PNS4

Question 1

Through what foramen does the optic nerve enter the orbit?

Answer 1

Optic Canal

Question 2

Through what foramen do CNs III, IV & VI enter the orbit?

Answer 2

Superior Orbital Fissure

Question 3

From what part of the brain does CN III, the Oculomotor Nerve arise from?

Answer 3

The medial aspect of the CEREBRAL PEDUNCLE of the Midbrain

Question 4

What two nerve fiber types does the Oculomotor nerve have? What is each nerve types basic function?

Answer 4

Note: name oculoMOTOR nerve!

1. GVE fibers innervate most extraocular muscles
2. GSE fibers are PREGANGLIONIC SYMPATHETICS synapsing in the CILIARY GANGLION

Question 5

Where does CN IV, Trochlear Nerve, arise? What is special about its intracranial path?

Answer 5

The Trochlear Nerve (CN IV), exits the brain below the INFERIOR COLLICULUS on the DORSAL aspect of Midbrain. From there CN IV follow the LONGEST IntraCRANIAL course of any of the Cranial Nerves. Makes vulnerable to pathologies

Question 6

What fiber type does the Trochlear nerve have? What is the 1 extraocular muscle CN IV innervates?

Answer 6

GSE Fibers innervate the SUPERIOR OBLIQUE muscle ONLY

Question 7

Where does the Adbucent Nerve (CN VI) leave the brain? What is special about its Intradural path?

Answer 7

The abducent nerve leaves the brain from the INFERIOR PONTINE SULCUS. From there CN VI follows the LONGEST intraDURAL course of any CN. Leaves vulnerable to pathologies & is frequently involved in intracranial diseases.

Question 8

What nerve fiber type does the abducent nerve possess? What extraocular muscle does CN VI innervate?

Answer 8

GSE Fibers innervate the LATERAL RECTUS muscle ONLY

Question 9

What is the only nerve that innervates the eye that does not pass through the annular tendon?

Answer 9

The TROCHLEAR NERVE, CN IV

Question 10

As a rule, Postganglionic Axons arising from the Parasympathetic Ganglion in the head reach their targets by “piggy-backing” on branches of what CN?

Answer 10

CN V, The Trigeminal Nerve.

Question 11

Through what opening does CN V1, the Opthalmic Division of the trigeminal nerve, enter the orbit?

Answer 11

The SUPERIOR ORBITAL FISSURE

Question 12

CN V1 carries what single type of nerve fiber? In the orbit, what 3 structures of the eye do these fiber innervate?

Answer 12

GSA Fibers that innervate…

1. CORNEA
2. CONJUNCTIVA
3. Parts of the SCLERA

Question 13

What are the 3 main branches of V1 in the orbit? What is a pneumonic to help you remember their names?

Answer 13

NFL

1. Nasociliary Nerve
2. Frontal Nerve
3. Lacrimal Nerve

Question 14

The MEDIAL and LATERAL RECTUS muscles move the eyeball around a single axis only. In what way does each move the eye?

Answer 14

1. Medial Rectus: ADDUCTS the eye

2. Lateral Rectus: ABDUCTS the eye

Question 15

All but extraocular muscles but the lateral & medial rectus muscles move the eye around ALL 3 rotational axes. This is possible b/c of the disparity b/t the VISUAL (OPTICAL) axis and the ORBITAL axis. Explain this disparity.

Answer 15

There is a disparity between the VISUAL (OPTICAL) Axis and the ORBITAL Axis. The Visual axis is straight ahead while the Orbital axis follows the path of the muscles from where they enter the orbit, at the superior orbital fissure, to the center of the eyeball. This means there is about a 23 degree disparity b/t the 2 axis.

Question 16

In what 3 ways do each of the following 4 extraocular muscles move the eye?

