PNS 6

Question 1

What Cranial Nerve is CN XI?

Answer 1

Spinal ACCESSORY NERVE

Question 2

What Nerve fiber type does the Spinal Accessory Nerve - CN XI - contain?

Answer 2

GSE fibers

Question 3

CN XI - the spinal accessory nerve’s GSE fibers innervate what 2 muscles?

Answer 3

1. Sternocleidomastoid &

2. Trapezius Muscles

Question 4

The Spinal Accessory Nerve (CN XI) enters and then exits the Posterior Cranial Fossa of the Skull via what two foramena?

Answer 4

1. FORAMEN MAGNUM transmits the Spinal Root of CN XI INTO the posterior cranial fossa
2. JUGULAR FORAMEN transmits CN XI OUT of the posterior cranial fossa.

Question 5

What 3 Cranial Nerves are transmitted OUT of the posterior cranial fossa by the Jugular Foramen?

Answer 5

1. CN IX - Glossopharyngeal
2. CN X - Vagus
3. CN XI - Spinal Accessory

Question 6

What part of CN XI branches off to join the Vagus Nerve after leaving the jugular foramen and doesn’t participate in innervation of sternocleidomastoid or trapezius?

Answer 6

The CRANIAL ROOT of CN XI

Question 7

The SPINAL ROOT of CN XI arises from what Nucleus in the CNS?

Answer 7

ACCESSORY NUCLEUS

Question 8

The Spinal Root of the Spinal Accessory Nerve travels w/in the lateral ventral horns of what Cervical Spinal segements?

Answer 8

C1-C5

Question 9

At what point is CN XI most vulnerable to lesion? What is often a cause?

Answer 9

The spinal accessory nerve is vulnerable to lesion as it crosses the POSTERIOR CERVICAL TRIANGLE as it descends posteriorly to innervate Trapezius. Often IATROGENIC (caused by a physician).

Question 10

Lesions of CN XI may cause what 2 problems?

Answer 10

1. Ipsilateral (same side) Shoulder Drop. Right Trapezius paresis, due to CN XI lesion, will result in drop in Right shoulder.
2. Contralateral (opposite side) difficulty rotating head. Due to paresis of sternocleidomastoid. Right SCM paresis –> Difficulty rotating head to left.

Question 11

The CERVICAL PLEXUS by contributions from what 4 Ventral Rami?

Answer 11

C1-C4 ventral rami.

Question 12

There are 7 cervical vertebrae (C7-C1). How many Cervical Spinal Nerves are there?

Answer 12

8 b/c C1 spinal nerves come off the top of C1 while C8 spinal nerves come off the bottom of C8

Question 13

How are cervical nerves numbered differently than other spinal nerves?

Answer 13

Cervical nerves are numbered for the cervical vertebrae that is contributing to the INFERIOR MARGIN of the intervertebral foramen. All other spinal nerves are named for the OVERLYING vertebra

Question 14

What branch of the Cervical Plexus innervates all but 1 of the INFRAHYOID “STRAP” MUSCLES? What’s the 1 exception?

Answer 14

ANSA CERVICALIS innervates all infrahyoid “strap” muscles except for the THYROHYOID, which is innervated by C1 fibers.

Question 15

From what Cervical Nerves do the SUPERIOR (or DESCENDENS HYPOGLOSSI) and INFERIOR ROOTS of Ansa Cervicalis arise from?

Answer 15

1. Superior Root (Descendens Hypoglossi) arises from C1

2. Inferior Root arises from C2 & C3

Question 16

The PHRENIC NERVE arises from the Cervical Plexus. From what 3 cervical nerve ventral ramis does the phrenic nerve derive from? Which makes the largest contribution?

Answer 16

C3, C4 & C5. C4 makes the largest contribution to the Phrenic Nerve.

Question 17

From the Cervical Plexus, where does the Phrenic Nerve go? What structures does the Phrenic Nerve innervate?

Answer 17

The Phrenic Nerve descends through the neck along the anterior scalenes to reach the thoracic cavity. There the Phrenic Nerves innervate the DIAPHRAGM & the PARIETAL PLEURA lining the Thorax.

Question 18

What is a rhyme to help you remember the origin of the Phrenic Nerve & what the Phrenic innervates?

Answer 18

“C3, 4, 5 keep the diaphragm alive!”

Question 19

Pain due to compression of the gall bladder beneath the Diaphragm is often felt as Referred Pain in the Right Shoulder. Why might this be?

