Cartilage
26
What is stage 2 of ossification (endochondral bone formation)?
Chondroblasts--> chondrocytes
27
In stage 2 of ossification fill in the blanks or answer the questions
1. What occurs to chondrocytes
2. What is perichondrium converted to?
3. Furthur invasion of what causing what?
1. Chondrocytes (cartilage cells) *increase in size* (hypertrophy), the *matrix calcifies*, and the cells die.
2. Perichondrium is converted to *Periosteum* once it is surrounded by a thin layer of bone deposit.
3. Further Invasion by *blood vessels* surrounding the periosteum breaks the cartilage.
28
What is stage 3 of ossification (endochondral bone formation)?
osteoblast/clast-->bone remodeling-->bone lengthening
29
In stage 3 of ossification fill in the blanks or answer the questions
1. What do some osteoblasts become?
2. What part of the bone is remodeled and how?
3. Where does lengthening of bones occur and how?
Osteoblasts, via blood vessels, reach the developing bone & some **become hemotopoietic (stem) cells** (bone marrow).
This process continues toward the epiphyses (ends of the bones). The **spicules of bone are remodeled** by **the action of marrow derived multinucleated osteoclasts (resorb bone tissues)** & osteoblasts (deposit new bone tissue).
Lengthening of bones occurs at the *diaphyseal-epiphyseal junction*, as the *chondrocytes proliferate* at the *epiphyseal cartilage plates* (growth plates).
30
In stage 4 of ossification fill in the blanks or answer the questions
1. what 2 things are formed?
2. how is ossififcation spread and what remains cartilaginous?
3. by age 20 what 3 things occur?
Formation of the **medullary cavity** & **secondary ossification centers** in the epiphyses appear in most bones.
Ossification spreads *radially*, and only the *articular cartilage (near joints)* & *transverse epiphyseal cartilage plate* remain cartilaginous.
By age 20, the *cartilage plate is replaced by spongy bone*, the *epiphyses and diaphysis fuse* & *elongation of the bone stops*.
31
During the 6th week (day 42 onwards), What occurs on the 6th week (day 42 onwards)
Condensed mesenchyme forms in the joint inter-zone between the two bones.
| developement of bone joints
32
Joints are classified as:
Fibrous joints
Cartilaginous joints
Synovial joints
33
During the development of **cartilaginous joints**, the inter-zonal mesenchyme between the developing bones differenties into what? Give an ex for each
(a) Hyaline cartilage (e.g., costochondral joints)
(b) Fibrocartilage (pubic symphysis).
34
During the development of **fibrous joints**, the inter-zonal mesenchyme between the developing bones differenties into what? Give an ex
* dense fibrous tissue
* ex: sutures of the cranium are fibrous joints.
| NO FORMATION OF CARTILAGE
35
During the development of **synovial joints (knee joint)**, the inter-zonal mesenchyme between the developing bones differenties into what?
Peripherally, the inter-zonal mesenchyme forms the joint capsule and ligaments.
Centrally, mesenchyme disappears, & the space becomes the synovial cavity (joint cavity).
36
What does the synovial membrane line and secrete?
* The Synovial membrane lines:
(a) Joint capsule &
(b) Articular surfaces
* Synovial membrane secretes synovial fluid (hyaluronic acid) filling the joint capsule (fibrous capsule + synovial membrane).
| Need fuild because of lub., maintain pressure and nutrition to the joint
37
What occurs on the 4th week (day 28) of axial skeleton formation?
movement of myotomes and scletotomes
38
On the 4th week (day28) of axial skeleton, d/t the movement of tissues, what occurs? What cells do we see?
* Due to movement of tissues, ventromedially, the sclerotomes surround the neural tube (primordium of spinal cord) & notochord, forming the primordia of the vertebrae.
* Sclerotome cells: Loosely Packed (cranially) & densely packed (caudally).
39
What does the axial skeleton comprise of?
1. The Cranium (skull)
2. The Vertebral Column
3. The Ribs
4. The Sternum
40
What is inbetween each vertebra?
intersegmental arteries
41
What occurs on the 5th week (day 35) of axial skeleton formation?
formation of intervertebral disk
42
On the 5th week (day 35) of axial skeleton formation during the formation of IVD what is condensed?
Condensation of sclerotome cells around the notochord/neural tube forms a mesenchymal vertebra.
