BIOL2010
Human Anatomy & Physiology

The Special Senses

Eye and Associated Structures Information

• 70% of all sensory receptors are in the eye
• Most of the eye is protected by a cushion of fat and the bony orbit
• Accessory structures include eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic eye muscles
• Lubricating glands associated with the eyelids
• Meibomian glands and sebaceous glands
• Ciliary glands lie between the hair follicles
• Conjunctiva transparent membrane that:
• Lines the eyelids as the palpebral conjunctiva
• Covers the whites of the eyes as the ocular conjunctiva
• Lubricates and protects the eye

Eye and Associated Structures Self-Check

Palpebrae (Eyelids) Information

An eyelid is a thin fold of skin that covers and protects the eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily. The human eyelid features a row of eyelashes which serve to heighten the protection of the eye from dust and foreign debris, as well as from perspiration. "Palpebral" (and "blepharo") means relating to the eyelids. Its key function is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. They keep the eyes from drying out when asleep. Moreover, the blink reflex protects the eye from foreign bodies.

Palpebrae (Eyelids) Identification

Lacrimal Apparatus

The lacrimal apparatus is the physiologic system containing the orbital structures for tear production and drainage. It consists of:

(a) the lacrimal gland, which secretes the tears, and its excretory ducts, which convey the fluid to the surface of the eye;

(b) the lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct, by which the fluid is conveyed into the cavity of the nose, emptying anterioinferiorly to the inferior nasal conchae at the nasolacrimal duct.

(c) the nerve supply of lacrimal apparatus done by carotid plexuse of nerves along artery internal and external sympathetically but parasympathetic from lacrimal nucleus of the facial nerve

Lacrimal Apparatus Identification