Anatomy of the Orbit week 2 Flashcards
7 bones comprise the orbit and give it a pyramidal shape.
What bones form the roof, floor, medial, and lateral walls of the orbit?
The roof: is comprised mainly by the Frontal bone with a small contribution from the Sphenoid
The Medial wall: Maxilla, Lacrimal, Ethmoid, Sphenoid
The Floor: Maxilla (mainly), Zygomatic, and Palatine
The Lateral Wall: Zygomatic and Sphenoid
What is the relationship of the maxillary, frontal, and ethmoid sinuses to the orbit?
What is the name for the periosteum lining the bones of the orbit?
The maxillary sinus lies below the floor of the orbit, the frontal sinuses are superior and medial to the orbit, and the ethmoid air cells lie medial to the orbit.
The periosteum lining the bones of the bones that form the orbit is called periorbita.
Identify the indicated structures.
The _____ covers the posterior surface of the eyelid and reflects onto the outer surface of the sclera of the eyeball. When the eye is closed the ____ forms a sac anterior to the eye.
The Conjunctiva covers the posterior surface of the eyelid and reflects onto the outer surface of the sclera of the eyeball. When the eye is closed the conjunctiva forms a sac anterior to the eye (conjuctival sac).
What is the orbital septum?
What muscle does the orbital septum lie deep to?
What does the orbital septum attach to in the upper eyelid? In the lower eyelid?
The Orbital Septum is an extension of the periosteum in the upper and lower eyelid which lies deep to the orbicularis oculi.
It attaches to the tendon of levator palpebrae in the upper eyelid and the tarsus in the lower eyelid.
Identify the indicated anatomical structures.
What is the function of the superior and inferior tarsus (tarsal plates)?
What are they composed of?
How are they attached to the bone of the orbit?
What kind of glands are found within the tarsal plates? What is the purpose of this gland?
The superior and inferior tarsus provides support for each eyelid. Both are formed of dense connective tissue which is attached to the bone of the orbit medially and laterally by the palpebral ligaments.
Within the tarsal plates are modified sebaceous glands which empty onto the free margin of each eyelid, increasing the viscosity of tears.
What muscle is the superior tarsus assoicated with?
What kind of muscle is the superior tarsus muscle? What kind of innervation does it receive? (somatic, paraysmpathetic, sympathetic)
What does the superior tarsus muscle do?
The superior tarsus is associated with the levator palpebrae superioris.
In companion to the levator palpebrae superioris is a collection of smooth muscle fibers passing from the levator to the superior tarsus. This muscle, the superior tarsal muscle, is innervated by postganglionic sympathetic fibers. It helps to unconsciosly keep the eye open.
What nerve innervates the orbicularis occuli?
What nerve innervates the levator palpebrae superioris?
What is the function of each of these muscles?
What would be the result of loss of innervation to the orbicularis occuli, levator palpebrae superioris, or the superior tarsus muscles?
Motor Innervation to the Eyelid:
CN VII: Orbicularis Oculi (Closure)
CN III: Levator Palpebrae Superioris (Holds eyelid open)
Postganglionic Sympathetic Fibers: Superior Tarsal Muscle (Holds eyelid open)
Ptosis, or a drooping eyelid would result from loss of innervation to these muscles.
Where is the lacrimal gland found within the orbit?
Explain the release of lacrimal gland secretions into the eye.
What is the connection of the nose and the lacrimal gland?
The lacrimal gland is found in the superior lateral region of the orbit.
Numerous ducts empty secretions which are moved across the eyeball as the eyelids blink. Fluid accumulates and enters the lacrimal canaliculi which join together to enter the lacrimal sac posterior to the medial palpebral ligament.
A small part of the orbicularis oculi muscle, the lacrimal part, lies posterior to the lacrimal sac. When this muscle contracts during blinking, the lacrimal part compresses the lacrimal sac forcing fluid into the nasolacrimal duct which drains into the inferior meatus of the nasal cavity.
What nerve provides sensory innervation to the lacrimal gland?
Sensory neurons return from the lacrimal gland to the CNS via the lacrimal branch of V1 (Ophthalmic nerve).
Explain the sympathetic and parasympathetic innervation of the lacrimal gland.
Parasympathetic secretomotor fibers stimulate fluid secretion from this gland.
- The preganglionic fibers leave the CNS in CN VII, enter the greater petrosal nerve and continue as the nerve of the pterygoid canal.
- This nerve carries the preganglionic fibers to the pterygopalatine ganglion where they synapse on postganglionic neurons.
- The postganglionic fibers travel with the maxillary nerve (V2) and continue with its zygomatic branches and eventually reach the lacrimal gland via the zygomaticotemporal branch.
Sympathetic innervation follows a similar path:
- except the postganglionic fibers originate in the superior cervical ganglion, follow blood vessels to reach the head, and form the deep petrosal nerve prior to joining the nerve of the pterygoid canal.