1. Inferior Oblique
2. Superior Rectus
3. Superior Oblique
4. Inferior Rectus

Answer 16

1. Inferior Oblique:
ELEVATES, ABDUCTS & EXTORTS
2. Superior Rectus:
ELEVATES, ADDUCTS & INTORTS
3. Superior Oblique:
DEPRESSES, ABDUCTS & INTORTS
4. Inferior Rectus:
DEPRESSES, ADDUCTS, EXTORTS

Question 17

To maximize the work a muscle does what axis do you line it up with? What axis to minimize?

Answer 17

Maximize: Visual (optical) axis
Minimize: Transverse axis

Question 18

How would you isolate the following muscles?

1. Inf Oblique
2. Sup Oblique
3. Inf Rectus
4. Sup Rectus
5. Lat Rectus
6. Med Rectus

Answer 18

1. Adduct then elevate (CN III)
2. Adduct then depress (CN IV)
3. Abduct then depress (CN III)
4. Abduct then elevate (CN III)
5. Adduct (CN VI)
6. Abduct (CN III)

Question 19

What Sinus do CNs III, IV, VI pass through, before coursing through the superior orbital fissure on their way to the orbit, that leaves them vulnerable to compression and lesions?

Answer 19

CAVERNOUS SINUS

Question 20

As CNs III, IV & VI pass through the cavernous sinus what are four possible causes of compression or lesion?

Answer 20

1. Septic Thrombosis (infection & swelling) of the Cavernous Sinus
2. Intracavernous Internal Carotid Artery ANEURYSMS (ballooning of artery due to weak walls)
3. ANEURYSMS of components & branches of Circle of Willis (Such as PCOM)
4. Laterally expanding Pituitary Tumors

Question 21

What is Ophthalmoplegia?

Answer 21

PARALYSIS of extraocular musculature

Question 22

What are some things that happen as a result of a lesion in CN III, Oculomotor Nerve? Give 2

Answer 22

1. PTOSIS: Drooping of eyelid due to paralysis of Levator Palpebrae Superioris
2. Eyeball drops Down & Out because the lateral rectus (CN VI) and Superior Oblique (CN IV) muscle are unopposed.

Question 23

What are some things that happen as a result of a lesion in CN VI, Abducens Nerve? Give 2

Answer 23

1. Paralysis of Lat Rectus is one cause of STRABISMUS, the inability to direct both eyes towards the same object. This produces DIPLOPIA (Double Vision)
2. Eyeball adducts due to unopposed pull of Medial Rectus.

Question 24

What are some things that happen as a result of a lesion in CN IV, Trochlear Nerve? Give 2

Answer 24

1. Strabismus leading to VERTICAL DIPLOPIA when attempting to depress the affected eye. Particularly alarming when descending stairs
2. Eyeball is Elevated and Adducted

Question 25

Contraction of what muscles are responsible for increasing the curvature of the LENS, enabling ACCOMODATION, an adaptation to focus on images as they move nearer to the eye?

Answer 25

CILIARY MUSCLES

Question 26

In addition to ciliary muscle contraction leading to increased lens curvature what else is needed for Near Vision?

Answer 26

Constriction of the pupil & Convergence of the eyes

Question 27

How is Convergence of the eyes accomplished?

Answer 27

Bilateral contraction of the Medial rectus muscles.

Question 28

The Pupil is the central aperture of the IRIS, which functions like the diaphragm of a camera. The diameter of the Pupil/Iris is under the control of what two Antagonistic muscles?

Answer 28

The CONSTRICTOR (parasympathetic) and DILATOR (sympathetic)

Question 29

ANISOCORIA is an inequality in the size of the pupils under changing light conditions. This suggests a lesion in what pathway?

Answer 29

Anisocoria suggests a lesion in a pupillary autonomic pathway, often CN III (remember is addition to GSE it has GVE fibers going to the Ciliary Ganglion.

Question 30

The Pupilary Constrictor and Ciliary Muscles are innervated by Postganglionic Parasympathetics arising from what ganglion?

