Spinal cord and spinal nerves Sanjaya Adikari Department of Anatomy

Spinal cord Extends from the foreman magnum to the lower border of L1 Divided into five regions Covered by the meninges for protection CSF in the subarachnoid space

Coverings of the spinal cord

Spinal nerves Spinal nerves come out through the intervertebral foramina

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

Cauda equina Consists of sensory and motor nerve roots below L1 These are unmixed/pure nerves Pia mater continues below L1 as a cord named filum terminale

Length of the spinal cord Black line indicates dura and arachnoid together. Pia is in blue. T12 L1 L2 L3 L4 L5 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

Lumbar puncture What are the risks of lumbar puncture ? Performed to get CSF for investigation Vertebral column is fully flexed Needle inserted between L3 and L4 spines (or one space above) Collects CSF from subarachnoid space What are the risks of lumbar puncture ?

Cross section of spinal cord 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 sensory motor

Dorsal root ganglion Somatic Autonomic sensory motor

Dorsal and ventral roots Posterior roots contain afferent (sensory) axon Anterior roots contain efferent (motor) axons The anterior roots continue out from the spinal cord, and mix with their corresponding posterior nerve root at a point after the ganglion Combination of the two roots is called a mixed spinal nerve.

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)

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

Nerve plexus Is formed by nerves interlaced with numerous communicating branches What are the advantages of a nerve plexus? Last’s Anatomy, 10th ed. Page 13

Blood supply of spinal cord

Two posterior spinal arteries Arise from PICA Supply posterior 1/3 of spinal cord One anterior spinal artery Arise as two from vertebral arteries Supply anterior 2/3 of spinal cord Segmental spinal arteries Enter the vertebral canal through intervertebral foramina Divides into anterior & posterior radicular arteries. Radicular arteries accompany nerve roots

Ant/post spinal arteries become very small at thoracic region and the segmental spinal arteries and additional feeder arteries compensate for the deficiency

Great anterior medullary artery of Adamkiewicz

Venous drainage is into internal vertebral venous plexus