B and SC 1.3

Question 1

How many pairs of spinal nerves are there?

Answer 1

Thirty-one pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal) course from the spinal cord

Question 2

What is the the spinal cord surrounded by?

Answer 2

• 3 meningeal layers
  1. The innermost layer is the pia mater, which is closely applied to the spinal cord
  2. The middle layer is the arachnoid mater
  3. The tough, outer fibrous meningeal layer is the dura mater

Question 3

What forms the cauda equina?

Answer 3

Posterior and anterior roots of the lumbar and sacral spinal nerves form the cauda equina (horse’s tail).

Question 4

What is the terminal filum?

Answer 4

1. The terminal filum is an extension of pia mater from the tip (conus medullaris) of the spinal cord
2. It blends with dura at the apex of the dural sac and attaches to the dorsum of the coccyx. It helps anchor the distal spinal cord

Question 5

Where would you insert a needle into the back?

Answer 5

1. A spinal needle may be used to sample the cerebrospinal fluid in the subarachnoid space, 2. This procedure is done in the lower lumbar region where the needle will not penetrate the spinal cord (the cord ends at about the L1 vertebral level in adults)
2. The roots of the cauda equina, bathed and floating in cerebrospinal fluid, will part and allow the needle to enter the subarachnoid space without puncturing a root.

Question 6

What forms the posterior and anterior roots of the spinal nerve?

Answer 6

Posterior (dorsal) and anterior (ventral) nerve filaments combine in the intervertebral foramen to form the posterior and anterior roots of the spinal nerve

Question 7

What is the spinal ganglion?

Answer 7

The spinal ganglion contains the sensory nerve cell bodies

Question 8

What does each spinal nerve divide into?

Answer 8

Each spinal nerve divides into a very large anterior ramus and a much smaller posterior ramus

Question 9

What anchors the spinal cord to the dura?

Answer 9

About 20 pairs of denticulate ligaments

Question 10

What are denticulate ligaments?

Answer 10

are pial extensions that pass laterally between the posterior and anterior roots of spinal nerves to attach to the dura

Question 11

Where is CSF found?

Answer 11

Subarachnoid space

Question 12

What does subarachnoid space contain?

Answer 12

1. The subarachnoid space (brain and spinal cord) contains about 150 mL of cerebrospinal fluid.
2. The pressure of this fluid can be measured or sampled for laboratory analysis to determine if an infection is present somewhere in the central nervous system.

Question 13

How does the spinal cord connect to the sympathetic chain ganglia?

Answer 13

By rami communicantes

Question 14

Where are white and gray rami communcicantes found?

Answer 14

1. White and gray rami communicantes are found between the T1 and L2 spinal cord levels
2. but only gray rami communicantes are found at the other spinal cord levels.

Question 15

Where do anterior and posterior roots join to form the spinal nerve?

Answer 15

In the interverbral foramen

Question 16

What does the spinal nerve immediately divide into?

Answer 16

small posterior ramus, which supplies the skin and underlying intrinsic back muscles, and a much larger anterior ramus

Question 17

What is the epidural space filled with?

Answer 17

The epidural space (between the dura mater and the bony vertebral canal) is filled with fat and a rich vertebral venous plexus

Question 18

What could narrow the size of the intervertebral foramen and what could this cause?

Answer 18

Any pathology that narrows the size of the intervertebral foramen (excessive growth of adjacent bone, a tumor, an abscess) can impinge on the posterior or anterior roots or the spinal nerve and cause symptoms related to the nerve fibers carried in those roots or the nerve

Question 19

How do afferent nerve fibres return to the spinal cord?

Answer 19

1. Afferent (sensory) nerve fibers return to the spinal cord via the splanchnic nerve (pain sensation from viscera) and via the spinal nerve
2. The cell bodies of these sensory nerve fibers reside in the spinal (dorsal root) ganglion

Question 20

Where do the Preganglionic sympathetic efferent (motor) nerve fibers originate from?

