1. The typical spinal nerve
Medical Biomorphology 140
Stuart Bunt

2. Order of the lecture Embryology Evolution Anatomy Dermatomes
Peripheral nerve territories
Autonomics

3. Somites (blocks of mesoderm)
Somites appear early in development
Are characteristic of all vertebrates

4. Somites are found in all vertebrates
Chicken Embryos

5. In humans the segments are most obvious in the vertebrae
and segmental nerves of the thoracic area.

6. Somitic tissue migrates to form muscles
The somite blocks disperse and
the mesodermal cells contribute
to the dermis, muscles, bones
and connective tissue.

7. Somite splits in to dermo-myotome and the dispersing cells of the sclerotome
The sclerotome gives rise to the connective tissue and tissue derived from it such as the cardiovascular system and skeletal system
The dermo-myotome splits in to dermal and myotomal components
The former forms the deep layers of the dermis
The myotome forms the muscles

8. The myotome forms a dorsal epimere and a ventral hypomere
Epimere forms vertebral musculature, hypomere the rest of
the muscles of the body wall and limbs

9. While the somites are forming the neural tube closes
The crest of the neural tube migrates off in to the body
These cells form the dorsal root ganglia and contribute to
many other tissues from the facial skeleton to the adrenals

10. Nerves grow out in to the mesoderm
Nerve fibres follow surface clues (glyco proteins),
entering the front of each myotome
As limb buds grow the fibres extend and
innervate overlapping but regular areas
of the limb.

11. The area innervated by fibres from a single root is known as a DERMATOME

12. The area innervated by a single peripheral nerve is NOT the same as a Dermatome.
If you look carefully at the dermatome patterns in different books you will see that they often disagree.
This is because the patterns are variable and overlap considerably

13. Further growth gives rise to the adult pattern of a typical spinal nerve
Dorsal ramus
Ventral ramus

14. Spinal nerves 8 Cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
Each segment made of tissue from one somite

15. Dorsal root Contains sensory fibres
Cell bodies in the dorsal root ganglion
Runs in to dorsal horn of spinal cord
Distal process carries sensation from the periphery

16. Dorsal Root Ganglion contains pseudounipolar sensory cells
Schwann cells
Satellite cells
NO synapses

17. Ventral Root somatic motor axons visceral motor axons
Cell bodies in spinal cord grey matter
terminals on muscles or in autonomic ganglia

18. The spinal nerve Only part that contains ALL segmental nerves
Motor AND sensory
Short segment just outside vertebral canal

19. Dorsal and Ventral Primary Rami
Dorsal Ramus supplies
superficial structures on dorsal midline of body
skin, skeleton, muscles, meninges on post vert column
Ventral Ramus supplies
deep and superficial structures of lateral and anterior trunk
skin, skeleton, muscles, meninges

20. Grey and White Rami Communicantes
The grey rami contain unmyelinated visceral axons
heading out from the ganglia to the periphery
postganglionic axons
The white rami contain myelinated fibres (white)
Coming from the spinal cord to the ganglia
preganglionic axons
T1-L2

21. The sympathetic ganglia
Visceral autonomic ganglia
Postganglionic fibres innervate gut etc.
Connected by connectives
Run alongside the vertebral column

22. Splanchnic Nerves Innervate internal organs
preganglionic and postganglionic
sympathetic or parasympathetic