Limb Development Flashcards by Craig Breckenridge

What limb buds are seen first, upper limb or lower limb?

upper

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Where do limb buds first appear?

as elevations on ventrolateral body wall

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Where do upper limb buds develop from?

opposite the caudal cervical somites (C5-T1)

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Where do lower limb buds develop?

opposite the lumbar and upper sacral somites (L1-S3)

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What do limb buds consist of?

mesenchyme covered by ectoderm

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What are Apical Ectodermal Ridges (AER)?

thick band of ectoderm that induces limb development

- control patterning of limb in proximodistal axis

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Secretions produced in what induce the formation of the zone of polarizing activity (ZPA)?

AER

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What is the zone of polarizing activity?

group of mesenchyme cells in posterior margin of limb bud

- control patterning of limb in the ant-post axis

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Adjacent to AER what is mesenchyme doing?

rapid proliferating

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In week 6 digital rays form in mesenchyme of what?

handplate

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What happens to the intervals between digits which are filled with loose mesenchyme in week 7?

apoptosis

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What happens in week 8?

1* ossification centers in diaphyses

- separate fingers and toes visible

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When do most 2* ossification centers appear?

postnatally

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When do carpels and tarsals ossify?

1st yr after birth

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Where doe synovial joints form?

in interzonal mesenchyme between developing bones

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What does peripheral mesenchyme form in synovial joints?

joint capsule, synovial membrane, other ligaments

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What do central mesenchyme in synovial joints do?

disappears to become joint cavity

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What happens with restricted fetal movement?

abnormal limb development

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What are the most critical days for limb development?

day 24-36

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What is worse, early exposure or late exposure to teratogens?

early

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What is thalidomide?

sedative and antinauseant given to pregnant women
assoc. with many severe limb defects
nowadays treatment for leprosy etc

What are some other causes for limb anomalies?

genetics
environmental factors (drugs)
ischemia
low amniotic fluid (oligohydramnios)

What is amelia?

absence of limbs

What is meromelia?

absence of part of a limb

What is cleft hand or foot?

absence of one or more central digits | - failures of digital rays to form

What is syndactyly?

- cutaneous syndactyly - webbing of skin between digits due to failure to degeneration of webs - osseous syndactyly = fusion of phalanges (3-4th digits/2-3 toes) - notches fail to form between developing digital rays

What is brachydactyly?

shortness of the digits - due to reduction in length of phalanges - assoc. with short stature

What is polydactyly?

more than the usual # of digits - extra fingers usually medial or lateral - extra toes usually lateral

What is congenital clubfoot?

- deformity involving the talus - sole of foot faces medially and foot inverted - restricted mvmt in utero

What is achondroplasia?

- common cause of dwarfism - disrupted endochondral ossification of long bones - limbs short and bowed, forehead bulges

How do appendicular mm form?

myogenic cells migrate from myotomes of somites and differentiate in limbs into myoblasts => single large mm mass in each limb

Muscle mass separates into 2 components, what are they?

upper limb - dorsal component => extensors and supinator - ventral component => flexors and pronator lower limb - dorsal component => extensors and abductors - ventral component => flexors and adductors

Where do ligaments and blood vessels in appendicular mms derive from?

limb mesenchyme

How do upper limbs rotate?

laterally on longitudinal axis more than 90 degrees

What are the before and after rotation of upper limb?

Before => After - Elbows: laterally => dorsally - Thumbs: anteriorly => lateral - Extensors: dorsal => lateral and posterior aspect

How do lower limbs rotate?

medially on longitudinal axis less than 90 degrees

What are the before and after of rotation on lower limbs?

Before => After - Knees: lateral => ventrally - Big toe: anteriorly => medially - Extensors: dorsally => anterior aspect

What is the motor innervation of limbs?

- ventral motor axons from spinal cord => dorsal/ventral mm masses - result in formation of brachial and lumbosacral plexuses

What is the sensory innervation of limbs?

-sensory peripheral processes enter limb after motor axons and follow their paths

What surrounds both motor and sensory processes? what does it form?

neural crest cells - differentiate as Schwann cells

What is a dermatome of a limb?

segmental area of skin supplied by a single spinal n. and its ganglion - both dorsal and ventral ramus

Where do upper limb dermatomes progress?

- down lateral aspect (C5-7 supply preaxial border) | - back up medial aspect (C8-T2 supply postaxial border)

Where do lower limb dermatome progress?

- down anterior aspect (L2-L4 supply preaxial border) | - back up posterior aspect (L5-S3 supply postaxial border)

Where is there minimal overlap in dermatomes?

ventral axial line | - ant on upper limb and posterior on lower limb

What is the cutaneous n. area of limbs?

- skin supplied by a peripheral n. | - usually innervated by terminal br. of more than one spinal n.

What kind of sensory loss occurs with a dorsal root injury?

parietal sensory loss

Where does the primary axial artery form?

- forming as limb bud grows - br from intersegmental a. - initially grows adjacent to condensed mesenchyme forming the limb bones

What does the primary axial artery in upper extremity become?

- brachial a in arm - radial and ulnar aa. - common interosseous a in forearm

What does the primary axial a in lower limbs become?

- deep femoral a. - femoral a. - ant and post tibial aa.

What does the peripheral venous sinus become?

- cephalic and basilic veins in upper extremity | - greater and lesser saphenous vv. in lower extremity