43
On the 5th week (day 35) of axial skeleton formation of IVD, **What is formed from the cranial and caudal halves of sclerotomal masses**?
vertebral body
44
On the 5th week (day 35) of axial skeleton formation of IVD, **what surrounds the vertebrae, & What lie between the vertebrae.**
intersegmental arteries, spinal nerves
45
On the 5th week (day 35) of axial skeleton formation of IVD, d**oes the notochord degenerate?**
Yes, Notochord degenerates except forming nucleus pulposus (soft elastic/collagen layer) surrounded by annulus fibrosis (tough ring made of ligament fibers); both together forming the intervertebral disc.
46
What forms the intervertebral disc?
**nucleus pulposus** (soft elastic/collagen layer) surrounded by **annulus fibrosis** (tough ring made of ligament fibers)
47
What are the 3 Cartilaginous Stages of Vertebral Development
1. **Mesenchymal vertebra** with a defined *Costal process* and the *centrum*. (sclerotome start to condense around the nural tube to form centrum_
2. **Chondrification Centers** in a mesenchymal vertebra at 6 weeks. (The *neural arch is the primordium* of the *vertebral arch* of the vertebra.)
3. **Primary ossification** centers (*ventral & dorsal*) visible in a cartilaginous vertebra (7wks)
48
What are the 2 bony stages of vertebral development?
Thoracic vertebra at birth
Thoracic vertebra at puberty
49
What are the 3 bony parts of thoracic vertebra at birth?
1. Vertebral arch 2. Vertebra body & 3. Transverse processes.
50
What are the 2 secondary ossification centers of the thoracic vertebra at puberty?
1.**Superior & inferior anular epiphyses** forms the rim of the vertebral body.
2. **Secondary Ossification** at *ONE spinous* & TWO transverse processes.
51
Where do ribs originate from?
mesenchymal costal processes of the thoracic vertebrae.
52
During the development of ribs, what does the costal processes become and what do they join?
* Costal Processes become *cartilaginous* during the *embryonic period* and **ossify** during the *fetal* period.
* The Costal processes on either side join the vertebral body by *costovertebral synovial joints.* (ribs attach here)
53
Seven pairs of ribs (1-7) are called what ribs? Where do they attach?
* true ribs
* attach through their own cartilages to the sternum
54
Three pairs of ribs (8-10) are called what ribs? Where do they attach?
* False ribs
* attach to the sternum through the cartilage of another rib or ribs.
55
Last two pairs of ribs (11-12) are called what ribs? Where do they attach?
* Floating ribs
* do not attach to the sternum.
| Bc sternum is short
56
What are the 3 steps of the development of the sternum?
1. A pair of vertical mesenchymal bands (sternal bars) develop ventrolaterally. (before ribs touch)
2. Sternal bars Chondrifies as they move medially.
3. 10 weeks: Sternal bars fuse & ossify craniocaudally
57
In the development of the sternumm the sternal bars fuse and ossify craniocaudally in the median plane to form what 3 structures?
1. Cartilaginous Manubrium (mesenchyme + neural crest cells)-> attached is clavicle and first pair of ribes)
2. Sternebrae (segments of sternal body)
3. Xiphoid process (may never completely ossify-> never bone).
58
What is the cartilaginous manubrium made up of? ⭐️
mesenchyme + neural crest cells
59
During development of cranium, there are 2 parts with 8 bones. What are the 2 parts?
Neurocranium
Viscerocranium
60
* What is the neurocranium?
* What is the origin?
* What does it contain (the two subgroups)
* skull (vault)
* origin: Desmocranium (head mesenchyme) [Paraxial mesenchyme + Neural Crest cells]
* Membranous Neurocranium (Top cap): 6 bones
* Cartilaginous Neurocranium (Base of the skull): 2 bones-> Sphenoid & Occipital bones (solid bone to be able to carry head)
61
* What is the viscerocranium?
* What is the origin?
* What does it contain (the two subgroups)
* facial skeleton
* origin: [Pharyngeal arch mesenchyme + Neural Crest cells]
* Membranous Viscerocranium (facial skeleton)
* Cartilaginous Viscerocranium (splanchnocranium)-> solid bones (inner ear)
62
Fusion of membranous cranial plates (top)+ endochondral ossification (base)
forms what?
Neurocranium (8 bones)
* membranous ossification 6 bones: The Ethmoid bone, 2 Temporal bones, The Frontal bone , 2 Parietal bones
* cartilage--> endochondral ossification 2 bones: sphenoid, occipital
## Footnote
membranous ossification 6 bones: The Ethmoid bone, 2 Temporal bones, The Frontal bone , 2 Parietal bones
cartilage--> endochondral ossification 2 bones: sphenoid, occipital
63
What forms the 2 top bones of the neurocranium? What are these bones?
