1. Typical Spinal Nerve
Sanjaya Adikari
Department of Anatomy

2. CNS is covered by the skull and the vertebral column
PNS is outside
Skull
Vertebral column

4. Structure of a spinal cord segment
Posterior median septum
Posterior horn
Lateral horn
Anterior horn
Anterior median fissure
Central canal
Posterior white column
Lateral white column
Anterior white column
Anterior nerve root
Posterior nerve root

5. Dorsal root ganglion
Somatic
Autonomic

7. Dorsal and ventral roots
Dorsal roots contain afferent (sensory) axons
Ventral roots contain efferent (motor) axons
The ventral roots continue out from the spinal cord, and mix with their corresponding dorsal nerve root at a point after the ganglion
The combined dorsal and ventral roots are called a spinal nerve (therefore, spinal nerves are mixed).

8. Spinal nerve is mixed (motor + sensory + autonomic)

9. Spinal nerve is mixed (motor + sensory + autonomic)
Spinal nerve refers to the mixed spinal nerve
It is formed from the dorsal and ventral roots
Passes out through the intervertebral foramen
There are 31 bilaterally-paired spinal nerves
8 cervical nerves (C1-C8)
12 thoracic nerves (T1-T12)
5 lumbar nerves (L1-L5)
5 sacral nerves (S1-S5)
1 coccygeal nerve (Co)

10. Vertebral column
Spinal cord 7 12 5 8 1

11. Spinal nerves C1 C1 C2 C3 C4 C5 C6 C7 C8 C7 C8 T1 T1 T2 T2 T3 T4 T5 T6
L1, L2
L3, L4 L5
S, C C8 T1 T2
T10

12. Length of the spinal cord
Sacrum
Coccyx
Foetus
at 3 months
T12 L1 L2 L3 L4 L5
Sacrum
Coccyx
At birth S2
T12 L1 L2 L3 L4 L5
Sacrum
Coccyx
Adult

13. Anterior and posterior primary rami
The posterior primary rami have lateral and medial branches
They supply
back muscles and skin over the back
The anterior primary rami give off anterior and lateral cutaneous branches
the rest of the body wall
Anterior primary rami also give rise to the roots of the various nervous plexuses

14. Spinal nerves in the thoracic region
Anterior cutaneous branch
Lateral cutaneous branch
Medial
Lateral
Anterior
Posterior
These are typical spinal nerves

16. Rami communicantes Gray ramus communicans unmyelinated
White ramus communicans
myelinated

18. Nerve plexus
Formed by communicating branches between anterior primary rami of spinal nerves.
Anterior primary rami form the roots of nerve plexus
What are the advantages
of a nerve plexus?
Last’s Anatomy, 10th ed.
Page 13

19. Dermatome
Area of skin supplied by a single spinal nerve or spinal cord segment
Myotome
The muscle/s supplied by a single spinal nerve or spinal cord segment