dermatomes and development of limbs copy.pptx

development of limb bud, development of axis of limb. formation of apical ectodermal ridge. development of nerves in limbs. dermatomes in the upper limb. rotation of limb buds

1. CUTANEOUS INNERVATIONS AND DERMATOMES OF UPPER LIMB

2. DEVELOPMENT OF UPPER LIMB BUDS At 24 days. Opposite to pericardial sac.

3. From 4 th to 8 th week

4. EXTEND

5. Limb bud Surface ectoderm. Mesodermal core – derived from somatopleuric layer of lateral plate mesoderm. Contain mixed population of mesenchymal cells.

6. Mesenchymal cells Somatopleuric mesenchyme – connective tissue and dermis. Paraxial mesenchyme from somites – myogenic cells. Angiogenic mesenchyme – extensive vascular network. Sensory and motor nerves , melanocytes of skin – migrate later.

7. AXES OF LIMB Proximo distal – preaxial and postaxial border Craniocaudal Dorsoventral

8. From humerus to fingers ( proximodistal ). From thumb to little finger ( craniocaudal ). From extensor to flexor aspect ( dorsoventral ).

9. Apical ectodermal ridge Ridge like thickening. Differentiation of limb segment in proximo -distal sequence.

10. INITIATION OF LIMB DEVELOPMENT

11. BONE FORMATION

12. Bones of the limbs develop in following sequence – pectoral girdle ,upper arm bones, forearm bones, and hand bones.

13. DIGITS

14. MUSCLE DEVELOPMENT

15. Development of nerves in limbs Spinal cord opposite to the limb is specialised . Motor axons from spinal cord - enter limb bud – 5 th week – grows into dorsal and ventral muscle mass – followed by sensory axons. Motor axons – arrive at the base of the limb bud, where they join in a specific pattern – brachial plexus. Base of the limb act as a decision making region for the axon.

16. Preaxial border –placed cranially- represented by thumb – supplied by upper nerves of plexus (C 5 ,C 6 ). Postaxial border- placed caudally- represented by little finger- supplied by lower nerves of plexus (C 8 , T 1 ). Distal end- Intermediate nerves of plexus(C 7 ).

17. The areas supplied by C5 and C6 adjoint the area supplied by C8,T1,T2. The overlap between them is minimal at axial lines.

18. Dermatomes of upper limb The dermatome is the area of skin supplied by a single segment of spinal cord through its dorsal root.

19. AXIAL LINES Line of junction of two dermatomes supplied from discontinous spinal level. Minimal overlap . Anterior axial lines. Posterior axial lines.

20. Axial lines

21. ROTATION OF LIMB With the development of elbow ,forearm bend ventrally and adducted to the trunk. During this process upper limb is rotated laterally to 90 degree - elbow is pointed on the dorsal side- flexor surface of the upper limb faces ventrally.

22. Cutaneous innervations of upper limb A cutaneous nerve area is the area of skin supplied by a peripheral nerve. Each part of the plexus contain nerve fibres from more than one ventral ramus . All cutaneous nerves supplying the adjacent areas of skin overlap with each other to a considerable degree.

23. Cutaneous nerves of upper limb

24. CLINICAL SIGNIFICANCE Damage to cutaneous nerves – sensory loss in the skin. Dermatomal sensory loss result if the dorsal roots of spinal nerves are damaged. Neurological examination of a patient with nerve root lesion is incomplete without a thorough examination of the dermatome and cutaneous distribution of upper limb.

25. In herpes zoster (shingles) infection ,virus affect dorsal root ganglion – crop of cutaneous blisters in the dermatome of that particular nerve.

26. REFERENCES Cunningham’s manual of practical anatomy 15 th edition. Essentials of human embryology – A K Dutta . Grays Anatomy 41 st edition. Carlson human embryology and developmental biology 5 th edition. Clinical anatomy – Neeta V Kulkarni third edition. Langman’s medical embryology. Snell’s clinical anatomy by region tenth edition. Moore clinically oriented Anatomy.

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