What change occurs to the thumb during the upper limb rotation?
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The thumb is repositioned from cranial to lateral.
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What change occurs to the thumb during the upper limb rotation?
The thumb is repositioned from cranial to lateral.
Which muscles are associated with the dorsal/posterior side of the upper limb?
Extensor muscles.
Which muscles are associated with the ventral/anterior side of the upper limb?
Flexor muscles.
What is the degree of medial rotation of the lower limb during development?
90° medially.
How does the rotation of the lower limb affect the position of the knee?
It repositions the knee ventrally (anterior).
What change occurs to the big toe during the lower limb rotation?
The big toe is repositioned from cranial to medial.
Which muscles are associated with the ventral/anterior side of the lower limb?
Extensor muscles.
Which muscles are associated with the dorsal/posterior side of the lower limb?
Flexor muscles.
What is the pattern of dermatomes around the limb due to rotation?
Dermatomes spiral around the limb due to 90° medial rotation.
What spinal levels correspond to the big toe?
L4-5.
What spinal level corresponds to the little toe?
S1.
What is the cutaneous testing point for L1?
Point midway between inguinal ligament & L2.
What is the cutaneous testing point for L2?
Antero-medial thigh midway between medial condyle & inguinal ligament.
What is the cutaneous testing point for L3?
Medial femoral condyle.
What is the cutaneous testing point for L4?
Medial malleolus.
What is the cutaneous testing point for L5?
Dorsum of foot at proximal MPJ.
What are the three primary germ layers in embryology?
Ectoderm, Mesoderm, Endoderm
What structures are derived from the ectoderm?
Skin, CNS, neural crest cells
What are the derivatives of the mesoderm?
Muscle, bone, connective tissue
What do the lateral plates of the mesoderm develop into?
Limb bones and vessels
What are the components of the paraxial mesoderm?
Somites, which include sclerotomes, myotomes, and dermatomes
What do myotomes develop into?
Limb muscles
What do dermatomes give rise to?
Connective tissue and dermis
What is the inner lining of the gut and respiratory tubes derived from?
Endoderm
What are the adult derivatives of the sclerotome?
Vertebrae and intervertebral discs
What are the three axes along which limbs develop?
Cranio-caudal, Dorso-ventral, Proximo-distal.
What is the adult equivalent of the cranio-caudal axis?
Medio-lateral.
What is the adult equivalent of the dorso-ventral axis?
Dorso-ventral, antero-posterior.
How does the proximo-distal axis remain in adults?
It remains the same.
What does cranial correspond to in embryological directions?
Anterior.
What does caudal correspond to in embryological directions?
Posterior.
What does dorsal correspond to in embryological directions?
Back (like a dorsal fin).
What does ventral correspond to in embryological directions?
Belly.
What significant development occurs at 4 weeks of limb growth in a human embryo?
Limb buds form and the apical ectodermal ridge (AER) appears.
What happens at 6 weeks of limb growth in a human embryo?
Cartilaginous bone models form and digital rays appear in the foot plate.
What key development occurs at 8 weeks of limb growth in a human embryo?
Formation of primary ossification centers and differentiation of toes.
What anatomical features are indicated in the diagrams showing foot and lower leg development from 33 to 56 days?
Foot (digital) plate, future hip, future knee, toe (digital) rays, and future ankle.
When does the lower limb bud begin to develop?
Near the end of Week 4.
At which levels does the lower limb bud begin to form?
At L1/2-S1/2 levels, corresponding to the levels of the lumbosacral plexus.
What is the function of the Apical Ectodermal Ridge (AER) in limb development?
It controls the proximal-distal growth of the limb bud.
Where does the Zone of Polarizing Activity (ZPA) develop in the limb bud?
At the caudal end of the limb bud.
What does the ZPA control in limb development?
It controls cranial-caudal differentiation of the limb.
How does the lower limb bud relate to the upper limb bud in terms of development timing?
The lower limb bud develops after the upper limb bud.
What happens to limb development if the Apical Ectodermal Ridge (AER) is removed?
Limb development stops.
What is the consequence of failure of AER to form or maintain?
It results in complete absence of the limb.
What occurs if the AER is removed or fails at later stages of development?
It results in incomplete development of distal segments.
What role do HOX genes play in limb development?
They are involved in initial development and segmentation, as well as differentiation between leg and thigh elements.
What is the function of FGF-8 at the AER?
It promotes proximal-distal growth.
What does SHH in the ZPA influence?
It stimulates cranial-caudal differentiation and the development of the hallux versus the fifth toe.
What is the role of BMP and WNT in limb development?
