Module 1 The Nervous System

Reflect and Connect (optional)

Most people are left-brain dominant but some are are right-brain dominant. The dominance of one side of your brain over the other affects how you perceive what you see. Your brain is crucial in the integration, interpretation, and perception of what you see. Two people looking at the same thing may see it very differently!

 

Choose one of the following written response questions. Reflect upon the question and then respond in paragraph format. Store your response in your course folder for future reference:

Look at a picture, clock, or some distinctive object located on the other side of the room. Cover or close one eye. Concentrate on that object for a few moments. Now, cover or close the other eye. What happens to the image when you switch from viewing it first with one eye, then with the other? What does this simple experiment illustrate about vision?
 
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The actual visual sensation which we experience is not always an exact representation of the visual information that is picked up by our eyes. This is because the brain is susceptible to all sorts of past and present influences that modify our perception. Visual information modified by the brain image so that we see the image that our brain is conditioned to see. Do an Internet search using the term "old woman young woman perception." Your search engine will display a number of illustrations. Follow a link to an illustration that plays on perception. Look at the illustration. What do you see? It is possible to see a young woman, or it is also possible that you see an old woman. Perhaps you are able to see both. The image that you see, or your perception of the image depends on your brain and your life experiences.

 

Discuss

Would you have laser surgery to change the shape of your lens? Many nearsighted people are now considering laser surgery to eliminate the need for glasses. Research this technology and identify any possible benefits and risks associated with the procedure. Address and explain at least 2 benefits and 2 risks of the procedure. Post your findings on the discussion board. Ask classmates to comment on, based on your findings, whether or not they would have the surgery. You may prepare your findings as a chart that lists the pros and cons of the procedure, or you may record your findings in point form.

 

Reflect on the Big Picture

In this lesson you continued exploring the senses. Photoreception, or the sense of vision, involves the largest number of sensory receptors in the body.The eyes gather approximately 80 – 90% of the information about our external environment and transmit it to the brain. In the Big Picture you saw a person across the room. As you walked toward them, their image was kept in focus by what reflex? (as “pop-up text-the accommodation reflex”). The (“pop-up text - papillary reflex”) adjusted the amount of light entering the eye. (“as pop-up text –Cones”) were activated to allow you to see colours. The (as pop-up text - occipital lobes of the cerebral cortex) integrated and interpreted this information. Based on this information that you received and the visual perception that you formed, you decided to say hello to the person.

 

At this point, you should research any relationship between Alzheimer’s disease and vision. Store any additional information in your course folder in preparation for your module assessment. Keep the following key questions in mind when reviewing:

• What are the major structures of the eye?

• How do these structures function?

• How do they communicate with the nervous system to support the integrated act of seeing

Lesson Summary

In this lesson, you explored the following focusing question:

What are the major parts of the eye, how do these parts function, and how do they communicate with the nervous system to support the integrated act of seeing?

 

Through your readings, through the dissection you completed, through your research, and through the video presentations you learned about the structures of the eye and their functions. By exploring the structures of the photoreceptors, called the rods and cones, you learned how a nerve impulse is initiated and transmitted to the occipital lobe of the cerebrum. It is there that the sensations are interpreted. Things like: the frequency of nerve impulses, the origin of the impulse in the retina, and previous experiences and memory all factor into the interpretation of light stimuli. Not everyone will interpret these sensations in the same way as observed with optical illusions. Many common visual defects and/or disorders affect the functioning of the eyes and impede proper vision. Numerous technologies have been devised to correct these disorders.

