Lab 8 notes - Lab 8: The Eye and Ear The eye The...

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Lab 8: The Eye and Ear The eye The superficial aspect of the eye is a familiar structure, but it is more complex than you may think- you need to know both the external structure of the eye and eyelids as well as the structures within the eyeball, and the bony morphology and musculature of the orbit. On the external surface of the eye itself you can see the white of the eye called the sclera , the pupil of the eye, and the pigmented iris around the pupil. The transparent bulge in front of the pupil and iris is the cornea . When you look at the sclera in anterior view it is covered with a thin membrane called the conjunctiva (bulbar conjunctiva) . The eyelids are known as the palpebrae . The opening between the upper and lower eyelids is called the palpebral fissure . The conjunctiva extends over the inner surface of the eyelids ( palpebral conjunctiva ). The two end points of the palpebral fissure are called the medial canthus and lateral canthus . The lateral canthus is in contact with the eyeball. However, the medial canthus is separated from the eye by a number of named structures- there is a fleshy pink bump called the lacrimal caruncle , and a curved pink line lateral to the caruncle that is called the plica semilunaris . There are small holes in the medial end of the upper and lower eyelids, only visible when the eyelid is everted (turned out), called the lacrimal puncta (singular punctum). These puncta are the openings of the drainage system for tears that moisturize and clean the surface of the eye. The lacrimal puncta open into the lacrimal canaliculi leading to the lacrimal sac - the lacrimal sac drains into the nasolacrimal duct which empties into the nasal cavity (beneath the inferior nasal concha) Under these superficial structures you find the fibers of the orbicularis oculi muscle. Remember that this is the muscle of facial expression (innervated by CN VII) that is responsible for blinking and closing the eye forcefully. Deep to the orbicularis oculi muscle you find a fibrous sheet called the orbital septum separating the superficial structures surrounding the eye from the cavity containing the eyeball. Each eyelid has a cartilaginous plate underlying and stiffening the eyelid called the tarsal plate . The orbit – skeleton The bones that form the orbital rim are the frontal , zygomatic , maxilla , and lacrimal . The walls of orbit are formed by these bones together with the greater wing of the sphenoid , the lesser wing of the sphenoid , and the lateral surface of the ethmoid . Foramina in orbit- superior orbital fissure , inferior orbital fissure , optic canal , lacrimal fossa and nasolacrimal canal .
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Pathway of tears The lacrimal gland is found in the upper lateral part of the orbit. This can be counter intuitive because we usually see tears in the medial corner of the eye. The tear solution is produced by the lacrimal glands (parasympathetic innervation from the facial nerve via the greater petrosal nerve and the pterygopalatine ganglion). Blinking the eye washes the
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Lab 8 notes - Lab 8: The Eye and Ear The eye The...

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