- These sympathetic fibers then follow the parasympathetic fibers with the exception that they do not synapse in the pterygopalatine ganglion, but rather just pass through it.
Identify the muscles of the eye.
Identify the muscles of the eye.
State the movements of the eyeball.
State the actions of each of the extraocular muscles.
superior rectus
inferior rectus
lateral rectus
medial rectus
superior oblique
inferior oblique
superior rectus: lookup
inferior rectus: look down
medial rectus: look medially (adduction)
lateral rectus: look laterally (abduction)
superior oblique: look down, medial rotation (intorsion)
inferior oblique: look up, lateral rotation (extorsion)
The superior oblique is described as being a muscle important for reading, walking down stairs, etc. because of it’s action to pull the eyeball downward. In reality this downward motion of the eyeball is always accompanied by ____ (type of movement) of the eyeball via the action of ____ ____.
The superior oblique is described as being a muscle important for reading, walking down stairs, etc. because of it’s action to pull the eyeball downward. In reality this downward motion of the eyeball is always accompanied by adduction of the eyeball via the action of medial rectus.
What does the lacrimal artery supply with blood?
Where is the central artery of the retina located? What can occlusion of this artery cause?
What do the long and short posterior ciliary arteries supply?
What artery are the above arteries branches of? What foramina does this artery pass through?
Lacrimal Artery: Supplies the lacrimal gland, laterally located muscles, and parts of the eyeball and lid
Central Artery of the Retina: Enters the optic nerve. It is clearly seen in an ophthalmoscope when viewing the retina and if occluded it causes blindness.
Long and Short Ciliary Arteries: enter the eyeball posteriorly and pierce the sclera to supply internal structures
All of the above arteries are branches of the opthalmic artery which enters the orbit through the optic canal (along with the optic nerve, CN II).
What are the 2 venous channels of the orbit? Where are they located?
How may infections spread to the cranial cavity via these veins?
There are two venous channels in the orbit:
The Superior Ophthalmic Vein: This vein begins at the superior/anterior margin of the orbit as connecting veins from the supra-orbital and angular veins join.
The Inferior Ophthalmic Vein: Is a smaller vein at the inferior aspect of the orbit. Because ophthalmic veins communicate with veins of the face and the cavernous sinus, they are a means by which infections may spread from outside to inside the cranial cavity
What nerves innervate the extraocular muscles?
CN III: Innervates the levator palpebrae and superior rectus (via it’s superior branch) and the medial rectus, inferior rectus, and inferior oblique (via it’s inferior branch). This nerve also carries preganglionic parasympathetic fibers to the ciliary ganglion (more to come on this).
CN IV: Innervates the superior oblique mm
CN VI: Innervates the lateral rectus
Where is the lacrimal nerve located within the orbit? What does it innervate? What kind of innervation does it provide? (sensory, motor)
What kind of innervation does the frontal nerve provide? (sensory, motor) What does it innervate? What are the branches of the frontal nerve?
What kind of innervation does the nasociliary nerve provide? What structures does it innervate?
Lacrimal nerve: This nerve is located laterally in the orbit and in addition to receiving postganglionic sympathetic and parasympathetic fibers from the zygomaticotemporal nerve it carries sensory information from the lacrimal gland, conjunctiva, and upper eyelid.
Frontal nerve: is the largest of the branches of V1. It receives sensory information from areas outside of the orbit specifically the scalp, skin of the forehead, skin of the upper eyelid, and the conjunctiva via its supraorbital and supratrochlear branches.
Nasociliary nerve: is the most deeply placed branch of V1. Via it’s branches the nasociliary nerve provides sensory innervation to the eyeball and sympathetic innervation for dilation of the pupil (long ciliary nerves); sensory innervation to the nasal cavity and ethmoid air cells (anterior and posterior ethmoidal nerves); sensory innervation to the upper and lower eyelid and nose (infratrochlear nerve)
What nerve(s) synapse in the ciliary ganglion? What does it/do they innervate?
What nerve passes through the ciliary ganglion?
The ciliary ganglion is the parasympathetic ganglion of the oculomotor nerve (CN III).
- Preganglionic parasympathetic fibers from CN III synapse on postganglionic neurons in the ciliary ganglion.
- Postganglionic nerve fibers then leave the ciliary ganglion via short ciliary nerves to innervate 1) the pupillary sphincter responsible for constriction of the pupil; and 2) the ciliary muscle responsible for accommodation of the lens for near vision.
- The nasociliary nerve also receives some sensory fibers carrying information from all parts of the eyeball via the short ciliary nerves. These fibers will pass through the ciliary ganglion to connect into the nasociliary nerve en route to the CNS.
- Some postganglionic sympathetic fibers may pass through the ciliary ganglion en route to the eye (this is variable).
Identify structures in attached picture.