 

Lesson Glossary

accommodation: the process of changing the shape of the lens from round and fat to thin and flat and vice versa so that light can be focused on the retina to accommodate vision of objects near and far away

 

adaptation: the process by which the iris adjusts the diameter of the pupil based on light conditions thus controlling the amount of light that enters the eye and strikes the retina

 

anterior chamber: space in front of the iris and behind the cornea that is filled with aqueous humour

 

aqueous humour: a clear, watery fluid in the anterior chamber of the eye that maintains the shape of the cornea and provides oxygen and nutrients for the surrounding cells, including those of the lens and the cornea

 

astigmatism: uneven curvature of the cornea or lens resulting in uneven focusing which in turn results in poor vision

 

bipolar cells: specialized sensory nerve cells located in the retina that are stimulated by either rods or cones; cones mostly have a one to one ratio with bipolar cells, whereas several rod cells may communicate with one bipolar cell

 

blind spot: the area at the back of the eyeball that is deficient in rods and cones; the area where the sensory fibres come together to form the optic nerve

 

cataracts: cloudy or grey-white areas on the lens caused by deterioration of the protein composing the lens; prevents the passing of light to the photoreceptors of the retina

 

ciliary muscle: a ring of muscle behind the iris that is attached to the lens by suspensory ligaments; involved in changing the shape of the lens

 

choroid: middle layer of the eyeball that lies between the sclera and retina which is highly vascular and heavily pigmented; absorbs stray light rays not detected by the

photoreceptors of the retina

 

colour blindness: an x-linked inherited disorder that results in nonfunctional or deficient cone function; inability to see certain colours such as red, green, or blue

 

cones: one of two types of photoreceptors in the retina of the eye that is sensitive to different wavelengths of light and are thus responsible for distinguishing colour; there are three types of cones – one sensitive to red light, one to blue light, and one to green light; they are responsible for acute vision, or distinguishing detail

 

cornea: transparent portion of the sclera, located at the front of the eye; allows light to enter the eye and, in the process, bends the light rays so that they can be focused on the retina

 

depth perception: the ability to see in three dimensions

 

fovea centralis: an area of the retina that is located directly behind the centre of the lens; has a very high concentration of cones which makes this part of the eye responsible for great visual acuity

 

glaucoma: disorder caused by the malfunction of ducts that drain excess aqueous humour from the anterior chamber; the resulting pressure created by excess aqueous humour ruptures delicate blood vessels in the eye and causes deterioration of cells in the eye due to lack of nutrients; can result in blindness if left untreated

 

ganglion cells: special sensory neurons that communicate with bipolar cells in the retina to transmit a nerve impulse to the brain; these cells have long axons that converge at the back of the eye to form the optic nerve

 

hyperopia: farsightedness, or the inability to focus objects that are close; caused by an eyeball that is too short which causes light to be focused behind the retina

 

iodopsin: the general name of any of the three visual pigments found in cone cells that is stimulated by light to initiate a nerve impulse

 

iris: the circular, coloured part of the eye which is a circular muscle formed from the choroid; it contracts and dilates to change the diameter of the pupil

 

lens: clear flexible structure located behind the iris which focuses light on the photoreceptors of the retina

 

macular degeneration: a disorder that results in the degeneration and death of cells (cones) in the fovea centralis and the surrounding area (macula) causing a loss of vision in the centre of the field of view but not at the periphery; the person sees a black spot in the centre

 

myopia: nearsightedness, or the inability to focus objects that are far away; caused by an eyeball that is elongated which causes light to be focused in front of retina rather than directly on it

 

optic nerve: a collection of sensory neurons that carries sensory information from the photoreceptors to the brain

 

opsin: a protein that is the result of the decomposition of rhodopsin

 

pupil: hole in the middle of the iris; its diameter is adjusted by the iris to control the amount of light entering the eye

 

retina: the innermost layer of the eye which contains the photoreceptors

 

retinal: a derivative of Vitamin A (retinol) that is the result of the decomposition of rhodopsin; is instrumental in initiating a nerve impulse

 

rhodopsin: a visual pigment found in rod cells that is decomposed by light into opsin and retinal; the change initiates a nerve impulse

 

rods: one of two types of photoreceptors in the retina of the eye that are sensitive to light intensity and detect movement; they do not distinguish colour

 

sclera: the white, tough, protective outer layer of the eye that helps gives the eyeball its shape; sometimes called the white of the eye

 

tapetum: a reflective layer of cells located in the choroid, and in some cases directly in the retina,) of some nocturnal animals; increases the likelihood of dim light stimulating the photoreceptors

 

vitreous humour: transparent, amber coloured, jelly-like fluid in the posterior chamber of the eye which helps to maintain the shape of the eyeball