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Embryo > Muscle Development and Limbs > Flashcards

Muscle Development and Limbs Flashcards

1
Q

The muscular system develops from

A

mesodermal germ layer

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2
Q

Types of muscle

A

Skeletal, smooth and cardiac

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3
Q

Skeletal muscle

A

Derived from paraxial mesoderm

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4
Q

Smooth muscle

A

Derived from visceral splanchnic mesoderm

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5
Q

Myotome divides into

A

Dorsal epaxial
Ventral hypaxial

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6
Q

Dorsal epaxial

A

Gives rise to back muscles

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7
Q

Ventral hypaxial

A

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

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8
Q

Genes MyoD and MYF-5 are essential for…

A

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

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9
Q

Myogenesis

A

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

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10
Q

Myotubes

A

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

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11
Q

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

A

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

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12
Q

Myoblasts

A

embryonic muscle cells derived from mesenchyme

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13
Q

Muscle growth during development results from…

A

the ongoing fusion of myoblasts and myotubes

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14
Q

Myofilaments

A

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

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15
Q

Most skeletal muscle develops

A

before birth

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16
Q

Smooth Muscle Development

A

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

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17
Q

The growth factor responsible for activating smooth muscle development

A

Serum response factor (SRF)

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18
Q

Smooth Muscle vessels arise from

A

somatic mesoderm

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19
Q

As smooth muscles fibers develop they receive innervation from…

A

Autonomic nerves

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20
Q

Cardiac Muscle Development

A

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

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21
Q

Cardiac myoblasts

A

differentiate from this primordial myocardium.

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22
Q

Cardiac muscle fibers

A

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

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23
Q

Growth of cardiac muscle fibers results from the formation of new

A

myofilaments

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24
Q

Intercalated discs

A

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

25
Q

Purkinje cells

A

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

26
Q

Limb Emergence
4th week

A

Limbs buds become visible

27
Q

Limbs emergence
Parietal (somatic) layer of lateral plate mesoderm

A

From the bones and connective tissues of the limbs

Covered by a layer of cuboidal ectoderm

28
Q

Apical ectoderm ridge

A

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

29
Q

Development of the limbs

A

proceeds proximo-distally into its three components

30
Q

Three components

A

Stylopod
Zeugopod
Autopod

31
Q

Stylopod

A

humerus and femur

32
Q

Zeugopod

A

radius/ulna and tibia/fibula

33
Q

Autopod

A

carpels, metacarpals, digit/tarsals digit/metatarsals

34
Q

Limb Emergence
6th week

A

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

35
Q

Limb Emergence
8th week

A
  • 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
36
Q

Development of the upper and lower limbs is similar except …

A

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

37
Q

Upper limb rotates…

A

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

38
Q

Lower limb rotates

A

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

39
Q

Somites segments for upper limb

A

C5-T2

40
Q

Somites segments for lower limb

A

L2-S2

41
Q

Muscles are innervated by

A

Ventral primary rami

42
Q

Ventral primary rami

A

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

43
Q

Spinal nerves

A

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

44
Q

Molecular regulators of limbs

A

Retinoic Acid
HOXA11
HOXA13

45
Q

Retinoic Acid, MEIS1

A

Stylopod

46
Q

HOXA11

A

Zeugopod

47
Q

HOXA13

A

Autopod

48
Q

Growth factors of limbs

A

FGF10
FGF4
FGF8
Factor SHH
BMPs
HOX genes

49
Q

FGF10

A

*Secreted by lateral plate mesoderm cells
* Initiates limbs outgrowth

50
Q

FGF4 & FGF8

A

Secreted by the ridge
* Maintain the undifferentiated zone

51
Q

Factor SHH

A

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

52
Q

BMPs

A

Regulates dorsoventral axis

53
Q

HOX genes

A

Regulate the types and shapes of the bones of the limb

54
Q

Clinical correlations

A

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

55
Q

Amelia

A

Complete absence of one or more of the extremities

56
Q

Phocomelia

A

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

57
Q

Syndactylyl

A

Two or more fingers or toes are fused

58
Q

Polydactyly

A

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

Embryo (8 decks)

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