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Anat Exam 4: The PNS > PNS4 > Flashcards

PNS4 Flashcards

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1
Q

Through what foramen does the optic nerve enter the orbit?

A

Optic Canal

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2
Q

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

A

Superior Orbital Fissure

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3
Q

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

A

The medial aspect of the CEREBRAL PEDUNCLE of the Midbrain

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4
Q

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

A

Note: name oculoMOTOR nerve!

  1. GVE fibers innervate most extraocular muscles
  2. GSE fibers are PREGANGLIONIC SYMPATHETICS synapsing in the CILIARY GANGLION
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5
Q

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

A

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

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6
Q

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

A

GSE Fibers innervate the SUPERIOR OBLIQUE muscle ONLY

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7
Q

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

A

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.

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8
Q

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

A

GSE Fibers innervate the LATERAL RECTUS muscle ONLY

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9
Q

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

A

The TROCHLEAR NERVE, CN IV

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10
Q

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

A

CN V, The Trigeminal Nerve.

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11
Q

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

A

The SUPERIOR ORBITAL FISSURE

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12
Q

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

A

GSA Fibers that innervate…

  1. CORNEA
  2. CONJUNCTIVA
  3. Parts of the SCLERA
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13
Q

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

A

NFL

  1. Nasociliary Nerve
  2. Frontal Nerve
  3. Lacrimal Nerve
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14
Q

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

A
  1. Medial Rectus: ADDUCTS the eye

2. Lateral Rectus: ABDUCTS the eye

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15
Q

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.

A

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.

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16
Q

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
A 
1. Inferior Oblique:
ELEVATES, ABDUCTS & EXTORTS
2. Superior Rectus:
ELEVATES, ADDUCTS & INTORTS
3. Superior Oblique:
DEPRESSES, ABDUCTS & INTORTS
4. Inferior Rectus:
DEPRESSES, ADDUCTS, EXTORTS
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17
Q

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

A

Maximize: Visual (optical) axis
Minimize: Transverse axis

18
Q

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
A
  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)
19
Q

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?

A

CAVERNOUS SINUS

20
Q

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

A
  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
21
Q

What is Ophthalmoplegia?

A

PARALYSIS of extraocular musculature

22
Q

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

A
  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.
23
Q

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

A
  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.
24
Q

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

A
  1. Strabismus leading to VERTICAL DIPLOPIA when attempting to depress the affected eye. Particularly alarming when descending stairs
  2. Eyeball is Elevated and Adducted
25
Q

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?

A

CILIARY MUSCLES

26
Q

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

A

Constriction of the pupil & Convergence of the eyes

27
Q

How is Convergence of the eyes accomplished?

A

Bilateral contraction of the Medial rectus muscles.

28
Q

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?

A

The CONSTRICTOR (parasympathetic) and DILATOR (sympathetic)

29
Q

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

A

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.

30
Q

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

A

The CILIARY GANGLION

31
Q

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

A

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

32
Q

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?

A

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

33
Q

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

A 
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.
34
Q

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

A
  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
35
Q

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

A

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

36
Q

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

A

The SUPERIOR CERVICAL GANGLION

37
Q

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.

A

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

38
Q

What 3 structures do the Sympathetics innervate in the orbit?

A
  1. The PUPILLARY DILATOR MUSCLE
  2. The SUPERIOR TARSAL MUSCLE
  3. The OPHTHALMIC ARTERY and its Branches
39
Q

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

A
  1. Supraorbital
  2. Supratrochlear
  3. Dorsal Nasal
40
Q

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

A
  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.

Anat Exam 4: The PNS (7 decks)

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