Ophthalmic and maxillary divisions of trigeminal nerves

## Ophthalmic nerve

Smallest division of the trigeminal
Pure sensory
Arises from trigeminal ganglion
Enters lateral wall of cavernous sinus (below oculomotor and trochlear nerves, above the maxillary)
Receives sympathetic branches from internal carotid plexus
Gives off three branches prior to entering the orbit
Branches

Lacrimal

Smallest branch, enters outwith the tendinous ring
Joins the branch from the zygomaticotemporal branch of the zygomatic branch of the maxillary nerve which contains parasympathetic secretomotor fibres from the facial nerve
Also supplies the conjunctiva and skin of upper eyelid

Frontal: largest branch

Enters the orbit through the SOF outwith tendinous ring
Passes forward on the surface of the levator and gives branches halfway along
Supraorbital: leaves via the supraorbital notch to supply the skin and conjunctiva of upper eyelid
Supratrochlear: also supplies skin and conjunctiva of upper eyelid

Nasociliary

Enters orbit through SOF within tendinous ring between branches of oculomotor
Long ciliary branches arise as it crosses the optic nerve and pierce sclera close to optic nerve. Then pass forward in the choroid to the CB, iris (sympathetic) and cornea (sensory)
Infratrochlear branch: supplies lacrimal sac, conjunctiva, skin of medial upper and lower eyelids and lateral nose
Other branches supply ethmoidal (anterior and posterior ethmoidal nerves) and sphenoidal air sinuses

The infratrochlear nerve is the terminal branch of the nasociliary: Hutchinson's sign is the classic lesions of herpes zoster seen on the side/tip of nose indicating infratrochlear involvement suggesting the long ciliary nerves could be too (which also supply the globe, see below).

## Facial nerve

Both motor and sensory
3 nuclei

Main motor: pons.

Portion supplying muscles of the upper face receive bilateral innervation, whereas the portion supplying the lower face receive contralateral innervation only

Parasympathetic: posterolateral to main motor nucleus

Superior salivatory and lacrimal nuclei
Afferent fibres from the hypothalamus

Sensory: upper part of nucleus tractus solitarius

Motor and sensory roots
Emerge from the cerebellopontine angle
Posterior cranial fossa
Enters internal acoustic meatus then facial canal into inner ear
Turns backwards to descend along posterior wall of middle ear to exit via the stylomastoid foramen

## Olfactory nerve

Originates in the epithelium of the nasal mucosa
Neurones condense into the olfactory tract
Passes along olfactory groove in the cribiform plate
The anterior olfactory nucleus lies posterior to this
Tract divides into medial and lateral striae

Medial striae contains fibres from the anterior nucleus and pass to the anterior commissure
Lateral striae terminates in the amygdala and the primary olfactory cortex at the anterior end of the parahippocampal gyrus and uncus

The olfactory signals are unique in bypassing the thalamus