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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.