The Orbit Flashcards
Which bones are these?
Roof, lateral + floor of orbit?
Roof = frontal bone Lateral = zygoma Floor = maxilla
What is this?
Formed by?
Purpose?
Infraorbital foramen
Formed by maxilla
Purpose = infraorbital branch of CNV2 exits skull to provide sensory innervation to face
What is this?
Formed by?
Purpose?
Supraorbital ridges
Formed by frontal bone
Purpose = deflect blows away from the eyes
What is this?
Purpose?
Frontal notch/foramen
For supraorbital nerve and artery
Label this
Lacrimal bone associated with?
Nasolacrimal duct that carries excess lacrimal fluid (tears) into the nasal cavity
Sphenoid bone foramina? (3)
+ nerves that travel through them
What contributes?
Optic canal (CN II)
Superior orbital fissure (CN 3, 4, 5, 6)
Inferior orbital fissure (opthalmic veins)
Tiny contribution from palatine bone in wall of inf. orbital fissure
Label this
function?
Suspensory ligaments support eyeball
Check ligaments restrict medial and lateral recti
the sclera provides an attachment site for the recti muscles
aqueous humor found?
function?
made by?
circulation?
anterior chamber of eye - space between the lens and the cornea (anterior to lens)
helps to maintain intra-ocular pressure
Made by ciliary body, drains into corneo-scleral junction (canal of Schlemm)
posterior chamber of eye?
filled with?
function?
behind lens
vitreous humor
vitreous humor supports retina
intraocular muscles?
innervation?
also ciliary muscle (changes lens shape) - occulomotor nerve
…
….
extraocular muscles?
7 extraocular muscles -
levator palpebrae superioris from orbital roof to upper eyelid
Superior, inferior, medial and lateral recti from annular ring to sclera (anterior to equator)
Superior oblique (lesser wing sphenoid) and inferior oblique (orbital floor) to sclera (posterior to equator)
..
RADSIN is a mnemonic to help you remember the Recti ADDuct (except for lateral rectus) and the Superiors INtort (roll the posterior part of the eye inwards). The chemical style formula helps with the nerve supply – all are oculomotor except Lateral Rectus (CN VI) and Superior Oblique (CN IV).
CN II pathway?
The optic nerve leaves the orbit via the optic canal. CN II forms a chiasma over the pituitary fossa, then sends optic tracts towards the brain (for example, to the thalamus). The optic radiations then take information to be processed in the primary visual cortex. These communicate with association areas to put the images into context (give them meaning).
other ocular nerve other than CN II?
The other cranial nerves pass through the superior orbital fissure to enter the orbit and supply the intrinsic and extrinsic muscles of the eye. The trigeminal nerve supplies sensory innervation to the orbit and carries fibres from the facial nerve to the lacrimal gland.
what do ocular nerves pass through before superior orbital fissure?
cavernous sinus
Before the nerves reach the superior orbital fissure, they pass though the cavernous dural venous sinus. This lies around the body of the sphenoid bone and the pituitary fossa. CN III, CN IV and CN V pass along the walls close to the dura. CN VI passes through the middle of the sinus close to the internal carotid artery. So, the abducent nerve is the odd one out here.
As the nerves come into the posterior part of the orbit, they reach an annular ring of connective tissue that provides an attachment site for the recti muscles. Some nerves pass through the ring, but parts of the trigeminal nerve (frontal and lacrimal) and CN IV do not. So, the trochlear nerve is the odd one out here.
ophthalmic division trigeminal pathway?
branches?
ophthalmic division passes into the superior orbital fissure
frontal, nasocilliary, lacrimal
frontal divides to form supraorbital + supratrochlear branches which pass onto the face via the supraorbital notch to supply sensory innervation to the skin of the forehead
The nasociliary branch will form ethmoidal branches which pass through the ethmoid bone and will be discussed further in the presentation on the nose.
The lacrimal nerve acts as a carrier for parasympathetic secretomotor fibres from the facial nerve.
frontal branch passes over the superior surface of levator palpebrae superioris
occulomotor nerve divisions
ssuperior division = supplies levator palpebrae superioris and superior rectus with motor innervation
The inferior division = supplies medial rectus, inferior rectus and inferior oblique with motor innervation. It also carries parasympathetic fibres to the intrinsic muscles of the eye.
The ciliary ganglion is a small piece of nerve tissue posterior to the eye which communicates with CN III and sends short ciliary nerves into the eyeball
CN VI and CN IV are small as they only supply one muscle each. CN VI can be seen associated with the surface of lateral rectus and CN IV crosses the superior surface of superior oblique before piercing and innervating it.
blood supply to orbit?
pathway?
The blood supply to the orbit is from the ophthalmic artery – a branch of the internal carotid artery.
The ophthalmic artery also gives branches to the forehead and scalp (supraorbital supratrochlear, and zygomaticotemporal), to the nose (dorsal nasal and ethmoidal arteries).
The ophthalmic artery enters the orbit through the optic canal with the optic nerve.
venous drainage orbit?
The ophthalmic veins of the orbit communicate with the cavernous venous sinus through the superior orbital fissure + with the pterygoid venous plexus through the inferior orbital fissure + with the facial vein.
This creates a potential for the spread of infection from external structures to internal structures such as the dural meninges.
The tears wash across the surface of the eye and then are gathered through lacrimal punctum into the lacrimal canaliculi and then into a membrane lined space called the lacrimal sac. This sac communicates with the inferior meatus of the nose via the nasolacrimal duct
The facial nerve provides secretomotor fibres to the submandibular and sublingual salivary glands via the chorda tympani by joining with the lingual nerve (CNV3).
The fibres to the lacrimal gland also travel with the trigeminal nerve but in this case CNV2 and V1. The facial nerve branches to form the greater petrosal nerve (named as it passes across the petrous part of the temporal bone and is the bigger nerve – lesser petrosal is related to the pathway of CN IX to the parotid). It carries parasympathetic secretomotor fibres. It then joins with sympathetic fibres from a plexus around the internal carotid artery (called the deep petrosal nerve) to form the nerve of the pterygoid canal. This nerve passes to the pterygopalatine ganglion (at the fissure on the wall of the infratemporal fossa) to join with CNV2 (zygomatic branch) these fibres then join the lacrimal nerve (CNV1) to finally reach the lacrimal gland.
So, lesser petrosal and greater petrosal are parasympathetic from CN IX and CN VII respectively.
Deep petrosal are sympathetic fibres, and the nerve of the pterygoid canal has both type of fibres present.
