Sensory organs

Eyes –

organ of sight consisting of the eyeball and its accessory structures, contained within an orbit that is only partly boney,

extraocular muscles

associated with the ball of the eye, it can move them

periorbital fat

surrounds the eye and helps in cushioning the eye

eyelids and conjunctivae

the one that protects the eyeball

lacrimal apparatus

keeps its surface moist and provides the first barrier to infection and helps to nourish the cornea

upper and lower eyelids

two movable folds protecting the rostral surface of the eyeball

tarsus

fibrous plate supporting the margin of the eyelid and it contains the tarsal gland or the bibomian gland

eyelashes (cilia)

triangular prominence in the medial angle

lateral and medial commissures or canthi

the point where the eyelids meet

lacrimal caruncle

triangular prominence in the medial angle of the eye

lacrimal puncta

it is the openings into the lacrimal canal on upper and lower eyelids near the medial angle

conjunctiva

special mucous membrane lining the eyelid and the eyeball, farther divided into two, palpebral and bulbar

palpebral conjunctiva

lines the inner surface of the eyelid

bulbar conjunctiva

the reflection of the palpebral conjunctiva of the eyeball

nictitating membrane

it is known as the third eyelid; it is a fold of conjunctiva located between the eyelids medial angle and eyeball so that nictitating

Fibrous tunic of the eye

outer coat of the eyeball and it is divided into a sclera, cornea and limbus

Sclera

the caudal part of the fibrous coat consisting of fibrous tissues, gives shape and protects the inner structures of the eye

Cornea

the transparent anterior coat of the fibrous coat that lets light into the eyeball

Limbus

it is a junction between the cornea and the sclera

Vascular tunic of the eye

the middle layer of the eyeball, composed of ciliary bodies, choroid and the iris, made out of mainly blood vessels and smooth muscles that supply the nutrition to the eyeball

Iris

it is the colored part of the eye surrounding the pupil and it has two muscle layers, the pupillary sphincter, pupillary dilator

Pupillary sphincter

as circular smooth muscle constricting the pupil

Pupillary dilator

which is a radiating smooth muscle dilating the pupil

Pupil

it is the central opening of the iris that lets light into the eye

Choroid

posterior part of the vascular tunic it is thin, dark, highly vascular membrane inside the sclera

Ciliary body

it is the thickest portion of the vascular tunic between the choroid and the iris and it consists of the ciliary process and muscles

Ciliary muscles

smooth muscles that alter the shape of the lens to accommodate light going in the eye

Ciliary process

are folds on the inner surface of the ciliary body that anchors the zonular fibers

Zonular fibers

are suspensory ligaments that holds the lens in position

Tapetum lucidum

a specialized refractive area at the choroid and when the light enters it is reflected by it

Nervous tunic of the eye

inner most layer of the eyeball and is composed of the retina

Retina

is the inner coat of the eye that functions in image formation, it contains three layers, the photoreceptors, bipolar neuron, and the ganglion neuron

Photoreceptors

light sensitive and the first layer of the retina, it is further divided into two layers, the rods and the cones

Rods

are dendrites that are sensitive to dim lights or night vision

Cones

are dendrites that are sensitive to color and sharpness of vision

Bipolar neuron

the intermediate layer of the retina which receives impulse from the rods and cons and passes them to the neuronal ganglia

Ganglion neuron

the inner layer of the retina which passes the impulse to the optic nerve

Optic discs

the area on the retina where the axons from the ganglion neuron leaves the eye as the optic nerve having no rods or cons and is a blind spot

Lens of the eye

transparent, biconvex body of the eye that is suspended behind the iris and the zonular fibers

Anterior chamber

space between the cornea and the iris

Posterior chamber

a space between the iris and the lens

Vitreous chamber

the largest space between the lens and the retina and it is filled with the vitreous humor

humors of the eye

fluid or semi fluid substance in the eyes

Aqueous humor

it is a watery fluid similar to the cerebrospinal fluid filling the posterior and the anterior chamber, it is secreted by the ciliary process in the posterior chamber and it flows to the anterior chamber via pupil, it maintains the intraocular pressure and it serves as a medium for nutrient and waste transport

Vitreous humor

is more of a jelly-like substance that fills the vitreous chamber, it maintains the shape of the eye and holds the retina in place

Ears – organ of hearing and balance

divided into three portions, outer ear, middle ear, inner ear

External/outer ear

composed of the pina and the external auditory meatus

Pinna or auricle

the fleshy appendage attach to the side of the skull by muscles and ligaments, this functions to catch and direct sound waves towards the middle ear or the ear drum

Auricular cartilage

the elastic framework of the pinna and external auditory meatus and it is covered by the skin

External auditory meatus

is a passageway from the pinna to the eardrum or the middle ear, it has various structures, anthelix, scapha, helix, cutaneous marginal sac, tragus, antitragus, intertragic incisures

Anthelix

it is a transverse fold of cartilage on the concave surface of the pinna

Scapha

a large flat concave internal side of the auricle

Helix

the entire free margin of the auricle and passing over the apex

Cutaneous marginal sac

it is a fold of skin at the proximal lateral portion of the helix

Tragus

a thick blunt irregular quadrangular plate of cartilage that projects from the rostral border of the entrance to the external auditory meatus

Antitragus

a thin elongate projection of cartilage lateral to the tragus

Intertragic incisures

a notch separating the tragus and the anti-tragus

Middle ear

part of the ear inside the tympanic cavity containing the auditory ossicles and opening to the auditory tube

Tympanic membrane or eardrum

a thin semi-transparent partition between the external auditory meatus and the middle auditory meatus, it is vibrated by the sound waves

Auditory ossicles

made up of three bones (malleus, incus, stapes) extending across the middle ear from the eardrum to the oval window of the cochlea, they transmit and amplify vibrations from the eardrum

Malleus

known as the hammer bone, it is a small bone connecting the inner surface of the tympanic membrane

Incus

also known as the anvil, it is an ossicle between the malleus and the stapes

Stapes

known as the stirrup, it is the smallest bone of the body and its base fits into the oval window of the cochlea

Oval window (vestibular window)

one of the two openings between the middle ear and the inner ear and are filled with the base of the stapes

Round window (cochlear window)

is located below the oval window

Eustachian tube (auditory)

it is a passageway between the middle ear and the nasopharynx and it equalizes the pressure on both sides of the eardrum thus protecting it from rupture

Inner ear

consists of bony and membranous labyrinth which lies within the petrous temporal bone and is divided into three areas, the bony cochlea, bony vestibule and the boney semicircular canal each of which contains a corresponding part of the membranous labyrinth

Perilymph

is a fluid within the bony labyrinth surrounding the membranous labyrinth

Endolymph

is a fluid within the membranous labyrinth

Cochlea

it is a small snail shape like part of the inner ear associated with hearing, it has two channels, the scala vestibuli and scala tympani

Scala vestibuli

is a canal of bony labyrinth communicating with the vestibule middle ear of the oval window

Scala tympani

is the continuation of the scala vestibuli from the apex of the cochlea to the round window

Vestibule

the central expanded portion of the inner canal and it consists of two sacs, the saccule and the utricle, both this structure contains areas of sensory hair cells known as macula and is surrounded by jelly-like material containing calcium carbonate, function is to maintain balance when the animal is standing still

Semicircular canal

three bony canals arising from the vestibule arrange approximately at right angles at each other, anterior, posterior, and lateral

Ampulla

an enlarged swelling at the end of each semicircular canal