Special Senses

Medical Terminology

Sense of Smell

• Very important in many species• Warns the animal of approaching

dangers• Helps to find food• Connected to sex reflexes

• Primary peripheral organ is nose• “Naso” and “rhino”

• Organ of smell is olfactory epithelium. Vomeronasal organ helps in detecting sexual pheromones• “olfact”

Structures of smell

• Nostrils or nares• Turbinates• Philtrum- groove in middle of nose separating nostrils

Taste

Organs of taste are taste buds- located on tongue and mucous membrane of the soft palate.

Vision

• Orbit, optic, ocular, ophthalmo refer to eye• Eyeball is cushioned in fat and connective tissue

CONJUNCTIVA• mucous membrane that covers the inner surface of the

eyelid (palpebral conjunctiva) and the front portion of the eyeball (bulbar conjunctiva). Commonly becomes inflamed.

EYELIDS

• (palpebrae) protect the eye’s surface. Upper and lower join at the CANTHUS.

• Many animals also have a THIRD EYELID that originates at the medial canthus and spreads laterally across the eye passively when the lids close.

• Contains a lacrimal gland and a small piece of cartilage.

SCLERA

• opaque posterior fibrous portion of the eye that is continuous with the cornea. Also known as the white of the eye. Joins with the cornea at the LIMBUS.

• MUSCLES: 6-7 attach to each eye at the sclera to allow movement in any direction

CORNEA

• anterior, transparent portion of the eye where light enters.

• Circular in shape with a bulge at the cranial aspect.• No blood vessels within it which makes it prone to

infection after injury. • It is richly supplied with pain receptors.

CHOROID

• located between the sclera and the retina. Known as the vascular layer.

• Contains the TAPETUM LUCIDUM in all animals except pigs and humans which is a reflective layer that allows an animal to see in dimly lit conditions. Commonly seen when a light is directed into the animal’s eye in the dark.

CILIARY BODY

• wedge-shaped ring that connects to the lens and adjusts its shape, allowing the animal to focus. Also produces AQUEOUS HUMOR

• IRIS: doughnut-shaped ring that regulates the amount of light that gets through to the lens. Opening in the center is called the PUPIL .

•  • LENS: directly behind the iris, focuses the light on the

retina. Shape is controlled via the ciliary body.

COMPARTMENTS OF THE EYE

• AQUEOUS compartment is in front of the lens and is made of clear, watery fluid called aqueous humor produced continuously by the ciliary body. • -This compartment is further divided into the anterior

and posterior chambers. These help to maintain the shape of the eyeball and the intraocular pressure. Empties into the Canal of Schlemn, which is returned to the bloodstream.

• VITREOUS compartment is caudal to the lens and is made of soft gelatin called vitreous humor.

RETINA

• innermost layer that forms the visual image and converts it to nerve impulses that are sent to the brain via the optic nerve.

• Nerve fibers on the inside of the retina come together at the OPTIC DISC where they leave the eye to form the OPTIC NERVE that carries visual info to the brain.

• The retina is composed of cells called RODS and CONES that are receptors of light stimuli.

• CONES are the least numerous, adapted for bright light, color, and detail.

• RODS are sensitive for low light vision, but are color blind.

• Domestic animals can see colors, but most have very few cones. This allows them to see with the quality of an old colored photograph that has been over exposed (colors are pale and faded). Their vision is also not as sharp as humans.

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• There are no rods or cones at the optic disc so no visual images are formed, making it the blind spot of the eye.

LACRIMAL APPARATUS

• Includes the lacrimal gland, the gland within the 3rd eyelid, and the nasolacrimal duct. • The lacrimal gland produces tears to moisten, clean, and

deliver antibacterial substances to the surface of the eye.• The major lacrimal gland is located in the dorsolateral

portion of each orbit. • Blinking spreads the tears across the eye toward the

medial canthus to the tiny lacrimal punctum. • They then drain down the NASOLACRIMAL DUCT, which

is why you get the “sniffles” when your eyes water. Blockage of this duct forces the tears to drain on the face.