They are involved in ventral-dorsal differentiation, affecting the dorsum versus the sole of the foot.
What happens if there is a failure of HOX gene expression during limb growth?
It leads to a lack of development in specific segments.
What is the effect of SHH expression in the ZPA on digit development?
It stimulates the development of the pinky toe and lesser digits.
What occurs if SHH is absent in the cranial limb?
It leads to the development of the big toe.
What happens when the ZPA is transposed?
It leads to flipped digits.
What is the result of implanting a second ZPA?
It leads to mirrored digits.
What is Amelia in terms of developmental anomalies?
Absence of an entire limb.
What is Meromelia?
Absence of part of a limb.
Who is Nick Vujicic?
A motivational speaker born without arms or legs, representing Amelia.
Who is Mat Fraser?
An actor, musician, and disability advocate who specifically has phocomelia, representing Meromelia.
What does the prefix 'A-' signify in the term 'Amelia'?
It signifies 'without'.
What does the prefix 'Mero-' signify in the term 'Meromelia'?
It signifies 'part'.
What significant development occurs in the foot at week 7 of gestation?
Flattened foot plate forms and chondrification of digital rays occurs.
What key changes happen to the foot at week 8 of gestation?
Formation of separate digits and apoptosis of mesenchymal tissue between digits.
What is polydactyly?
A condition characterized by having more than five digits.
What is syndactyly?
A condition involving the fusion of two or more digits.
What is ectrodactyly?
A condition characterized by the absence of central digits.
What does the term '-dactyl' refer to?
It refers to digits.
What does the prefix 'poly-' mean?
It means many.
What does the prefix 'syn-' mean?
It means together.
What does the prefix 'ectro-' mean?
It means without.
What is the primary axial artery that supplies the early limb bud?
The sciatic or ischiadic artery in the lower limb.
What happens to the sciatic artery during limb development?
It degenerates and is replaced by the femoral artery and its branches.
What does the sciatic artery persist as after degeneration?
It persists as a tiny sciatic artery running with the nerve and portions of the popliteal and fibular arteries.
What is the clinical correlate associated with Thalidomide?
Thalidomide can induce amelia or meromelia.
How does Thalidomide affect limb development when administered to pregnant women?
It disrupts the formation of blood vessels, leading to limb malformations such as amelia or meromelia.
What arteries are fully developed in the definitive system of the lower limb?
The femoral, popliteal, and tibial arteries.
What is the process by which bones ossify in the development of the leg?
Endochondral ossification.
What are the three stages of bone development?
Mesenchymal, Cartilaginous, and Osseous stages.
At what week do the bones of the appendicular skeleton begin as condensations of mesenchymal cells?
Week 5.
During which weeks does chondrification occur in bone development?
Week 6 to 8.
What happens during the Osseous stage of bone development?
Cartilaginous bone models are replaced by bone, and diaphyses of long bones ossify first.
Which bones ossify first during the Osseous stage?
Large bones like the femur ossify first, followed by metatarsals and phalanges.
Which bones ossify last during the process of ossification?
Tarsals ossify last.
Until when does ossification and fusion continue?
Into adulthood.
What is the primary characteristic of a newborn's foot in terms of ossification?
The bones are mostly cartilage and not yet fully ossified, appearing translucent with only a few ossification centers visible.
How does the ossification pattern change from a neonate to a one-year-old?
More ossification centers are visible in the one-year-old's foot, especially in the toes and ankle, with clear gaps between the bones still present.
What is observed in the ossification of a four-year-old's foot?
Further ossification is seen, with more of the bones becoming solid and well-defined, and the tarsal bones in the ankle beginning to take shape.
What changes occur in the foot structure of a seven-year-old compared to a four-year-old?
The bones are more mature and larger, with fewer gaps between them, and the overall structure is becoming more like an adult's foot.
What is the condition of the bones in a fifteen-year-old's foot?
The bones are almost fully ossified, the growth plates are beginning to close, and the foot structure is very similar to an adult's with well-defined bones and joints.
What factors can affect ossification and fusion patterns?
Sex, ancestry, nutrition, and disease can affect ossification and fusion patterns.
Where do myogenic cells migrate from during limb development?
From the lumbosacral region (L2–S2).
What do myogenic cells differentiate into after migrating into the lower limb bud?
Myoblasts.
Where do myoblasts aggregate around during limb development?
Developing bones.
Which muscles are associated with the ventral side during limb development?
Flexors.
Which muscles are associated with the dorsal side during limb development?
Extensors.
What is the myotome action associated with L2?
Hip flexion.
What is the myotome action associated with L3?
Knee extension.
