Musculoskeletal

Question 1

The musculoskeletal system consists of skeletal muscle, bone & cartilage and is mainly ———— in origin with some ———- contribution

Answer 1

mesoderm, neural crest

Question 2

Layer where nearly all the connective tissues of the body are derived

Answer 2

Mesoderm

Question 3

Cells migrate through the ————- to form the —————.

Answer 3

Primitive streak, mesoderm layer

Question 4

Subsequently, 3 regions can be recognized in the mesoderm of a cross-sectioned embryo:

Answer 4

Paraxial mesoderm
Intermediate mesoderm
Lateral mesoderm

Question 5

Region that gives rise to the urogenital systems

Answer 5

Intermediate mesoderm

Question 6

Region nearest the neural tube

Answer 6

Paraxial mesoderm

Question 7

The region that forms the bulk of tissues of the body wall, the digestive tract and limbs

Answer 7

Lateral mesoderm

Question 8

Paraxial mesoderm accumulates under the ————– with thinner mesoderm laterally. This forms 2 thickened streaks running the length of the embryonic disc along the —————.

Answer 8

Neural plate

Rostrocaudal axis

Question 9

In humans, during the 3rd week, the paraxial mesoderm begins to segment into tissues called ———-.

Answer 9

Somites

Question 10

process of segmentation of the paraxial mesoderm within the trilaminar embryo body to form pairs of somites (balls of mesoderm)

Answer 10

Somitogenesis

Question 11

Somites appear ——————– at the same time and form earliest at the ———- end of the neural groove and add sequentially at the ——— end.

Answer 11

Bilaterally as pairs, cranial, caudal

Question 12

The first somite pair appears at day —– and adds caudally at —————— until on average ——- eventually form.

Answer 12

20,
1 somite pair/ 90 minutes
44 pairs

Question 13

Embryonic transitional organs that are formed through the segmentation of the paraxial mesenchyma.

Answer 13

Somites

Question 14

They are responsible for the segmental organization of the embryo and contribute to its restructuring.

Answer 14

Somites

Question 15

The —————– fuses dorsally to form a tube at the level of the ——— & “zips” up cranially & caudally & the neural crest migrates into the ———–.

Answer 15

Neural groove
4th somite
Mesoderm

Question 16

Segmentation of the paraxial mesoderm into somites continues caudally & a cavity (————————) forms in the lateral plate mesoderm separating ——— & ————.

Answer 16

Intraembryonic coelom
Somatic mesoderm
Splanchnic mesoderm

Question 17

■ closest to ectoderm
■ forms the body wall
■ osteogenic, chrondrogenic and fibrogenic

Answer 17

Somatic mesoderm

Question 18

■ closest to endoderm
■ forms the heart, smooth muscle of GIT & blood vessels
■ heart is the first organ to form in the embryo

Answer 18

Splanchnic mesoderm

Question 19

Cells in the somite differentiate medially to form the ————— (vertebral column) & laterally to form the ————————.

Answer 19

Sclerotome, dermatomyotome

Question 20

The dermatomyotome then forms the ————— & —————.

Answer 20

Dermotome (dermis)

Myotome (muscles)

Question 21

The myotome differentiates to form 2 components:

Answer 21

■ epimere dorsally —> epaxial muscles

■ hypomere ventrally —> hypaxial muscles

Question 22

The bulk of the trunk muscles comes from the ———— muscles.

Answer 22

Hypaxial

Question 23

In the cylindrical embryo, the somatic mesoderm constitutes the ———————-, & the splanchnic mesoderm forms the ——————————-.

Answer 23

Lateral & ventral body wall,

Mesentery and the wall of the digestive tract

Question 24

The somatic mesoderm of the lateral plate also forms the ———————–, which begin to appear late in the ———— of pregnancy.

Answer 24

Mesenchyme of the limb buds,

4th wk

Question 25

When do the human limbs form?

Answer 25

In the mid-4th week, human upper limb buds first form & lower limbs 2 days later.

Question 26

The limbs form at vertebra segmental levels -------- (upper limbs) & -------- (lower limbs).

Answer 26

C5-C8 (upper limbs) | L3-L5 (lower limbs)

Question 27

The limb bud is initially ----------- with an ------------ covering.

Answer 27

mesenchyme, ectodermal

Question 28

Initially, the limb bud consists exclusively of cells derived from -----------------.

Answer 28

Lateral plate mesoderm

Question 29

These cells give rise to the skeleton, connective tissues & blood vessels.

Answer 29

Cells dervied from the lateral plate mesoderm

Question 30

----------- from the somites migrate into the limb bud as precursors of muscle cells.

Answer 30

Myoblasts

Question 31

Other cells come from the neural crest which ultimately forms the ?

Answer 31

Schwann cells of the nerves | Pigment cells/ melanocytes

Question 32

At the tip of the limb bud lies a thickened ridge of ectoderm, the ------------------------, which has a role in patterning the structures that form within the limb.

Answer 32

Apical ectodermal ridge (AER)

Question 33

The majority of cell division (mitosis) occurs just deep to the AER & this region is known as the _____________.

Answer 33

Progress zone

Question 34

Another region at the base of the limb bud beside the body, the _______________________, determines the organization of the limb along its anteroposterior axis.

Answer 34

The zone of polarizing activity (ZPA)

Question 35

In the ____________, hand & footplates appear at the ends of limb buds & ridges form _____________.

Answer 35

5th wk, | Digital rays

Question 36

Cells between the digital rays are removed by ?

Answer 36

Apoptosis

Question 37

during week 8 for both limbs, there is:

Answer 37

■ more advanced development of upper limb at all stages (about 2 days). ■ growth in overall length. ■ rotation of limbs. ■ towards the end of this week the more obvious elbow/knee, shoulder/hip are seen. ■ there is development of digits (fingers, toes) from digital rays. ■ there is loss of cells by apoptosis between the digits.

