Animal Anatomy

Lei Zhihai

College of Veterinary Medicine, NAU

14 sensory organs

14 sensory organs

Sensory organs include the receptors and their accessory organs. The receptor receive the various stimuli from the external or internal enviroment of the body, and convert it into the nerve impulse. According to the position of the receptors and the origin of the stimulation, the receptors may be divided into three kinds.1 the exteroceptors they lie in the skin, the mucous membrane of the nasal cavity, paranasal sinuses and oral cavity, and the visual and auditory organs. They receive stimuli such as touch, pain, temperature, light and sound from the external environment.

14 sensory organs

2 the enteroceptors they lie in the walls of viscera and blood vessels, and accept the physical and chemical stimuli from the internal environment.3 the proprioceptors they lie in the muscles, tendons, joints, ligaments and the internal ear, and receive stimuli about the movement of the limbs and trunk, and the stimuli about the equilibrium.

14.1 visual organ

Visual organ 视觉器官The visual organ consists of eyeballand accessory organs of the eyeball.The eyeball can receive stimulationof light and transform it into the ner-ve impulse which is conducted throu-gh the visual pathways to the visual center in the brain. The accessory or-gans include the eyelid, conjunctiva, lacrimal apparatus, extraorcular mu-scles, the conective tissue in the orbit and so on.

14.1.1 eyeball

Eyeball 眼球The eyeball lies in the orbit, embeddedin the fat tissue of the orbit, and enclo-sed in a fascial sheath, posteriorly it isconnected with the diencephalon byoptic nerve.The eyeball is spherical in shape, however, the outline of the eyeball is not evenly rounded, but displays a larger curvature in its posterior part than in its anterior part, where the cornea bulges forward.Anterior polePosterior poleOptic axis (external axis)

14.1.1.1 wall of eyeball

Structure of the eyeball 眼球的结构

The eyeball comprises the wall of theeyeball and the contents enclosed.The wall of eyeball consists of threecoats, from outside to inwards, the fibrous tunic 纤维膜 sclera and corneathe vascular tunic 血管膜 choroid, ciliary body and iristhe retina 视网膜 optic part of the retina nonvisual retina

14.1.1.1.1 fibrous tunic

The fibrous tunic 纤维膜 , The fibrous layer of the eyeball is co-mposed of very dense collagenous ti-ssue, which is large responsible forthe shape of the eye. It is composedof two parts: the opaque, whitish sclera, which enclose approximately the posterior three-quarters of the globe, and the transparent cornea, which covers the anterior part of the globe. The two components meet at the corneoscleral junction, also referred to as the corneal limbus 角膜缘 .

14.1.1.1.2 vascular tunic

The vascular tunic 血管膜The vascular layer of the eyeball is in-terposed between the sclera and the retina. It is composed of connective ti-ssue, which contains pigment cells, ela-stic fibers, a nervous plexus and a den-se network of blood vessels. The vascu-lar layer consists of three parts:Choroid 脉络膜Ciliary body 睫状体Ris 虹膜

14.1.1.1.2.1 choroid

Choroid 脉络膜It is a pigmented, highly vascular layer that envelops the posterior part of theeyeball. Dorsal to the optic papillae is a half-moon-shaped area that has an ad-ditional reflective layer, the tapetumLucidum 照膜 . The tapetum lucidum is present in all domestic mammals oth-er than the pig. It aids vision during dawn and night. It has a distinctive colour in the different species and breeds (yellow in the cat, green in the dog, blue-green in the ox and horse) and accounts for the iridescent appearance of an animal’s eye.

14.1.1.1.2.2 ciliary body

Ciliary body 睫状体It is the thicked middle segment of thevascular tunic, between the choroid and the iris. This is an elevated ringfrom which ridges, the ciliary proces-ses, radiate towards the lens in the cen-tre. Zonular fibers extend from the ciliary processes to the equator of the lens to suspend it around its periphery. The ciliary body can be subdivided into the: Ciliary ringCrown of ciliary body: contains ciliary processesCiliary muscle: parasympathetic innervation, contract, focu-ses on near objects; sympathetic innervation, relax, distant ob.

14.1.1.1.2.3 iris

Iris 虹膜It is the most anterior part of the vas-cular layer. It is a thin ring of highlyvascular tissue that rests against the anterior surface of the lens. The freemargin of the iris borders the pupil,through which light enters the posterior part of the eye. The iris separates the space between cornea and lens into anterior and posterior chambers of the eye, which communicate thro-ugh the pupil. It contains two smooth muscles, the sphincter and dilator of the pupil, which regulate the size of the pupil and consequently the amount of light that reaches the retina. The sphincter muscle consists of circular smooth muscle fibe-rs near the pupillary margin of the iris.

14.1.1.1.2.3 iris

The dilator of the pupil is composed of radially arranged mu-scle fibers. The pigmented cells of the iris contain melanin, which protec-ts the retina from intense light. The number and size of the pigments determines the colour of the eye.blue or grey: in pig and goat. paucity of pigmented cells.dark brown: in ox and horse. many pigmented cells.lighter, yellow: in dog, pig, small ruminants. Fewer pigmen-ted cells.red: in albinosThe upper and lower pupillary margins of the iris of rumina-nts and horses show irregular outgrowths that contain coils of capillaries, the granula iridica 虹膜粒 , which can secrete aqueous humour.

14.1.1.1.3 retina

The retina 视网膜The inner layer of the eyeball is theretina. It can be divided into the fol-lowing parts:Non-visual retina (blind part)-ciliary part of the retina and iridial part of the retinaOptica part of the retinaThe optic part of the retina lines the internal surface of the choroid, and extends from the optic disc to the ora serrate which is the demarcation between non-visual and optic parts. In the ventrotemporal quadrant of the retina the optic nerve pierces the retina and forms the optic disc, the form of which ranges from round to oval or triangular. The optic disc is a blind point, since there are no photo-receptor cells here. loca-ted a short distance of dorsotemporal to the optic disc is an area of maximum optic resolution, the macula 黄斑 .

14.1.1.2 contents of eyeball

The contents of the eyeball include theaqueous humor, the lens and vitreousbody. They are all transparent and ava-scular, with the cornea altogether formthe refractive media. Each plays a partin refracting the light entering the eye.Aqueous humor 眼房水 glaucoma 青光眼Lens 晶状体 老花眼、近视、远视、白内障It is a transparent and elastic, biconvex body lacking blood vessels and nerves. It is surrounded by an elastic membrane known as the lens capsule and attached to the inner side of the ciliary processes by the ciliary zonule.Vitreous body 玻璃体 is a colorless, transparent and jelly-like body.

14.1.2 adnexa of the eye

The adnexa of the eye include the fol-Lowing accessory structures:EyelidsLacrimal apparatusExtrinsic muscles of the eyeballOrbital fasciaeOrbit with the orbital fat bodyVessels and nerves

14.2 ear

The ear has three subdivisions:External ear 外耳-auricle-external acoustic meatus-tympanic membraneMiddle ear 中耳-tympanic cavity-auditory ossicles (hammer, anvil and stirrup)-auditory tubeInternal ear 内耳-bony labyrinth-membranous labyrinth

eyeball

ear

Middle and inner ear

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Corti organ