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Anatomy and Physiology of the Ear (Hearing - Mechanoreceptors)
The ear is the organ of hearing and balance. The parts of the ear include: External or outer ear , consisting of: o Pinna or auricle. This is the outside part of the ear. o External auditory canal or tube. This is the tube that connects the outer ear to the inside or middle ear. Tympanic membrane (eardrum). The tympanic membrane divides the external ear from the middle ear. Middle ear (tympanic cavity) , consisting of: o Ossicles. Three small bones that are connected and transmit the sound waves to the inner ear. The bones are called: the hammer (Malleus) the anvil (Incus) the stirrup (Stapes) o Eustachian tube. A canal that links the middle ear with the back of the nose. The eustachian tube helps to equalize the pressure in the middle ear. Equalized pressure is needed for the proper transfer of sound waves. The eustachian tube is lined with mucous, just like the inside of the nose and throat.
Inner ear , consisting of: o Cochlea - the cochlear duct is located in the center of the cochlea. The area above is the vestibular canal and the area below is the tympanic canal. o Vestibule. This contains receptors for balance. o Semicircular canals. This contains receptors for balance. The modiolus is part of the cochlea and is a conical-shaped structure that consists of spongy (porous) bone located in the center of the cochlea and contains the spiral ganglion. The spiral lamina projects from the modiolus. Abnormality of the modiolus results in sensorineural hearing loss .) Cochlea – 3 fluid filled sections: Scala vestibuli Scala tympani Scala media (Cochlear duct)
- Organ of Corti w/ **hair cells stereocilia
- Basilar membrane** separates media and tympani - Tectorial membrane pushes on hair cells when sound waves reach - The hair cell is a mechanoreceptor with an array of stereocilia emerging from its apical surface.) - High pitched sounds disturb short hair fibers close to the oval window - Low pitch sounds affect the longer hair fibers further along the cochlea
Anatomy of the Eye (light - Photoreceptors)
Vertebrate retina contains two photoreceptors (light-sensitive cells). Rods - black and white vision (photopigment – rhodopsin (Vit D)) – allow you to see in dem light or at night Cones - sharpness and color vision- photopigment – photopsins (red, blue, and green cones) – allow you to see detail & distinguish colors Color blindness - inherited lack of one or more types of cones. more common in men due to sex-linkage Night blindness (nyctalopia) is your inability to see well at night or in poor light Binocular vision - ability to perceive three-dimensional images and sense depth. Each eye sees object at a slightly different angle Blind Spot/ Optic disc – no photoreceptors Vestibulo-ocular Reflex - Connections between the vestibular system and the cranial nerves controlling eye movement keep the eyes centered on a visual stimulus, even though the head is moving. During head movement, the eye muscles move the eyes in the opposite direction as the head movement, keeping the visual stimulus centered in the field of view.
ABNORMALITIES
Cornea (no blood supply) The clear front window of the eye which transmits and focuses (i.e., sharpness or clarity) light into the eye. Corrective laser surgery reshapes the cornea, changing the focus. Lens Focuses light rays onto the retina. The lens is transparent, and can be replaced if necessary. Our lens deteriorates as we age, resulting in the need for reading glasses. Intraocular lenses are used to replace lenses clouded by cataracts. Lens attached by suspensory ligament to the ciliary muscles. Iris The colored part of the eye which helps regulate the amount of light entering the eye. When there is bright light, the iris closes the pupil to let in less light. And when there is low light, the iris opens up the pupil to let in more light. Pupil The dark center opening in the middle of the iris. The pupil changes size to adjust for the amount of light available (smaller for bright light and larger for low light). This opening and closing of light into the eye is much like the aperture in most 35 mm cameras which lets in more or less light depending upon the conditions. Retina The nerve layer lining the back of the eye. The retina senses light and creates electrical impulses that are sent through the optic nerve to the brain. Optic Nerve A bundle of more than a million nerve fibers carrying visual messages from the retina to the brain. (In order to see, we must have light and our eyes must be connected to the brain.) Your brain actually controls what you see, since it combines images. The retina sees images upside down but the brain turns images right side up. This reversal of the images that we see is much like a mirror in a camera.
