Orbital Nerves: Cranial Nerves II, III, IV and VI

List the extrinsic eye muscles

Levator palpebrae superioris m., superior oblique m., Lateral rectus m., Superior rectus m., Inferior oblique m., Inferior rectus m., Medial rectus m.

Which extrinsic eye muscles originate from the common tendinous ring?

Superior, Inferior, Lateral, Medial rectus

Major action of levator palpebrae superioris

Raise eyelid (assisted by superior tarsal m.)

Major action of superior oblique m.

Depression, ABduction

Major action of lateral rectus m.

ABduction

Major action of superior rectus m.

Elevation, ADduction

Major action of inferior oblique m.

Elevation, ABduction

Major action of inferior rectus m.

Depression, ADduction

Major action of medial rectus m.

ADduction

Where are intrinsic muscles located?

Within the eyeball

What is the role of intrinsic muscles?

Control lens shape and pupil size

CN II is also known as…

Optic n.

CN III is also known as…

Oculomotor n.

CN IV is also known as…

Trochlear n.

CN V1 is also known as…

Ophthalmic division of trigeminal nerve

CN VI is also known as…

Abducent n.

List the orbital nerves

CN II, CN III, CN IV, CN V1, CN VI

CN II fiber type

SSA

CN III fiber type

SM (GSE) and Parasympathetics (GVE)

CN IV fiber type

Somatomotor (GSE)

CN V1 fiber type

Somatosensory (GSA)

CN VI fiber type

SM (GSE)

CN II function/innervation

Special sense of vision

CN III function/innervation

GSE: Levator palpebrae suprerioris, Superior rectus, inferior rectus, medial rectus, inferior oblique

GVE: Sphincter pupillae, ciliary m.

CN IV function/innervation

Superior oblique

CN V1 function/innervation

Skin around the eye, eyelid, lacrimal gland, conjunctiva

CN VI function/innervation

Lateral rectus

List the orbital nerves that run along the lateral wall of the cavernous sinus (inferior → superior)

CN V1, CN IV, CN III

Which orbital n. passes through the cavernous? sinus (not along the wall)

CN VI

Path of sensory information from retina to visual cortex

Retina, L and R optic n., Optic canal, R and L optic n. join at optic chiasm in chiasmatic groove, Optic tract, Midbrain (postsynaptic), Visual cortex (in occipital lobe)

What covers CN II?

Pia, arachnoid, and dura mater

What a. travels along CN II?

Central retinal a.

Pupillary light reflex

Changes how much light enters eyes (dilate and constrict pupils)

Accommodation reflex

Changes focus with distance (change thickness of lens)

Where do L and R optic nerves cross each other?

Optic chiasm

Each eye has what 2 visual fields?

Nasal and temporal

Path of light from L nasal field

Light captured by R side of R eyeball, R optic nerve, R lateral geniculate body, R optic tract, Occipital lobe

Path of light from R nasal field

Light captured by L side of L eyeball, L optic nerve, L lateral geniculate body, L optic tract, Occipital lobe

Path of light from L temporal field

Light captured by R side of L eyeball, L optic nerve, Optic chiasm cross to R side, R lateral geniculate body, R optic tract, Occipital lobe

Path of light from R temporal field

Light captured by L side of R eyeball, R optic nerve, Optic chiasm cross to L side, L lateral geniculate body, L optic tract, Occipital lobe

If someone loses vision in 1 eye, what kind of lesion is this?

Prechiasmatic lesion (damage to retina or optic n.)

If someone loses temporal visual field, what kind of lesion is this?

Chiasmatic lesion

If someone loses input from the contralateral visual field from both eyes, what kind of lesion is this?

Postchiasmatic lesion

What are the main orbital branches of V1 (medial to lateral)

Nasociliary n., Frontal n., Lacrimal n.

What does the upper division of CN III innervate?

Levator palpebrae superioris and superior rectus

What does the lower division of CN III innervate?

Inferior rectus and inferior oblique

Which ganglia along the sympathetic trunk do sympathetics to the head and neck synapse at?

Superior cervical ganglia

What plexus carries post-synaptic sympathetics into the head?

Carotid plexus (ICA)

2 sympathetics pathways to vessels within the eye

ICA, Nasociliary n./Plexus branch, Ciliary ganglion, Short ciliary nn.

Path of sympathetics to dilator pupillae m.

ICA, Nasociliary n., Long ciliary n., Sclera, Dilator pupillae

Within the eye, what do parasympathetics innervate?

Sphincter pupillae (pupillary light reflex)

What do ciliary m. do?

Controls lens thickness for accommodation reflex

Shape of lens when ciliary m. are relaxed

Flattened

Shape of lens when ciliary m. are contracting

Thickened

What fibers attach lens to ciliary m.

Zonular fibers

Afferent limn of pupillary light reflex

CN II from stimulation to retinal ganglion cells

Efferent limb of pupillary light reflex

CN III parasympathetics via short ciliary nn. to sphincter pupillae

How to test for pupillary light reflex?

Shine bright light and observe if pupils change size

Afferent limb of accommodation reflex

CN II from stimulation of retinal ganglion cells

Efferent limb of accommodation reflex

CN III parasympathetics via short ciliary nerves to ciliary body and sphincter pupillae

How to test accommodation reflex

Ask patient to watch object (like a pen) as it gets closer (convergence, pupil constriction, lens thickening)

Describe Horner’s syndrome

Neurologic disorder that affects the sympathetics (especially to the head)

Where are lesions in Horner’s syndrome located?

Sympathetic ganglion/sympathetic chain

Clinical manifestations of Horner’s syndrome

Ptosis, miosis, and anhidrosis

Why would you observe ptosis in a patient with Horner’s syndrome?

Loss of control of superior tarsal muscle

Why would you observe miosis in patients with Horner’s sundrome

Loss of control of pupillary dilator m.

Why would you observe anhidrosis in patients with Horner’s syndrome?

Loss of control of smooth muscle within the aa. of the forehead

Goal of the H Test

Isolate actions to isolate specific nerves

Testing superior oblique m. (CN IV)

Look medially (ADduct) and downwards

Testing superior rectus (CN III)

Look laterally and upwards

Testing inferior rectus m. (CN III)

Look laterally and downwards

Testing medial rectus m. (CN III)

Look medially

Testing inferior oblique m. (CN III)

Look medially and upwards