A membranous part from the same brain mesenchyme originating from the occipital somites (paraxial mesenchyme)
* The Frontal bones
* The Parietal bones
64
What occurs to the frontal and parietal plate in the development of frontal and parietal bones?
Frontal plate + Parietal plate **ossify** into **flat bones** through *intramembranous ossification* and are connected by *connective tissue sutures* (Fibrous Joints).
65
What does the appendicular skeleton consist of?
1. Upper & Lower Limb bones.
2. Pectoral Girdle bones, Scapula and Clavicles
3. Pelvic Girdle bones
66
What is the mechanism of upper limb formation?
* Fifth week: Mesenchyme condenses in the limb buds
* Sixth week: The mesenchymal bone models in the limbs undergo chondrification to form hyaline cartilage bone models.
67
At the 28 days (4 wks), for the developement of appendicular skeleton upper limb formation, what occurs?
Upper limb bud: Apical ectodermal ridge induces the mesenchyme to grow/differentiate --> Cartilage.
68
What induces the mesenchyme to grow/differentiate into cartilage for upper limbs?
Apical ectodermal ridge
69
At the 35 days (5 wks), for the developement of appendicular skeleton upper limb formation, what does the upper bud form?
mesenchymal primordia of the forearm bones.
70
What occurs to the mesenchymal digital rays during upper limb formation?
The mesenchymal digital rays condense, chondrify, ossify & form bones of the hand
71
For upper limb formation, what is completed by the end of week 6?
Cartilage models ofthe bones
* Note the emergence of cartilaginous models Phalanges, Metacarpals & Carpus in the palm.
* Note the cartilaginous models of Ulna, Radius, Humerus and Scapula
72
For appendicular skeleton development, what occurs at 12 weeks?
formation of the clavicle
73
How does the clavicle intially form? What forms later?
* The Clavicle initially develops by intramembranous ossification.=> ONLY ONE
* Later Clavicle membrane forms growth cartilages at both ends.
74
What appears before before pelvic girdle & lower limb bones? and in what sequence?
* Pectoral girdle and Upper Limb bones models.
* The bone models develop in a linear proximodistal sequence.
75
What is completely cartilagionus at 12 weeks during appecdicular skeleton formation?
The carpus/tarsus & epiphyses of all long bones are wholly cartilaginous at 12 weeks.
76
at 12 weeks, how does ossification move? What is the exception?
* from primary centers of ossification to endochondral ossification in appendicular & axial skeleton.
* Exception: Cranial bones remains membranous and cartilaginous, called the Neurocranium. It ossifies after birth.
77
3 types of muscle
* Skeletal Muscles
* Smooth Muscles
* Cardiac Muscles
78
What is occuring on day 41 of embryo concerning the muscular system
Myotomes & developing muscular system
79
What is the origin of most Skeletal Muscles (limb & axial)? What is the exception (2)?
**Paraxial mesoderm** (myotome of the somites) & epitheliomesenchymal transformation from myogenic precursor cells called “myoblasts”.
Exception:
* Eye muscles of the IRIS (neuroectoderm origin).
* Esophagus muscle (from smooth muscle)
80
What occurs with skeletal muscle cell differention
* Multiple myoblasts fuse to form myotubes at first, and then long multi nucleated muscle fibers.
* Microfibrils form & the striations of actin + myosin patterning associated with skeletal muscle are visible
81
What early and late genes are involved in myogenesis?
* Early genes: MyoD + Myf5 -> mesodermal cell to myoblasts.
* Late genes: MRF4 + Myogenin later in the process are involved in myotubes & microfibril formation.
82
# Early Events in Skeletal Muscles Formation (Limb & Axial Muscles)
About ____ pairs form along the neural
tube in a ____ direction; some caudal
somites disappear to give ~____ pairs at birth
42-44 somite
cranio-caudal
35 somite
83
# Early Events in Skeletal Muscles Formation (Limb & Axial Muscles)
What are 2 ways that somite myotomes split and movein the early embryo of cells and they give rise to what musculature?
* Ventrolateral myotome :Hypaxial musculature (Ventral body wall + limb muscles)-3 layers
* Dorsomedial Myotome: Epaxial musculature ( dorsal back muscles)-2 layers
84
Hypaxial Myotome migrate & differentiate to form the 3 layers of muscle of the body. What are the 3 layers (muslces)?
