Spinal cord and spinal nerves

Question 1

Spinal cord

Answer 1

A part of the CNS, composed of 31 distinct segments of neural tissue, from which extends 31 pairs of bilaterally symmetrical spinal nerves. It occupies the spinal canal of the vertebral column, descending from the medulla oblongata of the brainstem to the conus medullaris at the L1/2 vertebral level in adults.

Question 2

31 spinal segments

Answer 2

• 8 cervical segments
• 12 thoracic segments
• 5 lumbar segments
• 5 sacral segments
• 1 coccygeal segment

Question 3

Cervical enlargement

Answer 3

Consists of spinal cord segments C4-T1 and provides innervation for the upper limb via the brachial plexus.

Question 4

Lumbar enlargement

Answer 4

Consists of spinal cord segments L1-S3 and provides innervation for the lower limb via the lumbosacral plexus.

Question 5

Conus medullaris

Answer 5

The cone-shaped caudal end of the spinal cord, terminating at vertebral level L1/2.

Question 6

Filum terminale

Answer 6

A connective tissue strand extending caudally to attach to the dorsal surface of the first coccygeal vertebra, continuous with the meninges.

Question 7

Foreshortening

Answer 7

Until the third month of fetal development, the spinal cord occupies the entire length of the spinal canal. As the rate of elongation of the vertebral column begins to exceed that of the spinal cord, each segment gradually lies higher that it’s associated vertebra.

Question 8

Relations of spinal segments to vertebra

Answer 8

Generally:

• cervical segments lie 1 spine higher
• thoracic segments lie 2 spines higher
• lumbar segments lie 3/4 spines higher

Question 9

Cauda equina

Answer 9

The “horses tail”; a whip-like bundle of lumbar and sacral nerve roots, which extend caudally below the conus medullaris to exit via the correct intervertebral foramina.

Question 10

Spinal meninges

Answer 10

Composed of dura mater, arachnoid mater and pia mater. The subarachnoid space is filled with CSF and conducts blood vessels. Although the spinal cord terminates at vertebral level L1/2, the arachnoid, dura and subarachnoid space continue caudally to S2, creating a sac.

Question 11

Lumbar puncture

Answer 11

A procedure in which CSF is drained from the sac-like subarachnoid space caudal to the termination of the spinal cord.

Question 12

Epidural space

Answer 12

The space between the dura and the bony wall of the vertebral canal, into which anaesthetics may be administered.

Question 13

Denticulate ligament

Answer 13

A flat, membranous continuation of the pia, folding out halfway between the dorsal and ventral roots of the spinal nerves, joining intermittently to the arachnoid and dura via lateral projections.

Question 14

Grey matter of the spinal cord

Answer 14

A central, butterfly-shaped structure consisting of neuronal cell bodies within the spinal cord. Can be divided into four horns, two dorsal and two ventral.

Question 15

White matter of the spinal cord

Answer 15

Composed of the axons of neurones within the spinal cord, forming funiculi which surround the grey matter.

Question 16

Central canal

Answer 16

Continuous with the ventricular system of the brain, carries CSF within the spinal cord.

Question 17

Afferent nerve fibres

Answer 17

Diverge from the mixed spinal nerve into dorsal roots and rootlets, terminating in the dorsal horn of the spinal cord. Their cell bodies are contained within dorsal root ganglia.

Question 18

Efferent nerve fibres

Answer 18

Emerge from the ventral horn of the spinal cord, converging from ventral rootlets into roots, which join with dorsal roots to form a mixed spinal nerve.

Question 19

Regional innervation

Answer 19

Each pair of spinal nerves provides sensory and motor innervation to the dermatomes and myotomes with which is it embryonically derived.

Question 20

Rami

Answer 20

Branches of the spinal nerves, which carry mixed fibres. The dorsal ramus tends to be smaller, while the ventral ramus tends to be larger.