Spinal cord and

spinal nerves

Sanjaya AdikariDepartment of Anatomy

Spinal cordExtends 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

7

12

5

5

8

12

5

5

1

Vertebral column Spinal cord

C2

C1

C4

C3

C6

C5

T1

C7

T3

T2

T5

T4

T7

T6

T9

T8

T11

T10

L1

T12

C1

C8

T3

T10

L1, L2

L3, L4

L5

S, C

C1

C7

C8

Spinal nerves

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

T12

L1

L2

L3

L4

L5

Sacrum

Coccyx

Foetus at 3 months

T12

L1

L2

L3

L4

L5

Sacrum

Coccyx

Adult

Length of the spinal cord

T12

L1

L2

L3

L4

L5

Sacrum

Coccyx

At birth

S2

Black line indicates dura and arachnoid together. Pia is in blue.

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

Autonomicsensory

motor

Dorsal root ganglion

Somatic

Autonomicsensory

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)

DermatomeArea 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

• Venous drainage is into internal vertebral venous plexus