Prenatal Limb Development Quiz

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Questions and Answers

What process leads to the formation of the cartilage model during bone development?

Cortical remodeling

Endochondral ossification (correct)

Appositional growth

Intramembranous ossification

Which muscle compartment is formed from myogenic precursors that migrate ventrally?

Extensor compartment

Rotator compartment

Accessory compartment

Flexor compartment (correct)

What occurs to the upper limb during limb rotation?

Rotates laterally, with the thumb lateral (correct)

Remains in the same position as before

Rotates medially, with the thumb medial

Does not develop any muscle mass

Which condition describes a complete absence of a limb?

Amelia Signup and view all the answers

What is the role of spinal nerves in limb bud development?

To facilitate the growth of muscle masses Signup and view all the answers

What is a characteristic of dermatome mapping?

It indicates a strip of skin supplied by a single spinal nerve Signup and view all the answers

Which defect results from a lack of apoptosis between digits?

Syndactyly Signup and view all the answers

During which phase of development do limbs rotate and change their position?

Limb rotation phase Signup and view all the answers

What is the role of the Apical Ectodermal Ridge (AER) in limb development?

It induces outgrowth and keeps the underlying mesenchyme undifferentiated. Signup and view all the answers

During which week of prenatal development do limb buds first appear?

Fourth week Signup and view all the answers

What is the function of the Zone of Polarising Activity (ZPA)?

It generates asymmetry in the limbs and influences patterning. Signup and view all the answers

What do limb buds consist of?

A mesenchyme core with a thickened ectoderm at the apex. Signup and view all the answers

How does proximal mesenchyme begin to differentiate during limb development?

Due to its distance from the AER. Signup and view all the answers

What occurs to the Apical Ectodermal Ridge (AER) during the development of the digits?

It breaks up and is maintained only at the tips of the digital rays. Signup and view all the answers

What is the significance of dorsoventral patterning in limb development?

It sets the axes of limb orientation and structure. Signup and view all the answers

What process shapes the interdigital spaces in the developing hand and foot?

Apoptosis. Signup and view all the answers

Study Notes

Prenatal Limb Development

Limb development initiates with mesenchymal activation in the somatic layer of lateral mesoderm, forming limb skeletons.
Somites contribute to limb musculature.
Limb buds form by the end of the 4th week, with lower limb development lagging by about 2 days.
Limb buds emerge ventro-laterally, initially extending ventrally, consisting of a mesenchymal core surrounded by thickened ectoderm known as the Apical Ectodermal Ridge (AER).

Limb Buds and Development

AER is essential for limb bud outgrowth and patterns limb development from proximal to distal.
AER maintains undifferentiated mesenchyme beneath it, which proliferates for elongation.
Proximal mesenchyme differentiates into specific tissues due to distance from AER signals.
AER influences digit development before regressing.

Zone of Polarising Activity (ZPA)

ZPA, located at the posterior limb bud base, generates limb asymmetry and controls patterning while maintaining AER.

Dorsoventral Patterning

AER marks the boundary between dorsal and ventral ectoderm, influencing mesenchyme through dorsalizing and ventralizing factors.
Patterning is coordinated along three axes:
- Anterior-Posterior: ZPA
- Proximal-Distal: AER
- Dorsal-Ventral: Ectoderm

Hand and Foot Formation

Digital rays form cartilage models of digital bones through mesenchyme condensation.
AER disperses but remains at the tips of digital rays, with interdigital spaces shaped by apoptosis.
Cartilage models develop through signals from AER and undergo endochondral ossification, forming primary and secondary ossification centers.

Limb Rotation

As limb buds extend, they rotate:
- Upper limb: Rotates laterally; thumb positions laterally.
- Lower limb: Rotates medially; big toe positions medially.
Pre-rotation positioning: thumbs upwards, elbows out, soles in, knees out; post-rotation: thumbs out, elbows down, soles down, knees up.

Limb Innervation

Upper limb bud originates near caudal cervical spinal segments; lower limb bud near lumbar and sacral segments.
Spinal nerves enter early in limb bud development; lack of innervation halts growth.
Muscles categorized into compartments with specific nerve supplies:
- Medial and lateral cords supply flexors (anterior divisions).
- Posterior cord supplies extensors (posterior divisions).

Nails and Dermatomes

Nails develop from nail fields migrating to dorsal surfaces with their nerve supply.
Dermatome: skin area supplied by one spinal nerve.
Myotome: muscle group supplied by a single spinal nerve.

Common Limb Defects

Occurrence of limb defects is about 6 in 10,000 live births; often hereditary but can be teratogen-induced.
Defect Types:
- Amelia: complete absence of a limb.
- Meromelia: partial absence of limb structures.
- Club Foot: abnormal foot positioning.
- Cleft hand and foot (lobster claw deformity): abnormalities in digit arrangement.
Digit Defects:
- Syndactyly: digits fused due to lack of apoptosis.
- Polydactyly: extra digits present.

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Description

Test your knowledge on the prenatal development of limbs in the musculoskeletal system. This quiz covers topics such as limb buds, dorsoventral patterning, and common limb defects. Dive deep into the intricacies of limb formation and innervation.