What is the myotome action associated with L4?
Ankle dorsiflexion.
What is the myotome action associated with L5?
Extension of hallux.
What is the myotome action associated with S1?
Ankle plantarflexion.
How does flexion/extension change directions at the knee joint?
Plantarflexion is considered flexion and dorsiflexion is considered extension.
What do motor axons grow from during neurogenesis?
They grow from the spinal cord into developing myotomes.
How do cranial and caudal axons differ in their innervation of muscles?
More cranial axons innervate more proximal muscles, while more caudal axons innervate more distal muscles.
What do anterior fibers innervate in muscle development?
Anterior fibers innervate flexors and adductors.
What do posterior fibers innervate in muscle development?
Posterior fibers innervate extensors and abductors.
What do sensory axons do during limb development?
They follow motor axons into the limb bud and diverge towards dermatomes.
What do neural crest cells form in the peripheral nervous system?
They form spinal ganglia and supporting cells, such as Schwann cells.
What is the segmental pattern in developing limb buds from L2 to S2?
It spirals around the lower limb when it rotates.
At what week do dermatomes begin to show a segmental pattern in the developing limb bud?
At 4 weeks.
What are the labeled regions in the dermatomes at 7 weeks?
T12, L1, L2, L3, L4, L5, S1, S2, and S3.
What does the term 'Preaxial' refer to in the context of dermatomes?
It refers to the cranial aspect of the limb.
What does the term 'Postaxial' refer to in the context of dermatomes?
It refers to the caudal aspect of the limb.
What is indicated by the arrows pointing to 'Big toe' and 'Plantar surface' in the 7-week illustration?
They indicate specific dermatome regions related to the foot.
What is the dorsal view of the foot showing at 8 weeks?
It shows dermatome regions labeled as S1, L5, L4, L3, L2, S2, and S3.
What is the degree of lateral rotation of the upper limb during development?
90° laterally
How does the rotation of the upper limb affect the position of the elbow?
It repositions the elbow dorsally (posterior).
What is the cutaneous testing point for S1?
Lateral calcaneal tuberosity.
What is the cutaneous testing point for S2?
Popliteal fossa.
What is the range of dermatomes for the anterior leg?
From T10 to L5.
What is the range of dermatomes for the posterior leg?
From L3 to S2.
What is the medical term for congenital clubfoot?
Talipes equinovarus
What is the orientation of the foot in talipes equinovarus?
The foot is inverted, with the sole pointed medially and the heel elevated.
What causes the heel to be elevated in congenital clubfoot?
Due to shortened tendons, including the calcaneal tendon.
What happens if congenital clubfoot is left untreated?
The feet become twisted inward, with the soles facing each other and abnormally shaped ankles.
What does the term 'Talipes' refer to in the context of clubfoot?
It is equated to 'foot'.
What does 'equinus' signify in the term 'Talipes equinovarus'?
It is equated to 'horse', indicating the elevated heel position.
What does 'varus' indicate in the term 'Talipes equinovarus'?
It signifies the inward orientation of the foot.
What is the critical period for limb development post-fertilization?
24–36 days (approximately weeks 3–5).
What does the limb bud consist of at the end of week 4?
Mesenchyme surrounded by ectoderm.
What role do HOX genes play in limb development?
They are involved in initial development and segmentation.
What is the function of FGF-8 in limb development?
It promotes proximal-distal growth.
What does SHH influence in limb development?
Cranial-caudal differentiation.
What occurs during weeks 7–8 of limb development?
Digital rays appear and digits separate.
What happens to mesenchymal precursors in lateral plates during week 5?
They undergo endochondral ossification between weeks 7–12, or postnatally for some tarsals.
How do myogenic cells organize during limb development?
They organize into extensor and flexor compartments.
What does the spiral pattern of dermatomes reflect?
A medial 90° rotation of the lower limb.
During embryological development, on which surface of the limb bud does the hallux begin developing?
Dorsal surface.
What condition is characterized by missing middle fingers, as depicted in the 2020 remake of Witches?
Ectrodactyly.
During embryological development, on which surface of the limb bud does the hallux begin developing?
Dorsal surface.
What condition is characterized by missing middle fingers as depicted in the 2020 remake of Witches?
Ectrodactyly.
When do limb buds begin developing in the embryo?
During the latter part of the 4th week post-fertilization.
Which limb buds appear first during embryonic development?
The upper limb buds appear first around day 26 or 27.
How many days later do the lower limb buds develop compared to the upper limb buds?
One to two days later.
What type of cells do the limb buds originally contain?
A core of mesenchymal cells derived from the somatic component of the lateral plate mesoderm.
