Exam 4 Review: Chapter 15: Accessory Structures of the Eye
accessory structures of the eye - The external protective appendages and supplementary components of the eye, external to the eyeball, which contribute indirectly to vision and image formation; they include the eyebrows, the eyelids and eyelashes, the conjunctiva, the lacrimal apparatus and the extrinsic eye muscles.
conjunctiva - The thin, protective, moist mucous membrane lining and lubricating the eyelids and covering the anterior surface of the eye itself, i.e., lining the conjunctival sac.
lacrimal apparatus - Those accessory structures of the eye which function in the production of tears including the lacrimal glands which synthesize the tears, and the drainage system for the tears, beginning with the openings, lacrimal puncta, to the lacrimal ducts, and the lacrimal sacs and nasolacrimal ducts; the tears moisten and lubricate the conjunctiva and contain protective compounds to inhibit microbes.
lacrimal gland - An acinous exocrine gland about the size and shape of an almond which secretes tears, and is situated laterally and superiorly to the bulb of the eye in a shallow depression on the inner surface of the orbit of the frontal bone; it is regulated by visceral motor commands from the Autonomic Nervous System. aka tear gland.
nasolacrimal duct - The major drainage tube (~1 cm) for tears from the nasolacrimal sac into the nasal cavity where the tears mix with nasal mucous secretions and are evaporated.
extrinsic eye muscles - The six skeletal muscles (four rectus (inferior, medial, superior, and lateral) and two oblique (superior and inferior) which originate on the bones of the orbit and insert into the sclera of the eye and move each eyeball; they are comprised of many small motor units and are, therefore, capable of very precise control of eyeball movement; they are regulated by the somatic motor commands from the frontal eye fields of the frontal lobes of the cerebrum.
intrinsic eye muscles - A set of smooth muscles within the eyeball: (1) The ciliary (smooth) muscle which inserts via the suspensory ligaments on to the periphery of the lens capsule; its state of contraction regulates the shape of the lens; (2) the circular smooth muscle of the iris which constricts the pupil when it contracts; (3) the radial muscle of the iris which dilates the pupil when it contracts; they are controlled by visceral motor commands from the Autonomic Nervous System.
An interesting footnote: The eyebrows "help shade the eyes from sunlight . . ." is the assertion of your textbook (8th ed.) on p. 548. I don't believe that claim myself (Dr. T.) Do you?
Maybe someday, some smart human being will invent a device to help shade the eyes from sunlight. I think it would be a big seller. Do you?