TBL 29: Oribt, eye, extraocular muscles, nerves & vessels, & ear Flashcards
What occupies the anterior and posterior portions of the orbit?
Anterior = Eye ball Posterior = Optic nerve (CN II) + extraoccular muscles surounded by white fat
What are the boundaries of the orbit? (lateral wall, medial wall, floor, & roof)
Lateral wall = zygomatic bone + flat great wing of sphenoid bone + ethmoidal air cells occupying the ethmoidal bone
Medial wall = mainly ethmoidal bone
Floor = maxilla (also happens to be the roof of the maxillary sinus that is right below the orbit)
Roof = frontal bone (also happens to be the floor of the frontal cranial fossa that is right above the orbit)
What demarcates the floor from the lateral wall of the orbit?
The inferior orbital fissure
What is the tarus?
A band on connective tissue found in the eyelid that provides extra support
What’s the role of lacrimal gland? How is the fluid spread and drained?
The lacrimal gland is responsible for secreting lacrimal fluid across you eye. The gland is found superolateral to the orbit. Thus, the fluid runs toward the medial angle of the eye.
It’s drained by the puncta in the lower eyelid that allow the fluid to leak through the nasolacrimal ducts into the inferior meatus in the nasal cavity
What are the sensory and motor innervations of the lacrimal gland?
Sensory: Somatic sensory form the lacrimal nerve (CN V1)
Motor: Lacrimal nerve transports post-synaptic parasympathetic motor fibers from the zygomatic nerve. These originally came from the greater petrosal nerve after it synapsed at the pterygopalatine fossa.
Describe the embryological formation of the eye. (include optic vesicles, optic cups, lens placode, lens vesicles, choroid fissure & hyaloid artery)
In the pharyngeal forgut, you have bilateral projections from the neuroectoderm of the diencephalon that produce optic vesicles. These optic vesicles continue to project outward (held to the diencephalon via optic stalks), until they reach the surface ectoderm.
At this point, the surface ectoderm begins to thicken, forming a lens placode. Meanwhile, the optic vesicles continue to invaginate forming double-layered optic cups. The lens placode continues to invaginate, forming the lens vesicles.
The lens cup and the optic stalk both have invaginations that form the choroid fissure. The hyaloid artery runs through this fissure to go to the lens placode.
Describe the important of mesenchyme in the optic cups and it’s role in the vasculature of the optic vesicle and the formation of the vitreous body
The mesenchyme infiltrates the optic cup via the choroid fissure and brings branches of the hyaloid artery to the developing lens. Eventually, these branches disappear and the space left is replaced by a gelatinous substance (eventually becomes the vitreous body)
What does the mesenchyme differentiate into in the optic cups? How is the optic nerve formed?
The outer most portion becomes a thin pigmented layer, while the inner portion starts to develop neurons and is thus known as the thick neural layer
The neural layer has neurons whose axons go to form the optic nerve. The nerve travels through the choroid fissure and encloses the hyaloid artery. Only w/ the closure of the choroid fissure is the optic stalk converted into the optic nerve.
After complete maturation, the optic nerve fully encloses the central artery and vein of the retina
What is the remnant of the hyaloid artery?
Central retinal artery
What is the choroid and sclera? How are they formed?
The choroid is a thin vascularized layer that is formed from mesenchyme directly external to the optic cups
The sclera is a fibrous layer that is found external to the choroid
Name the continuations of the sclera & the choroid
Sclera is continuous posteriorly w/ the cranial dura that surrounds the optic nerve and continuous anteriorly w/ the cornea
Choroid is terminates anteriorly at the ciliary body
What is the double epithelium of the ciliary body and the iris?
When the neural layer of the optic cup reaches the ciliary body, it barely produces any neurons and is turned into an inner non-pigmented retinal layer. This + the outer pigmented retinal layer form the double epithelial layer of the ciliary body & the iris
What forms the pupils?
The closure of the choroid fissure
What are the layers of the photoreceptors in the neural retinal layer? Describe how we see images can be viewed
From retinal surface of neural layer to the retinal pigmented layer
Ganglion –> bipolar cells –> photoreceptors (rods or cones)
Light impulses travel past the ganglion and bipolar cell layers to create impulses w/ the photoreceptors of the neural retinal layers. Then the impulses go to the bipolar cells and the ganglion cells, which send them to the brain through their axons that comprise of the optic nerve
Differentiate b/w rods & cones
Rods are more plentiful than Cones
Rods —> show you visual images in shades of gray from a dim light perspective
Cones —> show COLOR because they can be sensitive for wavelengths of red, blue, or green light
What is the optic disc?
Marks the exit of the optic nerve from the posterior eyeball