1. Intercostal muscles in the thorax
2. External oblique & internal oblique muscles
3. Transversus abdominis & Rectus abdominis muscles
85
Epaxial Myotome migrate and differentiate to form 2 muscles of the back. What are they?
Short muscle
long muscle
86
# Development of Myotomes
Each Myotome-part of a Somite divides into what 3 sections?
1. **Dorsal Epaxial division**: *Extensor muscles* of the *neck & vertebral column* & dorsal sacrococcygeal ligaments
2. **Ventral Hypaxial division**: Scalene, Prevertebral, Geniohyoid, and Infrahyoid Muscles (*neck*)
3. **The intercostal muscles** remain segmentally arranged like the somites (*between ribs*).
87
Spinal nerve divides and sends a branch to each myotome division. What does each nerve innervate?
* Dorsal primary ramus innervates the epaxial division.
* Ventral primary ramus innervates the hypaxial division.
88
what forms the the pharyngeal arch muscles?
Myoblasts from the unsegmented paraxial mesoderm & prechordal plate form the pharyngeal arch muscles for mastication, facial expression, pharynx, and larynx.
89
What forms the ocular muscles?
Origin is unclear; mesenchymal cells near the prechordal plate may give rise to **3 Preotic myotomes**.
90
What forms the tongue muscles?
Initially there are four **occipital (postotic) myotomes**; the first pair disappears. Myoblasts from the remaining **3 myotomes** form the tongue muscles.
91
Precursor myogenic cells of the limbs for limb muscle development originate from what?
originate from the somites near the ventro-lateral dermomyotome and migrate into the limb primordium.
92
What do Myoblasts around the bones form during limb development?
form dorsal (extensor) and ventral (flexor) limb muscles.
93
What are the 3 distinct origins of smooth muscle development?
1. Splanchnic mesoderm
2. Somatic mesoderm
3. Ectodermal cells
94
# Smooth Muscle Development
What does splanchnic mesoderm give rise to?
Splanchnic mesoderm gives rise to smooth muscle surrounding the primordial gut endoderm
95
# Smooth Muscle Development
What does somatic mesoderm give rise to?
Somatic mesoderm gives rise to smooth muscles of the blood and lymphatic vessels.
96
# Smooth Muscle Development
What do ectodermal cells give rise to?
gets converted to mesenchymal cells & forms myoepithelial cells in mammary and sweat glands and eye muscles (iris sphincter and dilator pupillae).
97
During smooth muscle development, what does Mesodermal cell develop? Does smooth muscle fuse?
* Mesodermal cell develop elongated nuclei in spindle- shaped myoblasts, which becomes smooth muscle cells.
* Unlike skeletal muscle, smooth muscle cells do not fuse.
98
What is the origin of cardiac muscle cells?
Cardiac muscle cells are derived from **lateral splanchnic mesoderm** forming the early heart tube.
99
How are cardiac myoblasts connected?
Cardiac myoblasts do not fuse to form fibers, but remain connected via intercalated discs.
100
What occurs to cardiac myoblasts in the 4th week during cardiac muscle development?
Cardiac myoblasts in the primordial myocardium differentiate & form heart muscles
101
Cardiac muscle fibers arise by ?
differentiation and growth of single muscle cells.
102
Later in cardiac muscle developement, what special, atypical bundles of muscle cells develop?
special, atypical bundles of muscle cells develop with few myofibrils and large diameter cardiac muscle fibers, called the **Purkinje fibers**, forming the **electrical conducting system of the heart.**
103
# Congenital Anomalies of Muscles Development
What is Poland Syndrome?
What is absent?
1. Absence of the *pectoralis* (major & minor) muscles near the sternal part associated with Syndactyly (fusion of digits), *ipsilateral breast hypoplasia*, and *absence of 2-4 ribs.*
2. Absence of *mammary gland* and/or *hypoplasia of the nipple.*
104
# Congenital Anomalies of Muscles Development
What is Arthrogryposis?
1. *Multiple congenital joint contractures* in multiple parts of the body, comprising of >300 disorders.
2. Connective tissue abnormalities restrict i*ntrauterine movemen*t causing **fetal akinesia**. E.g. “**Amyoplasia**” show *bilateral flexion contractures of the wrist & extension of the knees*.
## Footnote
Stiffness of the joints with hypoplasia of the associated muscles
