Fayrooz Abdelkader Sense Organs Anatomy of the Ear 1. The Outer Ear (hearing) - composed of the pinna/auricle and the external acoustic meatus - pinna or auricle: a shell shaped structure surrounding the auditory canal opening. - external acoustic meatus: short narrow chamber (1in long x ¼ in wide) carved into temporal bone, lined w skin bearing hairs, sebaceous glands, and modified apocrine sweat glands (ceruminous glands) that produce a waxy yellow substance called cerumen. Sound waves hit eardrum/tympanic membrane and causes it to vibrate. The tympanic membrane separates the middle ear and outer ear. 2. The Middle Ear (hearing) - small, air filled cavity within the temporal bone, ear drum is its lateral wall, has two openings: oval window and inferiorly, round window (membrane covered). Pharyngotympanic tube runs down obliquely to link middle ear to nasopharynx. Tympanic cavity is spanned by 3 smallest bones in the body (ossicles) which transmit vibratory motion of the eardrum. Connected together by synovial joints. Bones are named hammer (malleus), anvil (incus), and the stirrup (stapes). - pharyngotympanic tube (auditory tube) links middle ear cavity to the throat, mucosae lining the two regions are continuous. It is normally closed, but when swallowing and yawning it can open briefly to equalize pressure in the middle ear cavity. *important bc eardrums can’t vibrate freely unless the pressure on both sides is equalized. When the hammer moves, it transfers vibration to the anvil, which then passes it in to the stirrup, which presses on the oval window of the ear. The oval window’s movement sets the fluids of the inner ear into motion, eventually exciting hearing receptors. 3. The Inner Ear (hearing & equilibrium)- maze of bony chambers (cavities) located deep within the temporal bone, just behind the eye socket. Has two main divisions: bony labyrinth & membranous labyrinth - bony labyrinth: has three subdivisions: cochlea, vestibule, semicircular canals cochlea: connected to the middle ear by the oval window, involved w hearing, its a tube 3.5 cm long that’s coiled like a snail shell and filled w potassium ion rich endolymph. Contains organ of Corti (structure that contains 1000s of specialized sensory hair cells w cilia). Contains 3 scalae/chambers : scala vestibuli (continuous w vestibule), scala media (cochlear duct and contains endolymph), scala tympani (terminated @ round window & contains perilymph). Bc the liquids are incompressive, pressure is relieved by the round window by its moving in the opposite direction vestibule: central cavity between the semicircular canals & the cochlea along w the 3 semicircular canals are responsible for maintenance of the body’s balance. semicircular canals: there are 3 semicircular canals each oriented in one of the 3 planes of space. Semicircular canals also contain fluid and hair cells, but the hair cells are responsible for detecting movement. When you move your head, fluid within the semi-c. canals also moves, fluid motion is detected by the hair cells, which send nerve impulses abt your head and body position to your brain to allow you to maintain your balance Anatomy of the Eye 1. Fibrous Tunic (outermost) - divided into two regions: sclera and cornea - sclera: protective, thick, white avascular, the white of the eye, is continuous w dura matter where the cranial nerve connects - cornea: anterior central portion, modified to be crystal clear, a window for light that enters the eye, curved & spherical, can be transplanted w no worries of rejection *contacts sit on top of cornea to modify its curvature* Fayrooz Abdelkader 2. Vascular Tunic (uvea) (middle) - divided into three regions: choroid, ciliary body and iris - choroid: most posterior, has rich blood vessel supply (providing nutrition), contains dark pigment to prevent light from scattering in the eye - ciliary body: choroid is modified anteriorly to form 2 smooth muscles, attached to the lends by suspensory ligaments (ciliary zonules) - iris: pigmented iris is the most anterior portion of the uvea, has rounded opening (pupil), which is where light passes, regulates the amount of light entering the eye so people can see as clearly as possible 3. Retina (innermost) - divided into two layers: outer (pigmented) and inner (neural) - outer pigmented layer: single-cell-thick lining that covers the choroid & extends anteriorly to cover the ciliary body and posterior face of the iris, pigmented cells absorb light and keep it from scattering in the eye. They also act as phagocytes and remove dead/damaged photoreceptor cells & store vitamin A - inner neural layer: extends into the posterior margin of the ciliary body, the junction is called ora serrata (saw-toothed), however, only the neural layer plays a direct role in vision Rods and Cones - photoreceptor cells that respond to light, are not evenly distributed in the retina, have light-sensitive pigments derived from vitamin A rods: have deep purple pigment called rhodopsin which detects light & dark, most dense at periphery of the retina, decrease in number when nearing the center of the retina. They allow us to see grey tones in dim light and provide peripheral vision, but do not provide sharp vision. cones: operate on bright light and provide sharp colored vision, three types: responsive to blue light, green light, and the last responds to a variety of light wavelengths including red and green (called red cones bc they are the only ones that respond to red light) macula - bullseye of retina, contains a high concentration of cones, allows us to see fine details fovea - the very center of the macula, site of our sharpest vision blind spot (optic disc) - where the optic nerve leaves the eyeball. There are no rods/cones in this area so light focused on the optic disc can’t be seen Lens - a flexible, biconvex crystal-like structure that focuses the light on the retina by changing shape to allow clear vision for distance & reading. It’s held by a suspensory ligament, the ciliary zonule and is attached to the ciliary body. It’s avascular, made up of simple cuboidal epithelium, collagen fibers, GAGs (glycosaminoglycans), and crystallin proteins. It divides the eye into two chambers/segments: anterior aqueous and posterior vitreous aqueous segment: anterior to lens, contains a clear watery fluid called aqueous humor, which is similar to blood plasma (drains continually and is in constant motion), secreted by a special section of the choroid, supplies nutrients & oxygen to lens, cornea and to some retina cells. It’s reabsorbed into venous blood via scleral venous sinus at a steady rate of 16 mm Hg, supporting the eyeball internally vitreous segment: posterior to lens, filled w clear gel-like substance called the vitreous humor, forms in the embryo and lasts for a lifetime, is stagnant. It transmits light and helps prevent the eyeball from collapsing inward by reinforcing it internally Fayrooz Abdelkader Glands of the Eye Tarsal glands – modified sebaceous glands, edges of eyelids, secretes oily lubrication Ciliary glands – modified sweat glands, between eyelashes Chemical receptors respond to different types of chemicals; an example is taste receptors: sweet receptors (sugars, saccharine), sour receptors (acidity), bitter receptors (alkaloids), salty receptors (metal ions), umami (beef taste in steak and additive)
