10 Eye | Ear
Learning Objectives:
- Identify the bones of the orbit.
- Identify the structures that make up the eye.
- Identify the extraocular muscles of the eye and their actions.
- Identify the parts of the hearing and vestibular system.
- Review the bones and foramen of the skull and structures that pass through the foramen.
Terms to Know
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Eye
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Ear
Important Terms from Previous Labs
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Introduction
This lab will explore the special sensory anatomy that makes up our vision, hearing, and vestibular systems. These sensory systems work to contribute to our overall ability to see, hear, demonstrate balance, and navigate our surroundings with ease. When any of these structures are compromised, it has a profound impact on our daily function. Please review all the terms from the lab guide and pay special attention to the key terms that carry over from our previous lab sessions.
Lab Activities
Activity 1: The Eye
Eye:
There are several images in the Canvas slide show showing the internal and external anatomy of the eye. Some of these images show a superior or lateral view of the orbit, while others show cross-sectional images of the eye. Some are cadaver images, and others show diagrams or models. In addition to the optic nerve, chiasm, and tract and extraocular muscles, identify the following structures of the eye:
- Cornea: the transparent surface of the eye that bends (refracts) the light and focuses it on the back of the eye.
- Sclera: outer fibrous, white layer of the eyeball. The sclera and the cornea are continuous with each other but have different structures and functions.
- Lens: changes shape to be able to focus light on the back of the eye regardless of the distance of the object
- Suspensory ligaments and ciliary muscle: Suspensory ligaments connect the ciliary muscle to the lens of the eye. Contraction and relaxation of this muscle change the tension on the suspensory ligaments, which changes the shape of the lens to focus our vision on objects near or far away.
- Pupil: opening in the center of the iris through which light enters the eye.
- Iris: surrounds the pupil and contains smooth muscle to dilate or constrict the pupil. It contains a pigmented layer that gives our eyes their color.
- Vitreous humor: a jelly-like substance that fills the chamber of the eye posterior to the lens and gives the eye its shape. It transmits light to the retina.
- Choroid: highly vascular, darkly pigmented membrane that nourishes the retina.
- Retina: the neural layer of the eye, which contains the photoreceptors for vision
In the images and the digital atlas video on Canvas, examine the extraocular muscles. These muscles function to move the eye so that we can direct our visual attention. All but the inferior oblique muscle originate in a common tendinous ring at the posterior aspect of the orbit. Notice that the superior oblique muscle travels anteriorly to the medial corner of the orbit and then turns posteriorly and laterally to insert on the eye. There is a small pulley or trochlea (hence, trochlear nerve) that this muscle’s tendon runs through. Therefore, it depresses the eye when the superior oblique muscle contracts (causes the eye to look down). Also, observe the nerves that innervate these muscles.
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Extraocular Muscle |
Action |
Cranial Nerve Innervation |
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Lateral rectus |
Moves eye laterally (abducts) |
CN VI Abducens Nerve |
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Medial rectus |
Moves eye medially (adducts) |
CN III Oculomotor Nerve |
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Superior rectus |
Elevates the eye (look up) |
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Inferior rectus |
Depresses the eye (look down) |
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Inferior oblique |
Elevates eye and turns it laterally |
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Superior oblique |
Depresses eye and turns it laterally |
CN IV Trochlear Nerve |
Next, follow the optic nerve posteriorly from the eye. The optic nerves come together at the optic chiasm. Here, some of the fibers within the optic nerves cross. After the optic chiasm, these axons continue as the optic tract until the majority of them synapse in a nucleus of the thalamus.
In the cross-sections of the eye video on Canvas, observe the extra-ocular muscles and the optic nerve. You will view these in both the coronal and horizontal planes.
Activity 2: The Ear
Ear
There are several images and a video showing the anatomy of the ear. Again, some are cadaver images, while others are drawings and images of models. Use these images to identify the following structures of the ear.
- External ear
- Auricle: outer portion of the ear that is visible
- External acoustic meatus: short tube running from the auricle to the eardrum
- Tympanic membrane: eardrum
- Middle ear
- Auditory ossicles: bones of the inner ear
- Malleus: hammer
- Incus: anvil
- Stapes: stirrup
- Auditory ossicles: bones of the inner ear
- Inner ear
- Vestibule: contains the utricle and saccule, which are part of the vestibular system. These structures help us know the orientation of our head at any given time, and they sense the linear acceleration of the head.
- Semicircular canals: part of the vestibular system that senses the rotational acceleration of the head.
- Cochlea: snail-shaped chamber of the inner ear that houses the organ of hearing.
Wrap up and clinical connection
Today’s clinical connection looks at two injuries to the eye; retinal detachment and orbital blow-out fractures. A retinal detachment will cause permanent vision loss if not repaired. The clinical connection will review the risk factors, symptoms, and treatment options for a retinal detachment. A blow-out fracture is common from direct contact to the orbit/eye. The most common direction of a blow-out fracture is inferior. Fractures to the orbit can trap the extra-ocular muscles and limit eye movement. Displaced blow-out fractures will often need to be surgically repaired.
Click here to view the clinical connection slideshow.
