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Lecture 14

BGYB30H3 Lecture 14 Notes Autonomic and Somatic Control-Oct 27

Biological Sciences
Course Code
Ingrid L.Stefanovic

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BGYB30H3 Lecture 14 Notes
-cornea is the area of the eye where light enters, and the pupil can change amount of light
-lens focuses light onto the retina, which contains photoreceptor cells
-fovea has the highest visual acuity
-optic disk (blindspot) is found at the back of the retina and contains no photoreceptors
-zonules and cilary control the shape of the lens
-aqueous humour supports the lens while the vitreous humour controls the shape of the eye
-neural pathways from the eye go to the optic chiasm where it may crossover and synapse in
the lateral geniculate nucleus of the thalamus
-collaterals from thalamus to the midbrain synapse onto cranial nerve III to control pupil
-lens flip image to focus on the retina and changes shape through accommodation
-light rays refract in the fluid of the eye to produce an inverted image on the retina
-distance from centre of the lens to the focal point on the retina is the focal length
-presbyopia is the loss of the ability of the lens to change shape and occurs with aging
-when light is not bent, cilary muscles are relaxed and zonules contract
-when light is bent, cillary muscles contract and zonules relax
-distant objects of 20 meters or more causes the lens to be flat because light rays are parallel
-when object is closer than 20 meters, the lens becomes more convex to converge the image on
the retina
-rounding of the lens shortens focal length
-common visual defects occur because the eyeball is too long or short or the cornea is abnormal
in its curvature
-hyperopia is farsightedness in which the image is behind the retina (convex lens is needed)
-myopia is nearsightedness in which the image is in front of the retina (concave lens is
-ganglion cells converge onto the optic nerve (cranial nerve 2)
-photoreceptors are found at the back of the retina
-light hits the photoreceptors in the fovea directly
-outer segment of photoreceptors contains light sensitive visual pigment
-outer fibre of photoreceptor contains synaptic terminals that release glutamate onto bipolar
-rods are the most numerous and have the visual pigment rhodopsin that functions well in low
-cones are only found in the fovea and detect colour/daylight vision
-rhodopsin contains opsin and retinal
-in response to darkness, opsin and retinal bind to inactivate rhodopsin
-retinal is activated by light
-sodium influxes into the photoreceptor while potassium effluxes out of the photoreceptor in
the absence of light
-sodium influx is greater, causing the resting membrane potential to be depolarized
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