Veterinary Science: Anatomy and Physiology; Section 11 Eye & Ear

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Two major functions of the ear

hearing and balance.

Process of hearing

sound vibrations are transformed into a nervous impulse & transmitted to the brain by the auditory nerve.

Auditory nerve

cranial nerve VIII.

Process of balance

nerve endings in the ear sense changes in position of the head.

Three parts of the ear

external, middle, inner.

Pinna

funnel-shaped, made of skin and cartilage. narrow down to ear canal.

Ear canal is common for...

ear mites, and infections.

Tympanic membrane

ear drum. separates external ear from middle ear.

Tympanic bulla

middle ear. hollow chamber.

Eustachian tube

connects the pharynx to the middle ear.

Bones of the ear and function

hammer, anvil, stirrup. vibrate when noises heard.

Inner ear found in the...

petrous temporal bone.

Two parts of the inner ear and functions of each

Cochlear (hearing), vestibular (balance).

Cochlea

Snail-shaped, filled with fluid.

Organs of corti

Structures on the cochlea projecting outward, has cilia.

Deafness can be due to...

sound wave conduction problems, inflammation, injury, obstruction or nerve problem.

Equilibrium controlled in...

three semicircular canals oriented in three planes (transverse, horizontal, vertical), that contain fluid with small crystals.

Problems with the three semicircular canals

Vertigo (Dizziness), motion sickness, nystagmus.

Nystagmus

Rapid back-and-forth eye movement.

External layer of eye

Fibrous coat containing the cornea and sclera.

Cornea

Clear, anterior part of eye. Has nerves.

Sclera

White posterior part of eye; dense and opaque. Has blood vessels and nerves. Muscle attach to it.

Limbus

Area where cornea and sclera meet.

Optic nerve

Cranial Nerve II connected to back of eye.

Iris

Pigmented portion of eye. Ring of muscle that opens or closes to control amount of light let in.

Pupil

"Pupillary opening." Opening of the iris. Round in most species, elliptical in cats and snakes.

Lens

Behind iris. Biconvex, transparent, and elastic.

Cataract

Cloudy lens.

Vitreous chamber

Behind the lens, filled with vitreous humor, gelatinous.

Aqueous humor

In front of the lens, watery.

Anterior chamber

In front of iris.

Posterior chamber

Behind iris.

Glaucoma, and use what to measure

Aqueous humor made quicker than it can exit eye. Increased pressure. Use tonometer to measure pressure.

Ciliary body

Muscle that contracts to make lens thinner, and relaxes to make lens thicker.

Accommodation

Bending of light to focus on retina. Distance = thinner, Closer = thicker.

Retina

Used to see, 10 nervous tissue layers thick, picks up light and transmits it to brain down optic nerve, contains pigment.

Tapetum

Reflective part of retina, eye glows.

Optic disc

Where nerves in the retina join. Where optic nerve links eye to brain.

Fundus

Back of the eye where retina and optic nerve can be seen.

Ophthalmoscope

Used to examine eye.

Photoreceptors in eye

Rods and cones.

Rods

Cells very sensitive to light.

Cones

Cells used for detail and color perception.

Palpebra and function

Eyelids. Keep eye from drying out, make lubrication in glands in corner of eye.

Conjunctiva

Mucous membrane lining of eye.

Canthus

Corner of the eye. Medial and lateral.

Nictitating membrane

Third eyelid.

Cherry eye and common in...

Tear in gland attached to third eyelid, sticks out. Common in cocker spaniels.

Lacrimal glands

Tear glands found in dorso-lateral eye.

Function of tears

Wash away debris, lubricate, keep cornea moist.

Nasolacrimal ducts

"Puncta." Two small openings that drain fluid at the medial canthus.

Conjunctivitis

Inflammation/infection of the conjunctiva. Common in animals with URTI.

Ossicles

Bones in the ear.

Malleus

Hammer.

Incus

Anvil.

Stapes

Stirrup.

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