Vision By. Leanora Thompson, Karen Vega, and Abby Brainerd
Anatomy Outermost part of the eye is the Sclera. Cornea transparent part of outer layer Two cavities by the lens. Anterior cavity = Aqueous humor (watery) Iris changes the size of the pupil Opening of the eye is the pupil. Posterior cavity = Vitreous body (gel-like)
Anatomy cont. Lens Bulging - Nearby objects Flatten - Far objects Ciliary body connect iris to choroid, Ciliary muscle change the shape of the lens Choroid brings oxygen and nutrients into the eye
Light wavelengths Frequency of light wave determines its hue Short wavelengths at high frequency = Blue colors Long low frequency = Reddish Amplitude = amount of brightness Lower amplitude = Dull light Higher amplitude = Bright light
Anatomy cont. The layer at the back of the eyeball containing light sensitive cells is the Retina. The retina contains the bipolar, ganglion cells, and the Optic disc. Rods are Sensitive to light, and not color, while cones provide color vision and need bright light. The rods help us see in dim lighting with black and white colors mostly for peripheral vision. The cones come in three different colors: red, green, and blue. Fovea part of the retina that contains majority of cones
Physiology Eye responds to stimulus of light, and photoreceptor, or rods and cones respond to stimulus. Before light is focused by the lens, it needs to be refracted. This happens when light pases from air to cornea. As light refracts the Iris changes size to regulate the amount of light entering the pupil. The lens then further refracts light from the aqueous humor to a deeper lens. The lens provides extra refraction needed to focus light rays from an object toward a focal point, which is a point of intersection on the retina. The pigmented layer of the retina absorbs light, and provides vitamin A and nutrients to the neural layer which holds the photoreceptors responsible for processing the light signals.
Physiology con t Dark Disc in photoreceptors have sodium channels that are always open Photoreceptors always are depolarizing Neurotransmitters are sent to the bipolar cell which inhibits the bipolar cell to send a message to the ganglion cells. Light LIght acts as the stimulus Triggering the Na+ channels to close Hyperpolarization of the photoreceptors occur Photoreceptors stop sending the inhibitory neurotransmitters to the bipolar cell Bipolar cell creates a depolarizing graded potential to the end of the axon in order to send the message to the ganglion cells. Bipolar cells then release different neurotransmitters to the ganglion cells. Allowing a action potential to be formed. Action potential travels down the axon of the ganglion cell forming an optic nerve
Physiology-Visual pathways The axons of ganglion cells form the optic nerve. At the optic chiasm, where the two optic nerves cross the fibers continue via the optic tracts. Each optic nerve carries all the information from the same half of the visual fields. The optic tracts run posteriorly around the hypothalamus, which sends most of their axons to synapse with neurons in the lateral geniculate body of the thalamus which processes the retinal input for delivery to the visual cortex. The axons of the thalamic neurons project through the cerebral white matter, which projects to the primary visual cortex, which then send it to the visual association cortex. Nerve fibers in the optic tract send branches to the midbrain which helps with reflexes.
Color Blindness the inability to see red, green, blue, or any mix of these colors. Cones are responsible for detecting color; there are three different types of cone cells, each sensing either red, blue, or green light Color blindness happens when one or more groups of cones are missing or aren't working properly Most common is red-green color blindness Gene that is responsible for it is carried on the X chromosomewhy men are more affected
Glaucoma Happens when aqueous humor builds in the front part of your eye because it doesn't circulate the way it should This results in extra pressure caused by extra fluid to cause damage to the optic nerve Condition is most commonly inherited No symptoms, other then slow vision loss, first sign is loss of peripheral vision Without treatment glaucoma can cause total permanent blindness in a few years
Blind Spot 1. 2. 3. 4. 5. 6. Hold paper close to your face Close your right eye Stare at the X Make sure you can see the circle in your peripheral vision Slowley move paper away from your face Circle should disappear at some point
Cited sources Martini, Frederic, et al. Fundamentals of Anatomy & Physiology. 7th ed., Pearson Education, Inc., 2018. Marieb, Elaine Nicpon, and Katja Hoehn. Human Anatomy & Physiology. 7th ed., Pearson Education, Inc., 2019. Baines, Francesca. Senses: How We Connect with the World. London, 2001.