Sight By Jess Kapp
Vision is the most dominant sense, about 70% of all sensory receptors in the body are in the eyes Accessory Structures of the eye : Eyelashes : Protect eye from debris and bacteria Eyebrows : Shade eyes from sunlight, protect from perspiration Eyelids : Anteriorly protect the eye, called mobile eyelids or palpebrae Separated by palpebral fissure or eyelid slit Contains the medial and lateral commissures(canthi), which are the corners of the eyes
Tarsal glands: produce an oily secretion that lubricates the eye Conjunctiva : Covers part of the exposed surface of the eyeball, fuses to the cornea via corneal epithelium Lacrimal apparatus and glands : Drain secretions into the nasal cavity and produce a saline solution to coat the eye Extrinsic eye muscles : There are 6 extrinsic (external) eye muscles which make it possible for the eye to follow an object
Internal structures of the eye Fibrous layer : outer layer, protective sclera (white connective tissue) and clear cornea Vascular layer:
Internal structures cont d Sensory layer : Contains the sensitive two layer retina, which extends only to the ciliary body Neural layer :
Internal structures cont d Optic disc : Photoreceptor cells are distributed throughout the entire retina besides where the optic nerve leave the eyeball, called the optic disc or blind spot
Physiology of sense - Light, the stimulus for sight, is refracted to the retina where photoreceptors called rods and cones pick up the message - In rods, the chemical rhodopsin breaks down to form scotopsin and retinal - Rhodopsin is regenerated in a slower chemical reaction - In cones, chemical reactions happen from different wavelengths of light. The types of cones are believed to be : - Red, blue, and green absorbing
- Impulses from the rods and cones are transmitted to bipolar cells, to amacrine cells, then to ganglion cells, which converge at the optic disc to become the optic nerve - Optic nerves from both sides converge at the optic chiasm, just in front of the pituitary gland
- At the optic chiasm medial fibers of the optic nerve cross to the other side - Visual areas are located in the occipital lobe and cerebral cortex of the brain
- Images appear on the retina upside down but the pathway vision takes through the brain rights the image, allowing us to see the way we do - Each eye transmits a slightly different image, but visual areas put them together to create binocular vision
- The main cranial nerve involved in sight is the optic nerve, which is the sensory nerve for vision and transmits signals to the brain - The other three cranial nerves involved are : oculomotor, trochlear, and the abducens
Homeostatic imbalance #1: Pink eye (conjunctivitus) - Pink eye is the inflammation of the conjunctiva, which is a thin clear membrane that line the eye and inside of the eyelid - Many things cause pink eye including: - Viruses, Bacteria, irritants and allergies - Spreads easily from person to person but is not serious if treated in a timely manner - If caused by bacteria, antibiotics will treat it, but if it is caused by a virus it must run its course
Homeostatic imbalance #2 : Cataracts - Cataracts are cloudy areas in the lens of the eye which cause changes in vision - Symptoms include blurred vision and sensitivity to glare - Can cause blindness - Treated with surgery
Activity!!! - Blind spot detection - You will be able to detect your blind spot which is the area where the optic disc allows the optic nerve to pass through, making a hole in the retina where information is not sent to the visual cortex of the brain
Work cited https://www.webmd.com/eye-health/cataracts/default.htm http://innvista.com/health/anatomy/physiology-of-vision/ https://nurseslabs.com/special-senses-anatomy-physiology/ https://www.hydroassoc.org/what-are-the-cranial-nerves/ https://www.sciencedirect.com/topics/medicine-and-dentistry/visual-pathway