Answer 20

originate from neurons in the intermediolateral cell column of the thoracic spinal cord

Question 21

Where do the Preganglionic sympathetic efferent (motor) nerve fibers leave the cord by?

Answer 21

leave the cord via the anterior root

Question 22

How do Preganglionic sympathetic efferent (motor) nerve fibers enter the sympathetic chain?

Answer 22

enter the sympathetic chain via a white ramus communicans

Question 23

What happens after the Preganglionic sympathetic efferent (motor) nerve fibers enter the sympathetic chain?

Answer 23

1. the nerve may continue via a splanchnic nerve to the celiac ganglion to synapse
2. pass up or down the sympathetic chain to synapse at a higher-level or lower-level chain ganglion
3. or synapse in the chain ganglion at the spinal cord level where it exited the cord

Question 24

What happens when the preganglionic fiber has synapsed on the postganglionic neuron?

Answer 24

When the preganglionic fiber has synapsed on the postganglionic neuron (in a chain ganglion or the celiac ganglion), postganglionic fibers course to innervate viscera, smooth muscle, glands, or arrector pili muscles of the skin (attached to hair follicles)

Question 25

How is the vagus nerve involved?

Answer 25

1. Parasympathetic efferent fibers course to the viscera via the vagus nerve
2. Reflex afferents from the viscera return to the brainstem also via the vagus nerve
3. Visceral afferents also convey pain from distention, inflammation, or ischemia and return to the spinal cord via the splanchnic nerve and posterior root (cell bodies in the spinal ganglion)

Question 26

Where are arteries supplying the spinal cord derived from?

Answer 26

branches of the vertebral, ascending cervical, posterior intercostal, lateral sacral, and lumbar arteries

Question 27

What generally courses the length of the spinal cord?

Answer 27

• a single longitudinal anterior spinal artery

- and 2 longitudinal posterior spinal arteries

Question 28

What accompanies the posterior and anterior roots of the spinal cord?

Answer 28

Segmental radicular arteries

Question 29

What do anastomoses between the anterior and posterior spinal arteries and the segmental medullary branches form?

Answer 29

a pial arterial plexus

Question 30

What provides the main blood supply to the spinal cord? What is it supplemented by?

Answer 30

• The anterior spinal artery and paired dorsal spinal arteries
• supplemented by radicular arteries from the aorta

Question 31

What happens if blood flow through the radicular arteries is impaired?

Answer 31

(e.g., during surgery or if a fracture, dislocation, or other injury has occurred), the spinal cord may become ischemic and a spinal infarct can result.

Question 32

What are the spinal veins?

Answer 32

Usually, there are 3 anterior and 3 posterior spinal veins (although veins are often variable)

Question 33

How do these 6 veins communiste and drain?

Answer 33

• These veins communicate freely with one another

- drain into segmental radicular veins

Question 34

What do the veins of the spinal cord and vertebrae form?

Answer 34

an internal vertebral plexus of veins

Question 35

What do the veins of the spinal cord snd vertebrae communicate with?

Answer 35

an external vertebral venous plexus surrounding the bony vertebrae

Question 36

Where does the vertebral venous plexus drain?

Answer 36

This vertebral venous plexus ultimately drains into intervertebral veins and then into the vertebral veins, ascending lumbar veins, azygos venous system, and inferior vena cava.

Question 37

Do viens in the vertebral venous plexus possess valves?

Answer 37

1. Most of the veins of the vertebral venous plexus do not possess valves
2. but recent evidence suggests that some do; because of the large region that they drain (entire spine), they provide a conduit for the spread of cancer cells (metastasis) from one region (e.g., the pelvic region) to distant sites (e.g., the lungs, brain).

Question 38

What do veins in the vertebral venous plexus provide a route for?

Answer 38

1. The vertebral venous plexus (of Batson) is a network of veins that course along the spine 2. provide a route for venous metastases of cancer cells from distal locations (e.g., the pelvis) to seed the spine and other organs located more proximally (e.g., the lungs, brain)