What are the three major axes along which the embryonic limb develops?
Proximo-distal, dorso-ventral, and cranio-caudal axes.
What does the apical ectodermal ridge (AER) define in limb development?
The border between dorsal and ventral parts of the limb.
What is the role of fibroblast growth factor (FGF) in limb development?
It plays an important role in proximo-distal development of the limb.
What happens if the AER is prematurely removed?
It stops limb development.
What effect does introducing FGF-8 at the site of AER have?
It stimulates limb growth.
What occurs if the AER is transposed to another location?
It causes the growth of ectopic limbs at the site of transposition.
What is the role of the zone of polarizing activity (ZPA) in limb development?
It guides development along the cranio-caudal axis by expressing sonic hedgehog (SHH).
How does the level of sonic hedgehog (SHH) affect digit development?
Higher levels of SHH lead to the development of the 5th digit, while lower levels lead to the development of the big toe or thumb.
What happens if SHH levels are experimentally reduced during limb development?
Fewer digits develop.
What is the consequence of experimentally increasing SHH levels in limb development?
It stimulates the development of extra digits (polydactyly).
What role do Wnts and BMPs play in limb development?
They are involved in differentiation along the dorso-ventral axis of the limb bud.
What are homeobox-domain (HOX) genes responsible for in limb development?
They are major players in the proliferation of mesenchymal cells and the division and segmentation of the limb.
When do digital rays appear in the hand and foot plates during development?
Digital rays are present by the end of the 6th week in hand plates and by early week 7 in foot plates.
What process leads to the separation of individual digits during limb development?
Programmed cell death (apoptosis) in the mesenchymal tissue between digital rays.
What is syndactyly and how does it occur?
Syndactyly is the condition where one or more digits remain attached due to interrupted apoptosis.
What is the primary axial artery in limb development?
It is the artery that supplies the limb bud and differentiates into adult structures.
What happens to the sciatic artery during lower limb development?
The sciatic artery degenerates, leaving remnants that form small arteries accompanying the sciatic nerve.
When does ossification begin in the appendicular skeleton?
Ossification begins at the end of week 7 or beginning of week 8.
What are primary ossification centers and when do they form?
They are areas where ossification begins in the diaphyses of long bones, forming during weeks 7-12.
What is the origin of myogenic cells in limb development?
Myogenic cells originate from the dermomyotome region of the somites.
What do the lumbosacral myotomes provide precursor cells for?
The pelvic girdle.
What do dermomyotomal cells give rise to in the limb?
The dermis of the skin.
How do motor axons grow in relation to developing myotomes in the limbs?
Motor axons grow from the spinal cord into developing myotomes in a proximal-distal pattern.
What is the typical pattern of sensory axon invasion into the limb bud?
Sensory axons invade from cranial to caudal.
From where are spinal ganglia and supporting cells of the peripheral nervous system derived?
From neural crest cells.
In which direction do the upper limbs rotate during development?
Laterally along their long axis.
What is the rotation pattern of the lower limbs during development?
Medial rotation.
How does the rotation of the upper limb affect the position of the thumb and elbow?
The thumb moves from cranial to lateral and the elbow moves from lateral to dorsal.
What is the effect of lower limb rotation on the position of the big toe and knee?
The big toe moves from cranial to medial and the knee moves from lateral to ventral.
When are limb buds most susceptible to developing pathologies?
Between 24-36 days post-fertilization.
What is a well-known teratogen that causes limb defects if consumed during early pregnancy?
Thalidomide.
What led to a widespread increase in limb abnormalities in the late 1950s and early 1960s?
The prescription of thalidomide to treat morning sickness before its effects were known.
What is adactyly?
Absence of all digits on a limb.
What does amelia refer to?
Absence of an entire limb.
What is arachnodactyly?
Elongated digits.
What is brachydactyly?
Short digits.
What is congenital clubfoot (talipes equinovarus)?
A common anomaly occurring in approximately 1/1000 births, characterized by habitually inverted feet with soles pointing medially.
What causes congenital clubfoot?
A combination of genetic and environmental factors, though the exact cause is not well known.
What is ectrodactyly?
Also known as cleft hand or cleft foot, resulting from the failure of FGF-8 expression in the central portion of the AER due to a genetic mutation.
What is meromelia?
Absence of a part of a limb; phocomelia is a specific case where proximal limb structures are absent.
What is polydactyly?
The presence of extra digits, which may be caused by an upregulation of SHH.
What is syndactyly?
Fusion of digits, which can be simple (cutaneous) or complex, caused by incomplete apoptosis in the tissue between digital rays.
