Spinal Cord

Question 1

Describe the structure of the spinal cord.

Answer 1

Begins from the medulla oblongata of the brain stem

Has 2 enlargements in the cervical and lumbar regions (thickest here)

Cord ends at L1/L2 in a bluntly shaped conus medullaris, then continues as the cauda equina, a bundle of spinal nerve roots

Cylindrical structure, flattened anteroposteriorly

Protected by vertebrae, ligaments and muscles, meninges, and CSF

Question 2

Describe the development of the spinal cord.

Answer 2

Embryonic period: cord occupies full length of canal, spinal nerves exit laterally through IV foramen

Fetal period: column grows faster than cord

Birth: conus medullaris is at L4/5 level, cord still shorter than canal so spinal nerves exit obliquely

Adult: cord ends at L1-2 and continues as cauda equina encapsulated by the lumbar cistern

Question 3

Describe the spinal nerves.

Answer 3

31 pairs of spinal nerves

8 cervical nerves for 7 vertebrae

C1 exits between occiput and atlas

Cervical nerves exit ABOVE their proper vertebrae, then after C8 all subsequent nerves exit BELOW their proper vertebrae

Cord stops at L1/2 but the lower lumbar, sacral, and coccygeal nerves have to reach their proper levels as part of the cauda equina

Cord —> dorsal and ventral roots —> dorsal root ganglion —> spinal nerve —> dorsal and ventral primary rami

Spinal nerves exit IV foramina and immediately divide into dorsal and ventral primary rami

- dorsal primary rami innervate erector spinae and deep muscles of the back
- ventral primary rami innervate superficial structures

Question 4

Compare and contrast ventral and dorsal primary rami.

Answer 4

Ventral primary rami travel anteriorly and provide motor and sensory innervation, forming plexus in areas of concentrated innervation

- Cervical plexus C1-C4
- Brachial plexus C5-T1
- Lumbar plexus T12-L5
- Sacral plexus L4-S5

Dorsal primary rami are also motor and sensory, and travel posteriorly to innervate structures in the back

Question 5

Describe the spinal cord meninges.

Answer 5

Most superficial is the dura mater, then the arachnoid mater, then the pia mater.