Answer 30

The CILIARY GANGLION

Question 31

At what Nucleus in the Midbrain do the Pre (ciliary) ganglionic fibers arise? What are these preganglionic fibers?

Answer 31

The INFERIOR Branch of the OCULOMOTOR Nerve (GVE fibers of CN III) arise from the NUCLEUS of Edinger-Westphal

Question 32

What are the postsynaptic fibers that arise from the ciliary ganglion (note: this nerve will carry the GVE fibers from CN VIII)? What 2 muscles do they innervate?

Answer 32

The SHORT CILIARY (or NASOCILIARY) Nerve from CN V1 arise from the ciliary ganglion to innervate the Pupillary Constrictor and Ciliary Muscles.

Question 33

If the Ciliary Ganglionic parasympathetic pathway is lesioned, what will the affects be? Give 2/3

Answer 33

``` Pupillary Constrictor Muscle Effects 1. Pupil will be dilated 2. Pupillary Light Reflex will be lost Ciliary Muscle Effects 1. Near Vision will be impaired. ```

Question 34

A lesion of the Oculomotor Nerve, specifically its GVE fibers, will result in what 3 affects?

Answer 34

1. No pupillary light reflex 2. Dilation of Iris, since parasympathetics are disrupted. 3. No accommodation of lens b/c ciliary muscles are paralyzed --> Loss of near vision

Question 35

Almost ALL postganglionic SYMPATHETIC Fibers supplying the head are distributed through what Plexuses? These plexuses surround what arteries & their branches?

Answer 35

The PERIARTERIAL PLEXUSES (Note: name tells you 'around arteries'). The Periarterial Plexuses surround the INTERNAL & EXTERNAL CAROTID ARTERIES and their branches.

Question 36

From what Ganglion does the POSTGANGLIONIC SYMPATHETIC innervation of the HEAD arise?

Answer 36

The SUPERIOR CERVICAL GANGLION

Question 37

Preganglionic Sympathetic innervation of the orbit arises from the T1-T2 Cord Segments. Describe the path from there to the orbit (4 steps) that these Sympathetic Fibers take.

Answer 37

Start: T1-T2 Cord Segments 1. Preganglionic Sympathetics Ascend thru the CERVICAL SYMPATHETIC TRUNK and synapse in the... 2. SUPERIOR CERVICAL GANGLION 3. Postganglionic Sympathetics Ascend from the Sup Cerv Ganglion through the INTERNAL CAROTID NERVE and then PLEXUS... 4. the postganglionic sympahetics then run through the Ciliary Ganglion WITHOUT SYNAPSING and travel of LONG & SHORT CILIARY Nerves to reach their targets... End: In the Orbit

Question 38

What 3 structures do the Sympathetics innervate in the orbit?

Answer 38

1. The PUPILLARY DILATOR MUSCLE 2. The SUPERIOR TARSAL MUSCLE 3. The OPHTHALMIC ARTERY and its Branches

Question 39

What are the 3 branches of the Ophthalmic artery that distribute to the forehead, root, and bridge of the nose?

Answer 39

1. Supraorbital 2. Supratrochlear 3. Dorsal Nasal

Question 40

The Sympathetic innervation of the orbit is interrupted in HORNER'S SYNDROME. What symptoms characterize Horner's syndrome?

Answer 40

1. MIOSIS - A fixed, CONSTRICTED Pupil b/c pupillary DILATOR lost innervation. 2. Partial Ptosis - A droopy eyelid. Due to loss of Superior Tarsal Muscle (smooth muscle) function. Note: only Partial ptosis b/c Levator Palpebrae (skeletal muscle) is still functioning. 3. Loss of Forehead Sweating (ANHYDROSIS) - b/c sympathetic SUDOMOTOR innervation of the Supraorbital and Supratrochlear branches of the Opthalmic artery is lost. Sweating is no longer activated from neither phsychological nor physical sources.