musculosketal development - somites and bones

Question 1

what arises from somites? (3)

Answer 1

1. axial Skeleton
2. axial muscles
3. appendicular muscles

Question 2

what arises from limb buds?

Answer 2

appendicular skeleton

Question 3

what are somites produced from?

Answer 3

PSM - pre-somatic mesoderm (produces about 50 pairs)

Question 4

what direction are somites laid down?

Answer 4

cranially to caudally

Question 5

what four populations of cells do somites differentiate into?

Answer 5

1. sclerotome - bone
2. syndetome - tendons
3. myotome - muscles
4. dermatome - dermis / skin

Question 6

where does the syndrome develop?

Answer 6

between the sclerotome and myotome - tendons

Question 7

where does the sclerotome surround and condense?

Answer 7

neural tube

Question 8

what is the dark green circle in the sclerotome?

Answer 8

the notochord - nucleus pulposus.

Question 9

what parts of a sclerotome makes a vertebrae? and what is it separated by? (3)

Answer 9

cranial half of one somite
caudal half of one somite
(separated by growing spinal nerve from neural tube)

Question 10

what sclerotome makes the occipital bone?

Answer 10

the most cranial 5 somites

Question 11

what is the development of bones, that start off as cartilaginous precursors that slowly ossify with continued growth postnatally called?

Answer 11

endochrondrial bone development

Question 12

what is the bone development called when the bones of the face and skull ossify directly from their cells without a cartilage stage?

Answer 12

intramembranous bone development

Question 13

examples of abnormal segmentation of the sclerotome (3)

Answer 13

1. hemivertebrae, or fused vertebrae
2. scoliosis
3. kyphosis

Question 14

what is Klippel - Feil syndrome?

Answer 14

short neck due to reduced number of cervical vertebrae.

Question 15

what is spina bifida occulta caused by

Answer 15

failed fusion or non - union of arches

Question 16

where the bones of the appendicular Skeleton come from?

Answer 16

limb buds.

Question 17

what are the three phases of making limbs from one of the limb buds?

Answer 17

1. initiation (where am I going to grow the limb bud)
2. limb bud patterning
3. digit patterning and sculpting

Question 18

what is limb bud patterning?

Answer 18

patterned along:

1. proximal - distal (shoulder to finger)
2. cranial - caudal (little finger to thumb)
3. ventral - dorsal (back of hand to palm)

Question 19

how does digit patterning and sculpting occur?

Answer 19

programmed cell death - apoptosis

Question 20

how do signalling molecules work?

Answer 20

target cells receive, instructions via cell surface receptors coupled to an intercellular transduction cascade.
target cells respond to by changing gene transcription so that expression of gene is changed.

Question 21

what signalling molecule patterns proximal - distal development of limb bud and where does it come from?

Answer 21

1. FGF8

2. AER (apical ectodermal ridge)

Question 22

what signalling molecule patterns cranial to caudal development and where does it come from?

Answer 22

1. sonic hedgehog

2. ZPA (zone of polarising activity)

Question 23

what genes are involved in patterning of both the long bones and digits and give somites their identity?

Answer 23

Hox genes

Question 24

what are important signalling molecules in the separation of digits?

Answer 24

BMP

Question 25

what can blocking of apoptosis lead to?

Answer 25

syndactyly

Question 26

what is FOP? (3)

Answer 26

1. Fibrodysplasia ossificans progressiva
2. genetic abnormality - soft tissue turns to bone
3. mutation in BMP receptor

Question 27

what is the loss, extra and fusing of digits called?

Answer 27

1. ectrodactyly
2. polydactyly
3. syndactyly

Question 28

what are three disorders involving club hand or foot?

Answer 28

1. club foot (adducted and plantar flexed)
2. congenital hip dislocation (acetabulum roof flat)
3. amniotic bands (constriction/amputation of limbs or digits)