Lab 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

Eye

  • Extraocular Muscles
    • Lateral rectus
    • Medial rectus
    • Inferior rectus
    • Superior rectus
    • Inferior oblique
    • Superior oblique
  • Fibrous layer of eye
    • Cornea
    • Sclera
  • Vascular layer of eye
    • Choroid
    • Suspensory ligaments/zonular fibers
    • Ciliary muscle
    • Ciliary body
    • Iris
    • Pupil
  • Inner layer of eye
    • Retina
    • Optic disc (blind spot)
    • Lens
    • Vitreous humor/body
  • Orbit
    • Lacrimal sac
    • Optic nerve (CN II)
    • Optic chiasm
    • Optic tract

Ear

  • External ear
    • Auricle
    • External acoustic meatus
    • Tympanic membrane
  • Middle ear
    • Tensor tympani muscle
    • Pharyngotympanic (auditory/Eustachian) tube
    • Auditory ossicles
      • Malleus
    • Incus
    • Stapes
  • Internal ear
    • Vestibule
    • Oval window
    • Round window
    • Semicircular canals
      • Anterior, Lateral, Posterior
      • Ampulla
  • Cochlea

Important Terms from Previous Labs

  • Cranial nerves and brain structures
    • Abducens Nerve (CN VI)
    • Oculomotor nerve (CN III)
    • Trochlear nerve (CN IV)
    • Optic nerve (CN II)
    • Facial Nerve (CN VII)
    • Vestibulocochlear Nerve (CN VIII)
    • Occipital lobe
      • Primary visual cortex
      • Calcarine fissure
  • Bones of the skull that make up the orbit
    • Frontal bone
    • Sphenoid bone
    • Maxilla
    • Ethmoid bone
    • Zygomatic bone
    • Lacrimal bone
  • Internal acoustic meatus

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.

 


Lab Activity 1: Navigator – The Eye

Use the Navigator to explore the anatomy of the orbit and the structures within it. First explore the eye within the skull. Next, you can remove the skull. Click on the “View” icon and choose “Advanced.” In the left column, uncheck the skeleton box. Now you will have a clear view of the contents of the orbit. If you want to add the skull back in, you can check the skeleton box. DO NOT save any presents! 

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 the tendon of this muscle runs through. Therefore, when the superior oblique muscle contracts, it depresses the eye (causes the eye to look down). Also observe the nerves that innervate these muscles.

Extraocular Muscle

Action

Cranial Nerve Innervation

Lateral rectus

Moves eye laterally (abducts)

CN VI Abducens Nerve

Medial rectus

Moves eye medially (adducts)

CN III Oculomotor Nerve

Superior rectus

Elevates the eye (look up)

Inferior rectus

Depresses the eye (look down)

Inferior oblique

Elevates eye and turns it laterally

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 on as the optic tract until the majority of them synapse in a nucleus of the thalamus.

Observe the eye in both coronal and transverse cross sections. It can be helpful to have all three cross sectional views visible at the top of the screen. Click on the “Layout” icon on the toolbar and choose the view with three boxes at the top of the screen. As you move through the transverse (axial) cross section, you can observe the eye, medial and lateral rectus muscles on the sides of the eye, and the optic nerve leaving the eye posteriorly. As you move through the coronal view, you can observe the four rectus muscles of the eye as well as the optic nerve. Also notice the adipose (fat) tissue surrounding the structures of the orbit. This tissue fills the space within the orbit and provides protection for these structures.

Lab Activity 2: Plastic Eye and Ear Models

We have two plastic eye models as well as two plastic ear models for you to observe in this lab. Please be gentle when looking at the models, there are parts that come apart and can be damaged when trying to replace them or if they are dropped.

Review the models as well as the laminated images and key to identify structures from the terms to know list above. (the terms on the key in light gray are numbered on the laminated images, but you are NOT responsible to know them for lab, although they might help you for the lecture course)

 


Lab Activity 3: Slideshow Images – Eye and Ear

Study the images on the lab computers that show the anatomy of the eye and the ear.

Eye

There are several images 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: 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 structure and function.
  • 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 he pupil and contains smooth muscle to dilate or constrict the pupil. It contains a pigmented layer that gives our eyes their color.
  • Vitreous humor: 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

Also examine the extraocular muscles here (described earlier).

Ear

There are several images 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
  • Inner ear
    • Vestibule: contains the utricle and saccule, which are part of the vestibular system. These structures help us to know the orientation of our head at any given time, and they sense linear acceleration of the head.
    • Semicircular canals: sense rotational acceleration of the head, as in when we turn our head or our head rotates with our body. They are part of the vestibular system and function together with the utricle and saccule to give us a sense of balance, our position in space, and how our head is moving at a given time. 
    • Cochlea: snail-shaped chamber of the inner ear that houses the organ of hearing.

 


Lab Activity 4: Visible Body Digital Atlas: Orbit, Eye, & Ear

Observe the orbit, eye, and ear using the Visible Body Digital Atlas.

  • In the iPad atlas, open the Systems view and under the Skeletal Systems View click on 2. Skull. Use both this atlas and the skull itself to examine the bones that make up the bony orbit, which protects the eye:
    • Frontal bone
    • Sphenoid bone
    • Maxilla
    • Lacrimal bone
    • Ethmoid bone
    • Zygomatic bone
    • Palatine bone
  • Click on the sphenoid bone and isolate this bone (use icon that looks like a femur with multiple colors). The sphenoid bone can be a difficult bone to visualize given its deep position within the skull. For the sphenoid bone, this will take you to a different, color-coded view. Here you can examine some of the foramen that we discussed in previous labs.
  • You have not yet looked closely at the lacrimal or palatine bones this unit. We will discuss the palatine bone more with the oral cavity, as it only forms a very small part of the medial wall of the orbit. The lacrimal bone forms a larger portion of the medial wall of the bony orbit. Each contains a fossa and grove that holds the lacrimal sac and nasolacrimal duct, which functions to gather tears and send them to the nasal cavity. Click on these bones in the app and isolate them to see more of the surface features and also observe them on the skull.
  • Examine the rest of the bones of the orbit in the app and on the skull. Also observe the external acoustic meatus of the temporal bone on the skull. This is the tube that connects the external opening of the ear to the tympanic membrane (ear drum).
  • Go back to the main menu of the app and click on the microanatomy tab. Now click on 1. Eye and explore the structures in the list on page 1 of this guide. You can return to the microanatomy tab and then click on 3. Lens and Zonular Fibers. This will show the internal anatomy of the eye. “Zonular fibers” is another term for suspensory ligaments.
  • Back to the microanatomy tab, click on 7. Ear. From this view you will be able to see the auricle, external acoustic (auditory) meatus, and the tympanic membrane. If you did not zoom in to see the tympanic membrane, zoom in now to see the structures of the middle and inner ear. You will be able to see the malleus, incus, stapes, cochlea, vestibule, and the semicircular canals.
  • Be sure to click on the Facial nerve (CN VII) and observe how it runs very close to the middle ear before entering the stylomastoid foramen. This anatomy is why the facial nerve may be vulnerable during a middle ear infection, which can lead to Bell’s Palsy, as described in the previous lab.

License

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Human Anatomy Lab Manual by Julie Stamm, PhD, LAT, ATC and Patrick Hills-Meyer, EdD, LAT, ATC, CSCS is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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