SPECIAL SENSE ANTOMY AND PHYSIOLOGY EYE,EAR

1. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
Lab 14 :
Learning outcomes of the lab exercises:
1. Identify the major structures of the human eye and human ear in figures and on models; and
describe their functions.
2. Dissect an eye and identify its major features.
"A major role of sensory receptors is to help us learn about the environment around us, or about the state
of our internal environment. Stimuli from varying sources, and of different types, are received and
changed into the electrochemical signals of the nervous system. This occurs when a stimulus changes
the cell membrane potential of a sensory neuron. The stimulus causes the sensory cell to produce an
action potential that is relayed into the central nervous system (CNS), where it is integrated with other
sensory information—or sometimes higher cognitive functions—to become a conscious perception of
that stimulus. The central integration may then lead to a motor response."
SENSE OF SIGHT: Vision
A. Visual Accessory Organs:
1. Eyelids = protective shield for the eyeball.
a. Conjunctiva= inner lining of eyelid; = red portion around eye.
2. Lacrimal apparatus = tear secretion & distribution.
a. Lacrimal gland = tear secretion; located on upper lateral surface
o Tears contain an enzyme called lysozyme, which functions as an
anti-bacterial agent.
b. Nasolacrimal duct = duct which carries tears into nasal cavity (drainage)
3. Extrinsic muscles hold eyeball in orbital cavity; allow for eye movement.
- Superior rectus, Medial rectus, Inferior rectus, Inferior oblique all innervated
by
oculomotor nerve (CN III)
- Superior oblique innervated by trochlear nerve (CN IV)
- Lateral rectus innervated by abducens nerve (CN VI)

2. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
Fig 14.14 Extraocular Eye Muscles
B. Structure of the Eye:
The eye is composed of three distinct layers or tunics:
1. The Outer Tunic (fibrous) = protection.
a. Cornea = transparent anterior portion;
o Functions: helps focus (75%) incoming light rays.
b. Sclera = white posterior portion, which is continuous with eyeball except where
the optic nerve and blood vessels pierce through it in the back of eye.
o Functions:
● protection
● attachment (of eye muscles)
2. The Middle tunic (vascular) (uvea) = nourishment...
a. Choroid coat = membrane joined loosely to sclera containing many blood
vessels to nourish the tissues of the eye.
b. Ciliary body = anterior extension from choroid coat, which is composed of 2
parts:
o Ciliary muscles which control the shape of the lens (i.e.
Accommodation);
o Ciliary processes are located on the periphery of the lens.
● Suspensory ligaments extend from the ciliary processes on the
lens to the ciliary muscles (i.e. they connect above structures),
and function to hold the lens in place.
*Accommodation = the process by which the lens changes
shape to focus on close objects.
1. The lens is responsible (with cornea) for focusing incoming
light rays.
2. If light rays are entering the eye from a distant object, the lens

3. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
is flat.
3. When we focus on a close object, the ciliary muscles contract,
relaxing the suspensory ligaments. Accordingly, the lens
thickens allowing us to focus.
c. Iris = colored ring around pupil;
o thin diaphragm muscle;
o lies between cornea and lens;
● The iris separates the anterior cavity of the eye into an anterior
chamber and posterior chamber.
● The entire anterior cavity is filled with aqueous humor, which helps
nourish the anterior portions of the eye, and maintains the shape
of the anterior eye.
3. The Inner tunic (nervous, sensory)
a. Retina = inner lining of the eyeball; site of photoreceptors.
A picture of the retina can be taken with a camera attached to an
ophthalmoscope
o The optic disc is the location on the retina where nerve fibers leave
the eye & join with the optic nerve; the central artery & vein also pass
through this disc.
● No photoreceptors are present in the area of the optic disc=
blind spot.
o The posterior cavity of the eye is occupied by the lens, ciliary body,
and the retina.
● The posterior cavity is filled with vitreous humor, which is a
jelly-like fluid, which maintains the spherical shape of the
eyeball.

4. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
Fig 14.15 Structure of the Eye
DISSECTION OF THE SHEEP EYE
Complete the eye dissection as instructed by your instructor.
Please identify the items listed in BOLD for the eye dissection.
A. Fibrous Layer: Outermost layer of dense avascular connective tissue.
- The sclera is glistening white and opaque. It forms the bulk of the posterior portion of the eye.
- The sclera is pierced in the back by the optic nerve.
- The cornea is the crystal clear window located at the anterior pole of the eye.
B. Vascular Layer (The Uvea): Pigmented middle layer.
- The choroid is a vascular, dark membrane that forms the majority of the posterior.
- The ciliary body is a thickened ring of smooth muscle that surrounds the lens and helps to
control lens shape.
- The iris is the visible, colored portion of the uvea.
- The round opening in the iris is the pupil, which allows light to enter the eye.
C. Sensory Layer (The Retina): Innermost layer of the eye.
- The retina is often called the neural layer because it contains approximately 250 million
photoreceptor cells.
D. Lens:
- The biconvex, transparent lens is used to focus light onto the retina.

5. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
E. Humors: Humors are the fluids of the body.
- Vitreous humor located posterior to the lens. It is thick and gel-like.
- Aqueous humor produced anterior to the lens and is similar in composition to blood plasma.
A. EAR STRUCTURE:
1. External Ear:
a. Auricle = outer ear (cartilage);
o Function = collection of sound waves.
b. External auditory meatus = ear canal;
o Function = starts vibrations of sound waves and directs them toward
tympanic membrane.
2. Middle Ear:
Function = to amplify and concentrate sound waves.
a. Tympanic membrane = eardrum.
*Tympanic (attenuation) Reflex = protective mechanism for hearing
b. Tympanic cavity = air-filled space; separates outer from inner ear.
c. Auditory ossicles = 3 tiny bones in middle ear:
o Malleus (hammer) is connected to tympanic membrane;
o Incus (anvil) connects malleus to stapes;
o Stapes (stirrup) connects incus to the
*Oval window = the entrance to inner ear.
d. Auditory (Eustachian) tube = passageway which connects middle ear to
nasopharynx (throat).
o Function = to equalize pressure on both sides of the tympanic
membrane, which is necessary for proper hearing.
3. Inner Ear:
a. The inner ear consists of a complex system of intercommunicating
chambers and tubes called a labyrinth. Actually, two labyrinths compose
the inner ear:
o Osseous labyrinth = bony canal in temporal bone;
o Membranous labyrinth = membrane within osseous labyrinth.
b. Two types of fluid fill the spaces in the labyrinths:
o Perilymph fills space between osseous and membranous labyrinth;
o Endolymph fills the membranous labyrinth.
c. The inner ear labyrinth can further be divided into three regions (cochlea,
vestibule & semi-circular canals), each with a specific function:
o Cochlea = snail shaped portion;
● Function = sense of hearing.
o Semi-circular canals = three rings;
● Function = dynamic equilibrium.
o Vestibule = area between cochlea and semi-circular canals;
● Function = static equilibrium.
d. The osseous labyrinth of the cochlea can be divided into two
compartments:
o Scala vestibuli = upper compartment which extends from oval window
to apex;
o Scala tympani = lower compartment which extends from apex to round
window.
*Both compartments are filled with perilymph.

6. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
e. Between the two bony compartments, we find the membranous labyrinth =
cochlear duct.
o The cochlear duct is filled with endolymph.
f. There are membranes that separate the cochlear duct from the bony
compartments:
o Vestibular membrane separates cochlear duct from the scala vestibuli;
o Basilar membrane separates cochlear duct from the scala tympani;
Fig 14.15 Structure of the Eye

7. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
Fig 14.7 Cross Section of the Cochlea

8. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
REVIEW ACTIVITY - EYE LABELING FIGURE
EYE WORD BANK
Aqueous humor Optic nerve
Cornea Pupil
Choroid Retina
Ciliary body Sclera
Eye muscles Suspensory ligaments
Iris Vitreous humor
Lens
10.
11.
12.
13.

9. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
REVIEW ACTIVITY - EAR LABELING FIGURE
EAR WORD BANK
Auditory nerve Middle ear
Auricle (Pinna) Ossicles (Malleus, Incus, Stapes)
Cochlea Outer ear
Ear cartilage Semicircular Canals
Earlobe Temporal bone
(Region)

10. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
Eustachian tube Tympanic Membrane
External Auditory Canal (Ear canal) Vestibular nerve
REVIEW ACTIVITY
Indicate whether the following structures are part of the outer, middle, or inner layers
of the eye:
1. ___________________ Rods and cones 2, __________________ Cornea
3. ___________________ Iris 4. __________________ Ciliary body
Indicate whether the following structures are part of the outer, middle, or inner layers
of the ear:
5. ___________________ Auricle (Pinna) 6. __________________ Ossicles
7. ___________________ External auditory tube 8. __________________ Cochlea
FILL-IN-THE-BLANK: Identify the structures with the correct function
retina ; sclera ; choroid ; lens ; cornea ; ciliary body; cochlea ; tympanic membrane
9. _______________________ Eardrum
10. ______________________ Outer, transparent structure that refracts light and thus aids in
focusing light rays, contact lenses are placed here.
11. ______________________ Sense of hearing
12. _____________________ Hard, clear structure that changes shape to allow near and far
focus of the eye
13. ______________________ Contraction and relaxation of its muscle results in changing
shape of lens
14. ______________________ Contains blood vessels providing nourishment to retina.
15. ______________________ Tough, white protective layer which also provides a place for

11. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
attachment of extrinsic eye muscles.
16. ______________________ Contains the light receptors.
Multiple Choice Questions
1. What structure associated with the eye produces tears?
A. Lacrimal apparatus C. Lens
B. Conjunctiva D. Retina
2. What structure is responsible for most of the bending (refraction) of light entering the eye?
A. retina C. aqueous humor
B. cornea D. vitreous humor
3. Which is the proper order of the focusing system of the eye?
A. cornea, lens, aqueous humor, vitreous humor
B. aqueous humor, lens, vitreous humor, cornea
C. cornea, aqueous humor, lens, vitreous humor
D. lens, vitreous humor, cornea, aqueous humor
4. What is the function of the auricle of the ear?
A. Collects and directs sound waves
B. dynamic equilibrium detection
C. Something to hook glasses onto
D. static equilibrium detection
5. What structure transmits sound waves from the auricle to the ear drum (tympanic
membrane)?
A. Lacrimal gland B. External acoustic (auditory) meatus
C. Cochlea D. Ceruminous glands
6. What structure separates the outer ear from the middle ear?
A. auricle C. tympanic membrane
B. semicircular canals D. ceruminous glands
7. Which part of the inner ear is involved with the detection of sound?
A. semicircular canals C. cochlea
B. vestibule D. auditory (Eustachian) tube
8. What is the function of the auditory (Eustachian) tube?
A. Transmits sound waves to the inner ear
B. Transmits sound waves to the middle ear

12. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
C. Equalizes pressure on tympanic membrane in the middle ear
D. Transferring the sensation of equilibrium to the ear
9. Which region of the ear is responsible for dynamic equilibrium ?
A. semicircular canals C. cochlea
B. vestibule D. auditory (Eustachian) tube
10. Which region of the ear is responsible for static equilibrium ?
A. semicircular canals C. cochlea
B. vestibule D. auditory (Eustachian) tube
Problem Solving Activity (EAR)
The following problem solving assessment is presented in a multiple-choice format. Each choice
should be considered individually and an argument should be written for accepting or rejecting it. Since
the problem has one best answer, there should be one argument for acceptance and four for rejection.
For each response, you must first state whether you are accepting or rejecting that statement. Then,
you must write a detailed explanation why you accept or reject each of the choices.
PROBLEM 1:
A 20 year old biology student has been working in a nightclub as a DJ to earn money to pay for her
education. After several months, she notices that she is having problems hearing high-pitched tones.
Which of the following is most probable?
A. She is experiencing symptoms from a perforated eardrum.
B. She is experiencing symptoms from otitis media.
C. She is experiencing symptoms from damage to structures in the inner ear.

13. CVMU
INDUKAKA IPCOWALA COLLEGE OF PHARMACY
HAP-I
Special Senses
MRS.RISHITA D PATEL HAP-I
D. She is experiencing symptoms of otosclerosis.
E. What she is experiencing is quite normal and she should not worry about it.