Ocular A&P: Neuro 1 - Cranial and Afferent

Name 4 terms that can refer to a bundle of neurons in the CNS.

1) fiber tract

2) fasciculus = within the brainstem, for example the medial longitudinal fasciculus

3) peduncle

4) brachium

Describe a typical neuron pathway of the somatic nervous system.

Neuron (especially efferent) usually runs from CNS to target without a synapse in between

Do autonomic neurons usually synapse between the CNS and the target?

Yes

Which cranial nerves affect the eyes?

- II optic

- III oculomotor

- IV trochlear

- V trigeminal

- VI abducens

- VII facial

- VIII vestibulocochlear

Is the optic nerve afferent or efferent? What does it innervate? What is does provide?

Afferent - vision - axons of retinal ganglion cells

Is the oculomotor nerve afferent or efferent? What does it innervate? What is does provide?

Efferent - eye muscle control

- superior division (SR, levator)

- inferior division (MR, IR, IO) + parasympathetic fibers for ciliary ganglion to iris sphincter and to ciliary muscle

Is the trochlear nerve afferent or efferent? What does it innervate? What is does provide?

Efferent - eye muscle control - SO

How does the trochlear nerve exit the brain? Does it provide ipsilateral or contralateral innervation?

Exits the brain dorsally - provides contralateral innervation

It is trigeminal afferent or efferent?

Both - mostly sensory (afferent)

What are the 3 branches of the trigeminal?

V1 - ophthalmic

V2 - maxillary

V3 - mandibular

Is the ophthalmic (V1) branch of the trigeminal afferent or efferent? What does in innervate?

- afferent

- globe, adnexa, glands, sinuses, nose, forehead, scalp

- sympathetic fibers to the dilator muscle of the iris

Is the maxillary (V2) branch of the trigeminal afferent or efferent? What does it innervate?

- afferent

- middle of face and surrounding structures

Is the mandibular (V3) branch of the trigeminal afferent or efferent? What does it innervate?

Both.

- afferent: jaw and surrounding structures extending up above the ear

- efferent: muscles of chewing

Is the abducens nerve afferent or efferent? What does it provide/innervate?

- efferent

- eye muscle control (LR)

Is the facial nerve afferent or efferent? What does it innervate?

Both.

- efferent: muscles of facial expression and orbicularis oculi (closing eyelids)

- afferent: taste from front of the tongue + sensory from earlobe

- parasympathetic fibers for lacrimal and salivary stimulation from the pterygopalatine ganglion

What is Bell's Palsy?

Temporary hemifacial paralysis from CN VII (facial) swelling.

Patient can't close their eye - leads to dry eye

Is the vestibulocochlear nerve afferent or efferent? What is its role?

- afferent

- has role in control of eye movements - eyes maintain fixation when head moves

Which 2 tests can be performed to test vestibulocochlear nerve function?

1) caloric test: warm water in the ear causes eye movement to contralateral ear with nystagmus to ipsilateral ear - cool water is opposite

2) hearing: can patient hear tuning fork, watch ticking, etc.

What are the 3 major contributors to the ophthalmic division of the trigeminal?

1) nasociliary

2) frontal

3) lacrimal

Which nerves contribute to the nasociliary nerve?

1) long ciliaries

2) short ciliaries

3) posterior ethmoid

4) anterior ethmoid

5) infratrochlear

How many long ciliary nerves are there?

2

How many short ciliary nerves are there?

6-10

What is innervated by the long ciliary nerves?

- iris diLator (sympathetic)

- ciliary muscle (inhibitory)

- cornea

- conjunctiva

- uvea

What is innervated by the short ciliary nerves?

- cornea

- uvea

- iris Sphincter/ciliary body (parasympathetic)

- choroid (sympathetic - vasoconstriction)

What do the short ciliary nerves pass through? Do they synapse here?

Pass through the ciliary ganglion WITHOUT synapsing and into the sensory root (ramus communicans) and then to the nasociliary nerve.