Question 38

______________ is responsible for sculpting the interdigital spaces in the developing hand & foot.

Answer 38

Cell death

Question 39

If interdigital cell death does not occur, a soft tissue web connects the digits on either side. This is the basis of formation of _____________.

Answer 39

Syndactyly

Question 40

Presence of additional toes or fingers. The condition is often treated surgically in the infant.

Answer 40

Polydactilia/ polydactylism

Question 41

1st major tissue of the limb to show differentiation

Answer 41

Skeleton

Question 42

Formation of the skeleton is seen as a ________________________________________.

Answer 42

condensation of mesenchymal cells in the central core of the proximal part of the limb bud.

Question 43

Initially, a cartilage of a bone is formed from the ______________.

Answer 43

Mesenchymal cells

Question 44

By the process of ________________, there is replacement of cartilage with bone (week ?).

Answer 44

Endochondral ossification | Wk 5-12

Question 45

Early ossification occurs where?

Answer 45

At the ends of long bones

Question 46

Another process of bone formation is ________________, where bone is formed from a mesenchymal membrane.

Answer 46

Intramembranous ossification

Question 47

Specialized form of ossification that occurs in the skull & clavicle.

Answer 47

Intramembranous ossification

Question 48

Differentiation of the cartilaginous skeleton occurs in a ________________.

Answer 48

proximodistal sequence In mammals the postaxial structures of the distal limb segments differentiate before the preaxial structures.

Question 49

The postaxial skeleton of the arm

Answer 49

Ulna, Digits 4 & 5, The corresponding carpal elements

Question 50

the preaxial skeleton

Answer 50

Radius, Digits 1,2,3 Corresponding carpal bones

Question 51

many or all of the preaxial or postaxial components of the limb are missing

Answer 51

Hemimelia

Question 52

(Joints) | Earliest mesenchymal rudiments of long bones are essentially __________.

Answer 52

Continous

Question 53

As they pass into the _______________, the sites of the future joints can be discerned as intervals of less concentrated mesenchyme.

Answer 53

Precartilage stage

Question 54

The mesenchymal tissue between the cartilage rudiments ___________ & a __________ is formed.

Answer 54

Disappear | Joint cavity

Question 55

In most joints, a complete joint cavity is formed. In other joints, instead of disappearing, mesenchymal tissue gives rise to a fibrous sheet (_______________) that completely divides the joint into 2 separate compartments.

Answer 55

Intraarticular disc Ex. Temporal bone & mandible

Question 56

In others, the fibrous sheet is incomplete centrally forming a crescentic sheet that projects into the single joint cavity.

Answer 56

Articular menisci Ex. Knee joint

Question 57

The muscles are from __________ that migrate into the very early limb bud from the somites. The fusion of __________ into early _________ begin to occur during these early stages of muscle development

Answer 57

Myogenic cells Myoblasts Myotubes

Question 58

These myogenic cells begin to coalesce into 2 common muscle masses:

Answer 58

■ precursor of flexor muscles | ■ precursor of the extensor muscles

Question 59

Next stage is the splitting of the ___________________ into anatomically recognizable precursors of the definitive muscles of the limb.

Answer 59

Common muscle masses

Question 60

Earliest vasculature of the limb bud is derived from:

Answer 60

- endothelial cells: from several segmental branches of the aorta & the cardinal veins - angioblasts: endogenous to the limb bud mesoderm.

Question 61

Initially, the limb vasculature consists of fine capillary network, but soon some channels are preferentially enlarged, resulting in a _______________ that supplies blood to the limb bud.

Answer 61

Central artery

Question 62

From the central artery, blood is distributed to the periphery via a mesh of capillaries & then collects into a _____________, which is located _________________________.

Answer 62

marginal sinus, beneath the apical ectodermal ridge

Question 63

With the establishment of the digital rays, the _____________ of the marginal breaks up, but the _____________ persists into adulthood as the _______________________ of the arm.

Answer 63

Apical portion Proximal portion Basilic & cephalic veins

Question 64

Branches arising from the ________________ ultimately take ascendancy especially in the forearm, leaving the original artery a relatively minor vessel (the ________________ ) in the forearm.

Answer 64

Primary axial artery | Interosseus artery

Question 65

When do the motor axons from the spinal cord enter the limb bud?

Answer 65

5th wk

Question 66

Neurons in the medial positions in the spinal cord send axons to the _______________ , whereas those located more laterally in the spinal cord supply the _________________.

Answer 66

Ventral muscle mass | Dorsal muscle mass

Question 67

_____________ enter the limb bud after the motor axons & use them for guidance.

Answer 67

Sensory axons

Question 68

These cells of the neural crest surround both motor & sensory nerve fibers to form the coverings of the nerves in the limbs.

Answer 68

Schwann cells

Question 69

? Wks : Upper & lower limbs have formed as finlike appendages pointing ____________ & ___________.

Answer 69

5 wks | Laterally & caudally

Question 70

At ? weeks – Limbs bend _________, so that elbows & knees point __________, palms & soles face the ________.

Answer 70

6 wks Anteriorly Laterally Trunk

Question 71

At ? weeks – Upper & lower limbs have undergone ________ about their long axes, but in opposite direction, so that elbows point _________ & knees point _______.

Answer 71

7 wks 90* torsion Caudally Cranially

Question 72

At ? weeks – Torsion of lower limbs results in ____________ arrangement of their cutaneous innervation.

Answer 72

Twisted or "barber pole"

Question 73

3 basic germ layers in the embryo

Answer 73

1. ectoderm - CNS 2. mesoderm – skin, limbs, circulatory & urogenital systems 3. endoderm – digestive system