1. DEVELOPMENT OF CRANIAL NERVES & AUTONOMIC NERVOUS SYSTEM
Dr Samina Anjum

2. CRANIAL NERVES 4th week- All cranial nerve nuclei are present
III –XII CN arise from brainstem
Only III CN arise outside the region of hind brain

3. SEGMENTATION IN HINDBRAIN
In the hind brain, Proliferation centers in the neuroepithelium establish eight distinct segments – Rhombomeres which give rise to motor nuclei of CNs

4. CRANIAL NERVES
Motor neurons for Cranial nuclei are within the brain stem while sensory ganglia are outside the brain.
Organization of CNs is homologous to the spinal nerves, but all CN don't contain both sensory & motor fibers.

5. CRANIAL NERVE - SENSORY GANGLIA
Originate from:
Neural crest cells
Ectodermal placodes:
Otic
Nasal
4Epibranchial

6. EPIBRANCHIAL PLACODES
Represented by ectodermal thickenings dorsal to pharyngeal arches
Contribute to ganglia for the nerves of the pharyngeal arches.

7. PARASYMPATHETIC GANGLIA
Visceral efferent ganglia are derived from neural crest cells, & their fibers are carried by CN III, VII, IX & X

9. AUTONOMIC NERVOUS SYSTEM
Functionally, the autonomic nervous system can be divided into two parts:
Sympathetic portion in the thoracolumber region
Parasympathetic portion in the cephalic and sacral region

10. SYMPATHETIC NERVOUS SYSTEM
In the 5th week, cells originating in the neural crest of the thoracic region migrate on each side of the spinal cord toward the region immediately behind the dorsal aorta.

11. NEURAL CREST CELLS

12. SYMPATHETIC GANGLIA
Neural crest cells form a bilateral chain of segmentally arranged sympathetic ganglia. interconnected by longitudinal nerve fibers.
Together, they form the sympathetic trunks on each side of the vertebral column.

13. EXTENT OF SYMPATHETIC CHAIN
From there position in the thorax, neuroblasts migrate toward the cervical & lumbosacral regions, extending the sympathetic trunk to their full length.

14. FUSION OF GANGLIA
Initially the ganglia are arranged segmentally, later this arrangement is obscured, in the cervical region, by fusion of the ganglia.

15. PREAORTIC GANGLIA
Some sympathetic neuroblasts migrate in front of the aorta to form preaortic ganglia, such as
CELIAC
SUPERIOR MESENTERIC
INFERIOR MESENTERIC

16. SYMPATHETIC ORGAN PLEXUSES
Other sympathetic cells migrate to the heart, lungs, and gastrointestinal tract, where they give rise to sympathetic organ plexuses.

17. VISCEROEFFERENT COLUMN & PREGANGLIONIC FIBERS
Once sympathetic trunks have been established, nerve fibers originating in the visceroefferent column (intermediate horn) of the thoracolumber segments (T1-L2,L3) of the spinal cord penetrate the ganglia of the trunks (paravertebral ganglia).
They are known as preganglionic fibers (Myelinated, form white communicating rami)
Hence, white rami are found only from L1-L2 or L3 segments of the spinal cord.

18. POSTGANGLIONIC FIBERS
Axons of the sympathetic ganglion cells, the postganglionic fibers, have no myelin sheath.
They either pass to other levels of sympathetic trunks or extend to the heart, lungs, and intestinal tract.
Other fibers, the gray rami communicantes, pass from the sympathetic trunk to spinal nerves & from there to peripheral blood vessels, hair, & sweat glands.
Gray rami are found at all levels of the spinal cord.

19. Fate of cephalic fibers: Synapse with ganglia in cervical region
Fibers pass without synapsing, as preganglionic fibers of greater(T5-9), lesser(T10-11) and least splancnic nerves(T12) to prevertebral ganglia.
A few fibers from Gr.Spl N
end directly in adrenal medulla
ACh
Fate of caudal fibers: Synapse with ganglia in lower lumber & sacral regions region
Post ganglionic fibers to Smooth muscle and glands of viscera

21. SUPRARENAL GLAND
The suprarenal gland (adrenal gland) develops from 2 components:
MESODERMAL
/Mesenchyme
ECTODERMAL/
NCcells

22. FORMATION OF CORTEX OF THE SUPRARENAL GLAND
During the 5th week of development, mesothelial cells between the root of the mesentery & the developing gonad begin to proliferate & penetrate the underlying mesenchyme, differentiate into large acidophillic organ which form fetal cortex, or primitive cortex.

23. Cont….
Shortly after, a 2nd wave of cells from the mesothelium penetrate the mesenchyme and surrounds the original acidophilic mass definitive cortex of the gland.
These cells smaller than those of first wave, later forms the definitive cortex of gland.

24. Cont…
While fetal cortex is being formed, cells originating in the sympathetic system (NC cells) invade its medial aspect, where they are arranged in cords and clusters. These cells give rise to medulla of suprarenal gland.
They stain yellow brown with chrome salts, hence are called chromaffin cells.
During embryonic life chromaffin cells are widely distributed through out the embryo, but in adult they are limited to adrenal medulla only.

25. FORMATION OF MEDULLA OF THE SUPRARENAL GLAND

27. Cont…
After birth fetal cortex regresses rapidly except for its outer most layer, which differentiate into reticular zone. but zona reticulosa is recognizable until the end of 3rd year.
Recent studies show that a transitional zone is located b/w fetal cortex and adult cortex. It has been suggested that zona fasciculata is derived from this zone.
The zona glomerulosa and zona fasciculata are present at birth
Adult structure of cortex is achieved at puberty.

28. Cont…
Suprarenal glands of human fetus are 10-20X larger than in adult due to extensive size of fetal cortex , which produces steroid precursors that are used by placenta for the synthesis of estrogen.

29. PARASYMPATHETIC NERVOUS SYSTEM
Neurons in the brainstem & the sacral region (S2-4) of the spinal cord give rise to preganglionic parasympathetic fibers.
Fibers travel via the III, VII, IX, & X nerves.
Post ganglionic fibers arise from ganglia derived from neural crest cells and pass to structures they innervate (pupil of eye, salivary glands, viscera)

30. Red- Sympathetic NS
Blue : Parasympathetic nervous system

31. HIRSCHSPRUNG DISEASE Congenital Megacolon
Failure of parasympathetic ganglia to form in the wall of part or all of the colon & rectum because the neural crest cells fail to migrate.
The colon is dilated above the affected region, which has a small diameter because of tonic contraction of innervated musculature.

32. RADIOGRAPH OF COLON AFTER BARIUM ENEMA

33. Cranium Bifidum (bony defect in cranium)
Meningocele
Meningoencephalocele
Meningohydroencephalocele

34. Holoprosencephaly: Loss of midline structures

35. Schizencephaly: large clefts in CH, loss of brain tissue

36. Anencephaly

37. Hydrocephalus

38. Arnold Chiari Malformation

39. THANK YOU

40. OCULOMOTOR NERVE

41. FACIAL NERVE

42. GLOSSOPHARYNGEAL NERVE

43. VAGUS NERVE