What is innervated by the posterior ethmoid nerve?

- ethmoid sinus

- sphenoid sinus

What is innervated by the anterior ethmoid nerve?

- tip of nose

- nasal mucosa

- ethmoid sinus

What is innervated by the infratrochlear nerve?

- medial canthus

- medial eyelids

- upper nose

Which nerve causes the loop of axenfeld? Where is this loop located? Describe it.

Long ciliary nerve

- about 2mm from limbus

- surrounded by pigment

- painful to touch

Which nerves contribute to the frontal nerve?

1) supratrochlear nerve

2) supraorbital nerve

What is innervated by the supratrochlear nerve?

- medial forehead

- upper eyelid

How does the supraorbital nerve enter the orbit?

Through the supraorbital notch with the artery and vein of the same name

Does the supraorbital nerve ever form 2 branches?

Yes. One will pass through the supraorbital notch and the other will not.

What is supplied by the supraorbital nerve?

- central forehead

- upper eyelid

What is innervated by the lacrimal nerve?

- lateral eyelids

- upper eyelids

- lacrimal gland

- temple area

What does the lacrimal nerve contribute to the lacrimal gland?

Autonomic fibers from the communicating branch of the zygomaticotemporal nerve

How does the nasociliary nerve leave the orbit?

Through the common tendinous ring and the superior orbital fissure

How do the frontal and lacrimal nerves leave the orbit?

Above the common tendinous ring and through the superior orbital fissure

Describe what happens in the cavernous sinus drawing.

- CN III, IV, and VI contribute proprioceptive fibers to V1

- the ICA contributes sympathetic fibers to CN III and V1

Which 2 nerves converge to form the maxillary nerve (V2)?

- infraorbital nerve

- zygomatic nerve

What is innervated by the infraorbital nerve?

- upper cheek

- upper lip

- lower eyelid

- upper teeth

- maxillary sinus

How does the infraorbital nerve enter the orbit?

Through the infraorbital foramen along with the artery (ECA) and vein (external jugular) of the same name

Which nerves contribute to the zygomatic nerve?

1) zygomaticofacial nerve

2) zygomaticotemporal nerve

What is innervated by the zygomaticofacial nerve?

- lateral cheek

- lower eyelid

What is innervated by the zygomaticotemporal nerve?

- lateral forehead/temple

How do the infraorbital and zygomatic nerves leave the orbit?

Through the inferior orbital fissure - then the whole maxillary passes through the cavernous sinus and joins the trigeminal ganglion

What happens in the pterygopalatine fossa with the maxillary nerve?

While in the pterygopalatine fossa, autonomic fibers from pterygopalatine ganglion join the maxillary to make their way to the lacrimal gland

Describe the mandibular (V3) branch of the trigeminal.

- contains large sensory root from the lower face

- a small motor root provides innervation for some muscles of mastication and to some tiny muscles in the ear and a muscle which opens the Eustachian tube

What is the trigeminal ganglion? What is another name for it?

Where all 3 branches converge - also called the Gasserian ganglion

What is unusual about the trigeminal ganglion?

It is unusual for a cranial nerve to have its nucleus outside the brainstem

Which fibers synapse at the trigeminal ganglion? Which do not?

Sensory fibers synapse - motor fibers for mastication through the mandibular nerve do not synapse

How do the sensory fibers exit the trigeminal ganglion? What do the ascending and descending tracts carry and where do they end?

They exit after synapsing and enter the lateral aspect of the pons to deliver their signal to the sensory nuclei

Ascending tract carries touch and pressure sensation and ends in the principle sensory nucleus

Descending tract carries pain and temperature sensation and ends in the nucleus of the spinal tract

What is the primary site for a herpes virus to reside after infection?

The trigeminal ganglion

What might be indicated if the tip of the nose (anterior ethmoid dermatome) is involved in a herpes zoster infection?

Hutchinson's sign - indicates the nasociliary nerve may be involved