Special SensesWeek 12Dr. Walid DaoudA. Professor

Physiological Anatomy of the EyeI- Layers of the eye: . Outer fibrous layer (protective): Cornea, sclera and conjunctiva. . Middle vascular layer (nutritive): Iris, ciliary body and choroid. . Inner nervous layer ( light perception) Retina, optic disc and nerve.

Physiological Anatomy of the EyeII- Ocular chambers:1- Aqueous chamber: Anterior to the lens.2- Vitreous chamber: Behind the lens.

The CorneaTransparent anterior 1/6 of outer layer of eye wall. Sensitive to pain, touch, temperature.Protection of the cornea:1- Lids and lid reflex (blinking).2- Corneal reflex.3- Tears contain lysozymes (antibacterial).Nutrition and metabolism:Cornea is avascular and obtain O2 & glucose by diffusion from capillaries.

Functions of the cornea1- Refractive power of the eye.2- Transparency allows passage of light.3- Regular curvature forms sharp and clear retinal image.4- Eye protection: . Hardness. . Corneal reflex.

Causes of corneal transparencyI-Anatomical:- Regular arrangement of epithelial cells.- Regular arrangement of collagen lamellae.- Absence of bl. vessels & myelinated n. fibers II-Physical:-Relative corneal dehydration: Osmotic and metabolic pumps-Refractive index of collagen fibers is nearly the same

Factors maintaining corneal transparency1- Vitamin A.

2- Vitamin B12 (riboflavin).

3- Moistening of corneal surface by tear flow.

Intraocular fluidI- Aqueous humour: Function: - Refractive medium of the eye. - Nutrition and O2 supply of avascular cornea and lens. - Maintain intraocular pressure to keep shape of eye ball.

Intraocular fluidII- Vitreous humour: Functions: - Refractive medium of the eye. - Supports retina and maintain globular shape of eye ball. - Prevents backward displacement of the retina.

Uveal Tract1- Functions of iris: - Regulate amount of light entering eyes. - Increasing depth of focus by constriction. - Limits passage of light to central parts of lens forming clear image on the retina. - Diagnosis of disease affecting reflexes of pupil.

Uveal Tract2- Functions of Ciliary body: - Ciliary muscle: Diopteric power of lens. Accomodation on near vision. - Ciliary processes: Secrete aqueous humour.

Uveal Tract3- Functions of Choroid: - Gives nutrition to retina, ciliary body & iris. - Supports the retina. - Gives attachment to ciliary muscle. - Plays role in accommodation. - Choroid pigments prvent reflection of light from inside the eye.

1- Coditions associated with pupillary dilatation (Mydriasis)2- Coditions associated with pupillary constriction (Miosis)

Crystalline lensFunctions:1- Enables eye to see near objects.2- Refractive media of the eye.3- Protects retina from harmful effects of UV rays which is absorbed by lens & cornea.

Errors of Refraction1- Myopia (short-sight).2- Hypermetropia (far-sight).3- Presbyopia (old-sight).4- Astigmatism.

RetinaPhotoreceptors:1- Cones: for bright (day) vision.2- Rods: for dim (night) vision.Functions:1- Vision.2- Light and accomodation reflexes.3- Maintain tone, posture and equilibrium.Image formed in the retina is inverted but cerebral cortex interpret it in upright position.

Protective mechanisms of the eye1-Lacrimal apparatus: Functions of tears: -Keep cornea & conjunctiva moist & clear. -Bacteriolytic action by lysozyme.2- Eye lids: Function: -Regulation of light entering the eye. -Protection from excessive illumination or FB -Distribution and conduction of tears.3-Corneal reflex.

HearingPhysiological anatomy:1- External ear.2- Middle ear: bony ossicles & muscles3- Inner ear: cochlea and vestibular appartus.Mechanism of hearing.

TasteChemoreceptors stimulated by chemical substances:Taste buds: 3 types of cells:1- Taste (gastratory) cell.2- Supporting cell.3- Transitional cell.

Types of taste sensation1- Sweet taste.2- Salty taste.3- Bitter taste.4- Sour taste.

Factors affecting taste sensation1- Concentration of tasted substance.2- Contrast.3- Surface area stimulated.4- Temperature.5- Olfaction.6- Adaptation.7- Individual variation.

SmellOlfactory reception cell.Olfactory epithelium:1- Basal cell.2- Supporting cell.3- Bowman,s gland.4- Receptors.Abnormalities of olfactory sensation:1- Anosmia.2- Hyperosmia.