Muscle Development and Limbs

Question 1

The muscular system develops from

Answer 1

mesodermal germ layer

Question 2

Types of muscle

Answer 2

Skeletal, smooth and cardiac

Question 3

Skeletal muscle

Answer 3

Derived from paraxial mesoderm

Question 4

Smooth muscle

Answer 4

Derived from visceral splanchnic mesoderm

Question 5

Myotome divides into

Answer 5

Dorsal epaxial
Ventral hypaxial

Question 6

Dorsal epaxial

Answer 6

Gives rise to back muscles

Question 7

Ventral hypaxial

Answer 7

Gives rise to body wall muscles (abdomen and thorax)
Upper and Lower limb muscles

Question 8

Genes MyoD and MYF-5 are essential for…

Answer 8

for the development of the hypaxial and epaxial muscles, respectively. Both genes are involved in the development of the abdominal and intercostal muscles

Question 9

Myogenesis

Answer 9

Starts with the elongation of the nuclei and cell bodies of mesenchymal cells as they differentiate into myoblasts (primordial muscle cells)

Question 10

Myotubes

Answer 10

Elongated, multinucleated, cylindrical structures formed
by the fusion of myoblasts

Question 11

The beginning of Myogenesis and the induction of the myotome is regulated by…

Answer 11

Signaling molecules from the ventral tube (SHH), notochord (Noggin), dorsal neural tube (WNTs, NT-3), and the overlying ectoderm (BMP-4, WNT)

Question 12

Myoblasts

Answer 12

embryonic muscle cells derived from mesenchyme

Question 13

Muscle growth during development results from…

Answer 13

the ongoing fusion of myoblasts and myotubes

Question 14

Myofilaments

Answer 14

develop in the cytoplasm of the myotubes during or after fusion of the myoblasts; soon after that, myofibrils and other organelles characteristic of striated muscle cells develop

Question 15

Most skeletal muscle develops

Answer 15

before birth

Question 16

Smooth Muscle Development

Answer 16

differentiate from splanchnic mesenchyme
surrounding the endoderm of the primordial gut
and its derivatives

Question 17

The growth factor responsible for activating smooth muscle development

Answer 17

Serum response factor (SRF)

Question 18

Smooth Muscle vessels arise from

Answer 18

somatic mesoderm

Question 19

As smooth muscles fibers develop they receive innervation from…

Answer 19

Autonomic nerves

Question 20

Cardiac Muscle Development

Answer 20

Develops from the lateral splanchnic mesoderm, which gives rise to the mesenchyme surrounding the developing heart tube

Question 21

Cardiac myoblasts

Answer 21

differentiate from this primordial myocardium.

Question 22

Cardiac muscle fibers

Answer 22

arise by differentiation and growth of single cells, unlike striated muscle
fibers, which develop by fusion of cells

Question 23

Growth of cardiac muscle fibers results from the formation of new

Answer 23

myofilaments

Question 24

Intercalated discs

Answer 24

areas of adhesion between myoblasts in which the intervening cell membrane does not disintegrate

Question 25

Purkinje cells

Answer 25

form the conducting system of the heart * atypical cardiac muscle cells which develop less myofibrils and are larger in diameter than typical cardiac muscle fibers

Question 26

Limb Emergence 4th week

Answer 26

Limbs buds become visible

Question 27

Limbs emergence Parietal (somatic) layer of lateral plate mesoderm

Answer 27

From the bones and connective tissues of the limbs Covered by a layer of cuboidal ectoderm

Question 28

Apical ectoderm ridge

Answer 28

The ectoderm at the distal border of the limb thickens Also known as the undifferentiated zone As the limb grows cells begin to differentiate Into cartilage and muscle

Question 29

Development of the limbs

Answer 29

proceeds proximo-distally into its three components

Question 30

Three components

Answer 30

Stylopod Zeugopod Autopod

Question 31

Stylopod

Answer 31

humerus and femur

Question 32

Zeugopod

Answer 32

radius/ulna and tibia/fibula

Question 33

Autopod

Answer 33

carpels, metacarpals, digit/tarsals digit/metatarsals

Question 34

Limb Emergence 6th week

Answer 34

Limb buds become flattened to form the hand and footplates * Separated from the proximal segment by a circular constriction First hyaline cartilage models, foreshadow the bones of the extremities * Joints are formed in the cartilaginous condensations

Question 35

Limb Emergence 8th week

Answer 35

* By this time a second constriction divides the proximal portion into two segments * Fingers and toes are formed when cell death in the AER separates this ridge into five parts

Question 36

Development of the upper and lower limbs is similar except ...

Answer 36

that morphogenesis of the lower limb is approximately 1 to 2 days behind

Question 37

Upper limb rotates...

Answer 37

90 degrees Extensor muscles lie on the lateral and posterior surface *The thumbs lie laterally

Question 38

Lower limb rotates

Answer 38

90 degrees medially Placing the extensor muscles on the anterior surface * The big toe lies medially

Question 39

Somites segments for upper limb

Answer 39

C5-T2

Question 40

Somites segments for lower limb

Answer 40

L2-S2

Question 41

Muscles are innervated by

Answer 41

Ventral primary rami

Question 42

Ventral primary rami

Answer 42

Radial n. (Dorsal segmental branches) * Ulnar n. (Ventral branches) * Median n. (Ventral branches)

Question 43

Spinal nerves

Answer 43

Provide motor innervation for the muscles * Provide sensory innervation through the dermatomes * Reflect the original segmental pattern of the somites and demonstrate the early association of individual spinal nerves with the derivatives of each dermomyotome

Question 44

Molecular regulators of limbs

Answer 44

Retinoic Acid HOXA11 HOXA13

Question 45

Retinoic Acid, MEIS1

Answer 45

Stylopod

Question 46

HOXA11

Answer 46

Zeugopod

Question 47

HOXA13

Answer 47

Autopod

Question 48

Growth factors of limbs

Answer 48

FGF10 FGF4 FGF8 Factor SHH BMPs HOX genes

Question 49

FGF10

Answer 49

*Secreted by lateral plate mesoderm cells * Initiates limbs outgrowth

Question 50

FGF4 & FGF8

Answer 50

Secreted by the ridge * Maintain the undifferentiated zone

Question 51

Factor SHH

Answer 51

Contributes to the specification of the anteroposterior axis * Digits appear in the proper order

Question 52

BMPs

Answer 52

Regulates dorsoventral axis

Question 53

HOX genes

Answer 53

Regulate the types and shapes of the bones of the limb

Question 54

Clinical correlations

Answer 54

The most critical period of limb development is the 4th and 5th weeks of development. * Mutations in HOX genes have been implicated in the development of limb anomalies

Question 55

Amelia

Answer 55

Complete absence of one or more of the extremities

Question 56

Phocomelia

Answer 56

Absent long bones and rudimentary hands or feet are attached to the trunk by small, irregularly shaped bones

Question 57

Syndactylyl

Answer 57

Two or more fingers or toes are fused

Question 58

Polydactyly

Answer 58

Presence of extra fingers or toes * Extra digits frequently lack proper muscle connections