welcome to our module on special senses special senses in anatomy are the senses that have specialized organs devoted to them that includes the vision hearing imbalance olfaction or smell and the sense of taste in the previous modules we already discussed the anatomy of the tongue and the nose and in this particular module we will discuss in detail the anatomy of the eye and the ears this module is divided into two parts the first part is for the eye anatomy and the second part is for the ear anatomy specifically at the end of this module you should be able to identify the structures that are associated with the iadnexa identify the parts of the ietonix identify the boundaries of the eye chambers and identify the specific parts of the outer middle and inner ear the eye is the organ of sight and consists of eyeball and its successory structures they are contained within the orbit with the extraocular muscles that control its movement and surrounded by periorbital fascia and fat for caution purposes the extraocular muscles were already discussed in the module on muscular system the nexa by definition are the attachment or appendages which are involved in protecting or supporting the function of an organ the eye adnexa includes the eyelid the conjunctiva lacrimal paratus and the orbital soft tissue the eyelids and the conjunctiva protect the eye while the lacrimal paratus keeps the surface of the eye moist and provides the first barrier to infection and helps to nourish the cornea the eyelids are a thin layer of skin that covers the eyes the eyelids are also termed as palpibra normally there are two eyelids the upper and the lower eyelids however in dogs there is a third eyelid which is called the nictitating membrane which is usually hidden with only a small portion normally visible in this picture take a look at the third eyelid the tarsus is the fibrous plate supporting the margin of the eyelid it contains the tarsal or the meibomian gland that produces oily substance that prevents evaporation of the eye steer film the conjunctiva is a special mucous membrane lining the eyelid and the eyeball as you can see here is the location of the conjunctiva there are two conjunctiva the palpibral conjunctiva and the bulbar conjunctiva for easier visualization here is a schematic illustration of the eye showing the two types of conjunctiva palpebral concentra lines the inner surface of the eyelid while the bulbar conjunctiva is the reflection of the palpebral conjunctiva into the eyeball let us also identify the canthus the cantus is the point where the eyelids meet there are two kantai the medial cantus and the lateral canthus for orientation purposes let us assume that this is the area of the nose or the medial side and this is the area of the ear or the lateral side by the name itself the medial canthus is the point where the eyelids meet at the medial side while the lateral canthus is the point where the eyelids meet on the lateral side the lacrimal apparatus consists of the lacrimal glands which secrete the tears and the lacrimal suck and duck which convey the tears into the nasal cavity the lacrimal karankal is a triangular prominence in the medial canthus the lacrimal pungta are the openings into the lacrimal canals on the upper and lower eyelids near the medial canthus the eye is composed of three layers of tunics these include the outer fibrous layer the middle vascular layer and the inner nervous tonic let us begin with the fibrous tonic this is the outer coat of the eyeball and is divided into sclera and cornea the sclera is the white part of the eye it is the caudal part of the fibrous coat consisting of fibrous tissue it gives shape and protects the inner structure of the eye the cornea on the other hand is the transparent anterior coat of the fibrous coat that lets light into the eyeball the junction between the sclera and the cornea is called limbus the vascular tonic is the middle layer of the eyeball and is composed of the choroid the ciliary body and the iris they are composed mainly of blood vessels and smooth muscles that supply nutrients to the eyeball the choroid is the posterior part of the vascular tunic it is thin dark highly vascular membrane inside the sclera the tapetum lucidum is a specialized refractive area of the choroid and the reason for the glowing of the eyes when shine with light the ciliary body is the thickest portion of the vascular tonic between the choroid and the iris this consists of ciliary muscle and ciliary processes here are the ciliary muscles and the processes the ciliary muscles are smooth muscles that alter the shape of the lens in the process called accommodation while the ciliary processes are folds on the inner surface of the ciliary body that encore the zonular fibers the cellular fibers are the suspensory ligaments that hold the lens in position also part of the vascular tonic is the iris this is the colored part of the eye surrounding the pupil the iris acts like a shutter of a camera it has two muscle layers the pupillary constrictor which is a circular smooth muscle constricting the pupil and the pupillary dilator which is radiating smooth muscle dilating the pupil the pupil is the central opening of the iris that lets light into the eye the last innermost layer is the nervous tonic which is composed of the retina the retina is the inner coat of the eye that function in image formation it contains three layers of neurons which we will discuss in the next slide as mentioned the retina is composed of three layers from outer to inner the photoreceptors the bipolar neuron and the ganglion neurons the photoreceptor is the light sensitive in the first layer of the retina this basically composed of rods and cones rods are the ones sensitive to the dim light and shape while the cones are sensitive to the color and sharpness of vision bipolar neurons are intermediate layer of the retina which receives impulse from rods and cones and passes them to the neuronal ganglia ganglion neuron is the inner layer of the retina which pass the impulse to the optic nerve remember that the optic nerve is the second cranial nerve and will deliver the information to the brain interestingly every animal has a blind spot there is no image detection in this area this is because of the presence of the optic disc the optic disc is the area on the retina where the axons from the ganglion neuron leave the eye as the optic nerve having no rods or cones this is the blind spot not part of the tunics but important part of the eye is the lens the lens is the transparent by convex body of the eye suspended behind the iris and the cellular fibers the main optical function of the lens is to transmit light focusing it on the retina by changing its shape the lens change the focal distance of the eye the changes in the lens shape is made possible by the ciliary body the eyeball can also be divided into chambers since we are now familiar with the basic parts of the eye we can use them to locate and identify the boundaries of the different eye chambers the anterior chamber is located between the iris and the cornea the posterior chamber is located between the ivis ciliary body and the lens and the vitreous chamber is located behind the lens surrounded by the retina these chambers are filled with fluid the chambers in front of the lens which includes both the anterior and the posterior chambers are filled with a clear watery fluid called aqueous humor the large space behind the lens which is the vitreous chamber contains a thick gel like fluid called the vitreous humor or the vitreous gel these two fluids press against the inside of the eyeball and help the eyeball keep its shape and that ends our discussion on the first part of this module which is the anatomy of the eye as a recall we were able to tackle the eye at nexa the different tonics of the eye as well as the different chambers present in the eye you may now proceed to the next part of this module which is the anatomy of the ear