Answer 19

Pain sensation is referred to the SUPRACLAVICULAR Cutaneous Nerve in the C4 DIATOME that arises from the Cervical Plexus and innervates the skin at the base of the neck and shoulders.

Question 20

What 4 groups of Cutaneous Nerves arise from the Cervical Plexus?

Answer 20

1. Lesser Occipital
2. Greater Auricular
3. Transverse Cervical
4. Supraclavicular

Question 21

For each of the 4 Cutaneous Nerves arising from the cervical plexus, tell their source of nerve fiber and general location. Lesser Occipital, Great Auricular, Transverse Cervical, & Supraclavicular.

Answer 21

1. Lesser Occipital: C2 nerve fibers - ascends posteriorly to skin overlying inferior occipital bone
2. Great Auricular: C2 & C3 nerve fibers - ascends anteriorly to skin in front of the ear
3. Transverse Cervical: C2 & C3 Nerve Fibers - transverses to skin over center of neck, jugular
4. Supraclavicular: C3 & C4: descends to skin overlying lower neck and upper shoulder (clavicle)

Question 22

What 2 cutaneous branches from the Cervical Plexus join the cutaneous branches from CN V in providing cutaneous innervation to the face?

Answer 22

1. Lesser Occipital

2. Great Auricular

Question 23

The 4 Cutaneous Cervical Nerves may be blocked by an injection where?

Answer 23

ERB’S POINT or the PUNCTA NERVOSUM.

Question 24

Why might a shoulder drop occur from an injection at the Puncta Nervosum (Erb’s Point)?

Answer 24

B/c a branch of the ACCESSORY Nerve (CN XI) passes through the posterior cervical triangle on its way to innervating the Trapezius Muscle.

Question 25

What is CN XII?

Answer 25

Hypoglossal Nerve

Question 26

The Hypoglossal Nerve (CN XII) actually arises from MULTIPLE ROOTLETS that are derived from where?

Answer 26

PRE_OLIVARY SULCUS of the MEDULLA in the POSTERIOR CRANIAL FOSSA.

Question 27

The multiple rootlets, which arise from the pre-olivary sulcus of the medulla, of the hypoglossal nerve converge in what canal?

Answer 27

The HYPOGLOSSAL CANAL. Note: Makes sense, the *hypoglossal nerve forms in the *hypoglossal canal!

Question 28

What nerve fiber type does CN XII consist of?

Answer 28

GSE fibers

Question 29

The GSE fibers of the hypoglossal muscle innervate the all of the INTRINSIC and most EXTRINSIC muscles of what?

Answer 29

CN XII GSE fibers innervate all the intrinsic and most intrinsic muscles of the TONGUE

Question 30

What long, thin nucleus, located in the Medulla on the floor of the 4th ventricle, contains the cell bodies of the lower motor neurons (GSE) of CN XII?

Answer 30

HYPOGLOSSAL NUCLEUS

Question 31

CN XII exits the posterior cranial fossa of the skull through what opening?

Answer 31

HYPOGLOSSAL CANAL - where CN XII rootlets converge

Question 32

Specifically, the CN XII divides to supply what 3 extrinsic muscles of the tongue in addition to ALL intrinsic muscles?

Answer 32

1) Hyoglossus Muscle
2) Styloglossus Muscle
3) Genioglossus Muscle

Question 33

Carotid Endarterectomy is a procedure to clear blockages in the Carotid Arteries. Why might this endanger CN XII, hypoglossal nerve?

Answer 33

B/c as CN XII descends and moves laterally to its destination of the inferior tongue the hypoglossal nerve crosses the INTERNAL CAROTID Artery.

Question 34

After leaving the Descendens Hypoglossi, ventral rami originating from what Cervical spine join the Hypoglossal Nerve for a short time?

Answer 34

Fibers of the C1 VENTRAL RAMUS

Question 35

After leaving CN XII C1 fibers go on to do what 3 things?

Answer 35

1. Form the superior root of the ANSA CERVICALIS
2. Innervate the Thyrohyoid directly
3. Innervate the Geniohyoid directly

Question 36

To test a suspected unilateral lesion of CN XII a patient is asked to stick their tongue out? What will happen if there is a Right CN XII lesion? Why? What is an easy way to remember this?

Answer 36

Unilateral CN XII lesions will cause ipsilateral tongue protrusion, so that upon protrusion, the tongue will deviate to the right, the side of the protrusion. This is caused by the unopposed actions of the Genioglossus. The patient will “Lick Her Wounds”