Typical Spinal Nerve Sanjaya Adikari Department of Anatomy

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

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

Dorsal root ganglion Somatic Autonomic

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).

Spinal nerve is mixed (motor + sensory + autonomic)

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)

Vertebral column Spinal cord 7 12 5 8 1

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

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

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

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

Rami communicantes Gray ramus communicans unmyelinated White ramus communicans myelinated

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

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