Anatomy of the PNS

Question 1

Where does the T1 nerve emerge from?

Answer 1

From under the T1 vertebrae = this pattern begins at C8 nerve

Question 2

Where is the only place spinal nerves are found?

Answer 2

Intervertebral foramina

Question 3

What do spinal nerves connect with?

Answer 3

Structures of the soma via rami

Spinal cord segments of the same number via roots and rootlets

Question 4

What are the differences between the anterior and posterior rami?

Answer 4

Anterior rami = larger, anterolateral body wall

Posterior rami = smaller, posterior body wall

Question 5

What join together to form roots?

Answer 5

Rootlets

Question 6

When do spinal nerves split into the posterior and anterior rami?

Answer 6

Once they leave the intervertebral foramina

Question 7

Where do all sensory axons pass?

Answer 7

From the spinal nerve into the posterior root, then into the posterior rootlets, then into the posterior horn

Question 8

Where do all motor axons pass?

Answer 8

From anterior horn into the anterior rootlets, then into the anterior root and finally into the spinal nerve

Question 9

What is a dermatome?

Answer 9

Area of skin supplied with sensory innervation from a single spinal nerve

Question 10

Why is it necessary to block all of T2-T4 if you only want to operate on the T3 dermatome?

Answer 10

Adjacent dermatomes show overlap in innervation by spinal nerves

Question 11

What is a myotome?

Answer 11

Skeletal muscles supplied with motor innervation from single spinal nerve = may be deep to dermatome of same spinal nerve (but not always)

Question 12

What are some important landmarks for dermatomes on the trunk?

Answer 12

Nipple = T4 segment
Umbilicus = T10 segment

Question 13

How does trunk dermatomal segmentation differ from limb segmentation?

Answer 13

Trunk segmentation is relatively horizontal and regular, but limb segmentation is more complex

Question 14

Why is C1 not considered to have a dermatome?

Answer 14

Up to 50% of people lack posterior rootlets in the C1 segment

Question 15

What are nerve plexuses?

Answer 15

Intermingled anterior rami from a number of adjacent spinal nerves

Question 16

What are the symptoms of Horner Syndrome?

Answer 16

Miosis, ptosis, reduced sweating (anhydrosis), increased warmth and redness
All occur ipsilaterally

Question 17

What is the underling pathology of Horner Syndrome?

Answer 17

Impaired sympathetic innervation to head and neck due to compression of the cervical parts of the sympathetic trunk

Question 18

What are some possible causes of Horner Syndrome?

Answer 18

Root of neck trauma
Carotid dissection
Internal jugular vein engorgement
Deep cervical node metastases 
Pancoast tumour