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BIOLOGY 165 SPECIAL SENSES LAB MANUAL
NOTE: You may be asked to identify any structure, cell, tissue, or organ labeled in the figures/pictures within
this lab manual. In addition, you may be asked to name one function of each labeled item and one location
within the human body where it can be found. You are only responsible for the specific information contained
within this lab manual. Although the pictures in this packet show a particular model, you should look at all
similar models we have in the lab; any model in lab can be used during the practical.
THE EYE
1. Accessory structures – includes the eyebrows, eyelids, eyelashes and lacrimal apparatus.
a. The lacrimal apparatus includes the following structures:
i. The lacrimal glands – secrete lacrimal fluid (tears).
ii. The excretory lacrimal ducts – empty tears from the lacrimal glands onto the surface of
the cornea.
iii. The lacrimal canals – funnel the tears into the lacrimal sac which in turn empties into the
nasolacrimal duct. This duct empties into the nasal cavity.
Be able to identify the structures shown in the pictures below, using any similar model we have in lab.
Superior Lacrimal gland
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Structure of the Eyeball
The eyeball can be divided into three principal layers: the fibrous tunic, the vascular tunic, and the nervous
tunic (retina).
1. Fibrous tunic – consists of the following structures:
a. Sclera – consisting of dense regular (white fibrous) connective tissue (the "white" of the eye). It
gives the eye its shape and helps to protect the delicate internal layers.
b. Cornea – the transparent portion of the fibrous tunic.
Vitreous Body
2. Vascular tunic – consisting of the following structures:
a. The choroid – a thin brown membrane that lines the interior surface of the sclera and contains the
blood vessels that serve the retina, and a pigment to darken the inner surface of the eye (together
with the pigmented layer of the retina) to absorb light rays so that they do not reflect light.
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b. The ciliary body – which contains the smooth muscles that alter the shape of the lens
(accommodation), and the cells that secrete aqueous humor into the anterior cavity.
c. The iris – the colored portion of the eye that controls the amount of light entering the eye by
regulating the size of the pupil.
i. Pupil – the hole in the middle of the iris through which light passes.
Iris
3. The nervous tunic (retina) – consisting of the following structures:
a. The central fovea of the macula lutea – the area of acute vision, where the light rays are focused
on the retina.
i. Contains only cones, which are responsible for color vision.
ii. The rest of the visual portion of the retina contains both rods and cones.
b. Optic disk (blind spot) – the part of the retina where the optic nerve attaches. It contains no rods
or cones.
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Other structures and cavities of the eye
1. The lens – is attached to the ciliary muscle by the suspensory ligaments. It changes shape to focus the
light image on the central fovea of the macula lutea.
2. The anterior cavity is located in front of the lens and is filled with aqueous humor. It is divided into two
chambers:
a. The anterior chamber, located between the cornea and the iris.
b. The posterior chamber, located between the iris and the lens.
3. The posterior (vitreous) cavity is located behind the lens and is filled with the vitreous humor (body).
Posterior chamber of anterior cavity
Anterior chamber of anterior cavity
Lens
Posterior
(vitreous) cavity
Posterior chamber of anterior cavity
4. The optic nerve – enters the back of the eye slightly toward the median surface of the eye. The blood
vessels that serve the internal structures of the eye enter through the sclera along with the optic nerve.
The optic nerve is sheathed in dura mater, which is continuous with the sclera.
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5. The extrinsic eye muscles – control the movement of the eye. Most lab models have at least two of the
six muscles illustrated. The six muscles are:
a. The superior oblique.
b. The inferior oblique.
c. The superior rectus.
d. The inferior rectus.
e. The lateral rectus.
f. The medial rectus.
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HISTOLOGY OF THE EYE
Seen below: light photomicrograph of the eye (400X).
Ciliary Processes
Seen below: light photomicrograph of cornea (100X).
Ignore this structure
Ignore this structure
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Seen below: light photomicrograph of the retina (400X).
Seen below: light photomicrograph of the eye (400X).
Ignore this
structure
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THE EAR
1. The ear can be divided into three principle regions – the external ear, middle ear, and internal ear:
a. The external (outer) ear – consists of the following structures that collect sound waves and direct
them inward:
i. The Pinna (Auricle) is the outer visible portion of the ear consisting of two regions:
1. The helix – the rim of the pinna.
2. The lobe – the lower dangling portion of the pinna.
ii. The external auditory meatus (canal) – contains hair and ceruminous glands, which
secrete wax.
iii. The tympanic membrane (eardrum) – converts sound waves into mechanical vibrations.
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b. The middle ear – a hollow space inside the temporal bone. It contains the following structures:
i. The auditory (Eustachian) tube – equalizes air pressure on both sides of the tympanic
membrane. It connects up with the nasopharynx.
ii. The auditory ossicles (ear bones) – transfer the mechanical vibrations of the tympanic
membrane to the oval window of the inner ear. The ossicles consist of three bones:
1. The malleus – shaped like a hammer – connects directly to the tympanic
membrane.
2. The incus – shaped like an anvil.
3. The stapes – shaped like a stirrup – sits directly on top of the oval window.
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c. The internal (inner) ear – also known as the labyrinth, consists of three divisions: the
semicircular canals, the vestibule, and the cochlea.
i. The semicircular canals – each has an enlarged base called an ampulla. These structures
function in dynamic equilibrium (help you keep your balance as you are moving). Inside
each ampulla is a balance organ called the crista ampullaris.
ii. The vestibule – the middle portion of the inner ear (between the cochlea and the
semicircular canals) contains two important structures (the utricle and the saccule) that
function for both dynamic and static equilibrium (helps you keep your balance while
standing still and moving). Other structures associated with the vestibule are:
1. The vestibular branch of the vestibulocochlear nerve (cranial nerve #8), which
emerges from the vestibule and the cochlea.
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2. The oval window – sits under the stapes and receives mechanical vibrations from
the auditory ossicles.
3. The round window – absorbs vibrations from inside the cochlea to prevent
"echoing" of sounds.
iii. The cochlea – the portion of the inner ear that functions for hearing. It contains the organ
of Corti, which changes mechanical vibrations into action potentials, which are
eventually interpreted by the brain as sound.
(within the black box)
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